U.S. patent number 3,721,230 [Application Number 05/091,629] was granted by the patent office on 1973-03-20 for high-gain monitor to determine electro-cerebral silence.
This patent grant is currently assigned to Marvin C. Overton, III. Invention is credited to Robert S. Ziernicki.
United States Patent |
3,721,230 |
Ziernicki |
March 20, 1973 |
HIGH-GAIN MONITOR TO DETERMINE ELECTRO-CEREBRAL SILENCE
Abstract
An apparatus for measuring physiological conditions of human and
animal bodies characterized by; in addition to a preamplifier,
filter, amplifier, recorder, and power supply; a common mode noise
rejection circuit and a shield for the noise-sensitive components;
whereby the apparatus may be employed at a patient's location, even
in the presence of electrical noise. The apparatus is characterized
by other improved concepts that are also disclosed; such as, front
end loading of paper for the recorder; a channel selector for
selecting the electrodes to be monitored; a small portable unit
that includes a self-contained calibrate and test circuit to ensure
correct operation regardless of the electrical noise in a given
area or location; and a specific electrical schematic diagram.
Inventors: |
Ziernicki; Robert S. (Dallas,
TX) |
Assignee: |
Overton, III; Marvin C. (Ft.
Worth, TX)
|
Family
ID: |
22228812 |
Appl.
No.: |
05/091,629 |
Filed: |
November 23, 1970 |
Current U.S.
Class: |
600/544; 128/902;
600/523 |
Current CPC
Class: |
A61B
5/369 (20210101); Y10S 128/902 (20130101) |
Current International
Class: |
A61B
5/0476 (20060101); A61b 005/00 () |
Field of
Search: |
;128/2.6B,2.6E,2.6G,2.6R,2.1B,2.1E,2.1R ;330/14,69 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Claims
What is claimed is:
1. Apparatus for determining physiological conditions in human and
animal bodies, said apparatus having a sensitivity 1,000 times
greater than that normally necessary for electrocardiographs and
sufficient to provide the criteria of death through indication of
electro-cerebral silence, comprising:
a. a plurality of electrode means for detecting bioelectric outputs
from spaced locations carried by said bodies and including leads
for connecting with a plurality of input terminals of a
preamplifier section;
b. a portable unit employing miniaturized, solid state circuit
elements, and including:
i. power conductor means for supplying power when connected with a
source of power;
ii. a preamplifier secton connected with said power conductor means
and having a common mode noise rejection circuit means that has a
plurality of input terminals that are connected with a plurality of
said electrode means; said common mode noise rejection circuit
means comprising a pair of operational amplifiers that are
connected in a differential amplifier configuration with a
noninverting input terminal of each operational amplifier being
connected with a respective one of said input terminals of said
preamplifier section and having a respective output conductor; a
feedback network for each operational amplifier; each operational
amplifier in the differential amplifier configuration having its
output conductor serially connected with its inverting input
terminal via said feedback network for feedback; and a
cross-coupling resistor that is serially connected with respective
inverting input terminals of said operational amplifiers; all such
that necessary high amplification of legitimate body signals is
effected while maintaining low noise amplification and high input
impedance sufficient to squelch gross noise signals, such as, a
patient sweating or an electrode means slipping;
iii. filter means connected with said preamplifier section for
removing predictable noise within a predetermined frequency range;
and
iv. power amplifier section connected with said filter means;
c. shield means carried by said portable unit and encompassing said
preamplifier section, said filter means, and said power amplifier
section;
d. recorder means connected with said power amplifier section for
recording with respect to time, an output therefrom;
e. a test switch connected with said input terminals; and
f. calibrate and test means carried by said portable unit and
having test output terminals that are connected with said test
switch for electrical connection with said input terminals of said
preamplifier section for testing and calibrating said
apparatus.
2. The apparatus of claim 1 wherein said filter means comprises a
twin tee notch filter.
3. The apparatus of claim 1 wherein a power supply is connected to
said power conductor means; said power supply providing the
requisite voltage when plugged into a conventional electrical
outlet and having discrete voltage taps with decoupling means to
minimize noise signals thereon.
4. The apparatus of claim 1 wherein said feedback network comprises
a parallel connected resistor-capacitor network for feedback.
