U.S. patent number RE37,970 [Application Number 09/620,641] was granted by the patent office on 2003-01-28 for pulse oximetry testing.
This patent grant is currently assigned to Clinical Dynamics Corporation. Invention is credited to Leo F. Costello, Jr..
United States Patent |
RE37,970 |
Costello, Jr. |
January 28, 2003 |
Pulse oximetry testing
Abstract
A method and apparatus for testing a pulse oximeter which is
based on the concept of an electrical interface between the testing
instrument and the oximeter rather than an optical interface. The
pulse oximeter signal processor is tested separately from the
probe, and still further, the optical elements, that is, the LEDs
and the photodiode, of the probe are tested separately from the
probe cable. With the probe disconnected from the oximeter, a
modulated electrical test signal representative of SpO.sub.2 values
and other parameters is generated in response to an electrical
signal from the oximeter, and the test signal is applied to the
oximeter signal processor, whereby the display of the oximeter
shows a value of SpO.sub.2 which is compared with the SpO.sub.2
value represented by the test signal. Independently, the probe
including the probe cable, the LEDs and the photodiode are
respectively and separately subjected to continuity and optical
sensitivity tests. Each of the main components of the oximeter is
thereby separately analyzed, and the source of a defect is
isolated.
Inventors: |
Costello, Jr.; Leo F. (Madison,
CT) |
Assignee: |
Clinical Dynamics Corporation
(Wallingford, CT)
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Family
ID: |
24222701 |
Appl.
No.: |
09/620,641 |
Filed: |
July 21, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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556749 |
Nov 2, 1995 |
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Reissue of: |
962149 |
Oct 31, 1997 |
05783821 |
Jul 21, 1998 |
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Reissue of: |
172586 |
Oct 14, 1998 |
01036620 |
Mar 21, 2000 |
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Current U.S.
Class: |
250/252.1 |
Current CPC
Class: |
A61B
5/14552 (20130101); A61B 5/1495 (20130101) |
Current International
Class: |
G01L
25/00 (20060101); G01L 025/00 () |
Field of
Search: |
;250/252.1,343
;356/40,41,42 ;128/633 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Technical Manual Nellcor Puritan Bennett TM Pulse Oximeter Tester
Model SRC-2", 1996. .
Criticare--Oxygen Saturation Simulator, Special Offer Sheet plus
pp. 2-1, 2-2, 2-3, and 2-4 plus Circuit Diagram Sheet 1/1 titled
Sp02/ECG Simulator (EProm Version) Oct. 6, 1991. .
Novametrix TB500B Front Panel, Service Manual, p. 3, Nov. 11,
1992..
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Primary Examiner: Porta; David P.
Attorney, Agent or Firm: Costello; Leo F.
Parent Case Text
This application is a .Iadd.REISSUE of Ser. No. 08/962,149 filed
Oct. 31, 1997 U.S. Pat. No. 5,783,821, which is a
.Iaddend.continuation of application Ser. No. 08/556,749, filed
Nov. 2, 1995, now abandoned.
Claims
What is claimed is:
1. An apparatus for testing a pulse oximeter having means for
optically sensing SpO.sub.2 values of living tissue, electrical
drive means for electrically activating the optically sensing
means, and electrical signal processing means responsive to the
optically sensing means for producing an oximeter signal
corresponding to the SpO.sub.2 value being sensed, said testing
apparatus comprising: first testing means bypassing the optically
sensing means and responsive to the electrical drive means for
generating selected first electrical test signals respectively
representative of selected SpO.sub.2 values in living tissue and
for transmitting said first signals to the electrical signal
processing means to test the ability of the signal processing means
to process said representative SpO.sub.2 values and produce
oximeter signals corresponding to the selected SpO.sub.2 values
represented by the test signals generated, and second testing means
for generating second electrical test signals, for transmitting the
same to the optically sensing means, for receiving response signals
from the optically sensing means in response to transmission of the
second test signals, and for providing an indication of said
response signals thereby to test the optically sensing means
separately from said testing by the first testing means.
2. The apparatus of claim 1, wherein: the optically sensing means
includes an LED, a photodiode for producing an electrical output
signal in response to activation of the LED, a first electrical
circuit including the LED, and a second electrical circuit
including the photodiode, said drive means being connected to the
first electrical circuit for electrically activating the optically
sensing means, said oximeter further including driven means
interconnecting the second electrical circuit and the signal
processing means for transmitting the electrical output signal from
the photodiode to the signal processing means: wherein said first
testing means is capable of transmitting said first test signals
instead of said photodiode output signal, to the driven means for
testing the drive means, the driven means and the signal processing
means, said second test signals including electrical continuity
test signals and electrical sensitivity test signals, wherein said
second testing means is capable of conducting the electrical
continuity test signals through both of said first and second
circuits to provide electrical continuity outputs, wherein said
second testing means is capable of conducting the electrical
sensitivity test signals through said first circuit to provide an
electrical sensitivity output in the second circuit, and further
including means for sensing said electrical continuity and
sensitivity outputs from said circuits in response to said
continuity and sensitivity test signals to test both the continuity
and the optical sensitivity of the optical sensing means.
3. An apparatus for testing a pulse oximeter capable of sensing the
SpO.sub.2 in living tissue and including a probe including LEDs and
a photodiode; and an electronic unit including an LED driver
providing output signals for activating the LEDs, an electronic
signal processor for receiving and processing input signals from
the photodiode in response to activation of the LEDs, and a display
for showing the SpO.sub.2 values represented by the input signals,
said probe releasably interconnecting the LED driver and the LEDs
and the photodiode and the signal processor, comprising: means
operable with the probe disconnected from the LED driver and the
signal processor for providing electrical test signals in response
to output signals from the LED driver; means for modulating said
electrical test signals so as to provide modulated electrical test
signals representative of selected SpO.sub.2 values corresponding
to those in living tissue; and means for transmitting said
modulated electrical test signals to the signal processor in place
of said input signals to cause the signal processor to process the
test signals as if they were said input signals whereby SpO.sub.2
values shown on the display can be compared with a range of
selected SpO.sub.2 values corresponding to the modulated electrical
test signals thereby to test said electronic unit over its normal
operating range.
4. The apparatus of claim 3, further including: electronic memory
means adapted to store an SpO.sub.2 profile including a plurality
of SpO.sub.2 values which vary over a predetermined time base; and
wherein said modulating means is adapted to modulate said
electrical test signals with selected SpO.sub.2 profiles so as to
provide modulated electrical test signals representative of
selected SpO.sub.2 profiles.
5. The apparatus of claim 4 further including: display means;
wherein said electronic memory means is also adapted to store a
cursor for said profiles, wherein said modulating means is further
adapted to feed a selected SpO.sub.2 profile and said cursor to
said display means so that a selected profile and cursor can be
displayed, wherein said memory means, said modulating means and
said display means cooperate to cause the cursor to move in steps
over the displayed profile at a predetermined rate stored in said
memory, with the position of the cursor at each step indicating on
the display means the value of SpO.sub.2 then modulating the test
signal whereby the oximeter can be tested with said profile of
SpO.sub.2 values sequentially delivered to the signal
processor.
6. An apparatus for testing the probe of a pulse oximeter having an
electronic unit including an LED driver and an electronic signal
processor; said probe including red and IR LEDs, a photodiode, and
a probe cable, said probe cable being releasably connected to the
driver and the signal processor when the probe is being used to
sense the SpO.sub.2 of living tissue and to feed a signal
representative of the same to the signal processor, comprising:
means for supplying current to the LEDs and the photodiode while
the probe is disconnected from the driver and the signal processor
to provide electrical continuity outputs from the LEDs and the
photodiode; means for driving the LEDs while the probe is
disconnected from the driver and the signal processor so as to
activate the photodiode and provide electrical sensitivity outputs
from the photodiode; and means for sensing said outputs thereby to
indicate the sensitivity and the continuity of the probe.
7. An apparatus for testing a pulse oximeter probe which includes
optical sensing means providing an LED circuit including red and IR
LEDs and a photodiode circuit including a photodiode, there being
an interactive red LED-photodiode combination and an interactive IR
LED-photodiode combination, said LED circuit, said photodiode
circuit, said interactive red LED-photodiode combination, and said
interactive IR LED-photodiode combination constituting first,
second, third, and fourth parts, respectively, of the optical
sensing means capable of being tested for continuity and
sensitivity, comprising: current supply means simultaneously
connectable to the LED and photodiode circuits for causing testing
current to flow in at least one of said circuits and for producing
test output signals representative of the test results on at least
one of said parts of the optical sensing means; and means for
receiving the test output signals and being responsive to the
magnitude thereof to produce an indication of the results of said
test to a user of the apparatus.
8. The apparatus of claim 7, further including: indicator means,
wherein said current supply means and said receiving means interact
to produce test output signals each of which individually
represents the test results for one of said parts of the optical
sensing means, and wherein said indicator means is capable of
indicating each of said individual output signals, whereby selected
parts of the optical sensing means can be separately analyzed.
9. The apparatus of claim 7, further including: indicator means;
wherein for said continuity test, the current supply means is
adapted to supply current simultaneously to each of said circuits
thereby to produce LED circuit continuity output test signals and
photodiode circuit continuity output test signals; wherein said
receiving means includes means for multiplexing said continuity
output test signals and means for feeding said multiplexed output
test signals to said indicator means; and wherein said indicator
means is adapted separately to indicate the LED and photodiode
continuity output signals thereby to enable individual analysis of
the continuity of the LED and photodiode circuits.
10. The apparatus of claim 7, further including: indicator means;
wherein said receiving means includes microprocessor means;
wherein, for said sensitivity test, the microprocessor means is
adapted to cause the current supply means to alternately supply
current to the red LED and the IR LED whereby said test output
signals are alternately red sensitivity signals and IR sensitivity
signals, said microprocessor means being adapted to develop red
sensitivity/IR sensitivity ratio signals from said red and IR
sensitivity signals, and said indicator means being adapted to
indicate said red sensitivity signals, said IR sensitivity signals,
and said red sensitivity/IR sensitivity ratio signals to a user of
the apparatus, thereby to enable the user to analyze the
sensitivity of said third and fourth parts of the optical sensing
means.
11. An apparatus for testing the continuity of a pulse oximeter
probe which provides an LED circuit and a photodiode circuit, said
apparatus comprising: means for activating each of said circuits so
as to produce an electrical test output in each circuit
representative of whether the circuit is open, continuous or
shorted; means for separating the test outputs representing the LED
circuit from the test outputs representing the photodiode circuit;
and means for analyzing each of said outputs to determine whether
or not the LED circuit or the photodiode circuit is open,
continuous or shorted.
12. The apparatus of claim 11, wherein: said activating means is
adapted to activate said photodiode circuit by causing current to
flow in a direction in said photodiode circuit opposite to the
direction current flows when light activates the photodiode.
13. The apparatus of claim 11, wherein said analyzing means
includes display means providing separate channels respectively
associated with the test outputs of the LED and photodiode
circuits, and wherein said analyzing means is capable of displaying
representations of said test outputs in the respective channels for
the LED and photodiode circuits so that a predetermined
representation indicates whether the respective circuit is open,
continuous, or shorted.
14. The apparatus of claim 11, wherein said analyzing means
includes display means, wherein said analyzing means is capable of
displaying representations of said test outputs on the display
means so that a predetermined representation represents a circuit
that is open, continuous, or shorted, and wherein said analyzing
means is capable of freezing the representation on the display
means when a circuit is open or shorted.
15. An apparatus for testing the sensitivity of a pulse oximeter
probe which provides red and infrared LEDs an a photodiode adapted
to be alternately activated by said LEDs, said apparatus
comprising: means for electrically alternately activating the LEDs
so as to produce electrical red and IR sensitivity test output
signals from the photodiode; means for producing red sensitivity/IR
sensitivity ratio signals from said red and IR test output signals;
and means for indicating each of said red sensitivity, IR
sensitivity and red sensitivity/IR sensitivity ratio signals to
determine the sensitivity of the optical sensing means.
16. The apparatus of claim 15, wherein said activating means is
adapted alternately to supply relatively low and relatively high
current to the red and IR LEDs to produce alternately low and high
red signals and low and high IR signals, said apparatus further
including means for subtracting the low red from the high red
signal and the low IR and from the high IR, and wherein said
producing means is adapted to produce said red sensitivity signal
from the difference between the high and low red signals and to
produce said IR sensitivity signal from the difference between the
high and low IR signals.
17. The apparatus of claim 15, wherein said indicating means
includes display means for respectively separately displaying said
red and IR sensitivities and said red sensitivity/IR sensitivity
and said red sensitivity/IR sensitivity ratio.
18. A method for testing a pulse oximeter having means for
optically sensing SpO.sub.2 values in living tissue, means for
electrically activating the optically sensing means, and electrical
means responsive to the optically sensing means for indicating the
SpO.sub.2 value in tissue being sensed, said method comprising the
steps of: generating first test signals representative of SpO.sub.2
values in living tissue in response to the electrically activating
means and independently of the optically sensing means,
transmitting the first test signals to the electrical responsive
means independently of the optically sensing means to test the
ability of the oximeter to indicate said representative SpO.sub.2
values, generating a second test signal independently of the
electrically activating means for testing the optically sensing
means, transmitting the second test signal to the optically sensing
means independently of the electrically activating means, and
receiving an output from the optically sensing means indicative of
the responses of the optically sensing means to the second test
signal, thereby to test the operability of the optically sensing
means.
19. The method of claim 18, wherein said generating step for
testing the optically sensing means is capable of testing the
electrical continuity of the optically sensing means.
20. The method of claim 18, including the further step of:
disconnecting the optically sensing means from the electrically
activating means and the electrical responsive means, wherein said
generating step includes receiving an output signal from the
electrically activating means and modulating said output signal so
as to provide a modulated test signal representative of a selected
value of SpO.sub.2 corresponding to that in living tissue; and
wherein said transmitting step involves transmitting said modulated
test signal to the electrical responsive means so as to provide a
modulated test signal representative of a selected value of
SpO.sub.2 corresponding to that in living tissue.
