U.S. patent number 3,875,929 [Application Number 05/381,982] was granted by the patent office on 1975-04-08 for patient movement monitoring apparatus.
This patent grant is currently assigned to Peak Technologies Limited. Invention is credited to John Thomas Grant.
United States Patent |
3,875,929 |
Grant |
April 8, 1975 |
PATIENT MOVEMENT MONITORING APPARATUS
Abstract
A system for monitoring cyclic movements, such as respiration of
a patient, and indicating when such movement ceases comprises a
scanner arranged in use to provide a movement-sensitive field. For
patient monitoring this field envelopes at least part of the
patient. Circuitry for monitoring variations in the field controls
indicator circuitry which provides the indication that movement has
ceased. The indicator circuitry provides a signal for each
successive group of a predetermined number of movement cycles and
responds to the absence of such a signal in a predetermined
interval from the preceding signal to provide the indication that
movement has ceased. In the case of monitoring respiration, an
alarm is given after a predetermined delay from cessation of
breathing unless the patient's movements provide signals in the
scanner output corresponding to a predetermined number of breathing
cycles. Extraneous movements near the patients are unlikely to
cause this to happen, so that the system is virtually certain to
provide an alarm as soon as possible after cessation of breathing
without being inhibited by extraneous movements.
Inventors: |
Grant; John Thomas (Guestwick,
EN) |
Assignee: |
Peak Technologies Limited
(Isleworth, Middlesex, EN)
|
Family
ID: |
10369819 |
Appl.
No.: |
05/381,982 |
Filed: |
July 23, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Jul 25, 1972 [GB] |
|
|
3477/72 |
|
Current U.S.
Class: |
600/429; 600/595;
5/940; 340/573.1; 600/534 |
Current CPC
Class: |
A61B
5/113 (20130101); A61B 5/4818 (20130101); G01S
13/02 (20130101); A61B 5/0507 (20130101); Y10S
5/94 (20130101) |
Current International
Class: |
A61B
5/11 (20060101); A61B 5/113 (20060101); G01S
13/00 (20060101); G01S 13/02 (20060101); A61b
005/08 () |
Field of
Search: |
;128/2R,2S,2A,2N,2.08,DIG.29 ;340/279,258A |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Howell; Kyle L.
Attorney, Agent or Firm: Phillips, Moore, Weissenberger,
Lempio & Strabala
Claims
I claim:
1. Movement monitoring apparatus comprising:
a. microwave radar means providing a limited movement-sensitive
field of microwave radiation;
b. monitor circuit means monitoring disturbances of said field and
providing at its output a pulsed signal indicative of the degree of
field disturbance;
c. resettable aggregating circuit means coupled to the output of
said monitor circuit means to aggregate said pulsed signal to
provide at its output a signal voltage the level of which is
indicative of said degree of field disturbance;
d. threshold circuit means defining a predetermined threshold
voltage and coupled to the output of said aggregating circuit means
to receive said signal voltage;
e. trigger circuit means to said threshold circuit means to be
activated thereby when said signal voltage reaches said
predetermined threshold voltage;
f. resetting circuit means coupled to the output of said trigger
circuit means and to said aggregating circuit means to re-set said
aggregating circuit means when said trigger circuit means is
activated;
g. resettable delay circuit means coupled to the output of said
trigger circuit means and providing a predetermined delay between
the appearance at its input of an input signal caused by activation
of said trigger circuit means and the appearance at its output of a
pre-determined output signal level, activation of said trigger
circuit means re-setting said delay circuit means to re-start said
pre-determined delay; and
h. alarm circuit means connected to the output of said delay
circuit means and activated by said pre-determined output signal
level thereof,
said predetermined threshold voltage and said predetermined output
signal level of said delay circuit means being so selected in
relation to the frequency of said pulsed output signal of said
monitor circuit means that said delay circuit means is repeatedly
re-set by the output of said trigger circuit means so long as there
is a predetermined degree of movement in the movement-sensitive
field and is not re-set after the degree of movement falls below
said predetermined degree until there is generated a sufficient
number of cycles of said pulsed output signal of said monitor
circuit means to provide at the output of said aggregating circuit
means a signal voltage sufficient to cause activation of said
trigger circuit means.
