U.S. patent number 3,726,270 [Application Number 05/182,053] was granted by the patent office on 1973-04-10 for pulmonary information transmission system.
Invention is credited to Roy A. Griffis, L. Thomas Rauterkus, Terence Torzala.
United States Patent |
3,726,270 |
Griffis , et al. |
April 10, 1973 |
PULMONARY INFORMATION TRANSMISSION SYSTEM
Abstract
A system by which signals pertaining to the pulmonary condition
of a patient are transmitted to a location which is remote from the
location of the patient. The signals are transmitted as the patient
is being tested. pulmonary information in the form of spirometry
data and total lung capacity volume are transmitted by means of
telephone lines or the like to a location remote from the patient,
and at the remote location the transmitted information may be
studied by a person who is well acquainted in the art of analysis
of such information. Patients at various locations provide
information to a central location at which studies of the
information are conducted. Thus, a specialist in the art of such
studies is in a position to receive information from various
patients who may be located at numerous widespread places and who
may be many miles from the specialist.
Inventors: |
Griffis; Roy A. (Dayton,
OH), Rauterkus; L. Thomas (Dayton, OH), Torzala;
Terence (Dayton, OH) |
Family
ID: |
22666894 |
Appl.
No.: |
05/182,053 |
Filed: |
September 20, 1971 |
Current U.S.
Class: |
600/532; 73/23.3;
128/904; 422/84 |
Current CPC
Class: |
A61B
5/0878 (20130101); Y10S 128/904 (20130101) |
Current International
Class: |
A61B
5/08 (20060101); A61B 5/087 (20060101); A61b
005/08 () |
Field of
Search: |
;128/2.08,2.07,2.1A
;23/254R,254E ;73/23,421.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Med. & Biol. Engineering, Vol. 9, pp. 247-254, Pergamon Press,
1971. .
Journ. of Assoc. for Advancement of Med. Instrumentation, Vol. 5,
No. 4 July-Aug., 1971, pp. 220-223..
|
Primary Examiner: Howell; Kyle L.
Claims
The invention having thus been described, the following is
claimed:
1. A pulmonary testing system for providing an electrical signal
indicating the peak percent nitrogen expired by a person in a
breath and the total nitrogen volume expired by said person during
repetitious breathing comprising:
means responsive to said person's repetitious breathing for
providing a first electrical signal proportional to the gas flow in
each expired breath,
analyzer means responsive to the repetitious exhaling of said
person for providing a second electrical signal indicating the
percent of nitrogen during each exhalation,
integrating means responsive to said first and second electric
signals for providing a third electrical signal indicating the
total volume of nitrogen exhaled by said person,
pulse generator means responsive to said second signal for
providing a series of pulse signals, each pulse signal indicating
the peak percent of nitrogen during a single exhalation,
and means for providing a system electrical signal by superimposing
said series of pulse signals upon said third signal such that said
series of pulse signals occur during the time an inhalation
occurs.
2. The invention according to claim 1 wherein said integrating
means includes multiplying means for multiplying said first and
second electrical signals prior to integrating the product
thereof.
3. The invention according to claim 1 wherein said pulse generator
means includes memory means for storing a value equal to the peak
percent of nitrogen during each exhalation and delay means for
providing said pulse generator means signal during the next
inhalation.
4. The invention according to claim 3 wherein said next exhalation
is detected by means determining that said second signal is below a
certain value.
5. The invention according to claim 3 wherein said second signal is
an analog signal having an instantaneous magnitude related to the
instantaneous percent of nitrogen during each exhalation and
wherein said memory means includes a capacitor which is charged to
a voltage related to the maximum magnitude of said second
signal.
6. The invention according to claim 5 wherein said pulse generating
means include means for discharging said capacitor by determining
that the instantaneous magnitude of said second signal is below a
certain value.
7. The invention according to claim 1 wherein said system further
includes minimum flow detector means for determining when said
first signal is below a predetermined value and minimum percent
nitrogen detector means for determining when said second signal is
below a predetermined value, said integrating means being inhibited
from providing a signal whenever said first or said second signals
are less than said predetermined values therefor, and said pulse
generating means being inhibited from providing a signal whenever
said second signal is below said predetermined value therefor.
8. The invention according to claim 7 wherein said integrating
means includes multiplying means for multiplying said first and
second signals prior to integrating the product thereof.
9. The invention according to claim 8 wherein said integrating
means further includes inhibiting means for inhibiting said
integrating means from integrating the product of said first and
second signals whenever either of said first or second signals is
less than said predetermined value therefor.
