Oxygen Control System With Blood Oxygen Saturation Sensing Means And Method For Closed System Breathing

Abstract

The blood circulating in the body of the subject, e.g. in the ear pinna, is tested at suitable time intervals to detect supersaturation of oxygen, using an optical oximeter and a temporary oxygen-deficient (anoxic) breathing mixture in conjunction with a timing device to develop a signal which varies inversely with the time required for the anoxic mixture to bring the oxygen level in the blood down to saturation level, which signal is used to control the duty cycle of a valve in the line supplying oxygen to the user's breathing bag, so that between tests the user is provided with oxygen at a rate responsive to his breathing requirements to maintain his system close to 100 percent saturation in oxygen; an over-riding control being exerted by the oximeter to increase the flow rate of oxygen to the user immediately whenever the oximeter detects an oxygen level below saturation; the anoxic mixture being provided by temporarily reducing the flow rate of oxygen through the valve to a suitable low value.

Parent Case Text

BACKGROUND OF THE INVENTION

This application is a Continuation-in-Part of an application Ser. No. 65,268 , filed on Aug. 19, 1970, now abandoned. This last mentioned application was a Streamlined Continuation of application Ser. No. 708,054, filed on Feb. 26, 1968, now abandoned.

Description

FIELD OF THE INVENTION

The invention relates to systems for supplying a suitable breathing mixture, with provision for automatic control of the rate of flow of oxygen in order to supply oxygen to the user in accordance with his needs from time to time, as while working under water, or while being operated upon, etc.

DESCRIPTION OF THE PRIOR ART

In the past, an optical oximeter has been used to monitor the oxygen level in the blood to produce an electric signal that is used to regulate the supply of oxygen to breathing apparatus carried by the user, e.g., a deep sea diver, increasing the oxygen supply when the oxygen level falls and decreasing the oxygen supply when the oxygen level rises. The object is to maintain the oxygen level in the blood of the user substantially at saturation value at all times. Light transmitted by the apparatus through blood varies in intensity and color as the oxygen level in the blood varies due to changes in the red corpuscles as they absorb oxygen, thus making it possible to determine quantitatively the oxygen level of the blood. However, a difficulty arises, in that when the blood becomes saturated with oxygen, supersaturation will occur if more oxygen is supplied to the blood stream, the excess oxygen being absorbed in the blood plasma or in adjacent tissues instead of in the red corpuscles, which latter can absorb no more. When this occurs, there is no further change in the color or intensity of the transmitted light, with the result that the oximeter is unable to measure any degree of supersaturation of oxygen in the system of the user. As it is known that supersaturation with oxygen is an undesirable condition for the user and, if carried to excess, can be dangerous to health, it is desirable that the breathing system be enabled to respond not only to a condition of oxygen deficiency, but also to a condition of supersaturation.

SUMMARY OF THE INVENTION

The invention provides a method and apparatus for using an optical oximeter to monitor the blood of the user to detect supersaturation of oxygen in the system of the user when this condition occurs, in order to generate a signal proportional to the degree of such supersaturation, which signal is used to reduce the oxygen supply as required to relieve the condition of supersaturation and thus maintain the system of the user substantially at 100 percent oxygen saturation. Supersaturation is measured by periodically putting the user on an anoxic breathing mixture of constant degree of oxygen deficiency which gradually lowers the oxygen level in the user's system. Return to a level just below saturation is detected by the oximeter after a certain time interval that is proportional to the degree of supersaturation that was present. A signal inversely proportional to this time interval is used to regulate the oxygen supply substantially to the 100 percent oxygen saturation level. An over-riding control is provided so that the anoxic breathing mixture will not be given to the user at any time when the blood is deficient in oxygen, but instead the rate of oxygen flow will immediately be increased.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE is a block-type schematic circuit diagram of the preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawing, 20 is an intermittently operable on-off valve connecting an oxygen supply to a breathing bag, under the control of an optical oximeter 22 actuated by changes in color and intensity of blood circulating in the body of the user, e.g. in the ear pinna. The valve 20 is opened and closed by electrical pulses from a controlled variable-width pulse generator 24 acting upon a solenoid valve-actuating device represented schematically by an inductance coil 26. The valve is open during each pulse and closed between pulses. A suitable oximeter for use herein and an improved earpiece therefor are shown and described in U. S. Pat. No. 2,790,438, issued Apr. 30, 1957 jointly to this applicant and to William Paul. In general, the device 22 may be any device capable of measuring the degree of oxygenation of the blood of the user from an oxygen-deficient level up to but not over, 100 percent of saturation in the blood corpuscles, at which latter level detectable changes in the blood corpuscles cease while saturation of the blood system as a whole can increase beyond 100 percent.