2. A system as set forth in claim 1, in which said aggregating
circuit means includes a reservoir capacitance charged via a
transistor.
3. A system as set forth in claim 1, in which said trigger circuit
means is a Schmidt trigger.
4. A system as set forth in claim 1, in which said re-setting
circuit means includes an inverter.
5. A system as set forth in claim 1, in which said alarm circuit
means is connected to the output of said delay circuit means
through an inverter which inhibits operation of said alarm circuit
means while the output signal level of said delay circuit means
exceeds said predetermined value.
6. A system as set forth in claim 1, in which said radar means
provides at its output Doppler frequencys signal indicative of
movements in the movement-sensitive field and in which said monitor
circuit means includes a frequency-selective amplifier for said
Doppler frequency signals, having a narrow pass-band centered on a
frequency corresponding to a particular class of movement to be
monitored, and further trigger circuit means connected to the
output of said amplifier and providing at its output said pulsed
output signal of said monitor circuit means.
7. A system as set forth in claim 6, in which said further trigger
circuit means is a Schmidt trigger.
Description
The present invention relates to improvements in the monitoring of
patients, and is more particularly concerned with an improvement in
the invention of the commonly owned prior co-pending Application
No. 225934 filed 14 Feb. 1972 which issued on Mar. 12, 1974 as U.s.
Pat. No. 3,796,208 and will hereinafter be referred to as the prior
patent.
The prior patent describes a system suitable for monitoring
movements of a patient and indicating when the degree of movement
is such as to require attention, the system comprising a scanner
arranged in use to provide a movement-sensitive field enveloping at
least part of the patient, circuitry for monitoring variations in
the field, and indicator circuitry controlled by the monitoring
circuitry to provide the indication that attention to the patient
is required.
The monitor system is particularly, but not exclusively, suitable
for use as a respiration monitor or apnea detector, registering the
respiration of a patient by means of the movements of the patient's
chest wall. Apnea is the cessation of respiration and is a common
condition in premature babies. As explained in the prior patent,
provided apnea is detected quickly enough, it is generally possible
to restimulate respiration.
The system described in the prior patent is made insensitive to
movements at frequencies higher than those likely to be encountered
in breathing, that is to say of the order of 80 cycles per minute.
This lessens the likelihood of the device being activated by
movements extraneous to the patient. With this system, it has been
found that the presence of persons standing within a foot or two of
a baby's cot did not appear to interfere with the operation of the
detector, provided that its sensitivity was appropriately
regulated.
The system of the prior patent has also been used for monitoring
respiration in adults, and it has been found that the presence of
staff alongside the bed and movements of patients in adjacent beds
have caused no interference in operation.
Nevertheless, it has been found that in some circumstances
movements other than those of the patient monitored can produce
anomalous operation. This is particularly so when the breathing of
a premature baby under intensive care is monitored, through the
acrylic or glass top of an incubator. This produces not only an
enforced extra distance between the monitor and the patient, and so
a larger irradiated area, but also the likelihood of scatter from
the incubator top.
The system activates an alarm after a predetermined delay from
cessation of breathing. The difficulty experienced is that
extraneous movements during this delay period may be interpreted by
the monitor system as a normal breathing cycle and may re-set the
alarm timer circuitry without the alarm being sounded. The
additional delay can have serious consequences for the patient.
The present invention is intended to provide a system in which this
disadvantage is substantially eliminated.
In accordance with the present invention a system for monitoring
cyclic movements of a patient and indicating when such movement
ceases comprises a scanner arranged in use to provide a
movement-sensitive field enveloping at least part of the patient,
circuitry for monitoring variations in the field, and indicator
circuitry controlled by the monitoring circuitry to provide the
indication that movement has ceased, the indicator circuitry
providing a signal for each successive group of a predetermined
number of movement cycles and responding to the absence of such a
signal in a predetermined interval from the preceding signal to
provide the indication that movement has ceased.