10. A pulmonary testing system for providing an electrical signal
capable of being transmitted over a single pair of telephone lines
to a recording device for causing, in response to said transmitted
signal, a graphic representation of the peak percent of nitrogen
expired by a person during each one of a plurality of successive
breaths, and the total volume of nitrogen expired by said person
during said plurality of breaths, said person, during said
plurality of breaths, inhaling a gaseous mixture containing
negligible nitrogen and exhaling a gaseous mixture containing a
decreasing percent of nitrogen, said system comprising:
means responsive to said plurality of successive breaths for
providing a first electrical signal having an instantaneous
magnitude proportional to the instantaneous gas flow resulting from
said breaths,
analyzer means responsive to said plurality of successive breaths
for providing a second electrical signal having an instantaneous
magnitude proportional to the instantaneous percent of nitrogen
contained in each exhalation,
multiplying means responsive to said first and second signals for
multiplying said first signal times said second signal to provide a
nitrogen flow signal,
integrating means responsive to said nitrogen flow signal for
integrating said nitrogen flow signal to provide a signal
indicating the total volume of nitrogen expired by said person,
pulse generating means responsive to said second signal for
providing one pulse for each exhalation, said pulse having a
magnitude proportional to the largest magnitude of said second
signal during that exhalation, said pulse being provided during the
inhalation immediately following that exhalation,
and output means to which is applied said pulse generating means
signal and said integrating means signal for adding said signals
applied thereto, thereby providing said system electrical
signal.
11. The invention according to claim 10 wherein said output means
further includes transmitting means which, in response to said
added signals, provides a modulated signal as said system
electrical signal.
12. The invention according to claim 10 wherein said system further
includes minimum detector means for determining whether said first
signal is above a first minimum magnitude and whether said second
signal is above a second minimum magnitude, said minimum detector
means including means causing said multiplying means to be
inhibited from providing a signal whenever either of said first or
second signals has a magnitude below said respective first and
second minimum magnitudes.
13. The invention according to claim 12 wherein said minimum
detector means includes means for inhibiting said pulse generating
means from providing a signal whenever said second signal has a
magnitude below said second minimum magnitude.
14. The invention according to claim 10 wherein said system further
includes means for providing a second system electrical signal
which represents the spirometry data of a single breath of said
person.
15. The invention according to claim 14 wherein said system further
includes switching means to select between said first and second
system electrical signals,
and wherein said system further includes transmitter means to which
the selected one of said first and second system electrical signals
is applied for providing a modulated signal representative of said
selected signal to a single pair of telephone lines.
16. The invention according to claim 10 wherein said pulse
generating means includes a storage capacitor for storing
electrical energy having a voltage proportional to the highest
magnitude of said second signal during each breath, and logic means
responsive to said second signal being below a certain magnitude to
cause said pulse to be provided during said immediately following
inhalation.
17. The invention according to claim 16 wherein said pulse
generating means further includes switching means responsive to
said logic means for causing said capacitor to discharge after said
pulse is provided and before the immediately following
exhalation.
18. Circuitry for transmission of pulmonary information from a test
location to a remote location by means of a telephone circuit
comprising:
a conduit adapted for communication with the respiratory system of
a patient,
a flowmeter joined to the conduit, the flowmeter having an
electrical output,
a percent nitrogen analyzer joined to the conduit and having an
electrical output,
a multiplier connected to the electrical output of the
flowmeter,
a minimum flow detector connected to the output of the
flowmeter,
a peak percent nitrogen follower,
a minimum percent nitrogen detector,
means connecting the output of the percent nitrogen analyzer to the
multiplier and to the peak percent nitrogen follower and to the
minimum percent nitrogen detector,
a gate member,
means connecting the outputs of the multiplier and the minimum flow
detector and the minimum percent nitrogen detector to the gate
member,
a percent nitrogen pulse generator including time delay means,
means connecting the output of the minimum percent nitrogen
detector to the peak percent nitrogen follower and to the percent
nitrogen pulse generator,
a transmitter,
means connecting the time delay means to the transmitter and to the
peak percent nitrogen follower,
an integrator,
means connecting the output of the gate member to the
integrator,
means connecting the output of the integrator to the
transmitter,
a central unit including a demodulator and a recorder,
means for connecting the transmitter and the demodulator to a
telephone circuit at opposite portions thereof,
means connecting the output of the demodulator to the recorder,
the transmitter thus transmitting to the central unit signals
representative of the peak percent nitrogen expired by a patient in
each breath and the nitrogen volume in each breath of the
patient.
19. The system of claim 10 in which the analyzer means comprises: a
high output impedance circuit which includes
first operational amplifying means, the first operational
amplifying means being an inverting amplifying means and having an
input and an output,
means including first unidirectional current conducting means for
coupling from the output thereof to the input of said first
operational amplifying means,
second unidirectional current conducting means,
second operational amplifying means, the second operational
amplifying means being high input impedance operational amplifying
means and having a noninverting input and an output, said output
being coupled to the input of said first amplifying means, and
means for connecting the input of said first operational amplifying
means through said second unidirectional current conducting means
to the output of said first operational amplifying means so that
current flows from the input of said second operational amplifying
means to the output of said first operational amplifying means.
