U.S. patent number 3,818,900 [Application Number 05/265,944] was granted by the patent office on 1974-06-25 for device for supervising the heart and breathing functions of a patient.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Bernd Nickel.
United States Patent |
3,818,900 |
Nickel |
June 25, 1974 |
DEVICE FOR SUPERVISING THE HEART AND BREATHING FUNCTIONS OF A
PATIENT
Abstract
A device for supervising the heart and breathing functions of a
patient has a common receiving member constructed as a rheographic
electrode for receiving a breathing signal and a first heart signal
as well as a further receiving member for receiving a second heart
signal. The current feeding generator for the rheographic electrode
as well as the device measuring the breathing signals at the
rheographic electrode are connected by condensers and by the
measuring device for the heart signals with receiving members via
low pass filters as well as with a common-mode rejection device.
The invention is particularly characterized in that as current
feeding generator is used a an alternating current generator with a
frequency lying in the kHz range and that for coupling the current
feeding generator or the breathing signal measuring device to the
rheographic electrode are used condensers having a capacity lying
in the pf range.
Inventors: |
Nickel; Bernd (Erlangen,
DT) |
Assignee: |
Siemens Aktiengesellschaft
(Munchen, DT)
|
Family
ID: |
5811796 |
Appl.
No.: |
05/265,944 |
Filed: |
June 23, 1972 |
Foreign Application Priority Data
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Jun 25, 1971 [DT] |
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2131618 |
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Current U.S.
Class: |
600/484 |
Current CPC
Class: |
A61B
5/0809 (20130101) |
Current International
Class: |
A61B
5/08 (20060101); A61b 005/04 () |
Field of
Search: |
;128/2.5R,2.6B,2.6R,2.6E,2.1R,2.1Z |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Attorney, Agent or Firm: Richards and Geier
Claims
I claim:
1. A device for supervising the heart and breathing functions of a
patient, comprising in combination, a rheographic electrode for
picking up a rheographic breathing signal and a first electrical
heart signal, another electrode for picking up a second electrical
heart signal, a third electrode, being the inactive electrode for
said rheographic electrode and said another heart signal electrode,
an alternating curreng generator, being electrically connected with
said rheographic electrode and said inactive electrode and having a
frequency in the kHz range, a first condenser inserted in the
electrical connection between said generator and said rheographic
electrode and having a capacity in the pf range, means for
measuring picked up rheographic breathing signals, an
electrocardiograph, electrically connected to said three electrodes
and including means for common-mode rejection of the picked up two
electrical heart signals, said device further comprising a second
condenser connecting said means for measuring picked up rheographic
signals with said rheographic electrode and having also a capacity
in the pf range and low pass filters inserted in the elecrical
connection beween said electrocardiograph and said three electrodes
and having a capacity in the low nf-range.
2. A device in accordance with claim 1, wherein the frequency of
said alternating current generator ranges between 30 to 100 kHz and
the capacity of said first and second condenser ranges between 20
to 100 pf.
3. A device in accordance with claim 2, wherein the frequency of
said alternating current generator is substantially 60 kHz and
wherein at a generator output voltage of substantially 75 V said
condensers have a capacity of 22 pf.
4. A device in accordance with claim 1, wherein the total capacity
of said low pass filters is substantially 1.5 nf.
Description
This invention relates to a device for supervising the heart and
breathing activities of a patient having a receiving member
constructed as a rheographic electrode for jointly receiving a
breathing signal and a first heart signal and a further receiving
member for receiving a second heart signal, whereby the current
feeding generator for the rheographic electrode as well as the
device measuring the breathing signals at the rheographic electrode
are connected by condensers and by the measuring device for the
heart signals with receiving members through low pass filters as
well as a common-mode rejection device.
In known devices of this type the rheographic electrode is fed with
current impulses at a repetition frequency of 60 kHz derived from
15 V. voltage impulses and a mark-to-space ratio of 1:1. For
coupling of the current feeding generator and the device measuring
breathing signals to the rheographic electrode are used solely
condensers with a capacity in the nF range (5nf). This capacitive
coupling makes certain that outgoing currents produced in case of a
distrubance will not flow through the patient.
The drawback is that these high capacity values greatly increase
the capacity of the common-mode rejection device so that
common-mode rejection in heart signals is made much worse.
In practice attempts were made to provide a diminution of the
capacity and thus to improve the suppression by using on the one
hand low pass filters poor in capacity and on the other hand at the
same time diminishing the capacity of coupled condensers. It was
then found that it is possible to achieve without difficulty a
small drop in the ingoing capacity by correspondingly dimensioning
the low pass filters and thus to also attain a small improvement of
the time measure suppression. A drop in capacity for the coupling
condensors which are absolutely necessary for the safety of the
patent and which would provide a more important influencing of the
suppression could not be carried out for practical conditions.
The reason for this is that when there is a drop in the coupling
capacities in the pf range, the middle frequency parts of the
feeding current impulses which are of importance as carriers for
the breathing signal information (in this frequency range at 5nF
coupling capacity the optional abolute change of carrier at a
carrier amplitude which is just barely sufficient for an
evaluation) are so greatly damped that their informational content
is greatly diminished or even lost completely.
