US2664880A - Electric stimulator for artificial respiration - Google Patents

Description

Jan. 5, 1954 N. B. WALES, JR 2,664,880 ELECTRIC STIMULATOR FOR ARTIFICIAL RESPIRATION Filed Nov. 23, 1951 unim -1 mu m uu HUM IN V EN TOR.

Patented Jan. 5, 1954 ELECTRIC STIMULATOR FOR ARTIFICIAL RESPIRATION Nathaniel B. Wales, Jr., Morristown, N. J. Application November 23, 1951, Serial N 0. 257,793

7 Claims.

This invention relates to a device for generating periodic groups of electric pulses suitable for artificial respiration by stimulation of the phrenic nerve.

It has been found that a superior form of artificial respiration may be administered to an accident victim or surgical patient by placing one electrode near the phrenic nerve on the surface of the neck, and a second electrode on another suitable skin surface, and by then impressing between these electrodes at the normal rate of respiration, a series of spaced electrical voltage pulses having a suitable wave form, a periodicity of approximately 60 cycles per second, and an amplitude on the order of 100 volts. In such a stimulation it is important that the ratio of induced inhalation time to exhalation time be adjustable from a value less than unity for patients in shock, up to or beyond unity for a normal patient.

The present invention achieves these requirements by a novel combination of interrelated elements which makes possible the manufacture of a portable, self-contained, compact and inexpensive device which is very much less complex than the devices presently available for this purpose. To this end, I disclose the use of a cold cathode triode gaseOus discharge tube connected in an R-C timing circuit so as to actuate periodically the driving solenoid of an electromechanical stepping switch.

The object of this invention is to provide a novel design of electric stimulator having few components, low cost, self-contained portability, and ease of adjustment for the desired rate, ratio and intensity of inhalation. Other objects are implicit in the following specifications and claims.

In the drawings:

Figure 1 is a schematic diagram of my invention; and

Figure 2 is the graph of one type of wave form recommended for electro-phrenic stimulation.

In Figure 1, the battery B1, which typically might be a 135 volt supply, is impressed through ofi-on switch S1, on the timing capacitor C1, through a series of timing resistors comprising limiting resistor R2, the rate adjusting variable resistance R1 and one of the two ratio adjusting resistors R4 or R5, according as switch leaf I I is in contact with contact l3 or 26 respectively. Typical values for these elements might be 01:4. mfd., R2=200,00'0 ohms,

In parallel with capacitor C1 is the branch series circuit including solenoid or magnetic actuator l, and the cold cathode gaseous discharge triode G having its plate 20 and grid I9 electrically tied together as one terminal, and the counterclockwise.

cold cathode l8 as the other. This diode connection of the triode gas tube causes the tube to fire at a relatively high voltage, but to extinguish at a substantially depressed voltage due to the continued generation of ions in the short low impedance gap between the grid and cathode. For this reason, the energy abstracted from condenser C1 during this discharge through the load presented by magnetic actuator solenoid I will be considerably greater than that which would occur if such a triode were connected in the conventional manner having the R-C control circuit connected to the grid alone, and having a constant voltage on its plate. This greater integral of energy under the voltage-time exponential decay curve of condenser C1 permits the direct operation of the electro-mechanical stepping switch from these periodic pulses. The interval of this pulsation is adjustable by R1 between and 2 C. P. S., thus giving any respiration cycle between 10 and 60 cycles per minute. The connecting wires 3|, 32, and 33 together with the coil of magnetic actuator or solenoid l form the circuit means responsive to a predetermined potential appearing across capacitor C1 for discharging discharge tube G. Similarly, the series inclusion of solenoid I in the circuit including elements C1, G, 3|, 32, and 33' form the circuit means responsive to the discharge of G to energize solenoid I. It is evident to those skilled in the art that other circuit means than those shown, such as by intervening coupling circuits or relays, can be used to accomplish the same responsive operations.

