US2532788A - Artificial respiration by electronic stimulation - Google Patents

Description

5. J. SARNOFF 2,532,788

ARTIFICIAL RESPIRATION BY ELECTRONIC swmuwnou Dec. 5, 1950 2 Sheets-Sheet 1 Filed Aug. 20, 1949 Dec. 5, 1950 5. J. SARNOFF 2,532,783

ARTIFICIAL RESPIRATION BY ELECTRONIC STIMULATION Filed Aug. 20, 1949 2 Sheets-Sheet 2 m mm Patented Dec. 5, 1950 ARTIFICIAL RESPIRATION BY ELECTRONIC STIMULATION Stanley J. Sarnofl, Boston, Mass.

Application August 20, 1949, Serial No. 111,424

1 Claims. 1

This application is a continuation in part of my application Number 399, filed January 3, 1948, now abandoned.

This invention relates to a method of stimulating a physiological function of an individual and more particularly to the inducing of artificial respiration.

The methods of inducing artificial respiration employed heretofore have been based on the principle of mechanically applying a cyclic pressure to the pulmonary cavities. This is done directly by forcing air or oxygen into the lungs via the nasopharynx and the trachea, or indirectly by enclosing either the chest or the entire body with the exception of the head and neck and cyclically pressurizing the enclosure so that the resulting chest movement stimulates natural breathing.

Although these methods successfully induce artificial respiration the apparatus required is large, expensive and complicated so that its use is largely confined to institutions and clinics. The patient is restricted in his movements by the enclosing apparatus and nursing care and medical examination are made correspondingly difllcult. The size of much of this type of apparatus prevents it from being readily portable and limits its use in emergencies and at remote locations. The high cost limits the number of units available for use during an epidemic. An important physiological consideration is that all these methods respire the patient by means of positive pressure breathing which is directly contrary to normal breathing. The method about to be described causes respiration by rhythmically producing a negative intrapleural pressure just as in spontaneous respiration.

The objects of this invention are to provide a method and apparatus which induces artificial respiration in a simple and natural manner, which does not limit the movement of the patient, which does not cause pain to the patient, which is small and convenient to use, which is readily portable and can be used anywhere, which is inexpensive to construct and which generally improves the the stimulation of a physiological function of an individual by applying to a nerve trunk a cyclically varying potential which recurrently rises art of respirator manufacture.

In a broad aspect the invention contemplates above the threshold value of the individual and 2 alternately falls to or below said value, the threshold value being that at which the diaphragm (or other part or parts to be stimulated) responds to the stimulus. Preferably each cycle of potential comprises a plurality of pulses which gradually increase in amplitude to a maximum and then gradually decrease. Throughout each cycle the pulses may be separated by gaps or the cycles may be separated by gaps or both. While the potential may fall to zero in the gaps, it need fall only to the region of the threshold value. The physiological effectiveness of the stimulation may be adjusted to the needs of difierent individuals and different ailments by varying the amplitude of the pulses; the duration of the pulses, the

length of the gap (if any) between successive pulses, the amplitude of the cycles, the length of each cycle, or the length of the gap (if any) between successive cycles or any combination of these variables.

While the potential may be applied magnetically or electro-magnetically, as for example by transmitting impulses from an external source to a small magnetic or radio receiver located partly or whollyinside the patient, it is preferably applied conductively by means of spaced contactors applied at spaced locations tothe skin of the individual or directly to the nerve in the form of probes. Excellent results have been obtained with probes applied directly to the phrenic nerve, but I have also found that it is possible to consistently obtain satisfactory respiration approximating normal spontaneous respiration, both as regards appearance of the respiratory effort and the physiologic effect on ventilation and circulation, by connecting the source of cyclically varying potential to a pair of electrodes, one of which is applied to the skin overlying the course of the phrenic nerve, so that the potential is applied to the nerve trunk indirectly through the skin. The second electrode is placed at some other point on the surface of the body, such as the back of the neck, with the result that the path of the stimulating current includes a portion of the phrenic nerve or one of its anatomical roots. The

electrode closest to the nerve preferably makes contact with the skin over a relatively small area, while the second electrode may make contact over a relatively large area of the skin. The smallcontact electrode is used as an exploring electrode to find the position which produces most satisfactory stimulation of the phrenic nerve.

It is similarly possible to cause ventilation of the lungs by cyclically stimulating the nerves to abdominal muscles which, upon contracting. force air out of the lungs, and, upon relaxing. P rmit air to reenter the lungs.