21. A method for testing a pulse oximeter over a range of values of
SpO.sub.2 expected to exist in living tissue said oximeter having a
probe including LEDs and a photodiode; and an electronic unit
including an LED driver providing an output signal for activating
the LEDs, an electronic signal processor for receiving and
processing input signals from the photodiode representative of
SpO.sub.2 values in living tissue in response to activation of the
LEDs, and a display for showing the SpO.sub.2 values represented by
the input signals, said probe releasably interconnecting the LED
driver and the LEDs and the photodiode and the signal processor,
comprising the steps of: disconnecting the probe from the driver
and signal processor; generating an electrical test signal in
response to the output signal from the LED driver; modulating said
electrical test signal so as to provide a modulated electrical test
signals representative of selected SpO.sub.2 values in living
tissue; transmitting said modulated electrical test signals to the
signal processor in place of said input signals to cause the signal
processor to process the test signals as if they were said input
signals thereby to test said electronic unit and, displaying the
selected SpO.sub.2 values so that a comparison can be made with the
SpO.sub.2 values displayed by the oximeter display to determine the
accuracy of the oximeter over a range of SpO.sub.2 values.
22. The method of claim 21, including the further steps of:
electronically storing an SpO.sub.2 profile including a plurality
of SpO.sub.2 values which vary over a predetermined time base; and
wherein said modulating step is adapted to modulate said electrical
test signals with selected SpO.sub.2 profiles so as to provide
modulated electrical test signals representative of selected
SpO.sub.2 profiles.
23. The method of claim 22 including the further steps of:
electronically storing a cursor for said profiles and a stepping
rate for the cursor, displaying a selected profile and said cursor;
and moving the cursor in steps over the displayed profile at said
stepping rate so that the position of the cursor at each step
indicates the value of SpO.sub.2 then modulating the test signal
whereby the oximeter can be tested with said profile of SpO.sub.2
values sequentially delivered to the signal processor.
24. A method for testing a pulse oximeter probe which includes
optical sensing means providing an LED circuit including red and IR
LEDs and a photodiode circuit including a photodiode, there being
an interactive red LED-photodiode combination and an interactive IR
LED-photodiode combination, said LED circuit, said photodiode
circuit, said interactive red LED-photodiode combination, and said
interactive IR LED-photodiode combination constituting first,
second, third, and fourth parts, respectively, of the optical
sensing means one or more of which is capable of being tested for
the parameters of continuity and sensitivity, comprising the steps
of: electrically activating said circuits so as to produce
electrical test output signals which are representative of at least
one of the parameters to-be-tested; and sensing the test output
signals and displaying an indication of whether one or more of said
parts meet the standards established for said at least one of the
parameters to-be-tested.
25. The method of claim 24, wherein: said activating step activates
the circuits so as to produce output test signals which are not
affected by ambient light on the photodiode.
26. The method of claim 24, wherein: said activating step involves
causing current to flow in the photodiode circuit in the opposite
direction from that occurring when the photodiode is activated by
light.
27. The method of claim 24, wherein: said activating step involves
alternatively supplying high and low current pulses in the red and
IR LED circuits, respectively, to produce alternate red high and
red low test output signals and IR high and IR low test output
signals, said activating step further involving subtracting red low
signals from the corresponding red high signals and IR low signals
from the corresponding IR high signals, thereby to produce said red
sensitivity and said IR sensitivity signals, respectively, and
including the further step of generating red sensitivity/IR
sensitivity ratio signals from said red sensitivity and said IR
sensitivity signals, and wherein said sensing step involves
analyzing said red and IR sensitivity signals and said red
sensitivity/IR sensitivity ratio signals thereby to determine the
sensitivity of the optically sensing means.
28. The method of claim 24, further including the step of:
displaying graphical representations of the test output signals
sensed from said circuits thereby to indicate the condition of the
continuity of said circuits, and displaying graphical
representations of the test output signals sensed from the
photodiode thereby to indicate the sensitivity of the optically
sensing means.
29. A method for testing the continuity of a pulse oximeter probe
which provides an LED circuit and a photodiode circuit, comprising
the steps of: activating each of said circuits so as to produce an
electrical test output in each circuit representative of whether
the circuit is open, continuous or shorted; separating the test
outputs representing the LED circuit from the test outputs
representing the photodiode circuit; and analyzing each of said
outputs to determine whether or not the LED circuit or the
photodiode circuit is open, continuous or shorted.
30. The method of claim 29, wherein said analyzing step further
includes: displaying representations of said test outputs so that a
predetermined representation represents a circuit that is open,
continuous, or shorted, and freezing the representation when a
circuit is open or shorted.
31. The apparatus of claim 1, wherein said first and second testing
means are capable of independently but simultaneously testing the
signal processing means and the optically sensing means.
32. The apparatus of claim 1, wherein there is a housing enclosing
both the first and second testing means, and wherein there are
spaced first and second connector means on the housing respectively
connected to the first and second testing means and respectively
adapted to be connected to the signal processing means and the
optically sensing means.
33. The apparatus of claim 1, wherein there are microprocessor
means for controlling the first and second testing means to enable
the first and second testing means to test either the signal
processing means or the optically sensing means separately or to
test both the signal processing means and the sensing means
simultaneously.
34. The apparatus of claim 1 wherein the optically sensing means
includes an LED, a photodiode for producing an electrical output
signal in response to activation of the LED, a first electrical
circuit including the LED, and a second electrical circuit
including the photodiode, said drive means being connected to the
first electrical circuit for electrically activating the optically
sensing means, said oximeter further including driven means
interconnecting the second electrical circuit and the signal
processing means for transmitting the electrical output signal from
the photodiode to the signal processing means; wherein said first
testing means is capable of transmitting said first test signals,
instead of said photodiode output signal, to the driven means for
testing the drive means, the driven means and the signal processing
means, wherein said second test signals are electrical continuity
test signals, wherein said second testing means is capable of
conducting the electrical continuity test signals respectively
through said first and second circuits to provide electrical
continuity outputs, and wherein there are means for sensing said
electrical continuity outputs and displaying an indication of the
continuity of the optical sensing means.
35. The apparatus of claim 1 wherein the optically sensing means
includes an LED, a photodiode for producing an electrical output
signal in response to activation of the LED, a first electrical
circuit including the LED, and a second electrical circuit
including the photodiode, said drive means being connected to the
first electrical circuit for electrically activating the optically
sensing means, said oximeter further including driven means
interconnecting the second electrical circuit and the signal
processing means for transmitting the electrical output signal from
the photodiode to the signal processing means; wherein said first
testing means is capable of transmitting said first signals,
instead of said photodiode output signal, to the driven means for
testing the drive means, the driven means and the signal processing
means, wherein said second test signals are electrical sensitivity
test signals, wherein said second testing means is capable of
conducting the electrical sensitivity test signals through said
first circuit to provide electrical sensitivity outputs in the
second circuit, and wherein there are means for sensing said
electrical sensitivity outputs and displaying an indication of the
optical sensitivity of the optical sensing means.
36. The apparatus of claim 3, wherein the apparatus includes means
for displaying the values of SpO.sub.2 represented by the modulated
electrical test signals whereby SpO.sub.2 values showing on the
oximeter display can be compared with selected SpO.sub.2 values
showing on the displaying means thereby to determine the accuracy
of the oximeter throughout a range of SpO.sub.2 values.
37. An apparatus for testing the continuity of a pulse oximeter
probe which provides LED and photodiode circuits connected to LED
and photodiode terminals of a probe connector, said apparatus
comprising: means simultaneously connectable to the LED and
photodiode terminals of the probe connector for activating each of
said circuits so as to produce an electrical test output in each
circuit representative of whether the circuit is open, continuous
or shorted; and means responsive to said test outputs for
displaying indicia representing whether said LED and photodiode
circuits are open, continuous or shorted.
38. The apparatus of claim 37, wherein the activating means is a
current source for each of said circuits.
39. The apparatus of claim 38, wherein the current sources are
simultaneously connectable to their respective LED and photodiode
circuits, and wherein the activating means causes current from the
current sources to supply current simultaneously to said
circuits.
40. The apparatus of claim 37, wherein the responsive means is
capable of sensing and displaying intermittent test outputs of a
predetermined threshold indicative of a glitch in either of said
circuits.
41. The apparatus of claim 37, wherein there are means for
combining the test outputs into a combined signal with alternating
LED and photodiode pulses, and wherein there are means for using
the LED and photodiode pulses to display an indication of whether
the LED and photodiode circuits are open, continuous or
shorted.
42. The apparatus of claim 41, wherein the combining means combines
the test outputs into a combined analog signal with said
alternating LED and photodiode pulses, wherein there are means for
converting the combined analog signal into discrete digital signals
representative of said LED and photodiode pulses; and wherein there
are means for sampling the digital signals and displaying the same
to indicate whether or not the LED circuit or the photodiode
circuit is open, continuous or shorted.
43. An apparatus for testing the continuity of a pulse oximeter
probe that has an LED circuit and a photodiode circuit, comprising
means for supplying testing current to each of the LED and
photodiode circuits to produce responses including separate analog
LED and photodiode continuity voltages, means for combining said
voltages into a single voltage signal with alternating LED and
photodiode pulses, means for converting the single voltage signal
into a series of discrete digital voltage pulses representative of
the alternating LED and photodiode pulses, means for sampling the
digital voltage pulses, display means, and means for activating the
display means with the signal samples to indicate whether the LED
and photodiode circuits are open, continuous, or shorted.
44. The apparatus of claim 15, wherein said indicating means
includes display means for respectively displaying bargraphs in
separate channels of said red and IR sensitivities and said red
sensitivity/IR sensitivity ratio.
45. The method of claim 18, wherein said generating step for
testing the optically sensing means is capable of testing the
optical sensitivity of the optically sensing means.
46. The method of claim 19, wherein said generating step for
testing the optically sensing means is capable of testing the
optical sensitivity of the optically sensing means.
47. A method for testing a pulse oximeter probe which includes
optical sensing means providing an LED circuit including red and IR
LEDs and a photodiode circuit including a photodiode, there being
an interactive red LED-photodiode combination and an interactive IR
LED-photodiode combination said LED circuit, said photodiode
circuit, said interactive red LED-photodiode combination, and said
interactive IR LED-photodiode combination constituting first,
second, third, and fourth parts, respectively, of the optical
sensing means to be subjected to such testing including the
parameters of continuity and sensitivity, comprising the steps of:
electrically activating said circuits so as to produce electrical
test output signals which are representative of the parameters
to-be-tested of said parts; electrically separating the test output
signals so that there is a test output signal representative of
continuity for each of said first and second parts and a test
output signal representative of the sensitivity for each of said
third and fourth parts; and analyzing each of said output signals
to determine whether or not said parts meet the standards
established for said parameters.
48. The method of claim 24 which involves the use of a testing
device capable of performing said activating, sensing and
displaying steps, further including the step of: electrically
connecting the testing device simultaneously to both the LED and
photodiode circuits prior to said electrically activating step
thereby to enable testing of selected ones of said parts.
49. A method for testing the continuity of a pulse oximeter probe
that includes an LED circuit and a photodiode circuit, comprising
the steps of: simultaneously connecting electrical activating means
to both of the LED and photodiode circuits, electrically activating
each of said circuits with test signals thereby to produce an
electrical test output in each circuit representative of whether
the circuit is open, continuous or shorted; and processing the test
outputs to provide a visual indication of whether or not each
circuit is open, continuous or shorted.
50. The method of claim 49, wherein the activating step involves
simultaneously supplying said test signals in the form of current
fed to each of said circuits from separate current sources
respectively associated with said circuits.
51. The method of claim 49 wherein the probe includes a probe cable
including conductors that are part of said circuits, including the
further step of: moving the cable around during the electrical
activating so that if one or more of the conductors has an open or
short condition that occurs only intermittently, such movement will
cause the open or short to occur.
52. The method of claim 51, wherein the moving step causes a
voltage spike in said test output of the circuit in which an
intermittent short or open condition exists; and wherein the
processing step is responsive to the voltage spike to provide a
visual indication of the same, whereby such intermittent short or
open conditions are not overlooked by the user performing the
test.
53. A method for testing the continuity of a pulse oximeter probe
that has an LED circuit and a photodiode circuit, comprising the
steps of: supplying current to both the LED and photodiode circuits
to produce responses including separate LED and photodiode
continuity voltages; sensing said responses and combining them into
a single voltage signal with alternating LED and photodiode pulses;
converting the single voltage signal into a series of discrete
voltage pulses representative of the alternating LED and photodiode
pulses; and using the discrete voltage pulses to display
indications of whether the LED and photodiode circuits are open,
continuous or shorted. .Iadd.
54. An apparatus for testing the sensitivity of a pulse oximeter
probe which provides red and infrared LEDs and a photodiode, said
apparatus comprising: a red current source that generates red LED
activating signals, applies them to the red LED, and generates red
high and red low outputs on the photodiode; an IR current source
that generates IR LED activating signals, applies them to the IR
LED, and generates IR high and IR low outputs on the photodiode;
sensor circuitry that is responsive to the red high and the red low
outputs on the photodiode and to the IR high and the IR low outputs
on the photodiode and that generates red testing signals and IR
testing signals from said outputs; and a display that is responsive
to the red and IR testing signals and produces an indication
thereof, said indication being an indication of the sensitivity of
the probe..Iaddend..Iadd.
55. The apparatus of claim 54, wherein the red current source
generates high and low red activating signals and applies them to
the red LED thereby to produce said high and low red outputs in the
photodiode; and wherein the IR current source generates high and
low IR activating signals and applies them to the IR LED thereby to
produce said high and low IR outputs in the
photodiode..Iaddend..Iadd.
56. An apparatus for testing the sensitivity of a pulse oximeter
probe which provides red and infrared LEDs and a photodiode, said
apparatus comprising: means for applying red high and red low LED
activating signals to the red LED so that red high and red low
outputs are on the photodiode; means for applying IR high and IR
low LED activating signals to the IR LED so that IR high and IR low
outputs are on the photodiode; means for sensing the outputs on the
photodiode and producing a red testing signal from the red high and
red low outputs on the photodiode and an IR testing signal from the
IR high and IR low outputs on the photodiode, said red and IR
testing signals being the differences between their respective high
and low outputs; and means for displaying an indication of said
testing signals whereby said indication is an indication of the
sensitivity of the probe..Iaddend..Iadd.