Solenoid l, on excitation, attracts armature 2 away from stop 22 and against bias spring 23 so as to cause pawl 4, pivoted on armature arm 2, to extend its bias spring 5 and to engage the next successive tooth of ratchet wheel 6. At the end of the pulse energizing solenoid l, spring 23 returns armature arm 2 to stop 22, thereby advancing the ratchet 6 by one tooth. Restraining pawl l and its bias spring 8 assure that the progressive rotation of ratchet wheel 5 will be Shaft 3 on which ratchet wheel 5 is mounted and secured, also carries integrally secured to it, cam wheel Iii which is provided with protuberant cam surfaces 5. In this structure, the lands ill and the protuberances 9 are each in phase with one tooth of ratchet wheel 6. Cam follower arm 12 with its bias spring 2| and roller ll form with contacts 13 and 25 a two position ratchet switch which thus alternately opens and closes circuit l2l3 upon successive pulsations of the magnetic actuator i The period of these intervals of closure corre spond to the intervals P; of Figure 2, whereas the intervals of opening of ratchet switch contact l3 correspond to intervals P2 of Figure 2.

The vibrator reed I5 is of the type well known to those skilled in the art and is supplied with magnetic exciter coil H in series with the normally closed --interrupter contact It. This combination is designated as reed switch l. Thus, current supplied through coil l4 and reed l5 causes vibratory oscillation of reed [5 at its natural frequency, which in this case is chosen to be approximately 60 cycles per second. It is to be noted that a certain minimum current through coil i4 is required to attract reed l5 away from its home position on contact 16. In a typical reed vibrator designed to operate on 135 volts, the resistance of coil l4 might be on the order of 10,000 ohms and, consequently, although reed It will vibrate when switch 12 directly connects it to battery B1 through contact l3, reed l5 will be inoperative when it is connected to the battery via switch [2, contact 26, resistance 28, double arm 29, and resistance 21, since this path will always put a constant resistance on the order of 1,000,000 ohms in series with coil i l regardless of the position of 29. This vibratory motion causes the normally open circuit between reed l5 and contact l! to be periodically closed at the frequency of vibration. This vibratory closure causes a fraction of the voltage of battery B1, as determined by the setting of potentiometer R3, to be periodically impressed across the output terminals 24-25 in a manner substantially corresponding to the pattern illustrated in Figure 2. Evidently, with respect to the arbitrary reference of terminal 25., the pulses will all be of one polarity. However, with reference to a suitable mean point of the circuit, the output square Wave will simulate the desired pattern of Figure 2. For this reason, the reed system l5 together with battery B1 comprise a generator of oscillatory pulses of potential. A limiting resistor or differentiating capacitor 30 in series with electrode 25 guarantees that only a safe amount of current can now through the patient regardless of the setting of potentiometer R3.

Ratchet switch I |-l3 may be considered ,to be the means for disabling the circuitryhy'means of which the vibratory voltagepulses delivered by reed I5 reach the ofiput terminals 25 and 25. This is'fioted since it is equally possible but less ,r "'desirable under the scope of my invention to cause the vibrator reed IE to operate continuously and to cause switch l3 to energize or disable contact I! alone.

The inhale -exhale ratio control 29 comprises a dual rheostat having variable equal linear resistance elements 21 and 28 so connected by a common shaft and wiper arm 29 that as the resistance of R4. decreases, the resistance of R5 increases, and vice versa. Thus, control 29 may comprises two rheost-ats having a common control shaft, and having their contact fingers connected together at junction point 29. For this reason, since time is linearly related to the R-C product effective fora given interval of pulsation, although the total time for an inhale-exhale cycle will be unaffected by changes in the setting of control 29, nevertheless, the ratio of the inhale period P1 to the exhale period P2 will vary upward and downward from unity as control 29 is moved away from its mid-position. It is evidently possible, but less desirable, to cause switch i l--l3-26 to introduce adjustably different capacitances in the R-C timing circuit for its alternate positions, to achieve the same purpose.