5. The apparatus of claim 4 wherein said preamplifier section
includes a conversion means that is connected with said output
conductors from said operational amplifiers and has a single second
output conductor for converting said differential output of said
common mode noise rejection circuit means to a single output; said
single second output conductor being connected with said filter
means; said conversion means comprising an additional operational
amplifier having a plurality of input terminals that are connected
with said output conductors from said operational amplifiers; a
parallel connected resistor-capacitor network; said additional
operational amplifier having its single second output terminal
serially connected with one of its input terminals via said
parallel connected resistor-capacitor network for feedback.
6. The apparatus of claim 5 wherein said operational amplifiers and
said additional operational amplifier are formed by at least medium
scale integrated circuit techniques such that at least each
operational amplifier is contained on a single monolithic
semiconductor chip, whereby size is reduced sufficiently that said
shield means can be employed and said unit still be practical and
hand portable.
7. The apparatus of claim 6 wherein said operational amplifiers and
said additional operational amplifier have an input off-set voltage
less than about 5 millivolt, input off-set current less than about
200 nanoampere, an input resistance greater than about 150,000
ohms, open loop gain greater than about 25,000, and a common mode
noise rejection ratio greater than about 70 decibels.
8. Apparatus for determining physiological conditions in human and
animal bodies, said apparatus having a sensitivity 1,000 times
greater than that normally necessary for electrocardiographs and
sufficient to provide the criteria of death through indication of
electro-cerebral silence, comprising:
a. a plurality of electrode means for detecting bioelectric outputs
from spaced locations carried by said body and including leads for
connecting with a plurality of input terminals of a preamplifier
section;
b. a unit including a shield means encompassing:
i. a preamplifier section having a common mode noise rejection
circuit means that has a plurality of input terminals that are
connected with a plurality of said electrode means; said common
mode noise rejection circuit means comprising a pair of operational
amplifiers that are connected in a differential amplifier
configuration with a non-inverting input terminal of each
operational amplifier being connected with a respective one of said
input terminals of said preamplifier section and having a
respective output conductor; a feedback network for each
operational amplifier; each operational amplifier in the
differential amplifier configuration having its output conductor
serially connected with its inverting input terminal via said
feedback network for feedback; and a cross-coupling resistor that
is serially connected with respective inverting input terminals of
said operational amplifiers; all such that necessary high
amplification of legitimate body signals is effected while
maintaining low noise amplification and high input impedance
sufficient to squelch gross noise signals, such as a patient
sweating or an electrode means slipping;
ii. filter means connected with said preamplifier section for
removing predictable noise within a predetermined frequency range;
and
iii. power amplifier section connected with said filter means;
c. a power conductor means connected with said preamplifier section
for supplying power when connected with a source of power; and
d. recorder means connected with said power amplifier section for
recording with respect to time, an output therefrom.
9. The apparatus of claim 8 wherein a parallel connected
resistor-capacitor network is provided for each said operational
amplifier; and each operational amplifier in said differential
amplifier configuration has its output conductor serially connected
with its inverting input terminal via said parallel connected
resistor-capacitor network for feedback.
10. The apparatus of claim 8 wherein said preamplifier section
includes a conversion means that is connected with said output
conductors from said operational amplifiers and has a single second
output conductor for converting said differential output of said
common mode noise rejection circuit means to a single output; said
single second output conductor being connected with said filter
means.
11. The apparatus of claim 10 wherein said conversion means
comprise an additional operational amplifier having a plurality of
input terminals that are connected with said output terminals from
said operational amplifiers; a third parallel connected
resistor-capacitor network is provided; and said additional
operational amplifier having its single second output conductor
serially connected with one of its input terminals via said
parallel connected resistor-capacitor network for feedback.
12. The apparatus of claim 11 wherein said operational amplifiers,
including said additional operational amplifier, are formed by at
least medium scale integrated circuit techniques such that at least
each operational amplifier is contained on a single monolithic
semiconductor chip, whereby size is reduced sufficiently that said
shield means can be employed and said unit be practical and hand
portable.
13. The apparatus of claim 12 wherein said operational amplifiers
have an input off-set voltage less than about 5 millivolt, input
off-set current less than about 200 nanoampere, an input resistance
greater than about 150,000 ohms, open loop gain greater than about
25,000, and a common mode noise rejection ratio greater than about
70 decibels.