57. A method for testing the sensitivity of a pulse oximeter probe
which provides red and infrared LEDs and a photodiode, comprising
the steps of: activating one of the LEDs with signals of high and
low amplitude thereby producing first high and low outputs on the
photodiode; sensing the first high and low outputs on the
photodiode; producing a first testing signal from said first high
and low outputs; activating the other of the LEDs with signals of
high and low amplitude thereby producing second high and low
outputs on the photodiode; sensing the second high and low outputs
on the photodiode; producing a second testing signal from said
second high and low outputs; and displaying an indication of said
first and second testing signals thereby to indicate the
sensitivity of the probe..Iaddend..Iadd.
58. The method of claim 57, wherein producing the first and second
testing signals involves obtaining the difference between the first
high and low outputs and the difference between the second high and
low outputs resulting respectively in first and second difference
signals..Iaddend..Iadd.
59. An oximeter tester for an oximeter that includes a signal
processor, an LED driver and a probe including LED and photodiode
circuits respectively including light emiting diodes and a
photodiode, the probe being releasably connected to the signal
processor and the LED driver, the tester comprising: a first sensor
having an input adapted to be connected to the LED driver in the
oximeter in place of the probe, the first sensor, when so
connected, receiving electrical red and IR drive signals from the
LED driver of the oximeter and producing red and IR pulses, a
de-multiplexer coupled to the sensor and separating the red and IR
pulses, a source of SpO.sub.2 waveforms corresponding to those
normally received by the oximeter when its probe is attached to a
human being, a modulator coupled to the de-multiplexer and
modulating the separate red and IR pulses with said SpO.sub.2
waveforms from the source and thereby generating first electrical
test signals representative of SpO.sub.2 waveforms of living tissue
corresponding to those normally received by the oximeter when its
probe is attached to a human being, a tester driver having an input
coupled to the modulator and an output adapted to be connected to
the signal processor in the oximeter and, when so connected,
delivering said first electrical test signals to the signal
processor thereby to test the ability of the signal processor to
process said SpO.sub.2 waveforms and produce oximeter read-outs
corresponding to SpO.sub.2 values represented by the test signals
generated; a current source adapted to be connected to one or more
diodes in the probe and, when so connected, coupling second
electrical test signals to said one or more of the diodes thereby
to activate the one or more diodes; a second sensor adapted to be
connected to one or more diodes in the probe and, when so
connected, receiving response signals from said one or more of the
diodes in response to the second electrical test signals; a
display; circuitry interconnecting the second sensor and the
display and applying signals to the display indicative of the
response signals from the second sensor; and a microprocessor
coupled to the modulator, the display and the source and
controlling the application of the SpO.sub.2 waveforms to the
modulator and the application of actuating current to said one or
more diodes, and the application of the signals to the
display..Iaddend..Iadd.
60. An apparatus for testing a pulse oximeter having an optical
sensor that senses SpO.sub.2 values of living tissue, an electrical
driver that produces an electrical signal that activates the
optical sensor, and a signal processor responsive to the optical
sensor that produces an oximeter signal corresponding to the
SpO.sub.2 value being sensed, said testing apparatus comprising:
.[.for.]. first .Iaddend..Iadd.testing circuitry that is responsive
to the signal from the electrical driver in the oximeter, that
generates first electrical test signals that are SpO.sub.2
waveforms simulating those generated by the probe of the oximeter
when the oximeter is used to check the blood oxygen level of a
patient, and that transmits said first signals to the signal
processor of the oximeter independently of the optical sensor,
second testing circuitry that generates second electrical test
signals, that transmits the second electrical test signals to the
optical sensor in the oximeter independently of the electrical
driver of the oximeter, and that receives response signals from
said optical sensor in response to transmission of the second test
signals, and a display that provides an indication of said response
signals from the second testing circuitry..Iaddend..Iadd.
61. The testing apparatus of claim 60, wherein the first testing
circuitry includes an electrical sensor that receives the
electrical signal from the electrical driver and produces an
output, a modulator that is connected to the electrical sensor and
generates the selected first electrical test signals respectively
representative of selected SpO.sub.2 waveforms in response to the
output from the electrical sensor, and a tester driver that is
connected to the modulator and transmits said first signals to the
signal processor in the oximeter..Iaddend..Iadd.
62. The apparatus of claim 61, wherein the first testing circuitry
includes an electronic memory that stores an SpO.sub.2 profile
including a plurality of said SpO.sub.2 waveforms; and wherein the
modulator modulates said electrical test signals with selected
SpO.sub.2 profiles and provides modulated electrical test signals
representative of selected SpO.sub.2 profiles..Iaddend..Iadd.
63. The testing apparatus of claim 60, wherein the second testing
circuitry includes a source of current that generates the second
electrical test signals, electrical connections that transmit the
second electrical test signals to the optical sensor, an electrical
sensors that receive the response signals from the optical sensor,
and wherein the display is connected to the electrical sensors of
the second testing circuitry and produces said indication from the
output of the electrical sensors..Iaddend..Iadd.
64. The apparatus of claim 60, wherein there is a housing enclosing
both the first and second testing circuitry, and wherein there are
spaced first and second connectors in the housing respectively
connected to the first and second testing circuitry and
respectively adapted to be connected to the signal processor and
the optical sensor..Iaddend..Iadd.
65. The apparatus of claim 60, wherein there is a microprocessor
that controls the first and second testing circuitry in testing the
signal processor and the optical sensor..Iaddend..Iadd.
66. The apparatus of claim 60 for testing a pulse oximeter the
optical sensor of which has an LED circuit, a photodiode circuit,
and an oximeter connector providing LED and photodiode terminals
respectively connected to the LED circuit and photodiode circuits,
wherein the second testing circuitry includes LED testing
circuitry, photodiode testing circuitry, and a tester connector
having LED and photodiode terminals respectively connected to the
LED testing circuitry and photodiode testing circuitry, the LED and
photodiode terminals in the tester connector corresponding to the
LED and photodiode terminals of the oximeter connector, so that
when the tester connector is connected to the oximeter connector,
the LED testing circuitry and photodiode testing circuitry are
respectively connected to the LED circuit and the photodiode
circuits..Iaddend..Iadd.
67. An apparatus for testing the probe of a pulse oximeter, said
probe including an LED, a photodiode, and a probe connector with
LED and photodiode terminals respectively connected to the LED and
photodiode, the testing apparatus comprising: a tester connector
having LED and photodiode terminals capable of connecting to LED
and photodiode terminals of the probe connector; a signal source
that generates probe testing signals and that is connected to
predetermined terminals of the tester connector for applying
testing signals on the said predetermined terminals so that the
testing signals will be applied to the probe when the tester
connector is connected to the probe connector; a signal sensor that
is connected to certain terminals of the tester connector, that is
responsive to outputs thereon resulting from application of the
probe testing signals to the probe, and that generates output
signals representative of the outputs from the probe; and a display
connected to the signal sensor for displaying an indication of said
output signals, thereby to test the operability of the
probe..Iaddend..Iadd.
68. The apparatus of claim 67, the probe having LED and photodiode
circuits respectively including the LED and the photodiode, wherein
the signal source generates probe continuity testing signals at the
LED and photodiode terminals of the tester connector; wherein the
signal sensor is connected to the LED and photodiode terminals of
the tester connector, is responsive to continuity outputs on said
LED and photodiode terminals resulting from the continuity testing
signals, and generates continuity output signals representative of
the continuity of the LED and photodiode circuits; and wherein the
display shows an indication of the continuity of the LED and
photodiode circuits..Iaddend..Iadd.
69. The apparatus of claim 67, wherein the signal source generates
probe sensitivity testing signals at the LED terminals of the
tester connector; wherein the signal sensor is connected to the
photodiode terminals of the tester connector, is responsive to
sensitivity outputs on said photodiode terminals resulting from the
sensitivity testing signals, and generates sensitivity output
signals representative of the sensitivity of the probe; and wherein
the display shows an indication of the sensitivity of the
probe..Iaddend..Iadd.
70. The apparatus of claim 69, the probe having red and IR LEDs,
wherein the probe sensitivity signals generated by the signal
source are high and low current signals for the red LED and high
and low current signals for the IR LED, thereby to enable high and
low red outputs and high and low IR outputs to be generated by the
photodiode when the tester connector is connected to the probe
connector; wherein the signal sensor is responsive to the high and
low red outputs and generates red difference signals representing
the difference between said high and low red outputs; wherein the
signal sensor is responsive to the high and low IR outputs and
generates IR difference signals representing the difference between
said high and low IR outputs; and wherein the display is responsive
to the red and IR difference signals and displays an indication
thereof to indicate the sensitivity of the red and IR
LEDs..Iaddend..Iadd.
71. A method for testing the continuity of a pulse oximeter probe
that includes an LED circuit and a photodiode circuit, said method
involving the use of a tester having a tester connector providing
terminals connected to an electrically actuating source and a
sensor in the tester, and a probe connector providing terminals
connected to said circuits, comprising the steps of: connecting the
tester connector to the probe connector and thereby simultaneously
connecting the electrically activating source and the sensor to the
LED and photodiode circuits, electrically activating each of said
circuits with said source, sensing each circuit with said sensor
for outputs in response to said electrical activation, producing
indications of outputs that are sensed, and determining the
continuity of the circuits from said
indications..Iaddend..Iadd.
72. A method for testing the sensitivity of a pulse oximeter probe
that has red and IR LED circuits and a photodiode circuit including
a photodiode, said method involving the use of a tester having a
tester connector providing terminals connected to an electrically
actuating source and a sensor in the tester, and a probe connector
providing terminals connected to said circuits, comprising the
steps of: connecting the tester connector to the probe connector
and thereby simultaneously connecting the electrically activating
source and the sensor to the LED and photodiode circuits,
electrically activating the LED circuits with said sensors, sensing
the photodiode circuit with the sensor for outputs in response to
said electrical activation, producing indications of outputs that
are sensed, and determining the sensitivity of the photodiode from
said indications..Iaddend..Iadd.
73. A pulse oximeter testing apparatus for testing a pulse oximeter
having an optical sensor that senses SpO.sub.2 values of living
tissue, an electrical driver that produces an electrical signal
that activates the optical sensor, and a signal processor
responsive to the optical sensor that produces an oximeter signal
corresponding to the SpO.sub.2 value being sensed, said testing
apparatus comprising: a current sensor that is responsive to the
electrical signal from the electrical driver in the oximeter and
produces simulated red and IR signals; an electronic memory storing
SpO.sub.2 waveforms that simulate SpO.sub.2 waveforms in living
tissue like those produced by the optical sensor in the normal
operation of the oximeter; a modulator responsive to the simulated
red and IR signals from the current sensor, modulating the
simulated red and IR signals with selected simulated SpO.sub.2
waveforms from the memory, and generating modulated test signals
respectively representative of the selected SpO.sub.2 waveforms in
living tissue; and a tester driver responsive to the modulated test
signals from the modulator, that produces electrical test signals
representative of the selected SpO.sub.2 waveforms, and that
transmits the test signals to the signal generator in the oximeter
to test the ability of the signal processor to process said
representative SpO.sub.2 waveforms and produce oximeter signals
corresponding to the selected simulated SpO.sub.2
waveforms..Iaddend..Iadd.
74. The combination of a pulse oximeter and a testing apparatus,
the oximeter having a signal processor, a display and a probe, the
probe normally receiving signals from the oximeter and delivering
modulated human signals to the signal processor resulting from a
human finger or other body part placed in the probe, wherein the
testing apparatus is connected to the oximeter in place of the
probe; wherein the tester thereby receives the signals from the
oximeter that would normally be delivered to the probe; wherein the
testing apparatus includes an electronic memory containing a
database of waveforms corresponding to those produced by human
fingers or other body parts when placed in the probe of an
oximeter; wherein the testing apparatus also includes a modulator
that modulates the signals received by the testing apparatus with
selected waveforms from the electronic memory thereby generating
modulated testing signals that simulate the modulated human signals
resulting from a human finger or other body part placed in the
probe when the oximeter is in its normal use; wherein the testing
apparatus delivers the modulated testing signals to the signal
processor; wherein the .[.modulating.]. modulated
.Iaddend..Iadd.testing signals are processed by the signal
processor as if the modulated testing signals were the
.[.modulating.]. modulated .Iaddend..Iadd.human signals thereby
producing processed signals; and wherein the processed signals are
displayed on the display whereby comparisons can be made with known
values..Iaddend..Iadd.
75. An apparatus for testing a pulse oximeter having an optical
sensor that senses SpO.sub.2 values of living tissue, an LED
driver, a signal processor responsive to the optical sensor that
produces an oximeter signal corresponding to the SpO.sub.2 value
being sensed and a display, said testing apparatus comprising:
first means for testing the LED driver and the signal processor of
the oximeter separately from the optical sensor of the oximeter,
the display in the oximeter displaying the results of the first
testing means; second means for testing the optical sensor of the
oximeter separately from the LED driver and the signal processor of
the oximeter; and means for displaying the results of the second
testing means..Iaddend..Iadd.
76. An apparatus for testing a pulse oximeter having an optical
sensor that senses SpO.sub.2 values of living tissue, a signal
processor responsive to the optical sensor that produces an
oximeter signal corresponding to the SpO.sub.2 value being sensed,
and a display that displays the said SpO.sub.2 values sensed, the
testing apparatus comprising: means for testing the signal
processor of the oximeter with testing SpO.sub.2 values
independently of the optical sensor; and means for enabling a
comparison of the testing SpO.sub.2 values with the SpO.sub.2
values displayed on the oximeter display..Iaddend..Iadd.
77. An oximeter probe tester for an oximeter probe having LED and
photodiode circuits, comprising: means for electrically activating
the LED circuit and the photodiode circuit of the oximeter probe so
as to produce electrical test output signals in the circuits that
are representative of the continuity of the circuits, means for
sensing whether or not the test output signals are present in the
circuits, and means for displaying an indication of the test output
signals sensed..Iaddend..Iadd.