20. The invention according to claim 19 wherein each of said first
and second unidirectional current conducting means is the
base-emitter junction of a transistor.
21. The invention according to claim 19 wherein said second
operational amplifying means further has an inverting input coupled
to the output of said second operational amplifying means.
22. The invention according to claim 19 wherein the output of said
circuit is the junction of said second operational amplifying means
and said second unidirectional current conducting means.
Description
BACKGROUND OF THE INVENTION
This invention relates to pulmonary testing and more particularly
to a pulmonary testing system for transmitting pulmonary data to a
central location.
In the past, tests related to the pulmonary condition of a patient
have been observed by a doctor or other specialist at the location
of the patient. The system of this invention provides means by
which a doctor or other specialist can receive by telephone lines
pulmonary test data from various locations, any of which may be
remote. For example, patients tested by the specialist may be in
cities remote from the location of the doctor or other
specialist.
So far as is known, systems now in use which transmit more than one
type of pulmonary test data employ more than one pair of telephone
lines.
SUMMARY OF THE INVENTION
In accordance with one preferred embodiment of the invention, there
is provided a pulmonary testing system for providing an electrical
signal indicating the peak percent of nitrogen expired by a person
in a breath and the total nitrogen mass or volume expired by the
person during repetitious breathing comprising means responsive to
the person's repetitious breathing for providing a first electrical
signal proportional to the gas flow in each exhaled breath,
analyzer means responsive to the repetitious exhaling of the person
for providing a second electrical signal indicating the percent of
nitrogen during each exhalation, integrating means responsive to
the first and second electrical signals for providing a third
electrical signal indicating the total amount of nitrogen exhaled
by the person, pulse generator means responsive to the second
electrical signal for providing a series of pulse signals, each
pulse signal indicating the peak percent of nitrogen during a
single exhalation, and means for providing a system signal by
superimposing the series of pulse signals upon the third electrical
signal such that the series of pulse signals occur during the time
an inhalation occurs.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram showing a system of this invention for
transmission of pulmonary information.
FIG. 2 is a portion of a chart showing the results of a typical
spirometry test of a patient tested by the circuitry of this
invention.
FIG. 3 is a portion of a chart showing peak nitrogen and functional
residual capacity data of a patient tested.
FIGS. 4 - 11 are schematic wiring diagrams of portions of the
electrical circuitry of this invention.
DETAILED DESCRIPTION OF THE INVENTION
This invention provides means by which a single pair of telephone
lines is employed to transmit spirometry, the percentage of
nitrogen present in each expired breath of a patient, and to
transmit a signal which is proportional to nitrogen volume or mass,
for the determination of functional residual lung capacity (FRC) of
the patient.
As shown in FIG. 1, a test unit 8 includes a flowmeter 10,
preferably a mass flowmeter, which is shown as having connected
thereto a fluid conduit member 12 which is adapted to cover the
nose and/or mouth of a patient, for communication with the
patient's respiratory system.
The flowmeter 10 provides an electrical output signal which is
proportional to a derivative of the volume or mass of the expired
breath. A suitable flowmeter, for example, is a device sold by
Datametrics Corporation and referred to as In-line Flow Transducer,
Series 1000. A switch arm 18 is connected to the input of a
transmitter 22 and when connected to a contact point 19, the
flowmeter 10 is electrically connected to the transmitter 22.
Preferably, the transmitter 22 is a frequency modulation
transmitter, preferably having an output frequency in the general
range of 1300 hertz. However, a transmitter of another frequency
may also be satisfactory. The connection of the switching arm 18 to
a contact 15 joins a precision oscillator 17 to the transmitter 22.
The transmitter 22 is joined to a start-stop switch 24, which is
connected to a telephone circuit 30. The telephone circuit 30 may
be a full duplex system and includes a pair of wires or lines. The
precision oscillator 17 is used to test the telephone circuit 30.
Also joined to the telephone circuit 30 is a signal filter 32 to
which is connected an alarm 34.
The telephone circuit 30 extends to a central receiver unit 40
within which is a demodulator 42 connected to the telephone circuit
30. The central receiver unit 40 may be very remote from the test
unit 8.
Also within the central unit 40 and joined to the telephone circuit
30 is a signal switch 44. Also within the central receiver unit 40
is an integrator and special purpose computer 45, and a chart
recorder instrument 48 which is connected to the integrator and
special purpose computer 45. The chart recorder 48 is also
connected to the demodulator 42.
Also within the test unit 8 and joined to the fluid conduit 12 is a
fluid conduit 60, which, through a valve 62, is connected to a
source of oxygen 64. Also connected to the fluid conduit 12 is a
fluid conduit 68 which through a valve 70, is connected to a
nitrogen percent analyzer 72. A suitable analyzer may for example,
be such a device sold by Med-Science Company and referred to as
Model 505 Nitralyzer.