14. Apparatus for determining physiological conditions in human and
animal bodies, said apparatus having a sensitivity 1,000 times
greater than that normally necessary for electrocardiographs and
sufficient to provide the criteria of death through indication of
electro-cerebral silence, comprising:
a. a plurality of electrode means for detecting bioelectric outputs
from spaced locations carried by said bodies and including leads
for connecting with a plurality of input terminals of a
preamplifier section;
b. a portable unit employing miniaturized, solid state circuit
elements and including:
i. power conductor means for supplying power to said portable unit
when connected with a source of power;
ii. a preamplifier section having a common mode noise rejection
circuit means that has input terminals that are connected with a
plurality of said electrode means; said common mode noise rejection
circuit means comprising a pair of operational amplifiers that are
connected in a differential amplifier configuration with a
noninverting input terminal of each operational amplifier being
connected with a respective one of said input terminals of said
preamplifier section and having a respective output conductor; a
feedback network for each operational amplifier; each operational
amplifier in the differential amplifier configuration having its
output conductor serially connected with its inverting input
terminal via said feedback network for feedback; and a
cross-coupling resistor that is serially connected with respective
inverting input terminals of said operational amplifiers; all such
that necessary high amplification of legitimate body signals is
effected while maintaining low noise amplification and high input
impedance sufficient to squelch gross noise signals, such as a
patient sweating or an electrode means slipping;
iii. filter means connected with said preamplifier section for
removing predictable noise within a predetermined frequency range;
and
iv. power amplifier section connected with said filter means;
c. shield means carried by said portable unit and encompassing said
preamplifier section, said filter means, and said power amplifier
section;
d. recorder means for recording comprising a pen means for marking,
pen drive means for driving said pen means, said pen drive means
being drivingly connected with said pen means and responsively
connected with the output of said power amplifier section; and a
chart drive means for advancing said chart at a predetermined rate
with respect to time; said recorder means having a front end panel
means that opens outwardly from the front end of said unit and that
has a mounting means for loading and unloading a roll of paper and
said chart comprises a roll of paper that is readily loaded into
said mounting means; said chart and said pen means being compatible
so that said pen means is able to make a record on said chart.
15. The apparatus of claim 14 wherein said pen is a thermal stylus
and said chart is a heat sensitive paper.
16. Apparatus for determining physiological conditions in human and
animal bodies, said apparatus having a sensitivity 1,000 times
greater than that normally necessary for electrocardiographs and
sufficient to provide the criteria of death through indication of
electro-cerebral silence, comprising:
a. a plurality of electrode means for detecting bioelectric outputs
from spaced locations carried by said bodies and including leads
for connecting with a plurality of input terminals of a
preamplifier section;
b. channel selector means connected with said plurality of
electrode means and having a selector switch means that has a pair
of output terminals and that is operable to select and connect a
predetermined pair of said electrode means with said output
terminals;
c. a portable unit employing miniaturized, solid state circuit
elements, and including:
i. power conductor means for supplying power when connected with a
source of power;
ii. a preamplifier section connected with said power conductor
means and having a common mode noise rejection circuit means that
has input terminals that are connected with said pair of output
terminals; said common mode noise rejection circuit means
comprising a pair of operational amplifiers that are connected in a
differential amplifier configuration with a non-inverting input
terminal of each operational amplifier being connected with a
respective one of said input terminals of said preamplifier section
and having a respective output conductor; a feedback network for
each operational amplifier; each operational amplifier in the
differential amplifier configuration having its output conductor
serially connected with its inverting input terminal via said
feedback network for feedback; and a cross-coupling resistor that
is serially connected with respective inverting input terminals of
said operational amplifiers; all such that necessary high
amplification of legitimate body signals is effected while
maintaining low noise amplification and high input impedance
sufficient to squelch gross noise signals, such as a patient
sweating or an electrode means slipping;
iii. filter means connected with said preamplifier section for
removing predictable noise within a predetermined frequency range;
and
iv. power amplifier section connected with said filter means;
d. shield means carried by said portable unit and encompassing said
preamplifier section, said filter means, and said power amplifier
section; and
e. recorder means connected with said power amplifier section for
recording with respect to time, an output therefrom.
17. The apparatus of claim 16 wherein a pair of short conductor
means are provided with said portable unit and said channel
selector means is carried by said portable unit and has its output
terminals connected therewith by said pair of short conductor
means.
18. The apparatus of claim 16 wherein a test switch means is
connected with said input terminals of said common mode noise
rejection circuit means for testing and calibrating said apparatus;
and said portable unit has a self-contained calibrate and test
means that has test output terminals that are connected with said
test switch means.
19. The apparatus of claim 18 wherein said test switch means is
also connected with said output terminals of said channel selector
means for connecting said input terminals of said common mode noise
rejection circuit means with either said test output terminals or
said output terminals of said channel selector means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to apparatus for detecting physiological
conditions in human and animal bodies; as in monitoring organs
connected with their nervous systems. This invention is
particularly useful in detecting conditions in the human brain and
in the human heart.
