Recherche dans les collections de brevets nationales et internationales
Certains contenus de cette application ne sont pas disponibles pour le moment.
Si cette situation persiste, veuillez nous contacter àObservations et contact
1. (WO1980000006) APPAREIL DE DIAGNOSTIC
Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

Title: Diagnostic Apparatus

This invention relates to diagnosis of heart conditions which may require defibrillation.
Ventricular fibrillation very often occurs during a coronary/heart attack and is commonly fatal unless treatment is applied very rapidly. Ventricular fibrillation is a condition in which the heart has ceased to pump or has spasmodically irregular contractions, accompanied by chaotic electrical activity.
This condition can be treated by defibrillation, i.e. by applying a controlled electric shock to the patient, normally through electrodes applied to the chest. This may be achieved using a defibrillator of the type described in our British Patents 1,435,709 and 1,481,469. Before
defibrillating a patient it is first necessary to diagnose his condition and a reliable diagnosis normally requires the use of an electrocardiograph, in which the electrical
activity of the heart is monitored through electrodes
attached to the body and the electric pulses displayed on a cathode ray tube or equivalent device.
Accurate interpretation of the signals obtained with an electrocardiograph requires considerable medical training. However in the event of a heart attack it is not always possible to summon a doctor before defibrillation treatment has to be applied. Diagnosis and treatment of the patient's condition then has to be carried out by paramedical or other personnel who may not be fully qualified medically.
The present invention is intended to provide diagnostic apparatus which is capable of detecting fibrillation in a patient automatically without the need for an operator to interpret the data received by the apparatus.
The present invention is intended to provide apparatus for detecting ventricular fibrillation, comprising a pair of electrodes capable of being put in electrical contact with the body of a patient (normally the patient's chest), a circuit capable of distinguishing a signal received from the electrodes characteristic of ventricular fibrillation from signals characteristic of other heart conditions, and indicating means to indicate to an operator when said signal is characteristic of ventricular fibrillation.
The electric signal received from the heart during normal operation by electrodes positioned on the chest is shown in the accompanying Figure 1, in which the voltage is plotted on the y -axis and time on the x—axis. This condition is known as the Sinus Rhythm. Ventricular fibrillation is characterised by a disordered trace of the kind shown in Figure 2, plotted in the same manner as in Figure 1.
In one embodiment of the invention, advantage is taken of the different energy contained in the signals of Figures 1 and 2 when they are amplified to the same amplitude.
Simple amplification of these signals will normally produce waveforms having different amplitudes. However if they are amplified using an automatic gain control unit set so that the amplitude obtained is the same regardless of the patient's condition, the automatic gain control unit being selective to the frequencies concerned, the amplified signal obtained on fibrillation gives much greater energy on integration than that obtained when the heart is
functioning normally. This integrated value may then be measured by a comparator to distinguish the fibrillation condition from normal heart operation.
However simple integration of the amplified signal can give an ambiguous result because of a possible condition known as ventricular tachycardia. This condition is characterised by a signal of the kind shown in Figure 3.
This trace is similar to that obtained from fibrillation
in that a similar overall energy is involved when the signal is amplified to the same level but it represents a condition which does not require defibrillation.
This problem may be overcome by clipping the amplified signals obtained from the electrodes to remove their positive and negative peaks. The signals obtained on clipping are shown below in Figures 1a, 2a and 3a corresponding to the unclipped signals shown in Figures 1, 2 and 3.
It will be seen that the energy obtained in Figures 2a and 3a is again greater than that obtained from Figure 1a. However signals 2a and 3a differ in that the energy obtained from the positive component of the wave of Figure 3a is much greater than that of the negative component whereas the positive and negative components of the wave of Figure 2a have similar energies. Signals 2a and 3a may thus be distinguished. This may be achieved by providing clipping units to remove the peaks of the positive and negative components of the amplified signal, integrating units to integrate the positive and negative signals received from the clipping units separately and feeding both results to a dual comparator set to operate indicating means when the magnitudes of the integrated signals show fibrillation.
In another embodiment of the invention, advantage is taken of the fact that the signal generated by ventricular fibrillation is essentially continuous and free from regular peaks (as shown in Figure 2) whereas an ordinary Sinus Rhythm shows regular peaks (Figure 1). This allows use of an analogue switch to actuate the indicating means and circuit means connected to the analogue switch to allow it to
operate only when a continuous signal substantially free from peaks characteristic of ventricular fibrillation is fed to the analogue switch.
In one arrangement the positive and negative components of the signal from the electrodes are summed, i.e. the polarity of one of these components is reversed and its magnitude is added to the other. The summed signal is then passed to an automatic gain chip where it may be
amplified and successively through a buffer amplifier and peak detector to the analogue switch.
Additionally, the summed signal may be split and the split signals passed respectively to a buffer and to a peak signal capacitor decay circuit and buffer. The outputs from these units are passed to a comparator which is