It will be appreciated that with this system an alarm is given
after a predetermined delay from cessation of breathing unless
extraneous movements around the patient are such as to provide
signals in the scanner output corresponding to the predetermined
number of breathing cycles. This is most unlikely to happen, so
that the system is virtually certain to provide an alarm as soon as
possible after cessation of breathing without being inhibited by
extraneous movements.
In the following detailed description, the circuitry of the
monitoring system will be described in detail, except where it is
very similar to that described in the prior patent. Likewise, the
detailed operation of the system will not be described in the
present specification, the reader being referred to the prior
patent for further details.
The invention will now be described in more detail, by way of
example and with reference to the accompanying diagrammatic
drawings in which:
FIGS. 1, 2 and 3 are three sections of the circuitry of the
monitoring system, being contained in a single unit with the radar
unit antennae;
FIG. 4 shows a remote alarm unit for connection to this unit;
FIG. 5 is a block diagram of the system; and
FIG. 6 is a waveform diagram related to FIG. 5.
Referring to FIG. 1, the receiver antenna of the radar unit is
associated with a mixer diode D1 whose cathode is connected to the
grounded horn antenna and whose anode is connected to ground
through electrolytic capacitance C1. The anode of the diode D1 is
also connected to a terminal P16 of a printed circuit board on
which the majority of the components shown in FIG. 1 are mounted.
The opposite ends of a variable resistance VR1 are connected to
terminal P16 and a further terminal P15. The variable tap of the
resistance VR1 is connected to a terminal P14.
Terminal P14 is connected through the series-connected combination
of a resistance R7 and an electrolytic capacitance C3 to the input
1 of an integrated circuit amplifier A1. The junction of resistance
R7 and capacitance C3 is connected to ground through an
electrolytic capacitance C7. Terminal P15 is also connected to
ground. A first power supply terminal 2 of the amplifier A1 is
connected to a terminal P13 through the series-connected
combination of resistances R2 and R3. It is also connected to
ground through an electrolytic capacitance C2. The junction of
resistances R2 and R3 is connected to the amplifier output 3
through a resistance R5 and to the cathode of a zener diode ZD2
whose anode is connected to ground. The cathode of the zener diode
ZD2 is also connected through the series-connected combination of
resistances R8 and R9 to terminal P16. The junction of resistances
R8 and R9 is connected to ground through an electrolytic
capacitance C22.
The second power supply terminal 4 of the amplifier A1 is connected
to ground.
The amplifier output 3 is connected to ground through the
series-connected combination of a resistance R6 and an electrolytic
capacitance C4. This series-connected combination is shunted by an
electrolytic capacitance C5, and the junction of resistance R6 and
capacitance C4 is connected to the amplifier input 1 through a
resistance R4. The amplifier output 3 is also connected through an
electrolytic capacitance C6 to a terminal P17.
FIG. 2 shows part of a second printed circuit board, a terminal P12
on which is connected to terminal P17 of the board shown in FIG.
1.
Terminal P12 is connected through a resistance R10 to the base of a
first NPN transistor VT1 whose emitter is connected to ground. The
collector of this transistor is connected to the positive rail A
through a resistance R12, and to the transistor base through a
resistance R11. The collector of transistor VT1 is further
connected through a resistance R13 to the base of a first PNP
transistor VT2 whose emitter is connected to the positive rail A.
The base of this transistor VT2 is connected to the positive rail A
through a capacitance C9. Its collector is connected through a
resistance R14 to the base of transistor VT1 and through a
resistance R15 to the anode of a light-emitting diode ILP1 whose
cathode is connected to ground through a preset variable resistance
VR16. The cathode of diode ILP1 is connected to the anode of a
diode D6 whose cathode is connected to a terminal P11 of the board
and is also connected to ground through diodes D3, D4, D5 and D16
connected in series and in the same direction of current flow, the
anode of diode D3 being connected to the cathode of diode D6 and
the cathode of diode D16 being connected to ground.
