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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and to an apparatus for measuring
the life functions of a human being, particularly of an infant, by way of
a support acting as a state-of-life monitor on the basis of pressure
changes, and which also comprises temperature sensors, humidity sensors,
and the like, and acts on a measuring and display device connected to the
support and operating on the basis of pressure changes.
2. Description of the Prior Art
The German published application 23 45 551, and the corresponding U.S. Pat.
No. 3,926,177, fully incorporated herein by this reference, discloses that
the respiration, particularly a potential cessation of respiration, as
well as an increased muscle activity of a human being, or of a test
animal, be identified by way of a capacitively-acting support. A measuring
instrument in accordance therewith has the disadvantage that only a
portion of the signals necessary for the subsidiary functions can be
communicated therewith. Cessation of respiration, cardiac arrests and
unexplained, other causes of death such as suddenly elevated temperature,
the failure of body occlusion openings, and the like, cannot be acquired.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a life function measuring
method and apparatus which provide information concerning the normal
condition or the deviation from the normal condition, particularly
concerning the deviation therefrom in a foreseeable time, under all
circumstances and using the most modern electronic amplification
technology.
The above object is achieved in that the support, which acts on the basis
of pressure changes, emits a signal which reproduces the rib cage movement
or, respectively, the diaphragm movement during respiration and the
movement of the cardiac muscles and also supplies a signal for the pulse
beat, particularly by way of an auxiliary sensor. The three essential
indications for a normal life function are thereby reproduced and provide
the first, rough grid for a display as to whether or not a life form
exhibits severe malfunctions of the life functions; and given the display
that severe malfunctions exit, a person (or a corresponding medical device
triggered by a malfunction condition) can undertake all resuscitation
actions that are necessary.
According to a particular feature of the invention, the signals of the
support, which acts on the basis of pressure changes, are subjected to an
image pattern recognition of a unit contained in the memory, being
subjected thereto on the basis of preselected tolerance curves
representing a normal condition. As a result thereof, it is possible to
register deviating characters which deviate from the normal life rhythm of
a life form and to recognize the same. As an image pattern, a normal life
form is supplied into the corresponding apparatus, i.e. into a
corresponding computer, and all deviations lying outside of the range of
tolerance are displayed. Two tolerance ranges are thereby preferably
displayed independently of one another, a normal tolerance range of
deviations still lying within the framework of what is tolerable and a
range of tolerance of deviations indicating a fatal malfunction. The
personal constitution of the life form being monitored can therefore be
taken into consideration.
According to another feature of the invention, the signals of the
pressure-sensitive support are subjected to a frequency analysis and are
further subjected to an analysis as to the amplitude level. It is possible
on the basis of these two criteria to differentiate the movement of the
individual muscles, for example of the cardiac muscles, of the large
muscles, for example the leg and arm muscles, of the muscles of
respiration and of the remaining muscles. A display of an unusual behavior
occurs only when one of the corresponding tolerance limits is
transgressed. It is advantageously taken into consideration that the
frequencies of the cardiac muscle, for example, and of the respiration
muscles, generally deviate from one another. They can be identical under
special circumstances, but that is usually a symptom of a disturbed
respiratory activity, particularly of an oxygen deficiency.
According to another feature of the invention, the signal evaluation occurs
by way of a differential circuit. Advantageously, the differential circuit
allows different weights of the life form whose life functions are to be
monitored and supervised and displayed independently of its weight. A
possibility of universal utilization therefore occurs without having to
carry out matching and balancing to the respective life form. The
requirement that monitoring be possible in a foolproof manner by simply
plugging in a plug without further fine adjustment is therefore met in the
best possible manner.
According to another feature of the invention, the support acts as an
active sensor independent of the weight and independent of the size of the
mat, the motional energy thereof output by the human body being amplified
and subjected to the image pattern analysis, to the frequency analysis or
to the amplitude analysis. This is the advantageously possible
construction of the life function monitoring apparatus of the invention. A
further construction can provide that the mat, acting weight-independent,
is divided into various fields, so that it is simultaneous possible to
identify the positions of the person whose life functions are being
monitored. Particularly for older persons, it is thereby possible to make
a preliminary display of a condition that indicates a fall from a hospital
bed.