78. An oximeter probe tester for an oximeter probe having a LED
circuit including LEDs and a photodiode circuit including a
photodiode, comprising: means for electrically activating the LEDs
of the oximeter probe so as to produce electrical test output
signals in the photodiode that are representative of the
sensitivity of the photodiode, means for sensing the test output
signals, and means for displaying an indication of the test output
signals sensed..Iaddend..Iadd.
79. An oximeter probe tester for an oximeter probe having an LED
circuit including LEDs and a photodiode circuit including a
photodiode, comprising: means for electrically activating the LED
circuit and the photodiode circuit of the oximeter probe so as to
produce electrical test output signals in the circuits that are
representative of the continuity of the circuits, means for sensing
whether or not the test output signals are present in the circuits,
means for electrically activating the LEDs of the oximeter probe so
as to produce electrical test output signals on the photodiode that
are representative of the sensitivity of the photodiode, means for
sensing the test output signals on the photodiode, and means for
selectively and separately displaying an indication of the test
output signals that are representative of the continuity of the
circuits and the test output signals that are representative of the
sensitivity of the photodiode..Iaddend..Iadd.
80. The apparatus of claim 54, wherein the red testing signals are
red difference signals that represent the difference between the
red high and red low outputs from the photodiode; and wherein the
IR testing signals are IR difference signals that represent the
difference between the IR high and IR low outputs of the
photodiode..Iaddend..Iadd.
81. The apparatus of claim 80, wherein the red and IR testing
signals also include ratio signals that represent the ratio of the
red difference signals to the IR difference
signals..Iaddend..Iadd.
82. A method for testing a pulse oximeter with a testing instrument
wherein the oximeter includes a probe, an LED driver, a signal
processor, an oximeter interface connector connected to the signal
processor and the LED driver, the probe including LEDs, a
photodiode, and a probe connector connected to the oximeter
interface connector in normal use of the oximeter, the LEDs being
responsive to LED drive signals from the LED driver and the
photodiode generating SpO.sub.2 waveforms for delivery to the
signal processor through the oximeter interface connector when the
probe is attached to the human being, and wherein the testing
instrument includes a housing, a probe testing connector mounted on
the housing, and a simulator testing connector mounted on the
housing, the method comprising the steps of: connecting either the
probe connector alone to the probe testing connector, the simulator
testing connector alone to the oximeter interface connector, or
both the probe connector and the simulator testing connector,
respectively, to the probe testing connector and the oximeter
interface connector; with the simulator testing connector to the
oximeter interface connector in place of the probe, generating
first test signals representative of SpO.sub.2 waveforms that
simulate said human SpO.sub.2 waveforms generated by the probe in
response to said LED drive signals; transmitting the first test
signals to the signal processor trough the interconnected simulator
testing connector and oximeter interface connector; with the probe
connector connected to the probe testing connector instead of to
the oximeter interface connector, generating a second test signal
independently of the LED driver; transmitting the second test
signal to the probe through the interconnected probe connector and
probe testing connector; receiving an output from the probe in
response to the second test signal; and displaying said
output..Iaddend..Iadd.
83. A method for testing either the continuity or the sensitivity
or both of a pulse oximeter probe that has an LED circuit including
red and IR LEDs, a photodiode circuit including a photodiode, and a
probe connector, the method involving the use of a housing
enclosing electrically activating sources and signal sensing
circuitry and mounting a probe testing connector providing LED and
photodiode terminals connected to the electrically activating
sources and the signal sensing circuitry, the method comprising the
steps of: interconnecting the probe connector and the probe testing
connector and thereby interconnecting the LED and photodiode
terminals and the LED and photodiode circuits respectively;
electrically activating both of the LED and photodiode circuits
with an electrical activating source in the housing if continuity
is being tested; electrically activating only the LED circuits with
an electrical activating source in the housing if sensitivity is
being tested; sensing both of the LED and photodiode circuits for
outputs in response to said electrical activation if continuity is
being tested; sensing the photodiode circuit for outputs in
response to said electrical activation if sensitivity is being
tested; displaying visual indications of the outputs that are
sensed, and determining the continuity and/or sensitivity of the
probe from said visual indications..Iaddend.
84. A method for isolating defects among certain parts of pulse
oximeters by enabling said parts to be tested separately, each such
oximeter having two principal parts, namely, a main instrument and
a probe respectively connected to a main interface connector and a
probe interface connector, the interface connectors being
separately connected to each other in the normal operation of an
oximeter when monitoring the SpO2 values of living tissue wherein
the probe produces SpO2 waveforms of the living tissue being
monitored and transmits those waveforms to the main instrument to
indicate thereon certain characteristics of said waveforms, the
method involving the use of a testing apparatus that includes a
simulator that can be drive to generate simulated SpO2 waveforms
corresponding to those produced by the probe in said normal
operation and a signal processor driver capable of driving the main
instrument of the oximeter like the probe does in said normal
operation, the testing apparatus further including a probe
driver-sensor unit capable of activating the probe and sensing
responses therefrom, a housing enclosing the simulator, the signal
processor driver, and the probe driver-sensor unit, first and
second testing interface connectors mounted on the housing, a
display mounted on the housing and connected to the probe
driver-sensor unit to display indications of characteristics of
said responses, and a microprocessor in the housing connected to
the simulator, the probe driver-sensor unit, and the display for
controlling the actions thereof, the method comprising the steps
of: connecting either the main interface connector to the first
testing interface connector, or the probe interface connector to
the second testing interface connector, or both the main interface
connector and the probe interface connector respectively to the
first and second testing interface connectors, if the main
interface connector is connected to the first testing interface
connector, causing the main instrument to drive the simulator and
cause the signal processor driver to drive the main instrument
which in turn causes an indication of the characteristics of the
simulated waveforms on the main instrument, if the probe interface
connector is connected to the second testing interface connector,
causing the probe driver-sensor to activate the probe and cause
responses therefrom to be sensed and indications thereof to be
displayed on said display, and if both the main and probe interface
connectors are both connected to the first and second testing
interface connectors, causing the main instrument to drive the
simulator and cause the signal processor drive to drive the main
instrument which in turn causes an indication of the
characteristics of the simulated waveforms on the main instrument,
and causing the probe driver-sensor to activate the probe and cause
responses therefrom to be sensed and indications thereof to be
displayed on the display.
85. A method for isolating defects among certain parts of pulse
oximeters by enabling said parts to be tested separately, each such
oximeter having two principal parts, namely, a main instrument and
a probe, each such main instrument including as subsidiary parts a
signal processor and an LED driver connected to an main interface
connector, and each such probe including as subsidiary parts an LED
circuit including red and IR LEDs and a photodiode circuit
including a photodiode, said circuits terminating in a probe
interface connector, the interface connectors of a main instrument
and a probe being separately interconnected in the normal operation
of an oximeter when monitoring the SpO2 values of living tissue
wherein the LED driver activates the LEDs which in turn activate
the photodiode and cause the photodiode to produce SpO2 waveforms
of the living tissue being monitored and to transmit those
waveforms to the signal processor that in turn drives the display
to indicate certain characteristics of said waveforms, the method
involving the use of a testing apparatus that includes a simulator
that can be driven to generate simulated SpO2 waveforms
corresponding to those produced by the photodiode in said normal
operation and a signal processor driver capable of driving the
signal processor of the oximeter like the photodiode does in said
normal operation, the testing apparatus further including a probe
driver-sensor unit capable of activating the LED and photodiode
circuits and sensing responses therefrom, a housing enclosing the
simulator, the signal processor driver, and the probe driver-sensor
unit, first and second testing interface connectors mounted on the
housing, the first testing interface connector being connected to
the simulator and the signal processor driver and the second
testing interface connector being connected to the probe
driver-sensor unit, a display mounted on the housing and connected
to the probe driver-sensor unit to display indications of the
characteristics of said responses, and a microprocessor in the
housing connected to the simulator, the probe driver-sensor unit,
and the display for controlling the actions thereof, the method
comprising the steps of: connecting either the main interface
connector to the first testing interface connector, or the probe
interface connector to the second testing interface connector, or
both the main interface connector and the probe interface connector
respectively to the first and second testing interface connectors,
if the main interface connector is connected to the first testing
interface connector, causing the LED driver to drive the simulator
and cause the signal processor driver to drive the signal processor
which in turn drives the display of the oximeter with an indication
of the characteristics of the simulated waveforms, if the probe
interface connector is connected to the second testing interface
connector, causing the probe driver-sensor to activate the LED and
photodiode circuits and cause responses therefrom to be sensed and
indications thereof to be displayed on the display of the testing
apparatus, and if both the main and probe interface connectors are
both connected to the first and second testing interface
connectors, causing the LED driver to drive the simulator and cause
the signal processor driver to drive the signal processor which in
turn drives the display of the oximeter with an indication of the
characteristics of the simulated waveforms and causing the probe
driver-sensor to active the LED and photodiode circuits and cause
responses therefrom to be sensed and indications thereof to be
displayed on the display of the testing apparatus.
86. The method of claim 85, wherein if the probe interface
connector is connected to the second testing interface connector,
causing the probe driver-sensor to activate the LED and photodiode
circuits with continuity signals thereby causing the responses to
be indicative of the continuity of said circuits.
87. The method of claim 85, wherein if the probe interface
connector is connected to the second testing interface connector,
causing the probe driver-sensor to activate the LED circuit with
sensitivity signals which in turn activates the photodiode circuit
thereby causing the responses to be indicative of the sensitivity
of said circuits.
88. The method of claim 83, wherein the electrical activation of
only the LED circuits involves applying high and low signals to the
LED circuits thereby producing high and low outputs in the
photodiode circuit; generating difference signals from said high
and low signals; and determining the sensitivity of the probe from
said difference signals.
89. A method for testing the sensitivity of a pulse oximeter probe
which provides red and infrared LEDs and a photodiode, comprising
the steps of: measuring the output of the photodiode as it relates
to one LED at different input levels to said one LED and producing
a difference signal therefrom; measuring the output of the
photodiode as it relates to the other LED at different input levels
to said other LED and producing a difference signal therefrom; and
displaying indications of said difference signals.
90. The method of claim 89, wherein each measuring step involves
causing each of the LEDs to be driven with different inputs and
measuring the output from the photodiode resulting therefrom.
91. A method for testing the sensitivity of a pulse oximeter probe
which provides red and infrared LEDs and a photodiode, comprising
the steps of: obtaining high and low outputs from the photodiode
that relate to one of the LEDs; measuring the high and low outputs
from the photodiode relating to said one LED and producing a
difference signal; obtaining high and low outputs from the
photodiode that relate to the other LED; measuring the high and low
outputs from the photodiode relating to said other LED and
producing a difference signal; and determining the sensitivity of
the probe from said difference signals.
92. The method of claim 91, wherein obtaining the outputs of the
photodiode that relate to said one LED is in response to causing
said one LED to be activated at high and low levels; and wherein
obtaining the outputs of the photodiode that relate to said other
LED is in response to causing said other LED to be activated at
high and low levels.
Description
FIELD OF THE INVENTION
This invention pertains to pulse oximeter testing and more
particularly to a method and apparatus for testing pulse
oximeters.
BACKGROUND
Pulse oximeters are commonly used in hospitals and other
patient-care facilities for monitoring the blood oxygen level of a
patient in a non-invasive, continuous manner. The basis of
operation of these instruments is the fact that blood absorbs red
(R) and infrared (IR) light in different amounts depending on the
level of oxygen in the blood (SpO.sub.2) and that a known
relationship exists between the ratio of red to infrared light
(R/IR) and blood oxygen level (SpO.sub.2).
Thus, a pulse oximeter functions by detecting the amount of red and
infrared light transmitted through a part of the body, usually a
finger, to establish the R/IR ratio. It then compares this ratio
with an internally stored database giving the relationship between
R/IR ratios and SpO.sub.2 levels, determines the SpO.sub.2 level
for the detected ratio, and displays the SpO.sub.2 value. Pulse
rate and other parameters may also be detected and displayed.
The popular pulse oximeters provide an optical sensor, typically
called a probe, which is an alligator- or clamshell-clip that
clamps on the index finger of a patient. One jaw of the probe clip
contains red and infrared light-emitting diodes (LEDs), and the
other jaw contains a light-detector such as a photodiode. The probe
cable is connected to the main unit or instrument of the oximeter.
Certain of the conductors in the cable connect the LEDs to a driver
circuit in the instrument which produces a signal to activate the
LEDs, and other conductors connect the photodiode to an amplifier
for amplifying the small signal generated by the photodiode when
light is transmitted through a finger and for transmitting it to
the signal processor of the oximeter.
Like any instrument for monitoring physiological functions, a pulse
oximeter needs to be tested on a regular basis to determine if it
is providing accurate readings. Although test equipment has been
developed for testing the accuracy of pulse oximeters, such
equipment has been based on a particular testing philosophy which
imposes certain undesirable limitations on the test results. This
philosophy is to provide a simulated finger, clamp this "finger" in
the oximeter probe, operate the oximeter to test the simulated
finger just as if it were a real finger, and determine if the
display provides a reading consistent with the simulation. An
example of this testing approach is disclosed in the Merrick et al.
U.S. Pat. No. 5,348,005. In this patented device, the artificial
finger is a long, narrow, finger-shaped object made of steel and
having slots on opposite sides respectively receiving an LED bar
and a pair of photodiode detectors. To test an oximeter, the
Merrick et al. artificial finger is placed in the oximeter probe,
and the oximeter is operated just as if it were monitoring a human
subject. That is, the red and IR LEDs of the oximeter emit flashes
of light that are detected in the "finger" by the photodiodes which
convert the light pulses into electrical pulses. These pulses are
modulated in the tester to provide signals which simulate the
signals that would be developed from a human finger. The modulated
electrical signals are then transmitted to the LEDs in the
artificial finger which converts them to light flashes that
activate the photodiode in the oximeter probe. Thus, the artificial
finger is an optical interface between the oximeter under test and
the test equipment.
The described testing approach is certainly the straightforward
approach in that it simply replaces a real finger with an
artificial finger and allows the oximeter to be used for the test
in a manner similar to its use in monitoring a patient. The only
difference appears to be the use of an electro-optical finger
instead of a real finger. Such an approach, however, has not proved
to be fully effective since the reliability of the testing can be
compromised or indeterminate and desired testing flexibility is
lacking, as hereinafter explained.