The variable tap of the resistance VR16 is connected through a
capacitance C10 to the base of a second NPN transistor VT3 whose
emitter is connected to ground through an electrolytic capacitance
C11. The collector VT3 is connected to the positive rail A.
The emitter VT3 is also connected to the anode of a diode D7 whose
cathod is connected to the base VT3. Diode D7 is shunted by a
resistance R17.
The emitter of transistor VT3 is connected through a resistance R18
to the anode of a diode D8 whose cathode is connected to the
collector of an NPN transistor VT11. The emitter of transistor VT11
is connected to ground.
The emitter of transistor VT3 is also connected through a
resistance R19 to the base of a NPN transistor VT4 whose emitter is
connected to ground and whose collector is connected to the
positive rail A through a resistance R21. The base of transistor
VT4 is connected to ground through a resistance R20 shunted by a
capacitance C12.
The collector of transistor VT4 is also connected through a
resistance R22 to the base of a PNP transistor VT5 whose emitter is
connected to the positive rail A. The base VT3 is connected to rail
A through a capacitance C13. The collector of transistor VT5 is
connected through a resistance R24 to the cathode of a zener diode
ZD17 whose anode is connected to ground. The cathode of zener diode
ZD17 is connected to the base of transistor VT11 through a
resistance R39. It is also connected through a resistance R23 to
the base of transistor VT4.
FIG. 3 shows the remainder of the printed circuit board of which
part is shown in FIG. 2.
Referring to FIG. 3, the anode of a diode D9 is connected to the
cathode of the zener diode ZD17 (FIG. 2), as indicated by the
arrows B in FIGS. 2 and 3.
The cathode of diode D9 is connected to ground through an
electrolytic capacitance C14 shunted by the series-connected
combination of a resistance R26 and a variable resistance VR27
whose variable tap is connected to ground. The cathode of diode D9
is also connected through a resistance R25 to the base of an NPN
transistoor VT6 whose emitter is connected to ground and whose
collector is connected to the positive rail A through a resistance
R33. The collector VT6 is also connected to the base of an NPN
transistor VT8 whose emitter is connected to the anode of a diode
D13 whose cathode is connected to ground. The collector of
transistor VT8 is connected to the positive rail A through a
resistance R32 and also to a terminal P3. It is further connected
through a capacitance C23 to the collector of an NPN transistor VT7
whose collector is connected to the positive rail A through a
resistance R31. The base of transistor VT7 is connected to the
positive rail A through a resistance R30. The base of this
transistor VT7 is also connected through an electrolytic
capacitance C16 to the collector of transistor VT8, and the
collector is connected to the base of transistor VT8 through an
electrolytic capacitance C15. The collector is further connected to
the anode of a diode D10 whose cathode is connected to the anode of
a diode D11 whose cathode is connected to ground through a
series-connected combination of resistances R28 and R29. The
junction of resistances R28 and R29 is connected to the gate
electrode of a controlled rectifier SCR1 whose cathode is connected
to ground and whose anode is connected to a terminal P2.
The collector of transistor VT8 is connected through a resistance
R34 to the base of an NPN transistor VT9 whose emitter is connected
to ground. The collector of this transistor VT9 is connected to the
positive rail A through a resistance R35 and also to a terminal
P18.
An NPN transistor VT10 has its emitter connected to a terminal P10
and its collector connected to a terminal P5. The collector is
further connected to the base through a resistance R37, the base
being connected to the cathode of a zener diode ZD15 whose anode is
connected to ground. The zener diode ZD15 is shunted by an
electrolytic capacitance C19.
A terminal P4 is connected to the positive rail A through a
resistance R36 and also to a first fixed contact 1 of a first
section S1A of a two-pole three-position switch. The second and
third fixed contacts of switch section S1A are unconnected and the
movable contact is connected to the positive rail A, as is the
movable contact of the other switch section S1B. Fixed contacts 1
and 3 of switch section S1B are connected together to a terminal
P22. The fixed contact 2 of switched section S1B is left
unconnected.
Between terminals P3 and P4 is connected an audible alarm LS1,
consisting of an oscillator and loudspeaker. The alarm LS1 is
shunted by a capacitance C24.