According to another feature of the invention, the analyzed, discrete
signals are separately displayed and trigger individual alarms. It is
therefore possible to display the many, different dangerous conditions of
a life form, particularly of a bed-ridden patient or of an infant in such
a manner that the nursing personnel can react before the event occurs. It
is thereby particularly advantageous that the discrete signals are
subjected to a tendency analysis and that the result of the tendency
analysis is displayed and fed to the individual alarm display apparatus.
This broadens the possibility of the displays of positional change and of
the possibility of a deterioration of the situation. Tendency analysis is
already well known in the art relating to industrial systems, particularly
for thermal systems, which can be applied without hesitation and also
indicates the approach to precarious conditions for a person in a
heretofore unobtainable manner.
The discrete signals are transmitted by teletransmission to a stationary or
mobile monitoring station and are successively or simultaneously displayed
and can trigger individual alarms at such a remote location. This is a
possibility of supervision by a minimum of personnel which accommodates
the current trend of eliminating personnel without having the occurrence
of a negative influence on the patient.
According to the invention, the method is implemented by an apparatus
comprising a capacitively-operating support as a life state monitor for
the life function of a human, particularly of a human, which apparatus
comprises a measuring and display device connected to the support for the
purpose of editing and amplifying the signals transmitted from the
capacitively-operating support. The apparatus contains a frequency
analyzer for simple tasks, an amplitude analyzer when a more thorough
reliability of the display is required, and an image pattern analyzer
which comprises a comparison to a normal reaction of a life line,
particularly an infant, and executes this comparison within the scope of
prescribed tolerance limits, and also comprises appropriate amplification
paths for the discrete signal. These are preferably identically
constructed in order to correspondingly reduce the costs of the overall
apparatus.
The amplification paths comprise a voltage source with an interface to the
pressure-sensitive capacitative support. It is therefore guaranteed that a
faulty connection cannot trigger a fatal current shock for the life form.
In the past, this has repeatedly turned out to be dangerous, even though
allegedly impossible. As with the design of the sensor mat, the interface
therefore most essential for the evaluation of the overall invention in
that it is actively operating element.
The circuit technology of the individual amplification paths shall be set
forth below and may be derived in terms of all of its details from the
following detailed description.
According to a particular embodiment of the invention, which exceeds the
current technology of the individual amplification technology,
independently of the other sensors, the pulsation of the patient, such as
an infant, is transmitted in a wireless manner by a sensor applied to the
skin, being transmitted to a receiver, particularly to the capacitively
acting mat which records the life function. Yet another, accurate
differentiation of the life function signals is therefore possible.
According to another feature of the invention, it is provided that the
individual life function signals are forwarded to a central display unit
which can be monitored by supervisory personnel. Therefore, a monitoring
of the individual patients which was heretofore only possible in intensive
care stations is established, and is far more economical and
simultaneously possible without endangering the patient as a result of
cables, hoses, etc. The actual construction is simple on the basis of
systems of the type introduced above, for example, in air and sea travel
for locating and rescuing persons. These systems operate free of
disruption to an optimum degree and on the basis of economical devices
produced in mass production.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the invention, its organization,
construction and mode of operation will be best understood from the
following detailed description, taken in conjunction with the accompanying
drawings, on which:
FIG. 1 is a graphic illustration of an ideal respiration signal;
FIG. 2 is a graphic illustration of an ideal pulse signal;
FIG. 3 is a graphic representation of a temperature signal;
FIG. 4 is a graphic illustration of a muscle contraction signal;
FIG. 5 is an equivalent circuit diagram of a sensor mat constructed in
accordance with the present invention;
FIG. 6 is a sectional view taken through a sensor mat constructed in
accordance with the present invention;
FIG. 7 is a perspective view of an electronic monitoring apparatus
constructed in accordance with the present invention; and
FIG. 8 is a schematic circuit diagram of an amplification system which may
be employed as an amplification channel for the type of signals
illustrated in FIGS. 1-4 in practicing the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates an idealized curve of a typical respiration signal,
whereby the time duration of a breath is indicated as T.sub.index
respiration. Half the period duration of a breath is identified as T/2 for
what is basically an idealized sine wave.
