U.S. patent number 3,760,794 [Application Number 05/176,983] was granted by the patent office on 1973-09-25 for respiration monitoring apparatus and method.
This patent grant is currently assigned to Electronic Monitors, Inc.. Invention is credited to Raymond B. Basham.
United States Patent |
3,760,794 |
Basham |
September 25, 1973 |
RESPIRATION MONITORING APPARATUS AND METHOD
Abstract
Apparatus and method for monitoring the respiration of a patient
through utilization of a force responsive transducer, which ideally
is a capacitor transducer constructed from alternate layers of
conductive and nonconductive materials that are flexible such that
when placed beneath a patient or a resilient patient support, such
as a mattress, the distance between the plates of the transducer
changes for the purpose of producing electrical responses that upon
amplification energize indicator means, such as a visual alarm or
an audible alarm. The transducer is responsive to the vertical,
reciprocating forces and motions caused by respiration and along
with the associated circuitry, is sufficiently sensitive to
energize an alarm upon sensing a cessation of respiration.
Inventors: |
Basham; Raymond B. (Fort Worth,
TX) |
Assignee: |
Electronic Monitors, Inc. (Fort
Worth, TX)
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Family
ID: |
22646696 |
Appl.
No.: |
05/176,983 |
Filed: |
September 1, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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97737 |
Dec 14, 1970 |
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Current U.S.
Class: |
600/535; 340/665;
601/41; 361/283.1; 340/573.1; 340/657 |
Current CPC
Class: |
A61B
5/6892 (20130101); A61B 5/113 (20130101) |
Current International
Class: |
A61B
5/11 (20060101); A61B 5/113 (20060101); A61b
005/08 () |
Field of
Search: |
;128/25R,25N,2.08,2.1R,DIG.17,2.5P ;73/398C,88.5R ;340/279
;317/261 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Howell; Kyle L.
Parent Case Text
This application is a continuation-in-part of U.S. Pat. application
Ser. No. 97,737 filed Dec. 14, 1970, now abandoned.
Claims
I claim:
1. A system for monitoring the respiration of a patient
comprising:
a flexible force responsive capacitor means for placement beneath a
patient or patient support for sensing the respiration of a
patient,
said capacitor comprising:
three layers of flexible sheets of electrically conductive
material,
a flexible sheet of electrically non-conductive material located
between adjacent sheets of conductive material to form alternate
layers of conductive and non-conductive sheets of material,
the outer conductive sheets being larger than the center sheet and
having their peripherical edges substantially contiguous to each
other so as to provide effective electrostatic shielding for the
center conductive sheet,
said flexible layers of conductive material being sensitive to
changes in forces applied thereto and caused by the respiration of
a patient,
an electrical conductor connected to the center sheet of conductive
material,
an electrical conductor connected to the outer sheets of conductive
material, and
flexible non-conductive material surrounding and covering said
outer layers of flexible sheets of conductive material,
means connected to said conductors for applying a substantially
constant voltage across said capacitor, and
monitor means coupled to said capacitor means for monitoring the
respiration of a patient.
2. A system for monitoring the respiration of a patient
comprising:
a capacitor transducer means capable of sensing force changes
applied thereto and caused by the respiration of a patient,
said transducer being a thin, flexible, pad-like member,
comprising:
a plurality of thin flexible layers of electrically conductive
material including two outer layers,
a thin flexible layer of electrically nonconductive material
located between adjacent layers of conductive material to form
alternate layers of conductive and nonconductive material,
two electrical conductors connected to certain ones of said
conductive layers to form a capacitor having two plate means, one
of which includes the outer conductive layers of material
electrically connected together,
the other plate means being located between said outer conductive
layers of material,
the outer layers of said conductive material having their
peripherical edges extending beyond said other plate means and
substantially contiguous to each other so as to provide effective
electrostatic shielding for said other plate means, and
flexible electrically nonconducting material surrounding and
covering said outer conductive layers
said flexible layers of conductive material being sensitive to
changes in forces applied thereto and caused by the respiration of
a patient,
means connected to said conductors for applying a substantially
constant voltage across said capacitor transducer, and
monitor means coupled to said capacitor transducer means for
monitoring the respiration of a patient.