Between terminals P1 and P2 is connected the series-connected
combination of an alarm indicator lamp ILP2 and an alarm indicator
reset button PB1.
Terminal P10 is connected to one side of the resonant cavity and
Gunn diode assembly GD14 of the transmitter aerial. The other
terminal of the cavity and Gunn diode are grounded. The cavity and
Gunn diode are shunted by capacitances C17 and C18.
Terminal P7 is connected to a common ground point for the circuitry
mounted on the boards of FIGS. 2 and 3, terminal P15 in FIG. 1
being also connected to this grounding point.
Terminals P5 and P22 are respectively connected to a smoothed and
an unsmoothed power supply (not shown).
By way of example, terminal P5 may be connected to P22 through a
low-value resistance the opposite ends of which are connected to
ground through respective high-value capacitances. Terminal P22
would be connected through a suitable resistance to the positive
terminal of a bridge rectifier, the negative terminal of which
would be grounded and the input terminals of which would be
connected to respective terminals of the printed circuit board for
connection to the secondary winding of a main transformer. A main
indicator lamp may be provided, connected in series with a
resistance across the primary transformer winding, and the live
connection to the transformer primary winding may be fused.
Terminals P11 and P 18 are connected to a socket for an external
alarm, which will shortly be described with reference to FIG.
4.
Terminals P13 and P5 are connected together. Terminals P17 and P12
are connected together.
Referring to FIG. 4, the external alarm has terminals X and Y for
connection to a plug for insertion in the socket connected to
terminals P11 and P18. To terminal X are connected the anode of a
diode D100 and the cathode of a diode D101. The cathode of diode
D100 is connected to terminal Y through an audible alarm LS2,
suitably identical to the alarm LS1 of FIG. 3, shunted by a
capacitance C100.
The anode of diode D101 is connected to the cathode of a
light-emitting diode ILP2 whose anode is connected to terminal
Y.
The overall operation of the system will now be described with
reference to FIGS. 5 and 6, of which FIG. 5 is a block diagram of
the system and FIG. 6 is a waveform diagram related to FIG. 5.
Referring to FIG. 5, the transmitting and receiving antennas, TX
and RX respectively are shown coupled to the Gunn diode cavity
assembly GD14 and the amplifier A1 respectively. The output of the
amplifier A1 is connected to the Schmidt trigger formed by
transistors VT1 and VT2, whose output is connected to the pump
circuit formed by the transistor VT3 and capacitance C11.
The voltage monitored at point A in FIG. 5 is the output voltage of
the amplifier A1, while that monitored at point B is the voltage
across the capacitance C11.
The output of the pump circuit is connected to the Schmidt trigger
comprising transistors VT4 and VT5, the output voltage of which is
monitored at point C. The output of the second Schmidt trigger is
also applied through an inverter A, formed by transistor VT11, to
the reset input of the pump circuit.
The second Schmidt trigger output is applied to the input of a
timer consisting of capacitance C14 and the associated circuitry,
the delay control resistance being variable resistance VR27. The
voltage at the output of the timer is monitored at point D, and is
applied through an inverter B to the audio alarm generator LS1.
The waveforms observed at points A to D are shown in the
correspondingly referenced lines in FIG. 6.
The amplifier has a frequency response centered in the region of 1
Hz, having roll-off points at 0.3 Hz and 3 Hz. It has been found
that normal extraneous movement in the close vicinity of the
monitor produces signals in the frequence range of 5 to 100 Hz,
with occasional signals in the 1 to 5 Hz region.
These frequencies are typically caused when a movement relative to
the monitor changes direction, so producing a frequency range with
a dip in the region of 1 to 5 Hz. This will result in a single
output cycle from the first Schmidt trigger.
Normally natural human movement around a patient under observation
will produce spurious responses at a rate of some 1 every 5 seconds
in the worst case.
Waveform A is the amplifier output typical of normal respiration at
a rate of 30 breathes per minute. Respiration at rates of between
10 and 150 breaths per minute will produce the waveform B at the
output of the pump circuit.