2. Description of the Prior Art
Several types of apparata are known in the prior art for measuring
physiological conditions by measuring bioelectric disturbances on
areas of the body adjacent the organ of interest, or even on the
organ itself. For example, a variety of electroencephalographs
(EEG's) and electrocardiographs (EKG's) are known. In these
devices, primary useage was made of thermionic emission type
electronic components as the active elements in a circuit network.
The prior art devices used heavily shielded enclosures with several
stages of high gain amplification, employing discrete vacuum tubes,
to achieve the necessary amplification. Aside from the extensive
shielding of the instrument, special shielding, such as metal
stretchers, were employed for the patient. Special hum-free power
supplies, filters and decoupling networks along with complicated
ground networks were required to provide the low electrical noise
environment for successful operation of prior art circuits. Even
with such precautions, the electrical noise in a normal
environment, such as in a room with neon lights, effected localized
excitations that gave spurious readings. Accordingly, a primary
need has been apparatus that could measure and respond to the very
low signal levels while screening out the frequently greater noise
signals in a normal environment; without having to be so careful
with circumstances such as lighting and movement about a patient
being tested. One of the ways in which the prior art devices have
attempted to solve the problem is to employ a push-pull amplifier
arrangement connected to respective electrode means and employing
staged amplification, up to four stages or more, such that the
signals that are in phase with each other are not amplified whereas
the signals which are out of phase with each other are amplified
more and more.
Such an arrangement of amplification has not been totally
satisfactory, however, and has required the shielding of the
patient referenced hereinbefore. With the advent of organ
transplants an urgent need has arisen for a device that can be
taken to a patient's location and yet have sufficient sensitivity,
at the patient's location and in the presence of the noise there,
to determine whether or not death has occurred. An excellent
article that illustrates the need for such an EEG is "Irreversible
Coma Associated with Electrocerebral Silence," Daniel Silverman,
Richard L. Maslin, Mitchell G. Saunders, and Robert S. Schwab,
NEUROLOGY, Vol. 20, June 1970, page 525-533. Other similar and
illustrative articles include "Cerebral Death and the
Electroencephalogram," Daniel Silverman, Mitchell G. Saunders,
Robert S. Schwab and Richard L. Maslin in JAMA (Journal of the
American Medical Association), Sept. 8, 1969, Vol. 209, No. 10; and
an editorial by Irving H. Page, Editor, Walter C. Alverez, MODERN
MEDICINE, Apr. 20, 1970, page 119. A sensitivity sufficient to
establish the criterion of death is 1 microvolt per millimeter. The
prior art devices that have had sufficient sensitivity have not
been portable and have not been usable in the absence of special
shielding precautions such as are available in a central room in a
hospital. Moreover, with such a portable unit, it is desirable that
a self-test and calibrate feature be employed on the unit to ensure
its accuracy in the environment in which it is to be taken and used
with a given patient. The shielding and noise elimination circuits
must obviously be sufficient to enable it to be used in the
environment about the patient, even if electrical noise be
present.
A portable instrument which is usable both as an EEG and an EKG for
monitoring either the brain, the heart, or any other organ for that
matter, is highly desirable and has not been provided by the prior
art.
Once the unit is made portable and taken from a central room in a
hospital, several other features become important. It becomes
important that the unit be conveniently loaded with paper since the
paper cannot be stacked beneath the unit as in a central room in a
hospital. Accordingly, it is desirable that easy loading, such as
front end loading of the paper, be effected. The portable unit
should have channel selectors where a plurality of electrode means
can be affixed to the patient's body and connected with the unit
and the output of selected pairs of electrode means monitored. Such
selector switch capability is made advisable because, in a portable
unit, a single pen recorder means will frequently be employed. In
any event, the plurality of six or seven pens is ordinarily not
practical in a portable unit and, hence, the selector switch
capability is advisable. In some instances, it may be desirable to
provide a plurality of plug-ins and a selector switch means that
can be placed near the patient whereas the portable unit may be
positioned remote therefrom to allow diagnosis with minimal
distraction of the patient. It is desirable that the unit, even
though portable, have the convenience features of the more
elaborate central facilities such as variable chart drive speeds,
and universal binding post connectors that are adaptable to
conventional EEG equipment.