First, the testing accuracy of an oximeter tester using an optical
interface, as described above, depends on proper placement of the
simulated finger in the probe to allow the optical elements to
interact properly. With a human finger, exact placement of the
finger in the probe is not critical since the entire circumference
of a finger presents human tissue to the LEDs. With an artificial
finger, however, the photodiodes and the LEDs in the artificial
finger must be placed exactly opposite the LEDs and photodiode,
respectively, of the probe or else the light flashes will not be
detected by the photodiodes. Thus, if this placement is not exact,
inaccurate readings will occur.
Before discussing other deficiencies of oximeter test equipment
employing an optical interface, it is important initially to
understand the construction of commonly used oximeter cables and
their normal use in a hospital. The cable referred to in one
popular brand of oximeter is actually two cables, namely, a preamp
cable and a probe cable. Although interconnected, these two cables
are of different construction; the preamp cable is relatively
strong and durable, whereas the probe cable is not as strong or
durable. The preamp cable is a thicker, somewhat flexible, heavy
duty cable, usually about 12 feet long, whereas the probe cable is
a thinner, very flexible, lightweight cable, usually about 3 feet
long. Whether or not the oximeter has a preamp cable, extension
cables (also referred to as patient cables) are often provided and
for the purpose of the present invention are equivalent to a preamp
cable. In referring to the preamp cable hereinafter, it will be
understood that such an extension cable is included.
The preamp cable is normally attached to and kept with its oximeter
instrument as the latter is moved about the hospital, whereas the
probe cable is normally kept separate from the oximeter instrument
and is not associated with any particular instrument since it can
be attached to any instrument of the same manufacture. The probe
cable may even be a disposable item.
In a hospital room, the preamp cable is long enough to serve as an
extension cord so that the oximeter instrument can be placed in a
convenient position and the preamp cable stretched to the bedside
of the patient. In contrast, the probe cable is clamped to the bed
or bedclothes of the patient's bed and coupled to the preamp cable.
The probe cable is made light and flexible so that it moves easily
and folds as the patient moves about and is less of an annoyance to
the patient. Thus, probe cables can easily fall on the floor by the
bedside and be subjected to abuse. Moreover, they are normally
folded, wound, or otherwise compressed and stored in a drawer,
sometimes rather haphazardly.
Because of the described construction, use and treatment of probe
cables and their probes, they are very vulnerable to damage and
defects. Field studies with hospital biomedical technicians have
shown that the majority of oximeter defects have been probe defects
and that these defects are caused by frayed probe cable wires, that
is, breaks or shorts, many of which occur intermittently.
Compounding this problem is the fact that as indicated above,
specific oximeter probes are not paired with specific oximeter
instruments, that is, the probes are interchangeable among
different oximeters and as stated above, the entire probe including
the cable and the clip may be disposable.
Using the above described testing approach with an optical
interface, i.e., inserting an artificial finger in the clamshell
probe of the pulse oximeter, the testing device performs the test
through the probe cable, that is, with the probe cable connected to
the preamp cable, just as if the oximeter were being used on a
human patient. If there is a defect in the probe cable, this
testing approach may miss it or fail to isolate it.
For example, if the probe cable has frayed wires, front end
circuitry in the oximeter may filter out the noise spikes caused by
the fraying, and the display will indicate normal functioning,
whereas in fact the probe cable is damaged and may later fail
completely at a critical time. Moreover, if the display on the
tester indicates an erroneous reading, it may not be possible to
determine if the problem is in the probe including the probe cable,
or in the signal processing circuitry. Furthermore, if the source
of the problem is suspected to be in the probe, the tester provides
no way of separately testing the probe cable and optics on the one
hand, and the signal processing circuitry on the other hand, to
isolate the problem area.
Thus, testing the oximeter as an integral entity, i.e., the probe
and signal processing circuitry together, as the optical-interface
approach requires, does not afford an unqualified independent
assessment of these main parts, and especially of the parts most
likely to fail. In fact, this testing methodology may introduce
other problems as explained above. In contrast, the oximeter
testing approach of the present invention differs from optical
interface concept described above and, as a result, avoids the
resultant problems.
SUMMARY
Pulse oximeter testing according to the present invention is based
on the concept of an electrical interface between the testing
instrument and the pulse oximeter rather than an optical interface.
Thus, the subject method and apparatus involve testing a pulse
oximeter signal processor separately from the probe, and still
further, testing the continuity of the probe, particularly the
probe cable, separately from the sensitivity of optical elements of
the probe.
For testing according to the present invention, the probe is
disconnected from the pulse oximeter. Then, a modulated electrical
test signal representative of blood oxygen saturation values is
generated in response to the electrical LED drive signal from the
oximeter and is electrically applied to the oximeter signal
processor. This signal causes the display of the oximeter to show a
value of blood oxygen saturation which is compared with the
saturation values represented by the test signal. Other parameters,
such as pulse rate and pulse amplitude, may also be tested.
Independently of the signal processor test, but simultaneously
therewith if necessary, the probe is subjected to continuity and
sensitivity tests and the results displayed. In this manner, each
of the main components of the pulse oximeter is separately
analyzed, and the source of a defect, if any, is isolated.
An object of the present invention is to test and verify the basic
operation of pulse oximeters used in hospitals and other patient
care facilities.
It is another object to test pulse oximeters in a more efficient,
effective, safe, and reliable manner than heretofore known.
Another object of the subject invention is to avoid the errors
which may be introduced into the testing of a pulse oximeter when
the oximeter is tested by clamping its probe onto a simulated
finger containing optical elements, thus requiring precise
positioning of the simulated finger in the probe.
Another object is to use an electrical, instead of an optical,
interface between the pulse oximeter and an instrument for testing
the oximeter.
A still further object is to be able to test the main components of
a pulse oximeter, namely, the oximeter electronic unit and the
optical sensor, separately from each other.
Yet another object is to test a pulse oximeter so as to isolate the
source of defects among the main parts of the oximeter.
Still another object is to facilitate testing both the continuity
of the probe and the optical functions of the probe independently
of each other and of the signal processing circuitry of a pulse
oximeter.
Another object is to eliminate doubts about the integrity of
testing a pulse oximeter which tests good although its probe cable
may have a emerging discontinuity causing intermittent noise spikes
which are filtered out by the oximetry circuitry but which could
eventually degrade and cause inaccurate or no readings during
critical use of the oximeter.
A further object is to be able to test oximeter probes, which are
interchangeable among different oximeters, independently of the
main oximeter test instrument.
A still further object is to be able to test an oximeter probe,
which are the source of most of the defects in an pulse
oximeter.
An additional object is to display waveforms representative of the
tests performed on the continuity of the probe of a pulse oximeter
and on sensitivity of the optical elements of the probe alone while
at the same time displaying digital readouts of blood oxygen level,
pulse rate and other parameters being tested.
Yet another object is to provide an apparatus for testing a pulse
oximeter which is able to test the most commonly used pulse
oximeters.
A still further object is to simplify the task of biomedical
equipment technicians and other trained healthcare personnel in
testing the basic operation of pulse oximeters used in hospitals
and other patient-care facilities.
Another object is to be able to subject a pulse oximeter to a
manually or automatically controlled sequence of test signals
including predetermined combinations of blood oxygen saturation and
other parameters, such as pulse rate and pulse amplitude,
representing either arbitrary test values or patient profiles, and
to determine the response to the oximeter.
A feature of this invention is to allow defects in the probe cable
of a pulse oximeter to be analyzed to determine if the cable can be
used, should be disposed of, or should be set aside for repair.
An additional feature of this invention is to allow the optical
elements of the probe cable of a pulse oximeter to be analyzed to
determine if the probe can be used, should be disposed of, or
should be set aside for repair.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic drawing showing a left side elevation of a
main unit or instrument of the pulse oximeter testing apparatus of
the present invention and showing the apparatus in readiness to be
connected to a commonly used pulse oximeter, with the probe
disconnected from the oximeter and in position to be connected to
the subject testing apparatus but also showing in phantom lines the
probe as it is normally connected to the pulse oximeter through the
preamp cable.
FIG. 2 is a diagrammatic view of the probe of FIG. 1 which includes
a probe connector, a probe cable and a finger clamp.
FIG. 3 is a detailed face view of the probe connector.
FIG. 4 is another diagrammatic view of the probe and its
components.
FIG. 5 is a schematic diagram of the red and IR LED circuit and the
photodiode circuit in the probe of FIGS. 2-4.
FIG. 6 is a right side elevation of the main unit of the pulse
oximeter testing apparatus of FIG. 1.
FIG. 7 is a front elevation of the main unit shown in FIGS. 1 and
6.
FIG. 8 is a functional block diagram showing the major components
of the subject testing apparatus and their connections to a pulse
oximeter under test.
FIGS. 8A-8D are pulse timing diagrams showing IR and red voltage
pulses occurring in the circuits of FIG. 8, and FIGS. 8E and 8F are
Pleth diagrams which are illustrated to assist in explaining the
circuits of FIG. 8, it being noted that, for illustrative purposes,
the scale of the pulses in FIG. 8D differs from FIGS. 8A-8C.
FIG. 9 is a functional block diagram of the continuity testing
section of the probe analyzer of the subject testing apparatus, the
probe analyzer being shown connected to the probe LEDs and
photodiode, it being noted in this Fig. and other Figs. herein that
the diagram boxes with square corners indicate functions
implemented in hardware, whereas the boxes with rounded corners
indicate functions implemented in software.
FIG. 10 is a functional block diagram of the sensitivity testing
section of the probe analyzer, the probe analyzer being shown
connected to the probe LEDs and photodiode.
FIG. 10A is a photodiode waveform occurring in the circuit of FIG.
10.
FIG. 11 is a functional block diagram and partially diagrammatic
view of a sequencing feature of the subject testing apparatus.
FIG. 12 is a functional block diagram showing how the testing
apparatus is connected to an oximeter and a printer for
automatically logging the results of a test.
FIGS. 13, 14, and 15 are diagrammatic views of the display screen
and part of the keypad of the subject testing apparatus showing
different displays and different menus which are available on the
display screen with the method and apparatus of the present
invention.
DETAILED DESCRIPTION OF THE APPARATUS
The pulse oximeter testing apparatus or analyzer of the present
invention is generally represented by the numeral 20 in FIG. 1,
which is a schematic drawing showing how the testing apparatus is
connected to a pulse oximeter 24. Since reference will made herein
to certain aspects of the pulse oximeter itself, it will be helpful
at the outset to provide a brief general description of a typical
pulse oximeter.
Thus, the pulse oximeter 24 (FIG. 1) includes a main unit 26 and a
probe 28 which includes a probe cable 30. The main unit includes a
signal processor 32, an LED driver 34, and upper and lower displays
38 and 40 for displaying the blood oxygen saturation SpO.sub.2 as a
percentage and pulse rate in beats per minute. The main unit of the
brand of oximeter shown and described herein also includes a preamp
cable 42. The preamp cable terminates at one end in a proximal
preamp connector 44 coupled to an interface connector 45 in the
main unit 26 and at the opposite end in a distal. preamp connector
46. A photodiode amplifier 48 is located in the distal preamp
connector. Some brands of oximeter do not employ an external
photodiode amplifier but incorporate all the necessary functions in
the main unit. The principles of the present invention are equally
applicable whether or not the oximeter uses an external
preamplifier and cable.
The probe 28 including the probe cable 30 is shown in greater
detail in FIGS. 2-5 to which reference is now made. The probe
includes a clamshell- or alligator-clamp or clip 50 which has
hinged upper and lower jaws 52. Red and infrared light-emitting
diodes (LEDs) 54 and 56, respectively, are mounted in the upper
jaw, and a photodiode 58 is mounted in the lower jaw. The LEDs are
electrically connected in inverse parallel relationship as shown in
FIGS. 4 and 5 and are positioned in the clamp so as to direct light
toward the photodiode. As is well-known, when the oximeter 24 is
used to monitor the blood oxygen level (SpO.sub.2) of a patient,
the probe clamp is clipped onto the index finger of the patient so
that light from the LEDs can be transmitted through the finger and
be detected by the photodiode.
A probe connector 62 (FIGS. 2 and 3) is attached to the probe cable
30 at the opposite end from the probe clamp 50. In the normal
operation of the oximeter, the probe connector 62 is connected to
the distal preamp connector 46, as shown in phantom in FIG. 1,
thereby to connect the probe 28 to the main unit 26. In accordance
with the principles of the present invention, however, the probe
connector 62 connects the probe to the subject testing apparatus
20, as will be subsequently described in detail.
The probe cable 30 (FIGS. 2-5) includes LED conductors 64
interconnecting the LEDs 54, 56 and terminals 66 in the probe
connector 62, thereby constituting an LED circuit, and photodiode
conductors 68 interconnecting the photodiode 58 and other terminals
70 in the connector, thereby constituting a photodiode circuit. The
probe cable also includes electromagnetic shields 72, 74, and 76
(FIG. 4) and outer insulation 78, all of which are well-known and
thus not described in greater detail.
With the foregoing brief description of a typical oximeter 24 is
background, reference is now made to the testing apparatus 20
(FIGS. 1 and 6-8) of the present invention. The testing apparatus
provides a main instrument 80 which includes a housing 81 that has
a left panel 82, a right panel 84, and a front panel 86, and which
encloses an electronic testing system generally identified by the
numeral 90 in FIG. 8. The testing apparatus also includes a
simulator adapter cable 92 (FIGS. 1 and 8) and an external DC power
supply 94. The simulator adapter cable has connector plugs 95 and
96 at opposite ends thereof.
The electronic testing system 90 (FIG. 8) provides an SpO.sub.2
simulator or signal processor 100; a probe analyzer 102; a
microprocessor 104; a user interface 106; an internal power supply
with battery 108; and interface connectors 112, 114 and 116 (FIG.