The time duration of the pulse, termed the pulse width, is determined by the time required for an adjustable time-variable one-shot multivibrator 28 to return to its stable state after being put into an unstable state by a pulse from a valve cycle rate adjuster 30. The time required by the multivibrator 28 to return to its stable state is in turn determined by a direct current signal, termed a d.c. level, applied to a control electrode of the multivibrator. The lower the d.c. level, the shorter the time interval determined by the multivibrator and hence the less the pulse width of the pulse applied to the solenoid 26 by the generator 24 and the shorter the open time of the valve 20. Similarly, the higher the d.c. level, the longer the open time of the valve 20. The total time interval or cycle time comprising a pulse and the space following the pulse is adjustable by means of the valve cycle time adjuster 30, which is arranged to deliver a pulse to the multivibrator 28 at adjustable regular intervals longer than the maximum time interval determined by the multivibrator. Thus, the frequency at which the valve 20 operates, as well as the duty cycle of the operation of the valve can be adjusted over suitable ranges. The valve 20 will ordinarily open and close every 2 to 5 seconds, although other frequencies of operation may be used. As the user breathes from a breathing bag in the conventional manner, the periodic closing of the valve 20 at these rates does not interfere with breathing and is a part of standard practice. The valve 20 performs the function of a make-up for keeping the breathing bag up pg,5 to suitable pressure at all times.

Three separate sources of d.c. level 31, 32 and 33 are provided for varying the time interval determined by the multi-vibrator 28. The source 31 has the lowest level, for establishing an anoxic mixture by cutting down the oxygen flow rate through the valve 20 to a suitable low value. This rate is adjustable by a potentiometer or other suitable device shown as a d.c. level adjuster 34. The source 32 has a range of intermediate levels and the level provided at any given time is varied in accordance with measurements made upon the degree of supersaturation in the user's blood obtained with the aid of the oximeter 22. The source 33 has the highest level and comes into play whenever a condition below a minimum safe percent saturation, e.g. 97 percent, is detected by the oximeter 22. The oxygen flow rate to the breathing bag at any given time depends upon which of the three sources 31, 32, 33 is at that time controlling the multivibrator 28. When the source 33 is in control, the valve 20 will have a duty cycle such that the valve is open most of the time, e.g., 19 twentieths of the time. Consequently, the oxygen deficiency alarm 33 is effective to increase the oxygen pressure in the breathing bag at a very rapid rate, thus assuring protection of the user from serious oxygen deficiency as detected by the oximeter 22.

A measurement to determine supersaturation of oxygen in the user's blood is initiated at time intervals of about one to five minutes, under the control of a sample interval timer 44, the length of the interval being adjustable by any suitable means, shown as a sample rate adjuster 46. The timer 44 sends start signals, (1) to a counter-clear device 48 connected to a counter 50 to re-set the counter to zero, (2) to operate a switch 52 to immediately admit a train of regularly spaced pulses from a counter time base pulse generator 54 to the counter 50 through the switch 52 to make a count, and (3) to turn on a flip-flop 56 by applying a signal to a conductor 58 causing the flip-flop to generate a high level or ON output signal on a conductor 60 connected to one input terminal of the linear gate 36, and to generate a low level or OFF output signal on a conductor 62 connected to one input terminal of the linear gate 38. The presence of the ON signal on the conductor 60 permits the d.c. level from device 31, which is always present on a conductor 64 connected to the second input terminal of the linear gate 36 to pass through that circuit to the signal mixer amplifier 40 with the result that the valve 20 is operated in a low duty cycle suitable to deliver the desired anoxic mixture for the saturation measurement. Linear gates of the type shown in schematic form are well known in the art. Such gates can be designed to transmit analog information and can be opened or closed by a controlling voltage.