3. The system of claim 2 wherein said means for applying a
substantially constant voltage across said capacitor supplies a
substantially constant voltage of less than 25 volts D.C.
4. The system of claim 2 wherein said plurality of layers of
electrically conductive material comprise an odd number of
layers.
5. The system of claim 2 including the combination therewith of a
memory system comprising:
a lamp indicator means,
circuitry means coupled to said capacitor transducer for
periodically energizing said lamp indicator means to cause said
lamp indicator means to flash on and off when respiration
ceases,
said circuitry including means for continuously energizing said
lamp indicator means if respiration begins following cessation
thereof.
6. The apparatus of claim 5 wherein said circuitry comprises:
normally electrically nonconducting means coupled to said lamp
indicator means and which is rendered electrically conductive by
the application of a signal thereto and which remains in a
conductive state following termination of said signal,
a normally conducting means coupled to said normally nonconducting
means for providing a flow path of energy from said normally
nonconducting means, and
oscillator means coupled to said normally nonconducting means and
to said normally conducting means and responsive to cessation of
respiration for producing periodic signals for rendering conductive
said normally nonconducting means and for periodically rendering
said normally conducting means nonconductive to periodically cause
said lamp indicator means to flash on and off.
7. A system for monitoring the respiration of a person
comprising:
a capacitor transducer means capable of sensing force changes
imparted to a mattress or the like due to the respiration of a
person while supported by the mattress,
said transducer being a thin, flexible, pad-like member
comprising:
alternate layers of thin flexible sheets of electrically conductive
and nonconductive material forming a thin and flexible capacitor
having a ratio of surface area in the plane of said pad-like member
relative to its thickness through said sheets of greater than 500
to one,
the number of layers of conductive material being greater than
two,
two electrical conductors connected to certain ones of said
conductive sheets of material to form a capacitor having two plate
means, one of which includes the outer conductive sheets of
material electrically connected together,
the other plate means being located between said outer conductive
sheets of material,
the outer layers of said conductive sheets of material have their
peripherical edges extending beyond said other plate means and
substantially contiguous to each other so as to provide effective
electrostatic shielding for said other plate means, and
thin flexible electrically nonconductive material surrounding and
covering said outer layers of electrically conductive sheets of
material,
said flexible sheets of conductive material being sensitive to
changes in forces applied thereto and caused by the respiration of
a patient,
means connected to said conductors for applying a substantially
constant voltage across said capacitor transducer, and
monitor means coupled to said capacitor transducer means for
monitoring the respiration of a patient.
8. The system of claim 7 wherein the number of layers of conductive
material comprise an odd number of layers.
9. A system for monitoring the respiration of a patient comprising
the combination of:
a capacitor transducer means capable of sensing force changes
applied thereto and caused by the respiration of a patient,
said capacitor transducer comprising a thin, flexible pad-like
member including alternate layers of thin flexible sheets of
electrically conductive and nonconductive material forming a thin
and flexible capacitor having a number of layers of conductive
material greater than two,
two electrical conductor means connected to certain ones of said
conductive sheets of material to form a capacitor having two plate
means, one of which includes the outer sheets of conductive
material electrically connected together and to one of said
conductor means,
circuitry means connected to said electrical conductor means and to
be supplied with energy from a supply of electrical energy for
producing a substantially constant voltage for application to said
capacitor transducer,
said circuitry comprising:
regulator means for producing a regulated supply of voltage from
said supply of electrical energy, and
a field effect transistor connected in a source follower
configuration and having its drain connected to the output of said
regulator means; its gate connected to the other of said conductor
means and hence to said other plate means of said capacitor
transducer; its source connected to said one conductor means by way
of a source biasing resistor and a load resistor; and a gate return
resistor having one terminal connected to said gate and the other
terminal connected to the juncture between said source biasing
resistor and said load resistor and
monitor means coupled to the source of said field effect transitor
for monitoring the respiration of a patient.