The peak voltage required to excite the motor fibers to the diaphragm or other muscles varies from patient to patient and from site to site on the same patient. This peak voltage required for motor fiber stimulation however, is below the threshold necessary to excite pain fibers and therefore effective respiratory activity can be produced without eliciting pain. When the potential is applied through the skin to volts are usually required but when applied directly to a nerve by a probe a fraction of a volt (say onehalf volt) is usually sumcient.

For the purpose of illustration, typical embodiments of the invention are shown in the accompanying drawing in which Fig. 1 is a wiring diagram of one embodiment of the invention;

Fig. 2 is an isometric view of one form of the probe;

Fig. 3 is a diagram of a typical potential wave as a function of time such as is obtained from the embodiment shown in Fig. 1;

Fig. 4 is a wiring diagram of another embodiment;

Fig. 5 is a diagram showing the wave shape of the potential delivered by the oscillator to the pulse generator at the line 5-5 of Fig. 4;

Fig. 6 is a diagram showing the wave shape of the potential delivered by the pulse generator at the line 6-5 of Fig. 4;

Fig. 7 is a diagram showing the wave shape of the potential delivered to the potentiometer at the line 1-1 of Fig. 4; and

Fig. 8 is a. diagram of the potential delivered by the potentiometer to the patient at the line 8-8 of Fig. 4.

In the particular embodiment of the invention chosen for the purpose of illustration a cyclic electrical potential for stimulating the phrenic nerve (or other nerves) of an individual is obtained from a vacuum tube oscillator 0s and a square wave generator G which may be of any of the types well-known to those skilled in the art. The connection between the oscillator 0s and the generator G is accomplished by joining a plate pl of the oscillator vacuum tube Vi to a generator input terminal ti and a tube cathode lci to a generator input terminal t! by the leads ii and i2 respectively. Between a tube control grid gi and the cathode kl is connected an oscillator tank circuit including a choke Li in parallel with a variable capacitor Ci. Connected between the generator terminals ti and ii is the output circuit of the oscillator which includes a capacitor C2 in parallel with a choke L2. The circuit elements of the oscillator 03 and the generator 0 are proportioned so that a cyclic potential having a square wave with a pulse duration of .001 of a second is obtained across the generator output terminals t3 and t. The output of the generator G is adjustable by any of the well-known means to give pulses with a peak potential which is variable between 0.0 and 60 volts.

The desired duration of the periodic variations in the peak potential are obtained by means of a regulator such as a potentiometer Re which includes a rotatable contact ii, an insulating segment II and a tapped winding ii. The taps of the winding ii are alternately connected to the terminal t3 by a rotary switch a and a wire ii. A wire it branches from the other end ii of the winding ii to connect with a generator output terminal t4 and a cathode M of a vacuum tube 122. A grid 02 and a plate 92 of the tube '02 are Joined by a wire is to one of the probes P of the probe support 8 (Fig. 2) which will be described in detail hereinafter. The other probe P is connected to the rotatable contact ii of the potentiometer Re by a wire 20.

The rotatable tap it is driven by a geared motor M which is connected to the power supply terminals :1 and c. To control the speed of the motor M, its shunt field F is connected in series with a variable resistor 1' across the terminals 0 and c.

As is shown in Fig. 2 the probe support 5 includes a trough 2i molded of yieldable insulating material such as semi-hard rubber. The trough II is semicircular in shape and has fastened to the inner surface thereof two metallic probes P which are connected to the flexible wires II and 20 respectively. The probes P are located in two respective planes which intersect the axis of the cylinder with a spaced relationship of approximately one centimeter therebetween. The trough inside and the probes P are so positioned as to form substantially a smooth surface to contact the sheath of the phrenic nerve N to which the stimulus is being applied.

A small slit is made in the neck of the patient is) that the phrenic nerve N is exposed. The probe support 8 is then slipped under the nerve N cradling it as is shown in Fig. 2. As the probe P projects above the inner surface of the support trough It, the nerve N is subjected to whatever electrical potential is applied across the probes P.