The idealized curve of the pulse illustrated in FIG. 2 is more similar to a
decaying, triangular wave having pauses. The repetition time of the pulse
is illustrated as T.sub.pulse. The individual, characterizing leading and
trailing edges of the signal are referenced T1/2, T2/2, T3/2, T4/2 and
Tn/2. These referenced signal portions can also be interpreted as parts of
superimposed oscillations, from which it may then be seen that the pulse
comprises a significantly higher proportion of higher-frequency
oscillations than does the signal of respiration, although the repetition
time of the respiration and that of the pulse can definitely lie on the
same order of magnitude.
FIG. 3, by contrast, shows an assumed signal curve of temperature. It may
be seen that the signal curve of the temperature need not necessarily
change periodically and that the change of the signal lies on a
significantly smaller order of magnitude than the amplitudes of the pulse
signal or of the respiration signal.
By contrast, again, the signal curve in FIG. 4 relating to muscle
contraction exhibits a significantly higher amplitude than the other
signals. This conspicuous feature is identified by the indicated amplitude
height. The curve of the signal allows conclusions to be drawn regarding
the frequency content which likewise differs from the remaining signal. In
accordance with the invention, the information for monitoring the various
life functions is acquired from the measured signal by the analysis of the
various frequencies and amplitudes.
The equivalent circuit diagram of a suitable measuring sensor, operating as
a signal generator, is illustrated in FIG. 5. An electric field is built
up between the center aluminum foil 1 and two outer aluminum foils 3a and
3b, on the one hand, as well as between a shield 4 and two other aluminum
foils 3a and 3b, on the other hand. An increase in the sensitivity is
achieved by the parallel connection of four capacitors. This is
schematically illustrated in FIG. 5. The shield foil is insulating at the
inside and conductive at the outside. As is the case with the center foil
1, the shield foil is connected to ground potential. The shield 4
therefore fulfills the following functions:
No electrical field can penetrate from the interior to the exterior or from
the exterior to the interior;
It lends the mattress a good, uniform appearance;
The grounding of the mat represents the second stage of protection for the
patient against potential overvoltages;
It fulfills capacitor functions relative to the capacitor plates 3a and 3b;
It serves the purpose of reflecting the body heat, this representing an
additional benefit in the case of new born infants which easily suffer
from hypothermia.
The capacitor plates 3a and 3b are constructed in the form of a foil which
is conductive on both sides. All foils (for example aluminum foils) are
secured against dislocation by way of two-sided adhesive strips. Adhesive
strips are only applied in punctiform fashion in order to not reduce the
overall sensitivity of the mat. The spacing between the capacitor plates
(aluminum foils) 3a and 3b is produced by an insulating spacing medium.
The connection to the device of FIG. 7 is provided by way of a shielded
coax cable and a diode plug.
The structure of the mat is illustrated in the sectional view of FIG. 6.
Again, the center aluminum foil is referenced 1, this being conductive on
both sides. An insulating medium 2 is applied to one side of the foil 1
and an insulating medium 3 is applied to the other side of the foil 1. A
pair of capacitor plates in the form of aluminum foils 3a and 3b are
respectively applied to the insulating layers 2 and 3, the layers 3a and
3b being conductive on both sides. A further aluminum layer 4 is provided
about the aforementioned elements, the layer 4 being conductive on the
inside and nonconductive on the outside. Two-sided adhesive strips 5 are
provided in punctiform fashion for connecting the aforementioned layers
together. A polyvinylchloride (PVC) film skin 6 is provided for hygiene
and insulation.
A textile covering 7 may also be provided, this not being a determining
factor in operation. A shielded coax cable 8 has a diode plug 9 at the end
for connecting the mat to the monitor.
Referring to FIG. 7, the housing of the electronic monitor is illustrated.
The housing may be aluminum, plastic or the like. Basically, the housing
fulfills shielding functions. A display device 101 for displaying the
respiration pulse is arranged in the housing. Further, a green
light-emitting diode 102 is provided in the front panel of the housing and
lights in synchronism with the respiration pulse. A further, red
light-emitting diode 103 represents an optical alarm display. An
adjustable time interval generator is referenced 104. Diode input sockets
for connection of the sensor mat are referenced 105a and 105b. An on/off
switch 106 is provided along with a green light-emitting diode 107 to
indicate the commercial power supply. Given battery operation or,
respectively, emergency operation, the light-emitting diodes 102 and 107
are automatically shut off. The supply connection and a 12 volt battery
connection are provided at the rear of the housing.