10. The system of claim 9 wherein said capacitor transducer means
includes three conductive layers of material, the outer layers of
conductive material being larger than the center layer and having
their peripherical edges substantially contiguous to each other to
provide effective electrostatic shielding for the center layer.
11. A method of monitoring the respiration of a person supported on
a mattress or the like comprising the steps of:
locating a capacitor transducer at a position sufficient to sense
force changes imparted to the mattress caused by the respiration of
the person while supported by the mattress,
said capacitor transducer comprising:
three layers of flexible sheets of conductive material,
a flexible layer of non-conductive material located on opposite
sides of the center sheet of conductive material,
the flexible layers of non-conductive material on opposite sides of
said center sheet of conductive material having their edges
connected together forming an inner member having a covering of
non-conductive material surrounding said center sheet of conductive
material,
an exterior flexible non-conductive layer of material covering the
outward facing side of each of the outer sheets of conductive
material,
the exterior flexible non-conductive layers of material having
their edges connected together forming an exterior covering of
non-conductive material surrounding said outer sheets of conductive
material with said inner member located between said outer sheets
of conductive material,
said outer sheets of conductive material being larger in their
planes than said center sheet of conductive material and having
their peripherical edges extending beyond the peripherical edges of
said center sheet of conductive material so as to provide effective
electrostatic shielding for said center sheet of conductive
material,
said flexible layers of conductive material being sensitive to
changes in forces applied thereto and caused by the respiration of
a patient,
an electrical conductor connected to said center sheet of
conductive material, and
an electrical conductor connected to said outer sheets of
conductive material,
applying a substantially constant voltage to said two conductors
and hence across said capacitor transducer,
sensing capacitive changes between said layers of flexible sheets
of conductive material due to force changes applied thereto due to
the respiration of said person,
converting said sensed capacitive changes into electrical
responses,
amplifying said electrical responses, and
applying said electrical responses to a monitor means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to patient monitoring apparatus,
particularly to apparatus adapted to monitor respiration for the
purpose of providing an alarm upon cessation of respiration.
2. Description of the Prior Art
A number of different types of methods and apparatus have been
proposed in the past for the purpose of monitoring respiration.
However, the previously known apparatus and methods have not yet
received widespread acceptance due to a number of severely limiting
disadvantages. One previously known method utilizes the connection
of electrodes directly to the skin of a patient to sense electrical
resistance changes during respiration in the skin surrounding the
expanding and retracting chest cavity. Connecting electrodes
directly to the patient is often irritating to the patient, whose
skin frequently rejects the saline solution commonly used to
produce satisfactory contact between the electrode and the patient.
And in addition, such method can be dangerous if a large voltage is
applied inadvertently or accidentally across electrodes secured to
a patient. A number of accidents of this type have been reported.
In addition, devices have been proposed for sensing force of motion
cessation that include the use of a photoelectric cell, but such
devices lack that degree of sensitivity leading to successful
operation.
SUMMARY OF THE INVENTION
It is the general object of the invention to provide improved
respiration monitoring apparatus and methods that accurately sense
respiration and cessation of respiration without need for direct
attachment to the body.
Another object of the invention is to provide respiration
monitoring apparatus that utilizes a capacitor transducer for
accurately sensing respiration and cessation of respiration.
Another object of the invention is to provide an apparatus and
method for respiration monitoring that utilizes electrical
responses from a capacitor transducer, that amplifies such
responses, and that transmits the responses to either an audible or
visual indicator and circuit means to notify a patient's attendant
that respiration has ceased.