connected to an automatic gain control unit provided with a direct-current pump with decay to the automatic gain control chip. The comparator is such that it emits a substantially continuous output when the signals it receives represent ventricular fibrillation but emits a pulsed output when the signals it receives show the peaks obtained from Sinus Rhythm. This pulsed output fed to the automatic gain control will prevent the automatic gain chip passing an amplified signal to the peak detector and hence the analogue switch: thus no amplified signal is passed when the
comparator detects the presence of peaks in the original signal.
The outputs from the peak signal capacitor decay
circuit and the buffer may also be fed to an event comparator provided with a direct current pump with decay connected to the analogue switch through an OR gate. The event
comparator is arranged such that if a significant number of pulses representing peaks in the original signal is received it generates no output and the analogue switch is closed. Thus the event comparator emits an output allowing the summed signal to pass the analogue switch only when the original signal represents ventricular fibrillation.
Provision may also be made to eliminate the effect short bursts of noise or other extraneous signals which may affect the circuit. This may be done by connecting a reset unit, emitting a reset signal at short intervals such as 3 seconds, to a direct current pump and buffer through which the output from the analogue switch is passed.
In all the above embodiments provision should be made for only the relevant frequencies in the signal from the patient to be processed. This may be achieved by passing the signal from the electrodes through a band pass filter passing only frequencies from 2 to 17 Hz: these are the frequencies generated by the normal Sinus Rhythm and by ventricular fibrillation. Finally noise from the mains can be removed by passing the signal from the electrodes through a filter removing the A. C. mains frequency
(generally 50 Hz).
The diagnostic unit may be self-contained, battery operated and by use of microcircuits wherever possible it may be made small and highly portable. It may be incorporated in the same unit as a defibrillator and may use the same electrodes as the defibrillator, with a relay or other device to isolate the diagnosis unit from the electrodes when a defibrillation shock is administered. With this arrangement the operation of a patient's heart may be
diagnosed and if defibrillation is required it can be
administered immediately through the same electrodes.
The indicating device may comprise any visual or
acoustic indicating device to inform the operator that
defibrillation is required. This device may be much smaller and simpler than the display system, generally a cathode ray tube, which is required by conventional electrocardiographs.
Apparatus according to different embodiments of the invention will be described by way of example with reference to the accompanying drawings in which:
Figure 1 shows an oscilloscope trace showing the normal Sinus Rhythm from a patient's heart,
Figure 1a shows the same trace after automatic gain amplification and clipping,
Figure 2 shows a similar trace of a signal received on ventricular fibrillation,
Figure 2a shows the trace of Figure 2' after automatic gain amplification and clipping,
Figure 3 shows a trace of a signal received on
ventricular tachycardia,
Figure 3a shows the trace of Figure 3 after automatic gain amplification and clipping,
Figure 4 is a schematic circuit diagram of diagnostic apparatus according to one embodiment of the invention, and
Figure 5 is a schematic circuit diagram of diagnostic apparatus according to another embodiment of the invention.
The various block components may be standard components known in the electronics and computer arts and so will not be described in detail.
The defibrillator part of the apparatus comprises
electrodes 1 and 2 arranged to be placed in electrical
contact with the body of a patient and connected in series with a choke 3 and capacitor 4 by relay-operated switches 5 and 6. Capacitor 4 may be charged to a high voltage by means of a high voltage source 7 powered by an
oscillator 8. The operation of this part of the apparatus is controlled by circuitry assembled as a hybrid package 9. The defibrillator part may be functionally the same as those described in British Patents 1,481,469 and 1,435,709.
The arrangement is such that switches 5 and 6 are normally open, the capacitor being connected to the electrodes only when a defibrillation shock is being delivered to the patient.
Electrodes 1 and 2 are also connected to leads 10 and 11 connected to the diagnostic part of the apparatus. This comprises an amplifier 12 in which the electric signals received by the electrodes from the patient are amplified to about 1 volt. The amplified signals are then sent to an automatic gain control unit 13 which is set to produce an output between the same positive and negative set levels regardless of whether the signals received represent Sinus Rhythm or ventricular fibrillation: the automatic gain control unit is tuned so that the automatic gain is selective
for the frequencies obtained from Sinus Rhythm and from defibrillation.
The output from the automatic gain control is then fed to positive and negative clipping circuits 14 which remove the positive and negative peaks of the output from the automatic gain control. The clipped outputs are fed to respective integrator and reset circuits 15 which integrate the outputs for about 3 seconds at a time. The outputs from the integrators are then fed to a dual comparator unit in which they are compared and their magnitudes measured. The comparator unit is provided with a system of AND gates such that a signal is emitted if the absolute magnitudes of the integrated signals, and the relationship between these magnitudes, indicate fibrillation. This signal actuates a visual indicating device 17 which indicates to the operator that defibrillation is required. A defibrillation shock can then be administered to the patient immediately through electrodes 1 and 2 which remain in contact with the patient.