The second Schmidt trigger will trigger at a predetermined voltage
which is reached by successive steps from the pump circuit. By
varying the pulse or step height, the number of pulses required to
reach the trigger level can be varied, but typically the pulse
height is set to allow three pulses before the second Schmidt
trigger is fired.
It is thus seen from the left-hand portion of FIG. 6, that during
uninterrupted respiration an output pulse is produced by the second
Schmidt trigger for every three cycles of the respiration waveform
A.
When the second Schmidt trigger is fired the voltage at the output
of the pump circuit is discharged to near ground potential by means
of the inverter A. A further three pulses can then be accepted
before the trigger is re-fired.
The right-hand portion of waveform B shows a cessation of
respiration after some 5 breath cycles. In this period two spurious
respiration pulses are shown, but it will be observed from waveform
B that these do not result in firing the second Schmidt
trigger.
Waveform D shows how the timer output is reset on the occurrence of
each output pulse from the second Schmidt trigger. On cessation of
breathing, however, when firing of the Schmidt trigger ceases, the
timer output voltage drops to zero, the time for this being
adjustable by means of the delay control VR27.
When the timer output reaches zero, the inverter B (transistor VT6)
no longer inhibits operation of the auidble alarm LS1, which
provides the appropriate alarm signal.
Referring again to FIGS. 1 to 3, the diode D1 produces a signal
corresponding to movements of the chest cavity and disphragm of the
patient. The amplifier A1 produces a substantially sine-wave output
within the frequency range 0.3 Hz to 3 Hz.
The amplifier output is passed to a Schmidt trigger consisting of
transistors VT1 and VT2 providing drive for the light-emitting
diodes ILP1 and ILP2. Drive is also provided to capacitance C10
which couples the pulsed amplifier output to the pump transistor
VT3, the capacitance C11 forming a reservoir.
Transistors VT4 and VT5 form a second Schmidt trigger with a wide
input differential. When the charge on capacitance C11 reaches a
predetermined level, after three pulses from the pumped transistor,
for example, the Schmidt trigger changes state to provide drive to
the timer reservoir capacitance C14 and transistor VT11. This
discharges capacitance C11 to a low level whereupon the Schmidt
trigger returns to its original "off" state.
If resistance VR16 is set to give a pulse height which results in
three cycles before Schmidt trigger is fired, it follows that
capacitance C14 would be re-charged every three pulses. Resistance
VR27 controls the discharge rate of capacitance C14 and therefore
varies the time delay between cessation of breathing and the
provision of an alarm.
Transistor VT6 is a clamp transistor which inhibits free-running of
the multivibrator formed by transistors VT7 and VT8. This
multivibrator has a free-running rate in the region of 50 to 100
cycles per minute and is used to drive the audible alarm LS1.
The controlled rectifier SCR1 drives a visual alarm indicator and
is triggered by the first cycle of the multivibrator. Transistor
VT9 forms a buffer amplifier which is used to drive the external
audible alarm unit (FIG. 4).
Transistor VT10 and the associated components provide a smoothed DC
power supply to the Gunn diode cavity GD14.
The switch S1 provides a standby facility by removing power from
the alarm circuit while maintaining power to the microwave
transmitter and receiver circuits, so avoiding delay due to the
charging of capacitances C1, C3 and C4, which have long time
constants due to the frequency response of the system.
During normal operation clamp transistor VT6 holds the base of
transistor VT8 at ground potential, so that transistor VT9 will be
fully conducting and its collector, and therefore one output
terminal of the external alarm socket, will be at ground potential.
The other socket terminal will have a voltage on it varying between
zero and some 2.8 volts, at the patient respiration rate. If this
is applied in the correct sense to the external alarm unit (FIG.
4), the light-emitting diode ILP2 can glow. When an alarm condition
exists transistor VT9 will have a voltage on it varying between
zero and 13 volts. This will cause a reverse potential to appear at
the remote alarm unit, thus activating the audible alarm LS2 and
extinguishing the light-emitting diode ILP2.
* * * * *