1) in the left panel 82. Interface connector 112 is connected to
the SpO.sub.2 simulator, and interface connectors 114 and 116 are
connected to the probe analyzer respectively for brand X and brand
Y pulse oximeter probes 28. The interface connector 112 is designed
to receive the plug 95 of the simulator adapter cable 92, and
interface connectors 114 and 116 are designed to receive the
connectors 62 of the probe cables 30 of the manufacturers of brand
X and brand Y oximeters, as 24. Interface connectors 118, 120, and
122 (FIG. 6) are mounted in the right panel 84 respectively for the
external DC power supply 94, for serial communication, and for a
printer (FIG. 12).
To best understand the testing functions of the subject apparatus
20, it will be helpful first to explain the user interface 106
(FIGS. 7, 8 and 13-15). The user interface includes an LCD graphic
display subsystem 130 (FIG. 8) which provides an LCD display screen
or panel 132 (FIG. 7 and 12-15) in the front panel 86 of the
housing 81 and a plurality of keys 134 in a keypad 136 below the
screen. The display screen is divided into an upper SpO.sub.2
simulator window 140, a middle graphing window 142, and a lower
soft-key menu window 144. In the disclosed embodiment, there are
five soft keys F1-F5, two hard keys M and P, and an on/off key O
(FIG. 7).
The LCD graphic display subsystem 130 (FIGS. 8 and 13-15) provides
several menus to be displayed in the lower menu window 144, and
these menus are selected by pressing the hard keys M and P. In the
disclosed embodiment, there is one root menu and four sub-menus,
namely, an SpO.sub.2 simulator sub-menu (FIG. 13), a sequencing
sub-menu, a probe continuity sub-menu (FIG. 14), and a probe
sensitivity sub-menu (FIG. 15). For each menu displayed, each soft
key F1-F5 has a different function which is displayed in the lower
menu window above the key, as shown in FIGS. 13, 14 and 15. The
root menu is not shown, but it is the default menu in which the
names of the four sub-menus are displayed in the lower menu window
above the keys F1 through F4. The sub-menus correspond to the
different modes of operation of the subject testing apparatus 20,
namely, SpO.sub.2 simulator mode, sequencing mode, probe continuity
mode and probe sensitivity mode and relate to the displays in the
upper and middle windows 140 and 142. The SpO.sub.2 simulator menu
relates to the upper or SpO.sub.2 simulator window 140, whereas the
sequencing, probe continuity, and probe sensitivity submenus all
relate to the middle or graphing window 142.
Considering first the SpO.sub.2 simulator mode using the SpO.sub.2
simulator sub-menu and its related upper, SpO.sub.2 simulator
window 140 (FIG. 13), the latter displays the parameter settings
selected and then generated by the SpO.sub.2 simulator 100 (FIG.
8). The SpO.sub.2 window includes an oximeter brand or status box
150, which displays the brand of oximeter under test; an oxygen
saturation display box 152, which displays SpO.sub.2 as a
percentage; a pulse rate display box 154, which displays pulse rate
in beats per minute; and a pulse amplitude display box 156, which
displays pulse amplitude as a percentage. Examples of typical
values are shown in boxes 152, 154, and 156.
Using the SpO.sub.2 simulator sub-menu (FIG. 13), the display boxes
152-156 are sequentially highlighted and thus selected by pressing
soft keys F2 or F3. When the SpO.sub.2 box 152 is selected, the
desired SpO.sub.2 percentage can be chosen by pressing the keys F4
or F5 which causes the percentage displayed s to increase or
decrease in increments of one percent. The SpO.sub.2 percentage
displayed corresponds to a particular R curve (relationship between
R/IR and SpO.sub.2) stored in the microprocessor and selected when
keys F4 or F5 are pressed. Similarly, the pulse rate and pulse
amplitude are selected and displayed in the boxes 154 and 156.
As previously indicated, the sequencing, probe continuity and probe
sensitivity modes all share the middle or graphing window 142. Each
of these modes, along with its sub-menu, is selected by pressing
the hard keys M or P. For the probe continuity mode, the key M or P
is pressed until the probe continuity sub-menu appears in the lower
window 144 (FIGS. 13 and 14) and the probe continuity display 158
appears in the middle window 142 (also FIGS. 13 and 14). The probe
continuity display provides an upper LED channel 160 and a lower
photodiode channel 162, both extending across the window. The
graphic display subsystem 130 provides a static graphic background
for the probe continuity display including: a matrix of dots or
graticules (FIG. 13) spaced horizontally in time preferably by five
milliseconds; the indicia "LED" and "PHOTO" along the ordinate
margins of the upper and lower channels, respectively; the indicia
"OPEN", "GOOD", and "SHORT" along the ordinate margin of each
channel; and the label "PROBE CONTINUITY" along the top of the
window. For the probe sensitivity mode, one of the keys M or P is
pressed until the probe sensitivity display 164 shown in FIG. 15
appears in the middle or graphing window 142 and the probe
sensitivity sub-menu appears in the lower window 144. For the probe
sensitivity mode, the graphic display subsystem 130 provides a
static graphic background in the middle window including: upper,
middle and lower bargraph channels 165, 166, and 168 which,
although not shown, are empty when no test is being conducted; the
indicia "RED," "IR," and "RATIO" along the left margin; the label
"PROBE SENSITIVITY" along the top of the window; the name of the
probe 28 being tested just below the label; and areas at the right
ends of the bargraph channels to display numbers respectively
representative of the amplitudes of the values displayed in the
bargraph channels.
As for the sequencing mode and sub-menu, more detailed reference is
made under the subsequent heading "Test the Main Unit-Sequencing
Mode." With the foregoing understanding of the user interface 106,
the SpO.sub.2 simulator 100 (FIG. 8) of the subject testing
apparatus 20 includes a current sensor 170 as its input stage. When
the testing apparatus is being used to test the pulse oximeter 24,
the connector 62 of the probe cable 30 (FIG. 1) is disconnected
from the preamp connector 46, and instead, the simulator adapter
cable 92 is connected to the preamp connector and also to the
interface connector 112, thereby establishing an electrical
connection between the input of the current sensor and the output
of the LED driver 34 of the pulse oximeter under test.
When the testing apparatus 20 is thus connected to the pulse
oximeter 24 under test (FIG. 1) and the oximeter 24 is powered up,
the LED driver 34 (FIG. 8) will then feed red and IR current pulses
to the current sensor 170 instead of to the probe LEDs 54 and 56.
The current sensor receives these red and IR current pulses and
converts them into IR and red voltage pulses (IR and R), as shown
in FIG. 8A, whose amplitudes represent the IR and red light
intensity that would have been produced by the probe LEDs in the
normal operation of the oximeter.
The SpO.sub.2 simulator 100 (FIG. 8) also includes a de-multiplexer
172 which is connected to the output of the current sensor 170. In
general, the polarity of the red and IR pulses from the oximeter's
LED driver 34 is different, and thus the polarity of the voltage
pulses (FIG. 8A) from the current sensor is different, for example,
the IR pulses are positive and the red pulses are negative. The
de-multiplexer detects this polarity and thus distinguishes between
red and IR pulses and splits the red and IR voltage pulses into
separate IR and red voltage pulse signals IR and R (FIG. 8B) and
feeds these signals to a DC attenuator 174 from where they are
transmitted to an AC modulator 176.
The attenuator and modulator 174/176 vary the IR and red pulse
signals IR and R in accordance with values of parameters stored in
databases in the memory of the microprocessor 104 and as displayed
in the boxes 152, 154 and 156. This attenuation/modulation
simulates what is caused by a real finger placed in the clamp 50 of
the probe 28 and thus simulates SpO.sub.2 levels, pulse rates and
pulse amplitudes such as those occurring when the oximeter 24 is
being used to monitor a patient.
For example, the DC attenuator 174 under the control of the
microprocessor 104 (FIG. 8) first modifies the IR and R pulse
signals (FIG. 8B) from the de-multiplexer 172 to simulate the
average component of the SpO.sub.2 simulation, that is, constant
physiological parameters caused by such factors as skin, bone and
venous blood as attenuated by a human finger. The DC attenuator
thus outputs IR.sub.DC and R.sub.DC voltage pulses, as shown in
FIG. 8C, to the AC modulator 176 and to a weighting adder 178.
Mathematically, these pulses are defined as:
where IR and R represent the voltage levels of the IR and R pulse
signals (FIG. 8B) from the de-multiplexer 172, and K.sub.IR and
K.sub.R are the attenuation constants for IR and red signals
respectively. Next, the AC modulator 176 under the control of the
microprocessor 104 (FIG. 8), modifies the IR.sub.DC and R.sub.DC
pulse signals (FIG. 8C--the arrows indicating modulation) from the
DC attenuator 174 to simulate the pulsatile or variable component
of the SpO.sub.2 simulation. This pulsatile component is the
variable physiological parameter of arterial blood, i.e., the
pulse, as attenuated by a human finger, and as represented by the
waveforms shown in FIGS. 8E and 8F which are based on Pleth
diagrams of arterial blood flow. The information represented by
these waveforms is stored in the memory of the microprocessor and
relates to the well known R-curves which give the relationship
between the R/IR ratios and SPO.sub.2 values. A user of the testing
apparatus selects an R curve and in so doing selects the waveforms
of FIGS. 8E and 8F to be used.
The AC modulator 176 (FIG. 8) outputs IR.sub.AC and R.sub.AC
voltage pulse signals, as shown in FIG. 8C, to the weighting adder
178. These signals are mathematically defined as:
where IR.sub.DC and R.sub.DC are calculated as indicated above and
IR.sub.PLETH(t) and R.sub.PLETH(t) are samples taken at
predetermined intervals, preferably 5 msec in the preferred
embodiment, from the Pleth waveforms of FIGS. 8E and 8F which, as
stated, are stored in the memory of the microprocessor.
As referred to above, the SpO.sub.2 simulator 100 (FIG. 8) includes
the weighting or scaling adder 178 which receives the four output
signals IR.sub.DC, IR.sub.AC, R.sub.DC, and R.sub.AC (FIG. 8C) from
the DC attenuator 174 and the AC modulator 176 and recombines these
signals into attenuated and modulated IR and red voltage pulse
signals (IR+R)', as shown in FIG. 8D, the arrows indicating
modulation. In so doing, the adder also applies weighting or
scaling factors to the IR.sub.DC, IR.sub.AC, R.sub.DC, and R.sub.AC
voltage pulse signals. In the disclosed embodiment, these weighting
factors are 1 for IR.sub.DC and R.sub.DC and 0.20 for IR.sub.AC and
R.sub.AC. That is, the level of the IR.sub.AC and R.sub.AC signals
is reduced to 1/5th of the level of the IR.sub.DC and R.sub.DC
signals. The output of the weighting adder is mathematically
defined as:
The output of the weighting adder 178 is fed to a current driver
180 that converts the modulated IR and red voltage pulse signals
(FIG. 8D) into modulated IR and red current pulse signals. These
current pulse signals are conducted to the photodiode preamplifier
48 by the simulator adapter cable 92 and then to the signal
processor 32 and the displays 38 and 40 of the pulse oximeter 24.
The modulated IR and red current pulse signals are thus processed
by the signal processor 32 just as if the current pulse signals had
come from the photodiode 58 as a result of the probe 28 being
attached to a real finger.
It is emphasized that the interface between the pulse oximeter 24
and the oximeter tester 20 is an electrical interface, with no
optics involved. That is, the LED driver 34 and the current sensor
170 and the photodiode preamplifier 48 and the current driver 180,
respectively, are electrically interconnected by the simulator
adapter cable 92. At this time, the probe 28 is disconnected from
the oximeter and is not involved in the testing of the oximeter's
ability to process detected signals and to display accurate
SpO.sub.2 and pulse measurements.
The probe 28, having been disconnected from the pulse oximeter 24
to allow electrical testing of the oximeter's signal processing
capabilities, is subjected to its own test by the probe analyzer
102 (FIGS. 8-15). The probe analyzer is part of the electronic
testing system 90 of the subject testing apparatus 20 and operates
under the control of the microprocessor 104 and the user interface
106. The probe analyzer tests the continuity of the probe circuits
and the sensitivity of the probe optics. Continuity testing is
described below with particular reference to FIGS. 5, 9, 13 and 14,
and sensitivity testing is described below with particular
reference to FIGS. 5, 10, 10A, and 15.
Considering continuity testing first, the probe analyzer 102 (FIGS.
8 and 9) includes LED and photodiode continuity current sources 181
and 182 which are connected to certain terminals in the interface
connectors 114 and 116. When the probe connector 62 is connected to
its matching interface connector 114 or 116, the continuity current
sources are respectively connected to the LED and photodiode
circuits through the conductors 64 and 68, respectively, at
terminals 2, 3 and 5, 9 FIGS. 4 and 5 to supply testing current to
these circuits and thereby to generate continuity testing voltages
across the LEDs 54, 56 and the photodiode 58. The probe analyzer
also includes a multiplexer 184 which receives the separate LED and
photodiode continuity voltages, combines them into a single voltage
signal with alternating LED and photodiode pulses, and feeds the
combined signal to an analog-to-digital converter 186. The A/D
converter transforms the signal into a series of discrete voltage
pulses representative of the alternating LED and photodiode
continuity voltages.
With continued reference to FIG. 9 in addition to FIGS. 13 and 14,
the microprocessor 104 circuitry includes a timer 189 which, in
general, generates clocking signals which call upon and cause
various sub-routines to be executed. For probe 28 continuity
testing, the timer executes the following software sub-routines:
display driving 190 (including sweep generation), glitch or spike
detecting 192, and sampling and scaling 194. The timer provides
hardware interrupts of preferably from 1 to 5 milliseconds during
which it executes the above-stated and subsequently described
service routines. The display driving routine activates the x-axis
of the LCD display screen 132 to provide horizontal sweep or time
lines 196 and 198 (FIGS. 13 and 14) in the upper and lower channels
at the "Good" level. The sampling and scaling routine samples and
scales the output of the A/D converter 186 at predetermined time
intervals, and the display driving routine applies these signal
samples to the display screen.
More specifically, the display driving routine 190 applies signal
samples representative of the continuity voltages from the LED
circuit 54, 56, 64 to the y-axis in upper LED channel 160 and
signal samples representative of the continuity voltages from the
photodiode circuit 58, 68 to the y-axis in lower photodiode channel
162. The glitch detecting routine 192 senses when a glitch or spike
of a predetermined threshold is sampled by the sampling and scaling
routine and causes the display driving routine to freeze the
display on the screen, as more fully described below.