To induce respiration a cyclic potential is applied to the probes P with characteristics as is shown in Fig. 3. This potential comprises a series of square pulses to with peak values which are varied so that the envelope e is formed. when the pulse wi is applied, the low peak value of the potential stimulates only a few of the fibers of the phrenic nerve N and the respective muscular segments in the diaphragm controlled by these fibers contract. As the peak voltage of the successive pulses to increases, more and more of the fibers in the phrenic nerve are stimulated and therefore more and more of the muscular segments of the diaphragm contract until the diaphragm as a whole undergoes a forceful contraction to expand the pleural cavity thereby drawing air into the lungs. The cessation of stimuli as the voltage returns to a constant low or zero value (as at 0 after the pulse wp, Fig. 3) results in relaxation of the diaphragm and a decrease in the size of the pleural cavity thereby allowing air to be expelled from the lungs. The sequence of constant low, gradually increasing and suddenly decreasing periods is then repeated.

The frequency of the pulses to, the maximum amplitude of the pulse rep, and the relative duration of the low potential and increasing potential periods are independently adjustable in accordance with the constitutional requirements of the patient as will be described hereinafter so that a normal breathing rate is attained. If the normal breathing rate is not known, experimental adjustments are made at low values which are gradually increased until the patient's appearance, for example the skin color and respiratory movement indicates that sufllclent oxygen is being taken up by the blood and sufllcient carbon dioxide is being blown off.

To generate the wave shape shown in Fig. 3 a sine wave from the oscillator 08 is applied across the input terminals ti and t2 to lock in the generator G. Theresultlng output at the generator terminals t3 and t4 is a series of square wave pulses 10 with a duration or .001 second and the same frequency as that of the sine wave. A regulator such as the capacitor Ci is adjusted so that the frequency of the sine waves from the oscillator Os and therefore the frequency oi! the square pulses w is in the region or from to 60 cycles per second with a usual frequency of approximately 40 cycles per second, the optimum being determined as described above. The output of the generator G is adjusted so that an optimum peak potential am is obtained in the range of from 0.1 to 60 volts. The tube V! is used as a current limiting device so that the probe current is always limited to a safe value.

The envelope e is developed by rotating the tap I3 of the potentiometer Rv clockwise by means of the geared motor M. As the tap i3 contacts the insulating segments II no connection is made and the potential between the probes P is zero as indicated at I) in Fig. 3. When the tap l3 first contacts the winding it as at ii a pulse across the probe P such as wi (Fig. 3) results. As the tap i3 progresses the resistance in series with the probe circuit decreases so that successive pulses w have peaks of increasing magnitude. When the point is reached where no resistance remains in the probe circuit and the pulse wp has a maximum peak value of approximately the same value as the peak potential of the pulses appearing across the generator terminals t3 and t4, the tap i3 then again contacts the insulating segments 14 and the potential across the probes P drops to zero. This sequence is repeated during successive rotations of the tap l3.

The frequency of the repetition of the sequences is controlled by the speed of the geared motor M, the output shaft speed or which can be varied from approximately 6 to 60 revolutions per minute thereby to give the optimum respiratory period duration in the range of from one to ten seconds. Adjustment of the absolute duration of the increasing potential period is obtained by means of the switch s.

The second embodiment of the invention shown in Fig. 4 comprises a vacuum tube Via. having a coil L2a in its plate circuit which is magnetically coupled with a. coil Lia, in th grid circuit of the tube so that the feed back causes the tube to go into oscillation. The bias for the tube grid is supplied by a leak resistor Ti and a capacitor 03 in the usual manner. The output of the oscillator, which varies according to the sine law as is shown in Fig. 5, appear at line 55 of Fig. 4.

The oscillator output is used as a trigger for a pulse generator being connected thereto by means of a coupling capacitor cl. The generator comprises two vacuum tubes V3 and VI hav ing their cathodes k3 and k4 connected together and their anodes a3 and 04 connected to the B+ power supply through the resistors 1'3 and rl respectively.

The grid 93 of the tube V3 is normally biased so that the tube conducts in the absence of a negative input signal from the oscillator. Such bias is obtained by connecting a bleeder resistor 16 across the B+" power supply. The resistor T6 is provided with two adjustable taps xi and x2. Tap xi is linked directly with the cathodes 1c! and k4. Tap :2, which is adjusted to a more negative potential than the tap :ri. is connected to the grid 03 by the resistors rfl and r8. The grid is also coupled to the anode oi oi the tube V! by a capacitor 06. The grid 0| is linked to the common junction or resistors r! and rli which are connected in series between the anode a3 and ground whereby with the tube VI conducting the grid cl is sufllclently negative so that the tube V4 is nonconducting.