The output of the flowmeter 10 is joined by a conductor 75 to one
input of an analog multiplier 76, shown schematically in FIG. 4,
and to the input of a minimum flow detector 78, shown schematically
in FIG. 5. The nitrogen percent analyzer 72 is connected by a
conductor 77 to a second input of the multiplier 76, by a conductor
79 to the signal input of a peak percent nitrogen follower 80,
shown schematically in FIG. 6, and by a conductor 81 to the input
of a minimum percent nitrogen detector 82, shown schematically in
FIG. 7. The multiplier 76 has an output connected by a conductor 83
to a multiplier output gate 84, shown schematically in FIG. 8. The
multiplier 76 may be any suitable instrument which is capable of
multiplication of two analog quantities. The multiplier 76 employed
herein is an instrument produced by Hybrid Systems and identified
as "107C Transconductance Multiplier" and is shown in FIG. 4 as
having a gain adjustment 89 and a balance adjustment 91 connected
thereto. The multiplier 76 also has an X terminal, a Y terminal,
and a Z terminal.
The peak percent nitrogen follower 80 has an output connected by a
conductor 85 to a percent nitrogen sample pulse generator 88, shown
schematically in FIG. 9. The percent nitrogen sample pulse
generator 88 includes time delay circuitry. The minimum flow
detector 78 is connected by a conductor 73 to a first inhibit input
of the multiplier output gate 84. The minimum percent nitrogen
detector 82 is connected by a conductor 71 to a second inhibit
input of the multiplier output gate 84 and to an inhibit input of
the percent nitrogen sample pulse generator 88. The percent
nitrogen sample pulse generator 88 has output conductors 67 and 69
connected to clear and read inputs of the peak percent nitrogen
follower 80.
An integrator 94 shown schematically in FIG. 11, is connected by a
conductor 95 to one input of a summer device 92 and receives a
signal through a conductor 97 from the multiplier output gate 84. A
pair of conductors 103 connects the switch 24 to control inputs of
the integrator 94. The summer device 92 is connected by a conductor
99 to a switch contact 96 which is joined through switching arm 18
to the transmitter 22. A conductor 101 connects the percent
nitrogen sample pulse generator 88 to a second input of the summer
device 92.
A breath switch 100 is connected to the input to the transmitter 22
and to a breath light 102. The breath switch 100 is any suitable
switch which, when receiving a signal directly or indirectly from
the flowmeter 10, causes the breath light 102 to become
energized.
OPERATION
The circuitry of this invention includes means for transmission of
spirometry test data as the patient exhales into the fluid conduit
12.
Prior to testing a patient, the switching arm 18 is placed in
contact with the switch contact 15, and the precision oscillator 17
applies a test signal to the transmitter 22, which in response
thereto applies a frequency modulated signal through the switch 24
to the flowmeter telephone circuit 30, and to the demodulator 42 of
the central receiver unit 40 for calibration of these elements.
During the spirometry test, the valves 62 and 70 are closed so that
all of the expired breath from the patient flows into the flowmeter
10, and the switching arm 18 is placed in contact with the switch
contact 19.
The flowmeter 10 provides an electrical signal which is transmitted
through the switch contact 19 and the switching arm 18 to the
transmitter 22. The breath switch 100 senses that an expired breath
of the patient has caused a signal to be applied to the transmitter
22, and the breath switch 100 causes the breath light 102 to become
energized to indicate to the operator that the patient's expiration
is causing a signal to be applied to the transmitter 22. The start
stop switch 24, when closed, for example by manual operation,
permits a signal from the transmitter 22 to flow through the
telephone circuit 30 to the demodulator 42 in the central receiver
unit 40. The analog signal which is received from the demodulator
42 by the integrator and special purpose computer 45 is integrated
with respect to time and the output of the integrator and special
purpose computer 45 flows to the chart recorder 48. A signal from
the demodulator 42 simultaneously flows directly to the chart
recorder 48.
The upper portion of FIG. 2 is a portion of a chart illustrating
forced expiratory flow of the patient, and the lower portion of
FIG. 2 is a portion of a chart illustrating the integration of the
flow to provide volume of the patient's forced exhalation.
When an operator at the central receiver unit 40 wishes to contact
the operator at the test unit 8, for example, to indicate that the
test is completed, the operator uses the signal switch 44 to apply
a signal of a different frequency to the telephone circuit 30, and
this signal is detected by the signal back filter 32 which
activates the signal back alarm 34. The operators at both units can
then connect telephones to the telephone circuit 30 for telephone
communication between the test unit location of the patient and the
central receiver unit 40.