Reference is now made to FIGS. 5, 8, 10, 10A and 15 for a
description the probe sensitivity testing features of the probe
analyzer 102 (FIG. 8). As shown in FIG. 10, the probe analyzer
includes red and IR sensitivity current sources 209 and 210
respectively connected to the red and IR LEDs 54 and 56. These
current sources are connected to certain terminals in the interface
connectors 114 and 116 so that when the probe connector 62 is
connected to its matching interface connector, the sensitivity
current sources are connected to their corresponding red and IR
LEDs.
The red and IR LEDs 54 and 56 are alternately activated by these
current sources 209 and 210 (FIGS. 5 and 10) to produce red and IR
light flashes. These flashes activate the photodiode 58 to generate
a voltage signal across the photodiode having alternating red and
IR pulses. The probe analyzer also includes an analog-to-digital
converter 212 which receives the voltage signal from the photodiode
58 and transforms the signal into a series of discrete voltage
pulses representative of the alternating red and IR sensitivity
voltages.
Referring to FIGS. 10 and 15, for probe 28 sensitivity testing, the
timer 189 of the microprocessor 104 executes the following software
routines: photodiode sample controlling 230, LED current source
controlling 234, sensitivity calculating 240, and bargraph and
readout generating 246. The photodiode sample controlling routine
activates the LED current source controlling routine alternately to
apply current to the red and IR LEDs. The sample controlling
routine also samples the IR and red pulses from the A/D converter
212 and develops red (R) low and red (R) high pulses and IR low and
IR high pulses.
From the pulses developed by the photodiode sample controlling
routine 230 (FIG. 10), the sensitivity calculating routine 240
generates a red sensitivity pulse from the red low and red high
pulses, an IR sensitivity pulse from the IR low and IR high pulses,
and an R/IR sensitivity ratio pulse from the red and IR sensitivity
pulses. The bargraph and readout generating routine 246 applies the
red sensitivity, the IR sensitivity and the R/IR sensitivity pulses
to the x-axis of the LCD display screen in the upper, middle and
lower bargraph channels 165, 166, and 168, respectively. Thus,
horizontal bargraphs representative of the response of the
photodiode 58 to the light flashes from the red and IR LEDs 54 and
56 are created.
DETAILED DESCRIPTION OF THE METHOD
Before describing the method for testing a pulse oximeter, as 24,
according to the present invention, the status of the oximeter
prior to the test, that is, the normal status of the oximeter is
summarized, as shown in the lower part of FIG. 1. The probe
connector 62 is normally connected to the preamp connector 46, as
shown in phantom lines in FIG. 1, so that the probe clamp 50 is
connected by the probe cable 30 and the preamp cable 42 to the main
unit 26 of the oximeter. To monitor a patient, the probe clamp is
clipped on the index finger of the patient whose SpO.sub.2 level,
pulse rate, and perhaps other parameters are to be checked. The
oximeter is then turned on, causing the LEDs 54 and 56 to flash
light at the finger and causing the photodiode 58 to receive the
light that is transmitted through the finger.
To test the pulse oximeter 24 in accordance with the present
invention, the first step is to disconnect the probe 28 (FIG. 1)
from the oximeter's main unit 26. Specifically, the probe connector
62 is disconnected from the preamp connector 46, thus disconnecting
the probe clamp 50 (including of course the LED and photodiode
circuits) and the probe cable 30 from the main unit, shown in the
center right in FIG. 1. At this point, the probe and the main
oximeter unit are ready to be tested.
Hospital technicians often wish to test only the probe 28 (FIG. 1)
center right including its cable 30, LEDs 54, 56 and photodiode 58,
and not the oximeter 24 as a whole: They wish to confirm probe
continuity and sensitivity, since the probe is often stored
separately from the main unit 26 and is more likely to be defective
than the remainder of the oximeter, as has been fully explained in
the Background, above. Of course, it is also desirable and
necessary to test the rest of the oximeter. The present method and
apparatus readily enables such testing versatility. Thus, following
disconnection of the probe connector 62 from the preamp connector
46, the next step of the method depends on what the technician
wants to test: the main unit 26; the probe 28; or both.
To test the main unit 26, the plug 96 of the simulator adapter
cable 92 is attached to the preamp connector 46, and the connector
plug 95 is inserted into the interface connector 112. Testing is
then continued as described below.
To test the probe 28, the probe connector 62 (FIG. 1) on the probe
cable 30 is plugged into the interface connector, either 114 or
116, which matches the brand of oximeter 24 under test. It will be
recalled that the testing apparatus is programmed to test various
brands of oximeters having different probes 28, and an interface
connector, as 114, 116, is provided for each brand to be
accommodated. In the embodiment of the apparatus shown, however,
only two brands, namely, brands X and Y, are capable of being
tested since currently these two brands are the most commonly used.
It will readily be understood, however, that the subject apparatus
20 could be modified to test additional brands without departing
from the scope of the present invention.
To test both the probe 28 (FIG. 1) and the main unit 26 at the same
time, the simulator adapter cable 92 and the probe cable 30 are
both connected to the testing apparatus 20 in the manner described
above. Even if only the probe or the main unit is to be tested to
the exclusion of the other, both cables may be connected to the
testing apparatus while either test is being conducted.
The description of the method of the present invention is continued
now with a description of the steps for testing the main unit 26
(FIG. 1) and thereafter the steps for testing the probe 28. Using
the keypad 136, the user turns on the testing apparatus 20 by
pressing the on-off key O (FIG. 7) whereupon the electronic testing
system 90 is activated and the default menu, that is the root menu,
appears in the soft-key menu window 144 (FIG. 13). The testing
apparatus as used to test the main unit is thereafter operated
either in a basic manual mode or in a sequencing mode, the latter
having both an automatic option and a manual option. The basic
manual mode is first described.
TESTING THE MAIN UNIT 26--BASIC MANUAL MODE
In the basic manual mode, the technician first chooses individual
values of SpO.sub.2 percentage together with values of pulse rate
and possibly pulse amplitude. To make this choice, the technician
presses the hard keys M or P (FIG. 7) to select the SpO.sub.2
submenu, as appears in FIG. 13. Then, using the keys F2 or F3, the
SpO.sub.2 display box 152 is selected, and with the keys F4 or F5,
the desired value of SpO.sub.2 percentage is set. Testing values of
pulse rate and/or pulse amplitude, if desired, are similarly set
and displayed in their respective boxes 154 and 156.
Next, the technician turns on the pulse oximeter 24, thereby
causing the LED driver 34 (FIG. 8) alternately to generate IR and
red current pulses which are directly fed to the current sensor 170
of the signal processor 100 of the testing apparatus 20. Again it
is noted that these red and IR current pulses, in the normal
operation of the pulse oximeter, would cause the red and IR LEDs in
the probe 28 to flash. Since the probe 28 is disconnected from the
oximeter 24, however, no such flashing occurs. Although believed
understood, the fact that the probe may be connected to the testing
apparatus at this time does not cause activation of the IR and red
LEDs by the LED driver since the oximeter's normal connection of
the LED driver to the probe is broken.
In response to the IR and red current pulses from the LED driver 34
(FIGS. 1, 8 and 8A) and as previously described, modulated IR and
red i current pulse signals are generated by the signal processor
100 under control of the microprocessor 104. This modulated current
represents the blood oxygen saturation (SpO.sub.2) level, pulse
rate, and pulse amplitude selected and displayed in the boxes 152,
154, and 156 (FIG. 13) and being used to test the oximeter 24. The
modulated IR and red current is transmitted to the photodetector
amplifier 48 (FIG. 8) by the simulator adapter cable 92 and is
processed by the pulse oximeter just as if the current had come
from the probe 28 attached to a real finger. The values of
SpO.sub.2 and pulse rate are read on the displays 38 and 40 of the
pulse oximeter and compared with the settings displayed in boxes
152 and 154 of the display screen 132 to determine whether the
oximeter is reading correctly. TESTING THE MAIN UNIT 26--SEQUENCING
MODE
In the sequencing mode of the testing apparatus 20, the subject
method and apparatus test the pulse oximeter 24 with a sequence of
programmed values of desired parameters (SpO.sub.2 , pulse rate,
and pulse amplitude in the disclosed embodiment). With reference to
FIG. 11, the sequencing mode includes a library 250 of profiles or
combinations 252 of parameters, each profile including a set of
parameter curves, for example, SpO.sub.2 curves, as 254: pulse rate
curves, as 256; and pulse amplitude curves, as 258, all of which
are loaded into the memory of the microprocessor 104. As suggested
above, more or fewer parameters could be included if desired.
These profiles 252 are user-defined and preferably include both
actual patient profiles from clinical studies and arbitrary,
user-created profiles. The front profile diagrammatically
illustrated in FIG. 11 is an arbitrary profile and includes an
SpO.sub.2 curve 254 declining in steps; a pulse rate curve 256
rising in steps, and a constant pulse amplitude curve 258. The
patient profiles, not shown, typify the various conditions that are
expected to be encountered in use of the oximeter, and for example,
include constant values, that is, straight lines, like the pulse
amplitude of FIG. 11, with intermittent deviations representative
of physiological irregularities, such as desaturation dips,
arrhytmia's, or the like deviations from the normal.
The sequencing mode (FIG. 11) can be operated either manually at an
operator-controlled rate (the manual option) or automatically at a
programmed rate (the automatic option). For this purpose, the timer
189 of the microprocessor 104 executes a sequence controlling
sub-routine 266 which is initiated from the keypad 136. The
sequence controlling subroutine feeds signals representing the
selected profile data to the AC/DC modulators 174/176 of the
SpO.sub.2 simulator 100 (FIGS. 8 and 11) and to the graphic display
subsystem 130 (FIGS. 8 and 11). In the disclosed embodiment, the
sequence controlling routine feeds only the SpO.sub.2 and pulse
rate curves 254 to the upper and lower channels 160 and 162,
respectively, of the display screen 132. Because of preferred space
limitations on the display screen, the pulse amplitude curve 258 is
not included, although it could be if desired.
Each profile 252 (FIG. 11) provides a cursor 270 (FIG. 12) which is
contained in the memory of the microprocessor 104 as part of the
profile data. The cursor is developed by the sequence controlling
routine as a vertical sweep in the middle window 142 of the display
screen 132 and its position at any given time corresponds with,
that is, indicates on the curves, the values of the parameters
being fed to the attenuator/modulator 174/176 and shown in the
displays 152, 154, and 156. The cursor is programmed in memory to
start at zero time base and to advance horizontally across the
screen at timed intervals depending on whether the manual option or
the automatic option is selected. If the manual option is selected,
the cursor advances from one step to the next upon pressing one of
the keys 134 and remains there until the key is pressed again, so
the timing of the intervals is under the immediate control of the
operator. If the automatic option is selected, the cursor advances
from one step to the next at a rate programmed into the particular
profile selected.
In use of the sequencing mode, the technician selects the desired
profile 252 (FIG. 11) and the manual or automatic option with the
keypad 136 and then turns on the pulse oximeter 24. As with the
basic manual mode, the LED driver 34 (FIG. 8) alternately generates
red and IR current pulses which are directly fed to the current
sensor 170 of the signal processor 100 of the testing apparatus 20.
The sequence controlling routine 266 feeds signals representing the
profile data to the DC attenuator/AC modulator 174/176 and feeds
the same profile signals plus the cursor signal to the graphic
display subsystem 130. The modulated red and IR current is
transmitted to the photodiode preamplifier 48 (FIG. 8) by the
simulator adapter cable 92 and is processed by the pulse oximeter
as in the basic manual mode.
TESTING THE MAIN UNIT 26--SEQUENCING MODE
Manual or Interactive Option
In the manual, that is, interactive, option of the sequencing mode,
the technician controls the advance of the cursor 270 across the
screen 132 by pressing the appropriate key 134 of the keypad 136
each time the technician elects to step to the next set of values
in the profile 252 selected. After each advance of the cursor, the
technician compares the values of SpO.sub.2, pulse rate, and pulse
amplitude at the location of the cursor, which are being fed to the
oximeter 24 and which are displayed in the display boxes 152, 156,
and 158, with the readings on the displays 38 and 40 of the
oximeter. Additionally, the technician may keep a datalog of the
test by entering the values read on the oximeter's displays into
the memory of the microprocessor 104 by pressing appropriate keys
134. Subsequently or at the same time, the test results stored in
memory can be printed-out by connecting a printer 280 to the
printer port 122 (FIG. 12).
TESTING THE MAIN UNIT 26--SEQUENCING MODE
Automatic Option
The automatic option of the sequencing mode allows two types of
tests especially useful for testing pulse oximeters, as 24, namely
a sweep test and a trend test. In the sweep test, a sequencing
profile 252 is selected and the automatic sequencing mode is
activated with the keypad 136 causing the cursor 270 to sweep in
steps across the screen automatically from one value to the next
and at a predetermined rate, preferably from about four to thirty
seconds intervals but slower or faster is of course possible, as
controlled by the timer 189. The interval depends on the
characteristics of the oximeter, e.g., the specified amount of
delay time needed by the oximeter to process and display the
readings after each successive input, and as explained above, is
built into the profile. Thus, the ability of the oximeter to
respond within the delay time specified by the oximeter
manufacturer can be tested. The results of the test are logged by
connecting a cable 282 (FIG. 12) from the oximeter to the serial
port 120 of the main unit 80 of the testing apparatus 20 whereby
the readings on the oximeter's displays are fed into the memory of
the microprocessor 104. Thereafter or simultaneously, and as
described above, these results can be printed by connecting the
printer 280 to the printer port 122.
The trend test is similar to the sweep test except that the
intervals between each stepped advance of the cursor 270 are much
longer, so that one complete cycle through the profile, as 254,
i.e., one pass across the screen, may be as long as an hour or
more. Here, it is first to be understood that certain pulse
oximeters, as 24, have the capability of running trend tests on
patients. For a trend test on a patient, the oximeter is connected
to the patient and readings are taken and recorded over an extended
period, up to an hour or more, to determine if there is a trend in
the patient's condition. Thus, it is desirable to test the
trend-taking capabilities of the oximeter. The subject method and
apparatus 20 allow such a test.