DESCRIPTION OF PREFERRED EMBODIMENTS
It is an object of this invention to provide apparatus for
determining physiological conditions in human and animal bodies by
detecting bioelectric outputs from spaced locations on the body and
to provide the needs and features delineated hereinbefore and not
provided by the prior art devices.
It is an object of this invention to provide a circuit
configuration that accomplishes common mode noise rejection in
combination with suitable shielding such that it can be employed in
any location, even if electrical noise be present, for monitoring a
patient.
It is a specific object of this invention to provide a portable
apparatus for determining physiological conditions in response to
bioelectric outputs with the common mode noise rejection and
shielding sufficient to be employed at the patient's location.
A variety of other objects will become apparent to one skilled in
the art when considering the following descriptive matter in
combination with the drawings; an illustrative object being to
provide a readily portable instrument having an overall instrument
sensitivity that is continuously variable and able to yield a
minimum sensitivity of one microvolt per millimeter, which is
sufficiently sensitive to establish the criterion of death during
patient monitoring.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of the device being employed as an
electroencephalograph in accordance with one embodiment of this
invention.
FIG. 2 is a partial isometric view showing the device with a
separable selector switch in accordance with another embodiment of
this invention.
FIG. 3 is a partial side elevational view, partly in section,
illustrating the feature of the front end loading of the recorder
paper in accordance with one embodiment of this invention.
FIG. 4 is an electrical schematic diagram of one embodiment of this
invention.
Referring to FIG. 1, the portable unit 11 is being employed as an
electroencephalograph (EEG). The portable unit 11 is a
single-channel apparatus for detecting physiological conditions in
a patient's body. Specifically, the portable unit 11 is connected
to the scalp of the patient by a plurality of electrode means 13
for detecting bioelectric outputs from predetermined spaced
locations. The predetermined locations are well known for a variety
of organs and for a variety of portions of a given organ such as
the brain. For example, a total of twenty electrodes and conductors
may be emplaced about the head of a patient to monitor the brain.
The typical placements of the electrode means are discussed in
patents such as U.S. Pat. No. 2,409,033 and U.S. Pat. No.
3,195,533. While as many as ten channels may be employed, work with
the portable unit of this invention has indicated that six channels
are sufficient for routine observation. For example, one channel
comprising a pair of electrode means may monitor the bioelectric
output, or signals, between a left frontal and a left central
electrode; a second channel monitors the bioelectric output between
a right frontal and a right central electrode; a third channel
monitor the bioelectric output between a left parietal and a left
occipital electrode; a fourth channel monitor the bioelectric
output between a right parietal and a right occipital electrode; a
fifth channel monitor the output between a left interior temporal
and a left mid temporal; and a sixth channel monitor the
bioelectric output between a right anterior temporal and a right
mid temporal. Each physician or user of portable unit 11 may
emplace the electrode means at the locations carried by the body of
the patient as he desires. Ordinarily, the electrode means 13 are
emplaced on the surface of the selected locations by way of a
conductive grease; such as, a silicon lubricant; and a suitable
adhesive patch emplaced thereover. As illustrated in FIG. 1, the
plurality of conductors 15 from the respective electrode means 13
are connected to respective receptacles 17. The receptacles are in
turn connected with a selector switch means 19. The selector switch
means 19 is then movable to monitor the desired pair of electrodes.
The output from selector switch means 19 is fed into the
preamplifier section 21, FIG. 4; and, thence, through a filter
means 23 to an amplifier section 25. The output from the amplifier
section 25 is sent to a recorder means 27, having a compatible
stylus 29 and chart paper 31. The paper 31 will be driven at one of
a plurality of variable rates with respect to time; for example, by
pinch roller 33 and power roller 49 frictionally engaging the
paper. Preferably, the paper 31 is held by means of a bracket in a
front-end loading panel, as illustrated in FIG. 3 and described in
more detail with respect thereto.
If desired, the plurality of conductors 15 from the electrode means
13 may engage receptacles 17 in a separable selector switch cabinet
35, FIG. 2. The selector switch (not shown) may then be dialed to a
given pair of electrodes. The given pair of electrodes are
connected with a simplified portable unit 37 by a pair of
conductors in shielded coaxial cable 39.
As illustrated in FIG. 3, the paper 31 may comprise a suitable roll
41 that is connected with a panel 43 that opens to the front by way
of suitable mounting bracket (not shown). The paper 31 traverses
over the exterior of a writing surface 45 and beneath stylus 29.
Stylus 29 may be appropriately moved by any means 47 that is
responsive to the magnitude of an electrical output from the
amplifier 25. For example, the stylus may be moved linearly along a
rotating and reversible shaft or it may be moved in one direction
against a spring force in the other, as in a galvanometer action.