The invention comprises respiration monitoring apparatus and
method, the apparatus including a force responsive transducer,
which ideally is a capacitor transducer with movable plates,
adapted for placement beneath a patient or a patient support such
as a mattress. The transducer senses changes in the forces and
movements caused by patient respiration. By suitably amplifying the
electrical responses generated with the transducer, these responses
may be fed to indicator means that provide either a visual or an
audible warning that signifies when the electrical responses cease
due to cessation of respiration. The indicator means are ideally a
lamp, for visual warning and an audible device such as a speaker,
for audible warning, to signify the cessation of electrical
response. Such apparatus and method are sufficiently sensitive and
accurate to sense cessation in the generally vertical,
reciprocating forces generated by patient breathing. Hence, should
this bodily function cease, the visual and audible alarms are
energized.
In one embodiment a memory device is provided that continuously
indicates that temporary cessation had occurred in the event that
the patient recovers and begins breathing again.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a perspective view of respiration monitoring apparatus
positioned relative to a patient lying in a conventional hospital
bed in accordance with the principles of my invention.
FIG. 2 is a perspective view of a force responsive transducer, with
portions thereof separated to show the construction thereof.
FIG. 3 is an electrical schematic diagram showing a preferred
circuit for energizing both a visual and an audible alarm to
indicate cessation of respiration.
FIG. 4 is an electrical schematic diagram of an amplifier circuit
shown in block form in FIG. 3.
FIG. 5 is an electrical schematic diagram of a lamp switching
circuit shown in block form in FIG. 3.
FIG. 6 is an electrical schematic diagram of an audio switching
circuit shown in block form in FIG. 3.
FIG. 7 illustrates in more detail the manner in which electrical
connections are made to the transducer.
FIG. 8 is an electrical schematic diagram of an alternative warning
system incorporating a memory device.
FIG. 9 is an electrical schematic diagram of a rate meter for
indicating the rate of respiration of a patient.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring initially to FIG. 1 of the drawing, the numeral 11
designates a force responsive transducer inserted between the
mattress 13 and springs (not shown), generally under the shoulder
region of a patient 15 in a reposed position in a conventional
hospital bed 17. The force responsive transducer 11 is connected by
a coaxial cable 19 with a console 21, which is in turn connected by
multi-line conductor 23 and plug 24 with a wall socket 25
associated with a 110 volt alternating current source. As shown in
FIG. 1 the console 21 has exposed on its exterior an audible alarm
27 and two visual alarms 29, 31, the operation and function of
which will be explained subsequently.
Referring to FIG. 2, the force responsive transducer 11 is
preferably a capacitor transducer comprised of layers of flexible,
alternately conductive and nonconductive material as follows. The
exterior of the capacitor 33 is of a nonconductive material such as
an acrylic or cellulose, the lower side of such covering material
having a flap 35 adapted to fold over and bond to the upper cover.
As shown in FIG. 2 the next material from the top is preferably a
flexible conductive sheet 37 of suitable material such as sheet
steel that is adjacent a nonconductive sheet of material 39 that in
turn lies adjacent a conductive sheet 41 on top of a nonmetallic
sheet 43 adjacent an exterior conductive sheet 45 that is covered
by material 33, as previously explained. The sheets 39, 41 and 43
are secured in this instance with a nonconductive strip 46. The
outer conductive sheets 37 and 45 not only provide the reference
plates to establish capacitance with respect to the inner plate 41
but also shield the inner plate from stray electric fields.
The coaxial cable 19 leading from the transducer to the console 21
has its center conductor 19A connected to the conductive sheet 41
as illustrated in FIG. 7. The shield 19B of cable 19 is connected
to the two outer conductive sheets 37 and 45 as illustrated by
connection 19B'. At the console the shield 19B is grounded as
illustrated at 47. An example of a satisfactory conductive material
is sheet steel metal of about 0.003 inch thickness, while a
satisfactory nonconductive material is acrylic having a thickness
of approximately 0.003 of an inch. The alternate layers of
conductive and nonconductive material may be approximately 6 inches
square. Hence, the composite transducer has the characteristics of
flexibility and pliability for the purpose of accurately sensing
force changes upon the mattress 13.