The coupling capacitor cl of the oscillator is connected to the common Junction 01' the resistors r] and r8 so that during the negative portion of the output wave the grid 93 is driven negative with respect to cathode kl to stop the current flow through the tube V3. The potential upon the grid at thereupon becomes more positive so that the tube V4 conducts drawing current through the resistor N. The resulting voltage drop across resistor r4 causes current to flow through the resistors 1'1 and r8 thereby gradually increasing the potential impressed upon the grid 93 until after a time interval determined principally by the time constant of the series connected capacitor 06 and the resistors 1'1 and r8 and to a lesser extent by the ohmic characteristic of 11 and the B+" supply voltage, the grid 93 becomes sufliciently positive so that the tube V3 again conducts. The voltage drop across r3 thereby impresses a relatively negative potential upon the grid g4 to cut of! the tube V4. By making the ohmic value of the resistor rl relatively small with respect to the total ohmic value of the resistors r! and r8, so that the current charging the capacitor c6 does not substantially afl'ect the magnitude of the voltage drop across the resistor r4, a rectangular voltage Pulse is produced across 1' which is similar in shape but has a lower peak value than the potential wave illustrated in Fig. 6. The period of the pulses across resistor r4 can be changed by varying either the value of the resistor 11 or the capacitance of (:8 thereby to change the time constant of the R.-C. circuit.

The rectangular potential wave is applied to the grid 95 of an amplifier tube V5 by means of a coupling capacitor 01 and a tapped resistor ri! which are connected in series between the anode at and ground. The grid g5 is linked to the tap to make the gain of the amplifier ad- Justable thereby determining the peak amplitude of the pulses shown in Fig. 6. Bias for the grid a5 is supplied by a resistor :13 connected between the cathode 1:5 and ground. The 8+ potential torethe anode a5 is supplied through a resistor r The output of the amplifier is fed to a peaking circuit comprising a capacitor c8 which is connected between one end or the parallel windings TI! and of a potentiometer Roi. The opposite end of the windings ril and H5 are grounded. Both the capacitance of the capacitor c8 and the parallel resistance of the resistors ril and rib are made small whereby the time constant of their series combination is short so that successive discontinuities in the square wave potential applied thereto alternatively charge and discharge the capacitor 08 through the potentiometer Ravi. The capacitor charging and discharging current flows through the potentiometer Roi are in opposite directions so that the voltage drop across the windings ril and H5 is a series of alternatively positive and negative sharply peaked pulses having the form shown in Fig. I.

The electrodes pi and p2 ior cyclically applying the peaked pulses to the patients body are connected respectively to the rotatable arm '3! of the potentiometer Roi and ground.

As described heretofore with respect to the first embodiment, modulation of the peaked pulses shown in Fig. 7 is accomplished by rotating the arm i3| of the potentiometer Rvi in a clockwise direction by means of a. motor Ml thereby to obtain a cyclic variation of the peak amplitude of the pulses having an envelope similar to that shown in Fig. 8.

When the arm liil of the potentiometer Roi is in its bottom position the potential between the electrodes pi and p2 is zero as at ll (Fig. 8). As the potentiometer arm l3l moves upwardly the electrode potential gradually increases to a peak e' when the arm Iii reaches the junction of resistors rll and H5. As the arm l3l descends along winding rli more and more resistance is cut into the circuit so that the electrode potential is reduced. As the winding H5 is considerably shorter than the winding rid the arm l3l, which moves at a uniform rate, drops the electrode potential to zero (0", Fig. 8) in a shorter time than the interval required for the potential to rise to the peak potential e. The zero potential dwell period between points Ii and il" in Fig. 8 results when the arm i BI is grounded during contact with the low resistance portion ill.

The probe electrodes pi and p2 may be similar to the probe P shown in Fig. 2 which is applied directly to the nerve trunk or may be surface electrodes of the conventional type applied to the skin adjacent the nerve whereupon the peak potential applied must be raised. By adjustment of the pulse frequency, the maximum amplitude of the stimulating potential, relative duration of the increasing voltage and decreasing voltage phases of the respiratory cycle, as described heretofore, a respiratory cycle meeting the constitutional requirements of the patient is attained. The appearance of the patient, for example the skin color and respiratory movement, will indicate when sufllcient ventilation is occurring. This may be more quantitatively determined by determination of blood pH or gas content or gas tensions or analysis of the patients expired air.