Such means are conventional and need not be described herein. The
paper 31 passes between and in frictional engagement with pinch
roller 33 and a power roller 49, which is driven at one of a
plurality of speeds by a variable speed motor. The chart speed is
determined by chart speed dial 51, FIG. 1. The significant element
is that panel 43 may be opened from the front and allow easily
replacing a roll 41 of paper 31, regardless of where the portable
unit is located.
The electrical schematic diagram employed in one embodiment of this
invention is illustrated in FIG. 4. The pair of conductors 53 and
55 are connected with contacts 57 and 59 of switch S1. Switch S1 is
a double throw-double pole switch used to switch the preamplifier
input to either the external input conductors 53 and 55 or to a
built-in calibrate and test circuit 67 that is connected with
contacts 61 and 63. Specifically, the contact 61 is connected with
the electrical common, or ground; and the contact 63 is connected
with conductor 65. Conductor 65 is, in turn, connected with the
calibrate and test circuit 67. The output terminals 69 and 71 of
switch S1 are serially and respectively connected with operational
amplifiers A1 and A2 via conductors 73 and 75 and resistors R1 and
R2. The operational amplifiers A1 and A2 are connected in
differential configuration and comprise the key elements in the
common mode noise rejection circuit 77. The amplifiers A1 and A2
are operationally connected with respective power sources 79 and
81. The power sources may be, for example, 15 volts direct current
(DC). The output from amplifier A1 is connected with terminal 83.
The terminal 83 is connected with another, or inverting, input
terminal 85 of amplifier A1 via parallel connected capacitor C4 and
resistor R5 for feedback. Similarly, the output of amplifier A2 is
connected with terminal 87. The terminal 87 is connected to
another, or inverting, input terminal 89 of amplifier A2 by
parallel connected capacitor C5 and resistor R6. The input
terminals 85 and 89 are serially connected via resistor R4. The
terminal 83 is serially connected with input terminal 91 of
amplifier A3 via coupling resistor R9 and coupling capacitor C7.
The terminal 87 is serially connected with the other input terminal
93 of amplifier A3 via coupling resistor R10 and coupling capacitor
C8. The amplifier A3 is a key element in the conversion means 95
serving to convert the two outputs from the differentially
connected amplifiers A1 and A2 into a single ended output. The
output of amplifier A3 is connected with terminal 97. The input
terminal 91 and the output terminal 97 are serially connected by
way of parallel coupled resistor R13 and capacitor C11. The input
terminal 93 of amplifier A3 is serially connected with ground via
capacitor C9 and input resistor R11. The amplifier A3 is
operationally connected with power source 96.
The terminal 97 is serially connected with the filter means 23 via
coupling capacitor C13. The output terminal 99 of the filter means
23 is serially connected with the input terminal 101 of amplifier
A4 via resistor R17. As illustrated, the filter means 23 is a twin
tee notch filter. The twin tee notch filter 23 comprises the
serially connected capacitor C14 and C15 connected in parallel with
serially connected resistors R14 and R15; with the juncture of
capacitors C14 and C15 being connected with ground via resistor R16
and the juncture of resistors R14 and R15 connected with ground via
capacitor C16. The twin tee notch filter is tuned at 60 Hertz (Hz)
to eliminate "60-cycle hum." Expressed otherwise, the filter means
23 will pass useful information below about 48 Hertz and above
about 70 Hertz but will reduce intermediate frequencies and will
substantially eliminate the 60-cycle per second electrical noise of
conventional electrical outlets. An illustrative relationship which
affords an operable twin tee notch filter is:
R14 = R15 = 2R16 and C14 = C15 = 1/2 C16, where
R14 = 1/(2.pi.fC14).
The amplifier A4 is operationally connected with power source 103.
The output of amplifier A4 is connected with terminal 107. The
terminal 107 is serially connected with input terminal 101 via
resistor R20 for feedback. The output terminal 107 is serially
connected with ground via resistor R21, capacitor C19 and gain
control resistor R22. The resistor R21 is a low value, series
compensation resistor for isolating the amplifier A4 output from
the capacitive load presented by C19. The potentiometer R22 is an
output gain control used to control the signal level applied to the
recorder pen drive amplifier. Specifically, a tap wiper arm 109 is
connected with a terminal 111 that is connected to the recorder pen
drive amplifier, which is conventional and therefore not shown.