The circuitry of this invention is also employed to transmit to the
central receiver unit 40 information regarding the percent nitrogen
in each expired breath of a patient and nitrogen volume, to
determine total lung volume and functional residual capacity of the
patient. These tests are referred to as "nitrogen washout" tests.
These tests are based upon the fact that air normally contains
approximately eighty percent nitrogen, and it is assumed that the
patient's lungs normally contain air having this percentage of
nitrogen.
For these tests, the valves 62 and 70 are opened and the switching
arm 18 is placed in contact with switch contact 96. The patient and
expires and expires through the fluid conduit member 12. The valve
62 permits flow of oxygen from the source 64 only when the patient
is inhaling. Thus, the patient inhales pure oxygen from the source
of oxygen 64. The patient exhales into the fluid conduit 12 and the
exhaled breath is sensed by the flowmeter 10. A very small portion
of the exhaled breath flows through the fluid conduit 68 to the
nitrogen percent analyzer 72. An electrical output signal having an
instantaneous magnitude proportional to expiratory flow travels
from the flowmeter 10 through the conductor 75 to the multiplier
76, and an electrical signal having a magnitude, proportional to
the percentage of nitrogen in the expired breath travels through
the conductor 77 from the nitrogen percent analyzer 72 to the
multiplier 76 and through the the conductor 79 to the peak percent
nitrogen follower 80.
During this test, each inspiration by the patient contains pure
oxygen and each expiration contains a percentage of nitrogen. As
inspiration and expiration continue, the percentage of nitrogen in
each expired breath should decrease.
The multiplier 76 thus receives a signal proportional to the
expiratory flow and multiplies therewith a signal proportional to
the percent of nitrogen in the expired breath, and a resultant
signal output of the multiplier 76 (nitrogen flow) travels to the
multiplier output gate 84.
The minimum flow detector 78, which is also joined to the
multiplier output gate 84, provides a signal to the multiplier
output gate 84 only when a signal above minimum flow is received
from the flowmeter 10. The minimum percent nitrogen detector 82
provides a signal to the multiplier output gate 84 only when the
percentage of nitrogen in an expired breath is above a given
minimum value. The multiplier output gate 84 is disabled and thus
does not transmit a signal from the multiplier 76 to the integrator
94 unless there is a signal received from the minimum flow detector
78 that an expired breath is occurring and a signal from the
minimum percent nitrogen detector 82 that the percentage of
nitrogen is above a given minimum.
The integrator 94 thus provides a signal proportional to nitrogen
volume in the expired breath. The output signal of the integrator
94 is transmitted through the summer device 92 to the transmitter
22 and then transmitted over the telephone circuit 30 to the
central receiver unit 40. The integration appears on the chart
recorder 48 in a manner similar to that represented by a reference
numeral 105 in FIG. 3.
The peak percent nitrogen follower 80 detects the peak percentage
of nitrogen in each expired breath. This peak signal is transmitted
to the percent nitrogen pulse generator 88, which includes time
delay circuitry. After the percent nitrogen, as detected by the
percent nitrogen detector 82, falls below a predetermined minimum
during the next inspiration of pure oxygen, and after a given time
delay, for example, one hundred and fifty milliseconds or the like,
the time delay circuitry transmits this signal to the summer device
92, and the peak signal travels through the summer device 92 to the
transmitter 22 and travels over the telephone circuit 30 to the
central receiver unit 40. The peak signals are superimposed upon
the integration signals at the chart recorder 48 in the manner
illustrated by a reference numeral 107 in FIG. 3.
Thus, it is understood that the peak signals 107 are transmitted to
the central receiver unit 40 during the time that the patient is
inhaling and the integration of the exhalation is transmitted to
the central receiver unit 40 during the exhalation period. Thus,
the signals corresponding to peak percentage of nitrogen and
signals pertaining to functional residual capacity of the patient
are transmitted to the central receiver unit 40 over a single pair
of telephone lines, and the information received at the central
receiver unit 40 appears on the chart in a manner such as that
illustrated in FIG. 3.
Details of portions of the system will now be discussed.
A first sample exhalation is actually taken before the first
inhalation of pure oxygen, and should indicate that 80 percent
nitrogen was present in the air of the conduit 12 immediately
before the beginning of the test. When the first inhalation of pure
oxygen is made, a sample nitrogen pulse indicating 80 percent
nitrogen should be generated. This may serve as a check on the
adjustment of the nitrogen analyzer 72 and may serve as a check to
indicate if oxygen was present in the breathing tube before the
test began.
Conductors 103 extending from the start-stop switch 24 to the
integrator 94 are momentarily shorted to discharge or reset a
capacitor 221 of the integrator 94, shown in FIG. 11.