Apparatus according to another embodiment of the
invention will be described with reference to Figure 5. In this embodiment the electrodes to be in contact with the patient are connected to a notch filter 1 in order to remove any interfering signal derived from the electric mains: this filter will remove 50 Hz components in countries where
this frequency is used for the public electricity supply.
The signals passing filter 21 and then passed through the band pass filter 22 which passes only frequencies from 2 to 17 Hz: these are the main frequency components obtained from the ventricular fibrillation condition and the central
frequencies obtained with a normal Sinus Rhythm from the heart.
The output from filter 22 is then fed to a unit which carries out negative summing of both the positive and
negative components of the signal. This unit comprises a buffer amplifier 23 and an inverting buffer 24, connected as shown with diodes 25 to give a negative summed signal at point 26. If the original signal represents the QRS complex obtained from normal heart operation the summed signal contains pronounced peaks corresponding to the peaks of the complex: if the signal received represents ventricular fibrillation the summed signal is much more uniform and does not contain such pronounced peaks.
The summed signal is passed to automatic gain control chip 27. Chip 27 is controlled by further circuitry described below. The signal may then be passed to buffer amplifier 28, peak detector 29 and analogue switch 30. Analogue switch 30 is arranged to actuate a visible or acoustic indicating means to indicate to an observer the existence of ventricular fibrillation in the patient. This indicating means may be of a conventional type and so will not be described.
The summed signal from point 26 is also fed by signal splitting device 31 to a buffer 32 and a peak signal
capacitor decay circuit and buffer 33 to a comparator 34, which is itself connected to an automatic gain control unit 35 having a direct-current pump with decay associated with the automatic gain control chip 27.

Comparator 34 is arranged so as to generate a
substantially continuous output when the summed signal received represents ventricular fibrillation but produces pulses corresponding to the Sinus Rhythm peaks when a normal Sinus Rhythm signal is received. The Sinus Rhythm pulses are fed to the control unit 35, which is arranged such that it prevents the signal received by chip 27 from point 26 being passed through the automatic gain when a summed signal displaying peaks is received.
Additionally, the outputs from units 32 and 33 are fed to an event comparator with a direct current pump with decay 36 and thence to an OR gate 37 which is itself connected to analogue switch 30. The event comparator is arranged to give an output to the OR gate only when the signal received represents ventricular fibrillation. The analogue switch 30 is opened on receipt of the output through the OR gate allowing the signal from peak detector 29 to pass through.
The analogue switch 30 is provided with an additional direct-current pump and buffer 38 connected to a reset device 39 and a unit 40 generating a 3-second interval reset signal. The purpose of this arrangement is to eliminate the effect of "short" bursts of noise or other signal not derived from the patient which may find its way through the circuit to this point.
With this arrangement, when a pair of paddles is applied to a patient's chest and the electric signals from the heart are fed into the device through filter 21, if the heart is in a state of fibrillation a "scrambled" signal of small amplitude with recognisable peaks is received: if the heart is not fibrillating a signal with more or less regular peaks (such as a Sinus Rhythm) is received. When such a peaked signal is received the negatively summed signal at point 26 actuates the comparator 34 to give a pulsed output: these pulses operate the pumping function of unit 35 and, if the pulses are received at a sufficient rate, unit 35 prevents the original summed signal from passing through automatic gain at 27: thus the signal does not reach the peak detector.
On the other hand, when the original signal has no or only a small number of peaks , corresponding to a substantially continuous low-amplitude signal , the automatic gain can operate and an amplified signal is transmitted.
The analogue switch 30 is controlled by the event comparator 36. When the number of pulses in the signal received reaches a certain number the pumping action of unit 36 is sufficient to operate the analogue switch to prevent any signal from peak detector 29 being passed.
Finally the reset arrangement 39 and 40 resets the pump and buffer 38 at 3-second intervals, thus preventing any stray signals received by the circuit affecting the output for more than a very short period.
The effect of this arrangement is to block signals received from the heart which do not show the characteristics of fibrillation while allowing a fibrillation signal to operate a fibrillation indicator.
The apparatus shown in Figure 5 may be incorporated in self-contained apparatus including a defibrillator, as in the embodiment of Figure 4.

.