To conduct a trend test on the oximeter 24, a patient profile 252
that incorporates parameters having deviations that show a trend is
preferably selected. Alternatively, an arbitrary profile with a
built-in trend may be selected. For example, the profile might
include an SpO.sub.2 curve that is essentially flat but has
momentary desaturation dips which increase over time. The purpose
of the trend test is to determine if the oximeter can detect these
momentary dips and the trend thereof accurately.
In summary of the testing of the main unit 26, it is again
emphasized that the optical interface of the pulse oximeter 24 is
changed to an electrical interface. There is a direct electrical
connection between the LED driver 34 and the current sensor 130 and
a direct electrical connection between the current driver 142 and
the photodiode amplifier 48. The probe 28 is out of the loop. Since
the electrical interface of the subject testing apparatus bypasses
the probe, the probe is not involved in the test of the oximeter's
signal processor 32, LED driver 34, displays 38, 40, and photodiode
amplifier 48.
TESTING THE PROBE 28--CONTINUITY TEST
The analysis of the probe 28 usually starts with a continuity test
since field experience shows that the majority of probe defects are
caused by frayed wires in the probe cable 30, many of which are
intermittent defects. The testing apparatus 20 is turned on by
pressing the on-off key 146. Then, the keys M or P are pressed to
select the probe continuity sub-menu, as shown in FIGS. 13 and 14,
thereby to display the continuity signals on the screen 132. The
continuity current sources 181 and 182 (FIG. 9) deliver current to
the LED and photodiode circuits while the probe cable is manually
wiggled back and forth by the technician in an effort to reveal
intermittent defects in the conductors 64 and 68.
Specifically, current of about 0.5 ma is sent through the
conductors 64 and just one of the LEDs, as 54 (FIG. 9), by the
current source 181. In the normal operation of the red and IR LEDs
54 and 56 as part of the pulse oximeter 24, current is caused to
flow first in one direction and then in the other through the
conductors 64, thereby alternately to excite the LEDs. For this
continuity test, however, only one of the LEDs is excited since the
principle objective is to check the continuity of the conductors
where defects are more likely to occur.
The other continuity current source 182 (FIGS. 2-5 and 9) supplies
a relatively low amperage current It, for example 0.5 ma, through
the conductors 68 and the photodiode 58 (FIG. 5). It is significant
here, and a feature of this invention, that the continuity current
It flows through the photodiode in the opposite direction, as
indicated by the arrow in FIG. 5, from the direction in which
current flows when the photodiode is excited by flashes of light.
This is a very practical feature since it causes the photodiode
continuity signal, which would ordinarily be sensitive to ambient
light, to be completely unresponsive to light. In this manner, the
probe 24 and cable 30 can be freely wiggled during the test without
any chance of artifact resulting from light sensitivity.
As shown in FIG. 9, and as previously described and under the
control of the timer 189, the LED and photodiode voltage samples
are applied by the display driving routine 190 of the
microprocessor 104 to the y-axes of the LED and photodiode channels
160 and 162 of the display screen 132. In a properly functioning
probe 30, there are no opens or shorts in the LED or photodiode
circuits, so no voltage spikes or glitches will be developed,
thereby causing the waveforms of the horizontal sweeps to be in the
middle of their channels 160 and 162, that is, along the levels
marked "Good," as shown in FIG. 13. If either circuit has a
discontinuity, that is, a broken conductor or wire, as 64 or 68, a
positive voltage sample, that is representing a glitch, will be fed
to the screen 160 and the waveform will rise to the position marked
"Open," such as shown in FIG. 14 with regard to the circuit for the
photodiode 58. Similarly, although not shown, if the circuit is
shorted, a negative sample also representing a glitch will be
delivered to the screen, causing the waveform to drop to the
position marked "Short."
What makes the probe continuity test according to the present
invention so valuable is its ability to detect intermittent opens
and shorts in the probe's red/IR circuit 54, 56, 64 and the probe's
photodiode circuit 58, 68 (FIG. 5). A simple static test of probe
continuity, such as a numeric display from a digital multi-meter,
is not able to detect these open or short circuit conditions
referred to as glitches that are characteristic of intermittently
defective probes 24 and particularly the probe cables 30. The
subject testing apparatus 20 provides simultaneous waveform
displays of both the red/IR circuit and the photodiode circuit so
that a single mechanical, i.e., manual, stress test, or wiggle
test, of the probe cable will reveal any intermittent opens or
shorts. In addition, any time a glitch is detected by the subject
apparatus, the waveforms are frozen on the screen, as more fully
described below, thereby eliminating any chance that the operator
may overlook a glitch.
In the probe continuity testing mode, with the continuity sub-menu
displayed as shown in FIG. 14, the soft key F3 toggles between an
auto trigger mode and a glitch trigger mode. In the auto trigger
mode, which is the typical operating mode, the waveforms (FIGS. 14)
sweep continuously across the screen 132 until a glitch is
detected. With reference to FIG. 9, when the glitch detecting
routine 192 detects a glitch, it sends a signal to the display
driving routine that causes the waveform, as 198 (FIG. 14), to
freeze on the screen at the end of the current sweep across the
screen. This captures or freezes the glitch waveform on the screen
so that it can not be missed by the technician.
By toggling the key F3 into the glitch trigger mode, with the
display screen 132 showing the probe continuity sub-menu (FIG. 14),
the waveforms 196 and 198 do not sweep across the screen until a
glitch is detected. This provides for maximum amount of glitch
signature or pattern on the screen and allows the technician an
opportunity carefully to examine the glitch. Another key F5 is used
to clear the screen after a glitch has been detected and froze and
to re-enable continuous waveform sweeping.
TESTING THE PROBE 28--SENSITIVITY TEST
If the probe 28 tests "Good" for continuity, it is next subjected
to the probe sensitivity test to evaluate the IR and red optical
performance of the probe. By pressing the hard keys M or P, the
probe sensitivity sub-menu is selected, as shown in FIG. 15. The
probe sensitivity test provides a quantitative method of evaluating
the probe's red, IR and red/IR ratio optical performances. It is
important to test this ratio because the ratio has a direct bearing
on how the oximeter works. If there is too much or too little red
(or too much or too little IR), there will be an imbalance so the
signal to noise ratio will be compromised and an inaccurate reading
will result.
With reference to FIGS. 10, 10A and 15, the bargraph and readout
generating routine 246 provides horizontal bargraphs, as 300, in
the bargraph channels 165, 166, and 168, together with
corresponding numerical readouts at the ends of the bargraph
channels. These bargraphs and readouts occur in response to
activation of the LEDs 54, 56 by the sensitivity current sources
209 and 210 which in turn activate the photodiode 58. The bargraphs
and readouts provide three measures of probe sensitivity, namely,
(a) red channel sensitivity, i.e., the sensitivity of the
photodiode to red light flashes; (b) IR channel sensitivity, i.e.,
the sensitivity of the photodiode to IR light flashes; and (c) the
red/IR ratio sensitivity. The formulas for these sensitivities are:
(a) red channel sensitivity=[red response @ 1 mA]-[red response @
0.5 mA] (b) IR channel sensitivity=[IR response @ 1 mA]-[IR
response @ 0.5 mA] (c) red/IR ratio sensitivity=red sensitivity/IR
sensitivity,
where red response @ x mA is the response of the photodiode when
the red LED is energized with x mA of current, and IR response @ x
mA is the response of the photodiode when the IR LED is energized
with x mA of current.
Based on the foregoing formulas, the photodiode sample controlling
routine 320 (FIG. 10) measures four photodiode responses, which are
taken across the photodiode 58 by the A/D converter and fed to the
sample controlling routine 230 as digital pulses, so that in
effect, the sample controlling routine is sampling the output of
the photodiode. These four responses are: [red response @ 1 mA],
[red response @ 0.5 mA], [IR response @ 1 mA], and [IR response @
0.5 mA]. From these responses, the sample controlling routine
produces the waveform shown in FIG. 10A, which also shows when the
four responses are sampled. The sample controlling routine produces
this waveform using the method set forth in the following
paragraph.
First, under the control of the timer 189, the sample controlling
routine 230 (FIG. 10) through the current source controlling
routine 234 completely de-energizes the IR LED 56 by turning off
the sensitivity current source 210, and energizes the red LED 54 by
turning on its current source 209 with 0.5 mA. After a two hundred
and fifty millisecond delay decremented by the timer, the
controlling routine 230 samples the photodiode 58 output to yield
the quantity "[red response @ 0.5 mA]." Secondly, the sample
controlling routine 230, together with the source controlling
routine 234, while maintaining the red LED de-energized, energizes
the red LED with 1.0 mA, and after another two hundred and fifty
millisecond delay, samples the photodiode output to yield the
quantity "[red response @ 1.0 mA]."
Thirdly, the sample controlling routine 230 completely de-energizes
the red LED 54 (FIG. 11) by turning off its sensitivity current
source 209 through the source controlling routine 234 and energizes
the IR LED 56 with 0.5 mA by turning on its current source 210 with
the source controlling routine. After the timer decrements another
two hundred and fifty millisecond delay (FIG. 12), the controlling
routine 230 samples the photodiode output to yield the quantity
"[IR response @ 0.5 mA]." Fourth, while keeping the red LED
de-energized, the controlling routines 230/234 energize the IR LED
with 1.0 mA by turning on its current source, and after another two
hundred and fifty millisecond delay, the controlling routine 230
samples the photodiode output to yield the quantity "[IR response @
1.0 mA]." The timer 189 causes this four-phase cycle to repeat once
a second.
The photodiode waveform (FIG. 10A) produced by the sample
controlling routine 230 in accordance with the methodology
described above is thus available for the sensitivity calculating
routine 240 (FIG. 10) to develop the red sensitivity, the IR
sensitivity and the red/IR sensitivity ratio signals. The bargraph
and readout generating routine 246 activates the x-axis of the
display screen 132 with the red sensitivity, the IR sensitivity and
the red/IR sensitivity ratio signals and creates red, IR, and
red/IR bargraphs, as 300 (FIG. 15), respectively in the bargraph
channels 165, 166, and 168. The generating routine also creates
red, IR, and red/IR numerical readouts at the ends of the
bargraphs, as also shown in FIG. 15.
The probe sensitivity test as described above measures the
sensitivity at two different current levels and takes the
difference which eliminates the effect of ambient light under
normal lighting conditions. By contrast, a very primitive test of
sensitivity would be to measure the output of the photodiode 58
when the LEDs 54 and 56 were driven with X amount of current and
this output analyzed and assumed to represent the sensitivity of
the components. However, this analysis would overlook the effect of
ambient light. Even with no electrical drive on the LEDs, ambient
light is always producing an output from the photodiode, so a
simple pulsing of the LEDs would always represent the effect of
both ambient light and the current source. By driving the LEDs with
current at two different levels, and subtracting the outputs, the
effect of ambient light is eliminated.
From the foregoing, it will be understood that the present method
and apparatus 20 for testing pulse oximeters 24 provides many
advantages. The fundamental concept of the subject invention is
that the testing philosophy is based on an electrical interface
between the oximeter and the testing apparatus, as contrasted with
the optical interface heretofore utilized. Many advantages flow
from this approach. Testing is more efficient and effective, safer
and thus more reliable, because the biomedical technician can more
readily determine whether a defect is in the main unit 26 of the
oximeter or the probe 28. Bypassing the optical interface also has
the advantage of not introducing error because of the need for
perfect placement of an artificial finger in the probe clamp 50 of
a pulse oximeter 24.
With the subject testing apparatus 20 electrically connected to a
pulse oximeter, as 24, the oximeter delivers signals to the testing
apparatus which would normally be delivered to the probe 28, and
the testing apparatus modulates these signals in a manner which
simulates the modulation resulting from a human finger placed in
the probe when the oximeter is in regular use. The modulated
signals are then fed back into the oximeter for processing by the
oximeter and shown on its displays so that comparisons can be made
with the known testing values. The subject method and apparatus
allows for testing with single values of the testing parameters or
with sequencing of profiles of the various parameters. Moreover,
the test results can be manually or automatically logged and
printed.
Experience of biomedical technicians in the patient care facilities
shows that defects are usually in the probe 28, especially the
probe cable 30. With the subject invention, it is possible to test
the probe, that is, the probe probe cable and optics 54, 56 and 58,
independently of the main unit 26 of the oximeter 24, whereas such
testing has not been possible with the prior oximeter testing
equipment. Also, since the probes are not unique to particular
oximeters, they are often stored independently of the oximeter
instruments, and sometimes in a manner which subjects them to undue
stress, causing defects. In the past, technicians who have wanted
to test only a probe which is separated from an oximeter instrument
have had to search around the hospital for an instrument, connect
the probe to the instrument, and then test them together just to
determine whether the probe is functioning properly. The subject
invention obviates this exercise since the subject testing
apparatus can readily test the probe alone.
It is also to be noted that the apparatus of the present invention
allows a technician to test the probe without the assistance of any
other person since the multiple terminals 66, 70 of the probe
connector are plugged into the interface connector 114 or 116 of
the testing apparatus 20, and the testing is performed. If a
technician, acting alone, were to attempt to test the continuity of
the probe with a multimeter, it would be virtually impossible, or
at least very impractical, to connect or contact the terminals of
the probe connector with the prongs of the multimeter while
simultaneously wiggling the cable and looking at the meter
reading.
Still further, the subject method and apparatus 20 improves the
integrity of testing of the oximeter because it improves the
testing of the probe 28, and especially the probe cable 30, where a
majority of the defects occur. This invention allows detection of
intermittent opens and shorts in the probe cable, whereas previous
testers might allow the oximeter to filter out spikes caused by
such intermittent defects and thereby mask a developing problem.
Still further, the subject method and apparatus displays the
results of the testing with waveforms which can be carefully
examined for a better analysis of the problems.
Although a preferred embodiment of the present invention has been
shown and described, various modifications and substitutions may be
made thereto without departing from the spirit and scope of the
invention. Accordingly, it is to be understood that the present
invention has been described by way of illustration and not
limitation.
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