Referring initially to FIG. 3, which is a schematic diagram of a
preferred circuit means, the numeral 11 designates the variable
capacitor transducer illustrated in FIGS. 2 and 7. The cable
conductor 19A is connected with the juncture 49 of a resistor 50
and a protective network 53 that comprises in this instance a
biasing resistor 55 connected in parallel with diodes 57, 59, which
are in turn connected with the juncture 61 of two source resistors
63 and 65, 65 being connected with ground 47 as shown.
Resistor 50 is connected with the gate 67 of a field effect
transistor 69 having its drain 71 connected with a 25 volt source
received from a 110 volt AC source, as will be explained in
connection with FIG. 4. The source 73 of the transistor 69 is
connected in series with the source resistor 63.
The juncture 61 between source resistors 63 and 65 is connected
with a capacitor 75, in turn connected in series with an amplifier
circuit means 77 that feeds first a lamp switching circuit 79 for
selective activation of two lamps 29, 31 (see also FIG. 1) or other
suitable visual indicators, and second an audio switching circuit
85 that drives a speaker 27 (see also FIG. 1).
Describing the FIG. 3 circuit operationally, the field effector
transistor 69 is connected in a source follower configuration with
the resistors 63 and 65, which are connected with the source, in
this instance the variable capacitor 11. The resistor 63 supplies
the bias to regulate the gate cut-off point on the field effect
transistor. The voltage developed across resistor 65 is supplied
back to the capacitor 11 through resistor 55, and polarizes the
capacitor transducer in such a way that it will act upon this
voltage but will produce a variable voltage that is inversely
proportional to the change in the capacitance of the transducer.
This variable voltage is then sensed through resistor 50 by the
gate 67 of the field effect source follower. The output of the
field effect source follower is transmitted to the juncture 61 of
resistors 63, 65, which are connected through capacitor 75 to the
amplifier. In operation each time pressure is applied to the
capacitor transducer 11, a signal appears at the output of the
amplifier circuit 77. The resulting amplified signal is applied to
the lamp switching circuit 79. The respiration lamp 29 responds to
cyclic breathing pressure applied through the mattress 13 to the
transducer. This lamp is adapted to flash each time there is
breathing motion applied to the capacitance transducer by the
mattress. So long as the cyclic mattress motion caused by patient
breathing continues, the respiration lamp 29 will continue to light
cyclically.
In the event of respiration failure of the patient, the respiration
lamp will extinguish and after a period of time determined by the
setting of adjustable resistor 225, the alarm lamp 31 will switch
on. This in turn applies an AC signal into the audio swtiching
circuit 85, which in turn closes the switching circuit in order to
excite an audible alert device that can be a buzzer, but preferably
is a solid state transistor signalling device that gives an audible
alarm simultaneous with the emergency lamp.
Referring to FIG. 4 for an explanation of a preferred amplifier
circuit, the drain 71 of the field effect transistor 69 is
connected at the juncture 87 of a resistor 89 which is connected in
series with the collector 91 of a transistor 93. The base 95 of the
transistor 93 is connected with the juncture 94 between the output
of capacitor 75 and a resistor 97, the collector 91 being connected
with the juncture 99 between resistors 89 and 97. The emitter 98 of
transistor 93 is connected to ground. The juncture 99 is connected
with a capacitor 101 connected in series with a resistance 103,
which in turn is connected at the juncture 105 of a resistor 107
and the base 109 of a transistor 111.
The juncture 105 and the base 109 of transistor 111 is connected
with a diode 113 through a juncture 115 leading to a capacitor 117.
A resistor 119 is connected with ground and with the juncture 121
between capacitor 117 and a capacitor 123, which is in turn
connected with the juncture 125 between resistance 127 and the
collector 129 of transistor 111, such juncture also connecting
resistors 107 and 127 as shown. Resistor 127 is connected at a
terminal 139 and thus across an unregulated 35 volts (DC). The
conductor 132 and terminal 134 define the output of the amplifier
circuit.
The 35 volt source is derived typically from a plug 24 of a 110
volt AC source that is connected across the primary 133A of a
transformer 133, the secondary 135 that in turn is connected
through a rectifier, which in this instance is a diode 137
connected between the juncture 139 between resistor 127 and
capacitor 141 connected to ground as shown.