The fundamental circuit of the apparatus is illustrated in FIG. 8 and will
be discussed in detail below with reference to the respiration signal.
This circuit essentially comprises four components, namely an amplifier
unit, an evaluation and alarm unit, a power pack and emergency power
supply and battery operation circuit, and a noise transmission alarm and
reception unit.
The central mat foil 1 and the outer protective foil 4 are connected to the
circuit via a terminal 205 which is, in turn, connected to an artificial
ground E. The upper capacitor foil 3a and the lower capacitor foil 3b are
respectively connected to the terminals 202 and 203. A pair of input
amplifiers A1 and A2 are provided as high-resistance amplifiers for
receiving the, for example, respiration signal. The output of the
amplifiers A1 and A2 is fed to an amplifier A3 for amplification by a
factor of 10. A further amplification at this stage is without meaning
since the applied offset voltages could lead to the output of the
amplifier A3 into limitation. The commercial supply hum and the high
frequencies are filtered out by a low-pass filter which is an active
filter including an operational amplifier A4. The upper limit frequency of
the low-pass filter lies slightly below 50 Hz. A following, passive
high-pass filter rids the output signal of the amplifier A4 of DC voltage
components which can still pass the preceding low-pass filter. The limit
frequency amounts to about 1 Hz. The signal is then amplified by a factor
of 1000 in an operational amplifier A5. Due to the high input impedance of
the amplifier A5, the highpass filter is not highly loaded. Noise and hum
components again enter into the signal due to the amplifier A5. These are
again filtered out by an active low-pass filter including an operational
amplifier A6, this filter being constructed in the same manner as the
active low pass filter which includes the amplifier A4. The DC components
are again extracted by a following, passive, high-pass filter before the
signal is again amplified by a factor of 200 with the assistance of an
amplifier A7. The output signal of the stage A6 may also be fed to a
computer interface for image pattern recognition stored in a memory as
initially set forth.
The respiration signal has now been amplified to such a degree that it can
be evaluated via a comparator having a variable reference value provided,
for example, by way of a potentiometer Pl. The difference between the
quiescent voltage of the mattress and the reference voltage thereby
amounts to 0.02 volts. Since the comparator still switches without fault
given a voltage differential of 105 .mu.v, the circuit can still be made
more sensitive by a factor of 100. Too high a sensitivity, however, leads
to self oscillation, for which reason the operating point should be
accurately set with the assistance of an oscilloscope. Whereas integrated
operational amplifiers have been employed for the circuits A1-A7, the
comparator A8 requires a different module because of the required
sensitivity, for example a commercially-available module designated LF
356. The output signal of the amplifer A8 is either 0 volts or 12 volts.
Each breath therefore leads to a voltage pulse at the output of the
operational amplifier A8, this pulse being displayed by a green
light-emitting diode (102) and forwarded to a following time function
element. The time function element is composed of a capacitor Cl having,
for example, a capacitance of 10 .mu.F and connected to the negative pole,
and a rotary potentiometer P2. The potentiometer P2 is preceded by a
resistor having a value of, for example, 100 k ohms. The potentiometer
enables a time interval setting from 0 seconds through 35 seconds.
A further capacitor C2, connected to the positive pole has the following
function. Without the second capacitor, the voltage level of the first
capacitor Cl always lies below the set reference voltage at the input of
the operational amplifier A10 when the device has not been switched on for
a period of time. This would lead to the fact that the relay triggering
the alarm would trigger, since the relay is a latching relay. The second
capacitor C2 increases the voltage level at the inverting input of the
operational amplifier A10 above the reference voltage at the non-inverting
input. The effect that the device indicates alarm immediately after being
switched on is thereby suppressed. The set reference voltage should lie in
the range between 0.5 volt and 1 volt. Each voltage pulse from the output
of the operational amplifier A8 therefore leads to charging of the
capacitor C1. This capacitor discharges via the 100 k ohm resistor and the
rotary potentiometer P2 (FIG. 7, 104). When voltage pulses fail, the
reference value at the non-inverting input 3 of the operational amplifier
A10 is downwardly transgressed and the operational amplifier A10 connects
through to drive a latching relay R. It causes illumination of the red
light-emitting diode 103 in FIG. 7 which is connected to the terminal 207,
which terminal is also connected to a device for generating an audible
alarm signal. In more intelligent versions, the module containing the
operational amplifiers A8 and A10 can optionally be replaced by a
microcomputer system.