As stated above, the multiplier output gate 84 is disabled when the
minimum flow detector 78 detects a flow signal below a minimum
value or when the minimum percent nitrogen detector 82 detects a
nitrogen level less than a minimum value. The reason for this is
that the multiplier 76, shown in FIG. 4, is not ideal. With a
voltage applied to one of the X or Y terminals and zero volts
applied to the other of the X or Y terminals, the output of the
multiplier 76 is not zero but is a positive voltage slightly above
zero. In addition, the zero adjustment of the output as set by the
balance potentiometer 91 has a slight drift. To limit the error due
to this non-ideal behavior, the multiplier output gate 84 is
employed, into which the output signal from the multiplier 76 is
connected. The multiplier output gate 84, shown in FIG. 8, includes
a coil 194 which operates a normally closed relay contact 196,
through which the multiplier output signal is applied to the
integrator 94. When either the flow or percent nitrogen of the
patient's expired breath is below a predetermined value, the coil
194 is energized and the relay contact 196 is open. This occurs
between expired breaths and after the nitrogen is completely
"washed out" of the patient's lungs.
The multiplier output gate 84 includes a transistor 192 having a
grounded emitter, and a collector which is connected through a coil
194 to a source of positive voltage V. The conductors 71 and 73 are
coupled together through respective forward biased diodes 188 and
190 to the base of transistor 192. Whenever a positive voltage
appears on either of the conductors 71 or 73, resulting from
detection of the respective minimum percent nitrogen or minimum
flow, the transistor 192 becomes conductive. This allows current to
flow through the coil 194, opening relay contact 196. A diode 198
is coupled in parallel with the coil 194 and allows the coil 194 to
discharge after the transistor 192 again becomes
non-conductive.
The minimum flow detector 78, as shown in FIG. 5, includes an
operational amplifier 200 operated in the inverting mode with the
base-emitter junction of a transistor 202 in the feedback loop
thereof. The inverting input to the operational amplifier 200 is
coupled to the conductor 75 through a resistor 204, and to a source
of negative voltage -V, through resistors 205 and 206. The junction
of resistors 205 and 206 is coupled to ground through a resistor
207. The resistors 204, 205, 206 and 207 are selected so that
whenever the voltage on the conductor 75 is below a minimum
voltage, a negative voltage is applied to the inverting input of
the operational amplifier 200, and otherwise a positive voltage is
applied thereto.
A positive voltage reverse-biases the emitter-base transistor
junction 202, causing the feedback impedance to become extremely
high, and the operational amplifier 200 attempts to saturate
positively. However, the emitter-base transistor junction 202
breaks down at a voltage before saturation occurs. The negative
current from a negative voltage is cancelled when the positive
voltage applied on the conductor 75 reaches a sufficiently high
value. When the total input voltage increases to a value greater
than the threshold, the output of the operational amplifier 200
becomes negative as a result of the net positive current at the
negative input. This negative output forward-biases the
emitter-base transistor junction 202, and the output of the
operational amplifier 200 becomes slightly negative. Thus, as long
as the voltage on the conductor 75 is above a minimum value, the
output voltage of the minimum flow detector 78 which appears on the
conductor 73 is near zero volts, and when the voltage appearing on
the conductor 75 falls below the minimum voltage, the output
voltage on the conductor 73 becomes substantially positive.
The minimum percent nitrogen detector 82, illustrated in FIG. 7
functions in substantially the same manner as the minimum flow
detector 78. The nitrogen threshold is a small percentage of full
nitrogen volume. The minimum percent nitrogen detector 82 includes
an operational amplifier 208, having a base-emitter transistor
junction 209 in the feedback loop thereof. The operational
amplifier 208 has a filter circuit 210 in the output thereof, which
makes possible smooth output voltage shifts as changes in nitrogen
levels occur above and below the trigger threshold of the detector
circuit.
The output of the multiplier 76 is connected through the conductor
83, the multiplier output gate 84, and the conductor 97 to the
input of the integrator 94. The integrator 94, as shown in FIG. 11,
includes an integrating operational amplifier 220 having a
capacitor 221 in the feedback loop thereof. The integrator 94 also
includes a unity gain inverter 224 which corrects for polarity
change which occurs within the operational amplifier 220. The gain
of the integrator 94 may, for example, be such that at the output
conductor 95 thereof 1 volt equals 1 liter. The input signal on
line 97 to the integrator 94 is a voltage proportional to nitrogen
flow in liters per minute, and the output of the integrator 94 is
nitrogen volume in liters. The gain of the integrator 94 is
adjusted by adjusting a potentiometer 228 at the input of the
operational amplifier 220.
The output conductor 95 of the integrator 94 is connected to the
summer device 92, shown in FIG. 10, which inverts the output signal
of the integrator 94 and superimposes upon the output signal of the
integrator 94 the signal received through the conductor 101 from
the percent nitrogen pulse generator 88. The output of the summer
device 92 then travels through the conductor 99, the switch contact
96, and switching arm 18 to the transmitter 22, as stated
above.