A regulator circuit comprises a transistor 143 having its emitter
145 connected at a juncture 147 between resistor 149 and a
conductor 151 leading to the juncture 87 between resistor 89 and
the field effect transistor 69. The collector 153 of transistor 143
is connected with the 35 volt unregulated supply via conductor 155,
and its base 157 is connected with the juncture 159 of a resistor
161 and the collector 163 of a transistor 165. The opposite
terminal 167 of resistor 161 is connected with the conductor 155
and thus the 35 volt unregulated source. The base 169 of transistor
165 is connected to the juncture 171 between resistors 149 and 173.
The emitter 175 of transistor 165 is connected with the cathode of
a Zener diode 177, the anode of such diode being connected to
ground and to resistor 173 as shown. In addition, the cathode of
the Zener diode 177 is connected with the juncture 179 between a
resistor 181 and the emitter 175 of transistor 165. The resistor
181 is connected at terminal 183 with the conductor 155 leading to
the 35 volt source.
The regulator circuit shown is of conventional form, using a 15
volt Zener diode as a reference and a voltage divider device
transistor 165 which in turn controls the base of the transistor
143, the output of the regulator then being the reference voltage
difference in the voltage divider defined by resistors 149 and 173
for setting the bias operation point for transistor 165, which
would be the 25 volt point plus the forward voltage drop across
transistor 165.
Operationally, the above described amplifier circuit consists of
two stages, that include respectively transistor 93 and transistor
111, having their capacitance coupled. Transistor 111 has a low
pass filter of the negative feed-back type connected between the
collector and the base of transistor 111. This filter consists of
capacitors 117, 123 and resistor 119. This network provides a
necessary frequency feed-back in order to give the amplifier
relatively low frequency roll off so that any signals above and
higher than the frequency of normal respiration signals are
rejected, and the gain of the amplifier is thus extreme for such
signals.
A preferred lamp switching circuit is illustrated in FIG. 5 with
the output 134 of the amplifier circuit being connected in series
with a resistor 185 and a capacitor 187, which is connected at the
juncture 189 between a conductor 191 and a resistor 193 leading to
ground 47. Conductor 191 leads to the juncture 195 between a
resistor 197 and a diode 199, also connected with ground. The
output of resistor 197 is connected with the gate 200 of a silicon
controlled rectifier 201 having its anode 203 connected in series
with the lamp 29, which is connected with the 30 volt source 204 as
shown, the cathode 205 of the rectifier being connected with
ground.
The anode 203 of rectifier 201 is connected through a juncture 209
with a resistor 207 in turn connected through a juncture 211
between a capacitor 213 that is grounded as shown. The diode 215 is
connected in series with a resistor 217, which is connected with
the juncture 219 between a capacitor 221, connected with ground,
and a resistor 223 connected in series with a variable resistor 225
connected to the 30 volt AC source applied to the conductor
227.
The gate 228 of a silicon controlled rectifier 229 is connected
with the juncture 219 between capacitor 221 and resistors 217, 223,
while the cathode 231 is connected to ground and the anode 233 is
connected with the lamp 31 and with a lamp 29 through conductor
227. An output conductor 235 leads from the juncture 237 between
lamp 31 and the anode 233 of the rectifier 229.
Operationally, the respiration lamp switching circuit 79 comprises
the silicon controlled rectifier 201 that switches the lamp 29 on
each time there is a respiration signal from the transducer 11. The
anode 203 of the rectifier 201 is connected to the capacitor 213 in
order to maintain a charge on this capacitor so that the emergency
lamp 31 will remain off during the time that the charge is
maintained. Each time rectifier 201 is energized and the
respiration lamp 29 is turned on there is a negative voltage
appearing at the anode 203 of the rectifier 201, and this in turn
maintains a negative charge on capacitor 213.