The power supply 113 is connected with a conventional electrical
outlet via conductors 115 and 117, including serially coupled
"on-off" switch 119. The power supply 113 is also connected with
the ground at the juncture of capacitor C9 and R11. A suitable
dropping resistor 121 and pilot light 123 are employed to indicate
when power is being supplied to the power source. The power source
has suitable positive and negative voltage taps 125 and 127. The
taps 125 and 127 are serially connected with ground via simple
respective decoupling and filtering capacitors C21 and C22 to
prevent hum and electrical noise. The power supply is a solid state
modular power supply providing equal magnitude supply voltages of
opposite polarities on the respective voltage taps 125 and 127, as
required by the operational amplifiers A1, A2, A3 and A4 and the
recorder pen drive amplifier. Expressed otherwise, the taps 125 and
127 supply power to power sources 79, 81, 96. 103, etc. The power
supply has a line regulation of .+-.0.02 percent and load
regulation of .+-.0.05 percent. The maximum RMS ripple is limited
to 500 microvolts.
The calibrate and test circuit 67 is basically an astable
multivibrator using two NPN transistors T1 and T2. The resistors
R23 and R24 are connected serially with the transistors T1 and T2
as collector load resistors. The RC networks R25 C21 and R26 C20 in
conjunction with resistor R27 control the pulse width and frequency
of the built-in test signal. The resistor R28 and potentiometer R29
act as a voltage divider and calibrator for the built-in test
signal to keep its range in the low microvolt region. The resistor
R29 is ordinarily internally set by being fixed in production to
determine the frequency and signal level. The resultant free
running multivibrator circuit 67 puts out a square wave, as a
calibrate and test signal of predetermined amplitude and frequency.
I have found that a 50 microvolt signal at 30 cycles per second
affords an operable calibrate and test signal.
The amplifiers A1, A2, A3 and A4 are linear integrated circuit
operational amplifiers, presently constructed using medium scale
integration techniques. They may be fabricated using large scale
integration techniques, if desired. These operational amplifiers
have the properties of input offset voltage less than 5 millivolts,
input offset current less than 200 nanoampere, an input resistance
greater than 150,000 ohms, transient rise time response less than 1
microsecond, open loop gain greater than 25,000 and a common mode
rejection ratio greater than 70 decibels. Each of the respective
operational amplifiers A1, A2, A3 and A4 have respective RC
networks R7 C1, R8 C2, R12 C10, R19 C17 and respective capacitors
C3, C6, C12 and C18 connected with respective terminals for
frequency compensation to stabilize the amplifier operating points,
as recommended by the operational amplifier manufacturer. The
capacitors C4, C5, C9 and C11 set the upper limit of the amplifier
pass band at about 100 Hertz. The resistor R4 cross couples the
input amplifiers A1 and A2 to set the common mode gain to unity and
by its ratio with the resistors R4 and R6 determine the
differential signal gain. I have found that a gain of about 100 is
adequate for amplifiers A1 and A2 when the operational amplifier A3
provides a voltage amplification of about 100 also. The capacitors
C7, C8, C13, C20 and C21 are large value; for example, at least 100
microfarads; coupling capacitors. The resistors R9, R10 and R21 are
low value coupling resistors; for example, about 50 ohms;
recommended by the manufacturer to avoid saturating the respective
amplifiers.
The portable unit 11 has the usual ground receptacle 131 and the
reference receptacle 133 in the event the unit is to be employed at
a location; such as, a patient's bed where grounding is difficult
or where a desired standardized reference electrode means is
available. In addition to the on-off power switch 119, an external
plug-in receptacle 135 is afforded if remote monitoring is desired.
In addition to the chart drive speed dial 51, the stylus 29 may be
set to zero by a suitable zeroing knob and rheostat 139. The gain
control rheostat R22 with its wiper arm 109 is operated by the gain
knob 141. The function of the switch S1 has been explained in
connection with FIG. 4.
Since the portable unit will be taken into many different
environments such as hospital rooms having neon lighting, a shield
means is employed about the sensitive electronic components to
further alleviate any problems with electrical noise.