In the specific embodiments described above the magnitude of the diaphragmatic contraction, and thus, the depth of respiration, is set by the amplitude control on the pulse generator, while the respiratory rate is controlled by the motor speed. In some cases it may be found advantageous to employ a pulse frequency which varies with the variations in peak potential. This variation can be obtained by coupling the pulse frequency control to the motor shaft. Although the embodiments described above show a separate oscillator and pulse generator it is entirely teasible to use a self-excited pulse generator, or to obtain the rectangular pulses directly from a sine wave source A. C. by suitable clipping and shapin circuits, or by a mechanically driven contactor. The embodiments described above show mechanically driven potentiometers for modulating the effective value of the stimulating potential; but it has also been found feasible to obtain such modulation by non-mechanical methods, for example electron tube circuits.

It should be understood that th present disclosure is for the purpose of illustration only and that this invention includes all modifications 8 and equivalents which fall within the scope of the appended claims.

I claim:

1. The method of artificially inducing resplration which comprises applying to the nerve trunk controlling respiration of an individual a cyclically varying electric potential which during each cycle rises to a. point above the threshold value of nerve stimulation of the individual and then falls substantially to or below said value and remains substantially at or below said value for a portion of the cycle to permit exhalation.

2. The method of artificially inducing respiration which comprises applying to the nerve trunk controlling respiration of an individual a cyclically varying electric potential which during each cycle rises to a point above the threshold value of nerve stimulation of the individual and then falls substantially to or below said value, each cycle comprising a succession of pulses, the amplitude of successive pulses gradually increasing and then decreasing during each cycle, the duration of the portion of each cycle following said point permitting exhalation.

3. Apparatus for artificially inducing respiration which comprises a generator of cyclic electric potential, electrode means for applying said potential to a nerve trunk, a control network connecting said electrode means to said generator, said network being adapted to gradually increase the peak value of the potential, quickly reduce it, hold it at the reduced value and in sequence repeat the increasing reducing and holding periods, and regulator means in said network for varying the relative durations of the increasing and holding periods.

4. Apparatus for artificially inducing respiration which comprises a generator of cyclic electric potential, electrode means for applying said potential to a nerve trunk, a control network connecting said electrode means to said generator, said network being adapted to gradually increase the peak value of the potential, quickly reduce it, hold it at the reduced value and in sequence repeat the increasing reducing and holding periods, a regulator for varying the frequency of the generator, and a regulator in said network for varying the relative durations of the increasin and holding periods.

5. Apparatus for artificially inducing respiration which comprises an electric circuit, means in said circuit for supplying for application to a nerve trunk of an individual, a cyclically varying potential which during each cycle rises to a peak above the threshold value of nerve stimulation of the individual and then falls substantially to or below said value, said means including a generator and a regulator to vary the rate of said cyclic variation, and means in said circuit for varying the length of the potential-rising portion of each cycle independently of the length of the cycle.

6. Apparatus for artificially inducing respiration which comprises an electrical circuit, means in said circuit for supplying for application to a nerve trunk of an individual, a cyclically varying potential which during each cycle rises to a peak above the threshold value of nerve stimulation of the individual and then falls substantially to or below said value, each cycle comprising a succession of pulses, the amplitude of successive pulses gradually increasing and then decreasing during each cycle, said means including a generator and a regulator to vary the rate of said cyclic variation, and means in said circuit for varying the length of the potential-rising portion of each cycle independently of the length of the cycle.

7. Apparatus for artificially inducing respiratlon which comprises an electrical circuit, means in said circuit for supplying for application to a nerve trunk of an individual, a cyclically varying potential which during each cycle rises to a peak above the threshold value of nerve stimulation of the individual and then falls substantiall to or below said value, each cycle comprising a succession of pulses, the amplitude of successive pulses gradually increasin and then decreasing during each cycle, said means including a gener- 15 ator and a regulator to vary the rate of said cyclic variation and a regulator to adjust said peak value, and means in said circuit for vary- 10 ing the length of the potential-rising portion of each cycle independently of the length of the cycle.

STANLEY J. SARNOFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,514,746 Wappler Nov. 11, 1924 1,693,734 Waggoner Dec. 4, 1928 2,099,511 Caesar Nov. 16, 1937 FOREIGN PATENTS Number Country Date 361,806 France Oct. 1, 1906

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