With respect to rectifier 229, the emergency lamp switching
rectifier, would normally keep the emergency light 31 energized if
it were not for the negative charge maintained on the capacitor
213. Failure of patient respiration or a failure of the respiration
lamp 29 would no longer maintain a negative charge on capacitor
213, and thus, the emergency lamp 31 would be excited. As a
consequence, that in the event of failure of the respiration light
29, the instrument will give alarm. Such a malfunction energizes
the emergency lamp 31 and the audible alarm (as explained
subsequently) so that the patient attendant would know that there
was either an emergency or there had been a failure of the
instrument. Any failure in the circuitry described thusfar will
energize lamp 31; this in turn tends to make the whole instrument
essentially fail safe.
A preferred audio switching circuit is illustrated in FIG. 6, in
which a resistor 239 is connected with the output 235 of the lamp
switching circuit and with a juncture 241 between resistor 239 and
a capacitor 245 connected to ground. The resistor 243 is connected
with the juncture 244 between a resistor 247 and the base 249 of a
transistor 251, having its collector 253 connected with the
juncture 255 between a resistor 257 and a resistor 259, and its
emitter 261 connected to ground as shown. Resistor 247 and resistor
257 are connected with a juncture 263 leading to the 35 volt DC
source.
Resistor 259 is connected with the juncture 265 between a base 267
of a transistor 269 and a resistor 271 connected in series with a
capacitor 273 connected with ground. The collector 275 of
transistor 269 is connected to the speaker 27 connected with the 35
volt DC source at junction 263, while the emitter 279 of the
transistor is connected to ground.
Operationally, the output of the emergency switch devices
(transistor) 229 of FIG. 5 charges capacitor 245 through lamp 31.
When the lamp 31 is switched on, it produces a negative charge on
capacitor 245 that biases the transistor 251 in the cut-off
condition so that its collector is at its maximum voltage. Under
these conditions a positive bias is supplied to the base of
transistor 269, which switches on the transistor and in turn causes
current to flow through an audible alert device such as speaker 27.
When the emergency lamp 31 is in the off condition, there is no
charge applied to the capacitor 245, such that transistor 251 is
biased in the forward direction through resistor 247. This in turn
drops the base current to zero in transistor 269, which in turn
cuts off this transistor to prevent current flow to the audio alert
device.
In hospitals, where a plurality of the devices of the present
invention may be employed simultaneously to monitor the breathing
of a plurality of newborn babies respectively, means is needed to
allow an attendant nurse to know if a given baby has experienced
temporary cessation of breathing but has subsequently recovered.
For example, while the nurse is attending to one baby, a baby
behind her may experience temporary cessation of breathing causing
the lamp 31 of its associated monitor to be energized and its alarm
27 to sound. By the time the nurse turns around, breathing may be
restored causing the monitor lamp 31 to turn off and the alarm 27
to terminate its sounding. Thus the nurse will not be able to know
which baby had temporary problems from observing the monitors
employed.
Referring to FIG. 8, there will be described a circuit arrangement
incorporating a memory device which will retain evidence of
cessation of breathing if it occurs by the baby being monitored by
a given monitor. This circuitry is a modification of that of FIG. 5
with additional components employed. In this respect, transistor
281 is substituted for silicon controlled rectifier 229 and the
lamp 31 removed from the position shown in FIG. 5. The lamp is
connected as shown at 31' in FIG. 8 to a silicon controlled
rectifier 283 which is employed for memory purposes. The remainder
of the circuitry of FIG. 8 comprises a transistor 285, a
unijunction transistor 287, a transistor 289 and a capacitor 297.
Transistor 287 and capacitor 297 form an oscillator. Normally when
a patient is breathing, transistor 281 is in a nonconductive state,
transistor 285 is conducting, unijunction transistor 287 is off or
in a nonconducting state, silicon controlled rectifier 283 is off
or in a nonconducting state and transistor 289 is conducting. Thus
lamp 31' is off and the sound or audible alarm 27 coupled between
the silicon controlled rectifier 283 and transistor 289 also is
off. When transistor 281 is off, a positive bias is applied to the
base of transistor 285 maintaining it in a conductive state. The
resulting low potential from the collector of transistor 285
maintains the transistor 287 in a nonconducting state. The
transistor 289 is biased to a conducting state through resistor
295.