While the operation is believed apparent from the foregoing
description, the following brief summary will clarify any
questions. The electrode means are connected with the patient and
the portable unit at the patient's bedside without having to
disturb the patient. A pair of the electrode means 13 are connected
with conductors 53 and 55 via selector switch 19. The switch S1 is
moved to connect terminals 57 and 59 with terminals 69 and 71 for
transmitting the respective bioelectric disturbances and any noise
signals that are sensed to the amplifiers A1 and A2. The noise
signals that are sensed are generally of the same polarity. Because
of the differential connection of amplifiers A1 and A2 and because
of their input circuit configuration, the noise signals will appear
on both sides of coupling resistor R4 and therefore present zero
potential difference to the following amplifier A3. On the other
hand, bioelectrical signals that are not in phase and not of the
same polarity with respect to each other will be respectively
amplified and sent to the respective input terminals 91 and 93 for
conversion to a single ended output that is impressed on terminal
97. The filter means 23 removes the 60 Hz noise due to the power
source at the patient's bedside. Since the useful information will
ordinarily have a frequency of less than about 30 cycles per
second, the filter means 23 does not remove any useful information.
Accordingly, the filtered, single ended output is sent to amplifier
A4. There it is suitably amplified to interface with the pen drive
amplifier that is connected with terminal 111, though not shown in
the electrical schematic. Accordingly, the bioelectric signals
detected by emplacement of the electrode means 13 about the body of
the patient are sent via their respective conductors to the
receptacles and via selector switch 19 to the electronic circuit.
Signals from a given pair of electrodes are converted to single
ended output and the magnitude of the differential between the
bioelectric outputs is recorded with respect to time on paper
31.
The fabrication of the operational amplifiers by integrated circuit
techniques enable making a unit small enough that it can be
shielded and yet be hand portable. Expressed otherwise, the
shielding is not so bulky as to prohibit hand portability, since
the electronic components, though relatively complex, are small
enough to be readily shielded without adding impractical bulk and
weight. The operational amplifiers operate differently electrically
from single stage amplifiers with discrete components, as is well
recognized in the art, having exceptionally high gain. The high
gain is tempered with suitable capacitance and resistance network
feedback to effect stability. When the operational amplifiers are
connected in a common mode noise rejection configuration as
described and illustrated herein, the noise rejection and the
operational stability is exceptionally good. The resistor R4
connected with input terminals 85 and 89 makes practical common
mode noise rejection and increases the noise rejection many
fold.
The combination of the shielding and the differential amplifier
configuration have been proven satisfactory in every environment in
which the unit has been employed to date. Moreover, the unit has
been tested by neurosurgeons against a standard unit employed in a
central facility in a hospital and has been found to afford a
sensitivity and accuracy that is as good as the elaborate central
unit. Yet the portable unit is only about 11 .times. 11 .times. 14
inches and weighs less than 16 pounds for easy portability. It sits
readily on a bedside stand. The calibrate and test unit 67, that is
included directly in the portable unit, ensures that the technician
employing the unit can check the response of the unit to a known
signal, and thereby monitor for the presence of spurious signals
such as would be induced by electrical noise. Medical technicians
have employed the unit and have pronounced it acceptable in
accuracy in a wide variety of different environments. They have
agreed that it affords a satisfactory output with sufficient
sensitivity to determine death even when carried to a patient's
bedside. Expressed otherwise, the portable unit has sufficient
sensitivity that it can effect a millimeter of pen travel for a
bioelectric response of one microvolt.
Once the principle of the invention is made clear to one skilled in
the art, a variety of different embodiments and structures will
become apparent. For example, if desired, a recorder means having a
plurality of pens and pen drive amplifiers may be employed.
Ordinarily, a single pen recorder has advantages in decreasing size
and increasing the portability of the unit.
From the foregoing it can be seen that this invention accomplishes
the objects set forth hereinbefore and provides the features
indicated to be desirable and not heretofore provided by the prior
art devices. Specifically, this invention provides a unit that has
shielding and amplifiers connected in a differential configuration
such that it can be employed in environments in the presence of
electrical noises that prohibit use of prior art devices for
monitoring bioelectric output from a plurality of locations on the
body of the patient. Moreover, this invention provides a unit that
is small and portable and can be readily taken to the location of
the patient with the resultant convenience afforded thereby. The
unit, even though portable, provides a sensitivity sufficient to
establish the criterion of death, even in the presence of
electrical noises that make prohibitive operation of prior art
devices in such an environment. Moreover, the unit has convenience
features to facilitate its use in the plurality of environments and
at a plurality of locations; typical of such convenience features
is the front end loading of the paper for the recorder means. In
addition, the unit provides all of the features that have been
employed heretofore and are desirable.
Although the invention has been described with a certain degree of
particularity, it is understood that the present disclosure is made
only by way of example and that numerous changes in the details of
construction and the combination and arrangement of parts may be
resorted to without departing from the spirit and the scope of the
invention.
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