In operation, a first electrode (not shown) connected to terminal 25 is placed-in contact with any general part of the patient, such as a shoulder, and a second electrode (not shown) connected to terminal 24 is placed on the motorsensitiveregionof the phrenic nerve :on the neck. Switch -S1.is thrown *closed and resistance R1 is adjusted to the desired rate of respiration. The ratio control 29 is then set at the indicated value and finally, potentiometer setting R3 is then adjusted to give'thedesired intensity of stimulation.

With these preparations complete, the operation of my invention is as follows: Assuming the system initially to be in the state shown in Fig. '1 but with S1 closed, current from B1 will flow through resistors R5, R1, and R2 to charge condenser C1. When the voltage across C1 has risen ,to the firing voltage of the .gas diode G (i. e., diode connected triode), diode Gwill discharge a portion of the "charge stored in C1 through .magnet 1 until thepotential of diode-G has dropped to the extinction value, at which point current through magnet I ceases. This pulse of current energization .in magnet 1 causes switch 12 to move from contact with 25 to contact with 13, as before described. Prior to the displacement of switch arm [2 from 25 to 13, vibrator Jreed I5 is unenergized (as .before explained), and consequently, no potential or physiological stimulus appears at terminals 24, 25. On contact between 42 and 1.3, reed 15 is energized and the stimulating pulses are impressed across the output terminals 2 l'25. These pulses are conveyedto the phrenic nerve of the patient where they cause contraction of the diaphragm with an attendant inhalation. The first charging interval described (P2) took place through resistor R5. However, when switch leaf 12 moves into contact with 13, capacitor C1 undergoes a renewal of 'the charging process, but during this interval of stimulus (P1) the charging is effected through R4. If the setting of 29 is such that R4=R5, the periods of inhalation and exhalation will be equal. varying positions of 29 will thus give varying ratios of. inhalation to exhalation, the limiting value in either case of R4 or R5='0 being the charging time to the firing voltage of G required by C1 with R1 and R2 alone in series with the battery 131. Also, this change in ratio is accomplished without changing the overall breathing rate, due to the constant sum R4+R5. At the end of the stimulation period P1, magnet l is again energized by the same process described and switch i2 is returned to the original position shown in Fig. 1. The consequent cessation of stimulating pulses delivered to the phrenic nerve and thence to the diaphragm permits the patient to exhale, thus completing the respiratory cycle.

What I claim is:

1. In an electro-phrenic stimulator, the combination comprising a source of potential, a timing capacitance, a timing resistance, circuit means for charging said capacitance through said resistance by said source of potential, said capacitance being in series with said resistance, a gaseous discharge tube, circuit means for applying the rising potentials appearing across said capacitance to said tube whereby to discharge said tube, a magnetic actuator, means for caus ing the discharge of said tube to energize said magnetic actuator, a two position switch, means responsive to the energization of said magnetic actuator for displacing said switch to its opposite position for each such energization, means responsive to the change of position of said switch for altering the impedance of said series capaci tance and. resistance with respect to their impedance value obtaining for the obverseposition of said switch, a pair of output terminals, a generator of oscillatory pulses of potential, and means responsive to one position of said switch for impressing a portion of the potentials of said generator across said output terminals whereby to excite periodically said terminals.

2. In an electro-phrenic stimulator, the combination comprising a source of potential, a timing capacitance, an adjustable timing resistance, a first adjustable ratio resistor, a second adjustable ratio resistor, circuit means for charging said capacitance from said source of potential through said timing resistance and one of said ratio resistances, a gaseous discharge tube, circuit means for applying the rising potentials appearing across said capacitance to said tube whereby to discharge said tube, a magnetic actuator, means responsive to the discharge of said tube for energizing said magnetic actuator, a two position switch, means responsive to the energization of said magnetic actuator for displacing said switch to its opposite position for each such energization, circuit means connecting said switch and said ratio resistors in such a way that said capacitance is charged through said first ratio resistor or said second ratio resistor according as said switch is in its obverse or reverse position respectively, a pair of output terminals, a generator of oscillatory pulses of potential, and means responsive to one position of said switch for impressing a portion of the potentials of said generator across said output terminals.