In theory these difficulties could be overcome if in case of a drop
in coupling capacities the amplitudes of the middle frequency parts
of the feeding current impulses would be raised, which can be
accomplished either by increasing the amplitude of the feeding
current impulses or by considerably strengthening the received
information. However, an increase in the amplitude of the feeding
current impulses is actually impossible for reasons of the safety
of the patient (even a comparatively small increase of the impulse
amplitude produces a srengthening of high impulse frequency parts
which are generally unuseable due to danger to patient's safety).
The second way is not practical, since this solution requires
amplifiers which are technically quite complicated and thus
expensive (in case of less complicated and cheaper amplifiers the
information is lost in the sounds of the amplifier).
An object of the present invention is to improve the described
prior art devices.
Another object is the provision of a device of the described type
which provides a substantial improvement of the suppression with
simultaneous optional evaluation of breathing signals with a
minimum of technical structure and without any danger for the life
of the patient.
Other objects will become apparent in the course of the following
specification.
In the accomplishment of the objectives of the present invention it
was found desirable to use as the current feeding generator
alternating current generator with a frequency lying in the kHz
range and to use for the coupling of the current feeding generator
and the breathing signal measuring device to the rheographic
electrode condensers having a capacity within the pf range. It was
found particularly advantageous to select for the frequency of the
alternating current generator a value in the range of 30 to 100 kHz
and for the coupling capacities a value in the range of 20 to 100
pf.
The present invention operates with a single feeding current
frequency lying in the kHz range and not with many frequencies
produced during the impulse operation. Coupling capacities in the
pf range dampen this frequency just as strongly as the
corresponding frequency in the spectrum of the impulses. However,
since there are no frequency contents having a substantially high
amplitude, there is then the possibility to balance the produced
damping by correspondingly raising the alternating current
amplitude without endangering the patient. The technical work is
small since instead of an impulse generator only alternating
current generator is used, while the heretofore used cheap
amplifiers for the electrode signals can be retained to a
substantial extent.
According to an advantageous emobidment of the present invention,
the frequency of the alternating current generator amounts to
approximately 60 kHz. At this frequency the relative amplitude
change is a maximum 0.5% as a rheographic resistance change of .+-.
0.5 ohm and a predetermined rheographic resistance of 1 kohm). An
optional absolute change at a simultaneous optimal suppression
(about 50 dB instead of prior about 30 dB) is attained when at a
alternating current amplitude of about 75 v. condensers with a
capacity of 22 pf are used. Then the capacity of the low pass
filters is approximately 1.5 nf.
The invention will appear more clearly from the following detailed
description when taken in connection with the accompanying drawing
the sole FIGURE of which is a circuit diagram illustrating the
device of the present invention.
The drawing shows a rheographic electrode 1 for receiving a
breathing signal and a heart signal while 2 indicates a EKG
electrode solely for receiving a further heart signal. The
electrode 3 is the common inactive electrode for the two electrodes
1 and 2.
To the electrode 1 is connected through a 22 pf condenser 4 an
alternating current generator 5 (75 V., 60 kHz) as feeding current
generator for the rheographic electrode 1. To the electrode 1 is
also connected through a 22 pf condenser 6 a measuring device for
breathing signals consisting of a high frequency amplifier 7, a
rectifier device 8, a demodulation low pass filter 9 as well as an
indicating device 10.
The electrodes 1 to 3 are also connected with deep low pass filters
13 and 14 consisting of inductances 11 and capacities 12 and with
an amplifier 15 for common-mode rejection (differential amplifier)
and a measuring device 16 for heart signals (electro-cardiograph).
The capacity of the low pass filters amounts to 1.5 nf, their upper
limit frequency is about 1 kHz.
The operation of the device of the present invention is as
follows:
The alternating current produced by the generator 5 is modulated in
amplitude by breathing signals at the patient's body. The signal
modulated in amplitude (electrode signal) is amplified in the high
frequency amplifier 7 of the measuring device for breathing
signals, it is rectified in the rectifier device 8, and demodulated
in the demodulation low pass filters 9, the breathing signals thus
produced being indicated in the indication device 10.
The developed EKG signals get through low pass filters 13, 14 (for
locking the high frequency electrode signal) and through the
suppressor 15 of the EKG indicator 16.
The described embodiment of the present invention produces a
rheographic voltage at the body of the patent of a total of 1 V
with a realtive change of electrode signals of about 0.5% at the
assumed rheographic patient resistance of 1 kohm. The equal tact
suppression for the EKG amounts to about 50 dB.
The use of small coupling capacities 4, 6 has not only the
advantage of a substantially improved common-mode rejection device.
The comparatively high capactive resistances required due to the
low capacitive values of these condensers and the comparatively low
frequency of the alternating current generator, are used at the
same time as current impressing resistances for the sinus-shaped
carrier current. Thus additional curent impressing ohmic
resistances, which were necessary in prior art devices, can be
eliminated.
* * * * *