The peak percent of nitrogen in each expired breath is determined
by the peak percent nitrogen follower 80, shown in FIG. 6. This
includes an operational amplifier 230, having the base-emitter
junction of a transistor 240 and an operational amplifier 232 in
the feedback loop thereof. The peak percent nitrogen follower 80
also includes an operational amplifier 234. The output voltage of
the operational amplifier 230 is applied through the transistor 240
and through a closed sample relay contact 242 to a storage
capacitor 236. When the input voltage appearing on the conductor 79
of the operational amplifier 230 begins to decrease, the output
voltage thereof does not decrease because the base-emitter junction
of the transistor 240 in the negative feedback circuit of the
operational amplifier 230 is reverse-biased by the value of the
previous higher voltage stored in the storage capacitor 236. In
order for the storage capacitor 236 to maintain the charge, the
impedance looking back into the operational amplifier 230 must be
extremely high. The operational amplifier 232, having a very high
input impedance, is employed for this purpose and, as shown and
discussed above, is in the feedback loop of the operational
amplifier 230. Use of the transistor 240 as a diode serves to
reduce to a negligible value any leakage in this portion of the
circuitry.
The operational amplifier 232 serves as a voltage follower buffer
with an input impedance on the order of 10.sup.11 ohms in the
negative feedback loop of the operational amplifier 230.
The negative feedback loop is the output loop, because the input to
the operational amplifier 230, which is an inverter, is a positive
voltage, for example, 10 volts full scale with 100 percent
nitrogen. In addition, the base-emitter junction of a transistor
238 and the transistor 240 are used as diodes, with the base being
coupled to the collector. Since the base-emitter transistor
junctions begin leakage at a voltage somewhat below actual
breakdown, the gain of the operational amplifier 230 is reduced to
about one-fifth in order to keep this leakage value negligible.
This attenuation is compensated for by a gain created in an output
buffer stage which includes the operational amplifier 234,
operating in a known manner, to provide the peak percent nitrogen
signal to the conductor 85.
When the nitrogen level value exceeds the threshold of the minimum
percent nitrogen detector 82 during an exhalation, the logic
circuitry in the percent nitrogen sample pulse generator 88 causes
a positive voltage to appear on the conductor 69, thereby rendering
a transistor 262 conductive and energizing a relay coil 241, shown
in FIG. 6, to cause the normally open relay contact 242, which is
located between the operational amplifier 230 and the storage
capacitor 236, to close. This permits the capacitor 236 to charge
up to a peak voltage.
When the nitrogen level goes below the minimum threshold during
inhalation of pure oxygen by the patient, the voltage ceases to be
applied on the conductor 69, the transistor 262 becomes
non-conductive and the coil 241 becomes deenergized and permits the
relay contact 242 to open, and a voltage proportional to the peak
nitrogen value is stored by the storage capacitor 236.
The storage capacitor 236 is connected to the input of the
operational amplifier 234 which has a high impedance input to
minimize capacitor discharge.
After the voltage manifesting the nitrogen level at the input
conductor 81 falls below the threshold of the minimum percent
nitrogen detector 82, there is a slight delay for a reason
discussed below, and then the percent nitrogen sample pulse is
generated on conductor 101 by percent nitrogen pulse generator 88.
Immediately after this, a normally-closed relay contact 252, in the
peak percent nitrogen follower 80, which had been open to allow
peak nitrogen sampling and storage, is closed by the logic in the
percent nitrogen sample pulse generator 88, causing zero voltage to
appear on the conductor 67, thereby rendering a transistor 260
non-conductive and deenergizing a coil 250 for closure of the
contact 252. The contact 252 remains in the closed position for
about 75 milliseconds to allow discharge of capacitor 236. The
capacitor 236 is then in a condition to be recharged to a new peak
value during the next exhalation.
As previously stated, the percent nitrogen pulse generator 88
functions in close conjunction with the peak percent nitrogen
follower 80. The primary control input signal to the pulse
generator 88 is the minimum percent nitrogen detector 82 signal
appearing on the conductor 71. When the output of the minimum
percent nitrogen detector 82 is a low voltage, indicating that the
nitrogen level is above the minimum threshold, a NAND gate 258
within a NAND gate unit 259 of the percent nitrogen pulse generator
88, shown in FIG. 9, provides a positive voltage to the conductor
69 to energize the coil 241 of the peak percent nitrogen follower
80 shown in FIG. 6, and closes the contact 242, thereby connecting
the output of the operational amplifier 230 to the storage
capacitor 236. During this time, the contact 252 is maintained in
an open condition, because the coil 250, associated therewith, is
energized through the operation of another NAND gate 261 in the
NAND gate unit 259.