When a patient stops breathing, transistor 281 becomes conductive
thereby causing transistor 285 to become nonconductive. This causes
the oscillator to begin oscillating for the production of positive
pulses which are applied to the gate of silicon controlled
rectifier 283 and negative pulses which are applied to the base of
transistor 289. The first positive pulse applied to the gate of
silicon controlled rectifier 283 renders it in a continuous
conductive state while each negative pulse applied to the base of
transistor 289 renders it temporarily nonconducting. Thus since
silicon controlled rectifier 283 is on and transistor 289 is turned
on and off, lamp 31' periodically is energized to flash on and off.
As the lamp 31' flashes on and off a negative pulse periodically is
applied to the sound alarm 27 by way of capacitor 291 to
periodically turn the sound alarm on and off also. If the patient
begins to breath again transistor 281 is turned off, transistor 285
turned on which terminates oscillation of oscillator 287. Thus
transistor 289 becomes conductive continuously again. Silicon
controlled rectifier 283 also remains in a conductive condition
thereby continuously energizing the lamp 31' providing a memory or
continuous record to allow the attendant to know from an inspection
of the lamp 31' that the patient had a temporary cessation of
breathing. In order to return the lamp 31' and silicon controlled
rectifier 283 to their normal conditions, the attendant merely has
to temporarily close switch 293 to ground the anode circuit of the
silicon controlled rectifier 283 in order to place the rectifier in
its normal nonconducting state.
Referring to FIG. 9, there is disclosed circuitry and a device
which may be employed as a visual indicator of breathing in
addition to the lamp 29. This circuitry comprises a rate meter and
may be coupled to the amplifier of FIG. 4 at terminal 134. In the
circuitry of FIG. 9, transistor 301 normally is off but is turned
on each time respiration occurs. Transistor 303 normally is on when
there is no respiration but becomes nonconductive when transistor
301 becomes conducting. A capacitor 305 is charged through
transistor 303 when it is conducting and transistor 301 is off.
When transistor 301 conducts, the capacitor 305 is discharged
through diode 307 and transistor 301. When this occurs, transistor
303 is cut off by the fact that its base is more negative than its
emitter. When transistor 301 turns off, transistor 303
simultaneously turns on in order to charge the capacitor 305 and
the charging current is measured across resistor 309 by way of an
integrator comprising capacitors 311 and 313 and variable resistor
315, the latter of which is adjusted or calibrated whereby the
respiration rate of the patient may be measured. The Zener diode
319 is provided in order to regulate the voltage that is supplied
to the capacitor 305 in order that the voltage supplied to it is a
very accurate reference voltage.
From the above apparatus and operational descriptions, it should be
apparent taht I have provided an invention having significant
advantages. By placing the force responsive transducer beneath the
patient as shown in FIG. 1, the respiration of the patient may be
sensitively monitored. The transducer is sensitive to the generally
vertical, reciprocating motions transmitted to the mattress 13 by
the patient's respiration. As a consequence, should the patient's
respiration be interrupted, the visual and audible alarms
associated with the console will be energized for the purpose of
alerting the patient's attendant. For the first time an apparatus
has been provided that possesses sufficient sensitivity to monitor
accurately respiration without requiring direct attachment to the
patient.
While the invention has been shown in only one of its forms, it
should be apparent to those skilled in the art that it is not so
limited but is susceptible to various changes and modifications
without departing from the spirit thereof. The specific form of
force responsive transducer is not limited specifically to the
capacitor transducer shown and described, and the configuration of
the capacitor transducer itself may be varied widely within the
broad scope of the invention. In addition, the invention is not
limited in its broadest sense to the specific form of circuitry
shown by way of preferred embodiment, since there are alternate
circuit configurations capable of producing the intended,
satisfactory result.
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