The symmetrical voltage supply which is indispensible for the operation of
the operational amplifier of the module A1-A7 is generated by the
operational amplifier All. The device is fed by a stabilized power pack
having an output voltage of 12 volts. The primary circuit of the power
pack is protected by a 10 mA fuse. The output voltage of the power pack is
available at the terminals 209 and 210. These terminals can also be
extended outside of the device to an external supply with an external
power pack or an external 12 volt battery. This, for example, can be
necessary when the apparatus is operated in an automobile. The low-voltage
region is again protected by a 100 mA fuse. This fusing is coupled to two
20 volt Zener diodes of 2.5 watts each.
The Zener diodes have the following function. If the transformer were to
receive a short from the primary winding to the secondary winding and the
power consumption of the power pack in the primary region remains below 10
mA, a voltage of 220 volts would be applied at the terminals 209 and 210.
Since this voltage is greater than 20 volts, the Zener diodes would
immediately become conductive and would therefore allow the 100 mA fuse to
separate. Each of the 20 volt Zener diodes is capable of this function.
The system therefore has the following devices available in the apparatus
for protecting the patient against overvoltages;
1. A 10 mA fuse preceding the powerpack;
2. A dual-pole on/off switch a.sub.1 ;
3. A galvanic separation of 220 volts and 12 volts on the basis of primary
and secondary windings;
4. A 100 mA fuse before the entrance to the low-voltage section;
5. Two Zener diodes which work independently of one another for triggering
the fusing in the low-voltage region; and
6. Operation of the sensor input portion in the microvolt range.
With respect to the mattress, the PVC insulating film protects the entire
mat and the grounded aluminum foil shields the entire capacitor.
Since there is a requirement that all unnecessary displays should be
disconnected given emergency operation/ battery operation, primarily in
order to save energy and to therefore extend the possible emergency
operating time, the displays for the commercial voltage (107) and
respiratory function (102) are only introduced into the circuit of the
commercial power supply devices, i.e. given outage of the power pack, the
current from these two displays can no longer flow to ground since a diode
inhibits the circuit. The negative pole of the moving coil instrument 101
and of the alarm diode 103 and the battery indicator remain uneffected by
this operation. The power pack having an output voltage of 12 volts DC
simultaneously feeds the emergency battery which is connected to a
terminal 211 and to the negative terminal 212. An additional resistor is
provided, this resistor having the function of effecting the current
limitation given long-term charging battery. The normal voltage of the
battery amounts to about 10.8 volts, so that there is always an adequate
potential gradient, for example, 1.2 volts each from 9 rechargeable cells.
Due to the resistor designed for 100 ohms, the charging current is limited
to 120 mA even given a completely uncharged battery. In normal operation,
the charging current of the battery amounts to 20 mA. The assumed
potential difference thereby amounts to 2 volts. The 100 ohm resistor is
followed by a diode which prevents the battery from discharging via the
secondary winding of the transformer or via the leakage currents of the
Zener diodes in its unconnected condition.
The apparatus designed provides that a noise transmission alarm is
integrated in the housing. In this case, the alarm signal can be taken at
a point 207 of the circuit. It is meaningful to supply the noise
transmission alarm and the apparatus via a central, stabilized power pack.
The power pack would then feed the current at the points 209 and 210. The
noise transmission alarm is intended to meet the following functions:
1. Transmission of the alarm (always); and
2. Transmission of the noise in, for example, a nursery (selection should
be possible by defining the response threshold).
The integration of the transmitter into the housing prevents the danger
that the transmitter and the receiver, having nearly all identical design,
could be confused with one another. Under given conditions, it may also be
meaningful for the noise alarm to be operated alone, in particular when
the patient has grown out of the at-risk age and is no longer in need or
respiratory monitoring.
Although I have described my invention by reference to particular
illustrative embodiments thereof, many changes and modifications of the
invention may become apparent to those skilled in the art without
departing from the spirit and scope of the invention. I therefore intend
to include within the patent warranted hereon all such changes and
modifications as may reasonably and properly be included within the scope
of my contribution to the art.
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