In order for the contact 252 to be held open, a series of
monostable multivibrators 270, 272, and 274 of the percent nitrogen
sample generator 88 shown in FIG. 9, are in the zero state, and a
function switch 280 is in the FRC (Functional Residual Capacity)
position. As the patient exhales the nitrogen from his lungs, a
voltage proportional to the peak nitrogen is stored by capacitor
236 in the peak percent nitrogen follower 80. When the patient
stops exhaling and again begins inhalation of pure oxygen, the
minimum percent nitrogen detector 82 provides a positive voltage on
the conductor 71. However, because the output voltage of the filter
210 in FIG. 7 rises slowly, the output voltage provided by a buffer
circuit 288 rises slowly. This permits the NAND gate 258 to provide
a near zero voltage to the conductor 69, thus deenergizing the
relay coil 241 and permitting the contact 242 to open. The zero
relay contact 252, however, is still open, because the monostable
multivibrators 272 and 274 are still in the low state. However, the
leading edge of the output pulse on the conductor 71 from the
minimum percent nitrogen detector 82 triggers the monostable
multivibrator 270 through the buffer 288. The time constant of this
monostable multivibrator 270 is selected so that the output thereof
provides a positive voltage for about 150 milliseconds. In
addition, the monostable multivibrator 270 is not actually
triggered until about 350 milliseconds after the output signal on
the conductor 71 from the minimum percent nitrogen detector 82
becomes positive. This is because of the slow rise of the output
voltage of the minimum percent nitrogen detector 82 and the buffer
288. The trailing edge of the output pulse of the monostable
multivibrator 270 triggers the monostable multivibrator 272.
Therefore, from the time the nitrogen level goes below the
threshold until the monostable multivibrator 272 fires, about
one-half second has elapsed. It is this monostable multivibrator
272 which renders a transistor 294, shown in FIG. 9, conductive,
thereby allowing current to flow through a coil 296 and moves a
contact 298 connected to the conductor 101 from a ground connection
to connection with the conductor 85 from the output of the peak
percent nitrogen follower 80. This generates a peak percent
nitrogen sample pulse about 75 milliseconds in duration in the
percent nitrogen sample pulse generator 88, which is connected
through the conductor 101 to the second input of the summer device
92. The pulse is then superimposed on the functional residual
capacity represented by reference numeral 105 and is shown by the
reference numeral 107 in FIG. 3.
The trailing edge of the monostable multivibrator 272 triggers the
monostable multivibrator 274 which also has a time constant
selected to generate a pulse 75 milliseconds in duration. The
output of the monostable multivibrator 274 is transmitted to the
NAND gate 261, which provides a positive voltage to the conductor
67, to the relay coil 250, through a transistor 260, as shown in
FIG. 6. When the monostable multivibrator 274 is in its high state
and the function switch 280 is in the FRC position, the signal
provided to the conductor 67 is near zero volts, so the relay coil
250 is deenergized, and the relay contact 252 closes. This
discharges the peak nitrogen storage capacitor 236 and prepares the
peak percent nitrogen follower 80 for the next exhalation.
As soon as the minimum percent nitrogen detector 82 again provides
a low voltage to the conductor 71, indicating that the nitrogen
level is above the minimum, the signal provided by the NAND gate
258 to the conductor 69 becomes positive and the sample relay
contact 242 closes again and the cycle repeats.
When the subject is completely "washed out" of nitrogen, the
minimum percent nitrogen detector 82 no longer detects nitrogen
above the minimum threshold during exhalation, and therefore the
voltage on conductor 71 remains positive.
At this point, the sample relay contact 242 remains open and no
additional percent nitrogen sample pulses are generated. In
addition, the multiplier output gate relay contact 196 remains open
and no additional functional residual capacity integration will
occur.
Thus, the operator in the central receiver unit 40 knows that
functional residual capacity computation is complete.
When the functional residual capacity computation is complete, a
function switch 282, shown in FIG. 1, is put in its grounded
position. This grounds the nitrogen inputs to the multiplier 76,
minimum percent nitrogen detector 82, and peak percent nitrogen
follower 80. This causes the minimum percent nitrogen detector 82
to apply a positive voltage to the conductor 71 which holds the
relay contact 196 open, thus preventing an output signal from the
multiplier 76. This also holds the sample relay contact 242 open
which, together with the closed relay contact 252, maintains the
peak percent nitrogen follower 80 ready for the first sample of the
next test. The relay contact 252 is closed, because the coil 250 is
deenergized as a result of the low voltage provided by the NAND
gate 261 as controlled by the function switch 280.
Although the preferred embodiment of the system has been described,
it will be understood that within the purview of this invention,
various changes may be made in the form, details, circuitry
components, the combination thereof and mode of operation, which,
generally stated, provide a system capable of performance in the
manner disclosed and defined in the appended claims.
* * * * *