3. In an electro-phrenic stimulator according to claim 2, an adjustment member common to both said ratio resistors whereby the increase of the resistance value of one is accompanied by a decrease in the resistance value of the other.

4. In a self-contained electro-phrenic stimulator, the combination comprising a battery, a timing capacitor, an adjustable resistor, conductive means for charging said capacitor from said battery through said resistor, a magnetic actuator, a cold cathode gaseous discharge tube, a branch circuit in parallel with said capacitor including said cold cathode discharge tube, a ratchet wheel, a pawl for driving said ratchet wheel, means for actuating said pawl by said magnetic actuator responsive to the discharge of said discharge tube, a cam, means to drive said cam by said ratchet wheel, a two position ratchet switch, means to actuate said ratchet switch by said cam so that alternate actuations of said magnetic actuator leave said switch in a given one of said two positions, a pair of output terminals, a reed-type vibrator switch, circuit means for impressing a portion of the potential of said battery across said output terminals on the oscillatory closures of said vibrator switch, and means responsive to one of the said two positions of said ratchet switch for disabling said circuit means.

5. In a self-contained electro-phrenic stimulator, the combination comprising a battery, a timing capacitor, an adjustable resistor, conductive means for charging said capacitor from said battery through said resistor, a magnetic actuator, a cold cathode gaseous discharge tube, a branch circuit in parallel with said capacitor including said cold cathode discharge tube, a ratchet wheel, a pawl for driving said ratchet wheel, means for actuating said pawl by said magnetic actuator responsive to the discharge of said discharge tube, a cam, means to drive said cam by said ratchet wheel, a ratchet switch, means to actuate said ratchet switch by said cam so that alternate actuations of said mag netic actuator leave said switch alternately in one of two positions, a pair of output terminals, a generator of oscillatory pulses of potential, and means responsive to one position of said ratchet switch for impressing a portion of the potentials of said generator across said output terminals.

6. In a self-contained electro-phrenic stimulator, the combination comprising a battery, a timing capacitor, an adjustable resistor, conductive means for charging said capacitor from said battery through said resistor, a magnetic actuator, a gaseous discharge triode having a plate, a cold cathode, and a grid adjacent to said cold cathode, an electrical connective path between said plate and said grid, a branch circuit in parallel with said capacitor and including in series connection said magnetic actuator and said diode-connected triode discharge tube, a ratchet wheel, a pawl for driving said ratchet, means for actuating said pawl by said magnetic actuator, a cam, means to drive said cam by said ratchet, a two position ratchet switch, means to actuate said ratchet switch by said cam so that alternate actuations of said magnetic actuator leave said switch in a given one of said two positions, a pair of output terminals, a reed-type vibrator switch, circuit means for impressing a portion of the potential of said battery across said output terminals on the closure of said vibrator switch, and means responsive to one of said two positions of said ratchet switch for disabling said circuit means.

7. In an electric stimulator, the combination comprising a source of potential, a timing capacitance, a first timing resistance, a second timing resistance, circuit means for charging said capacitance through one of said resistances from said source of potential, a gaseous discharge tube, means responsive to a predetermined potential appearing across said capacitance for discharging said discharge tube, a magnetic actuator, means responsive to the discharge of said tube for energizing said magnetic actuator, a two-position switch, means responsive to the energization of said magnetic actuator for displacing said switch to its opposite position for each such energization, means responsive to the obverse position of said switch to cause said capacitor to be charged by said first timing resistance and responsive to the reverse position of said switch to cause said capacitor to be charged through said second timing resistance, a source of electric stimulation, a pair of output terminals, and means actuated by the obverse position of said two-position switch to connect said source of electric stimulation to said output terminals.

NATHANIEL B. WALES, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,693,734 Waggoner Dec. 4, 1928 2,295,585 Lindquist Sept. 15, 1942 2,532,788 Sarnoff Dec. 5, 1950 FOREIGN PATENTS Number Country Date 719,831 France Nov. 24, 1931 OTHER REFERENCES The British Journal of Physical Medicine for November 1941, pp. 156-7. (Copy in Div. 55.)

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