The anoxic mixture is supplied to the user and, if the user's blood is supersaturated, the counter 50 counts until the oxygen level in the user's blood has fallen from the degree of supersaturation existing at the start of the count to approximately 100 percent saturation, at which time the oximeter 22 detects a lack of 100 percent saturation and sends a signal from a 100 percent saturation detection signal means 66 (1) to the switch 52 over a conductor 67 to stop entry of pulses into the counter 50 through the switch 52, thereby stopping the count, and (2) over a conductor 68 to reverse the flip-flop 56, putting a low level or OFF signal on the conductor 60 and a high level or ON signal on the conductor 62. The effect of reversing the flip-flop 56 is to disable the linear gate 36 and enable the linear gate 38. The stopped count remains stored in the counter 50 until the next time the counter-clear 48 is actuated. A digital to analog converter 70 is provided which at all times converts the count to a d.c. level which increases with the count. An inverter 72 is provided to give a d.c. level which decreases as the count increases, so as to provide for decreasing the flow rate of oxygen to correspond with an increase in the degree of supersaturation found in the test. The inverter 72 controls the d.c. level in the device 32. The converter 70 and inverter 72 are so adjusted that a zero count, indicating an absence of supersaturation will provide the proper d.c. level in device 32 to set the valve 20 for a flow rate suitable to just maintain 100 percent saturation.

The linear gate 38 remains in the enabled condition, transmitting the d.c. level from the device 32 to the signal mixer amplifier 40 continuously until the next operation of the sample interval timer 44 initiating a new measurement of the blood condition, the result of which measurement may be to increase the rate of oxygen supply, or to decrease the supply, or to continue the previous rate according to the user's blood condition. Diodes 41 and 42 are positioned so as to direct signals into the mixer amplifier 40 and to prevent the gates from interacting with each other.

However, if at any time, even during the progress of a count, the oximeter should detect an oxygen deficiency, that is, a blood condition a predetermined degree below 100 percent oxygen saturation, the device 33 is actuated to impress a high d.c. level signal upon the signal mixer amplifier 40. Because this high d.c. level signal is greater than any d.c. level ever applied to amplifier 40 either by device 31 or by device 32 the signal from device 33 is predominant and immediately re-sets the multivibrator 28 to produce a longer on-time of the valve 20, thereby quickly increasing the supply rate of oxygen to the user. Amplifier circuit 40 contains appropriate amplitude sensitive circuitry, including resistors, to allow the signal from device 33 to override the signal coming from either 31 or 32.

While illustrative forms of apparatus and methods in accordance with the invention have been described and shown herein, it will be understood that numerous changes may be made without departing from the general principles and scope of the invention.

Claims

I claim:

1. In apparatus for controlling the oxygen concentration in a breathing mixture for supplying a user, in combination, means to measure supersaturation of oxygen in the blood stream of the user by establishing the time required for an anoxic mixture to reduce oxygen content at said blood stream below saturation, means providing a control signal determined by said time, and means responsive to said control signal to adjust the oxygen concentration in said breathing mixture in relation to the measured degree of supersaturation.

2. Apparatus for measuring the degree of oxygen supersaturation in the blood stream, comprising, in combination, an oximeter of a type that can detect oxygen concentration up to 100 percent of saturation, means for temporarily supplying to the lungs a breathing mixture having a constant degree of oxygen deficiency, means employing said oximeter to continuously monitor the state of the blood and to generate a signal when the blood stream is reduced from whatever degree of supersaturation existed when the oxygen-deficient mixture was first supplied to a condition of substantially 100 percent saturation, and means to measure the time elapsed from the time at which the oxygen-deficient mixture was first supplied until the 100 percent saturation signal is generated by the oximeter, whereby the elapsed time is a measure of the original degree of supersaturation of the blood stream.

3. Apparatus in accordance with claim 2, together with means responsive to the length of said elapsed time for controlling the oxygen concentration of a breathing mixture normally supplied to the user in accordance with the measured degree of supersaturation.

4. A system for regulating the rate of oxygen supply for closed system breathing in such manner as to avoid either under or over saturation of the user's blood with oxygen, comprising in combination, an optical oximeter arranged for continuously monitoring the user's blood, said oximeter being capable of detecting under-saturation of oxygen in the blood of the user, means for periodically reducing the supply rate of oxygen to the user to a constant oxygen-deficient rate, means for counting a succession of time intervals of substantially equal duration, means to start a count in said counting means coincidently with the beginning of the oxygen-deficient supply to the user, means to generate a signal when the oximeter first detects an oxygen concentration less than 100 percent in the blood of the user, means to use said signal to increase the supply rate of oxygen to a non-deficient value and to stop the said count, and means to use the magnitude of said count to regulate the said non-deficient rate of oxygen supply to the user in response to the measured degree of supersaturation.

5. A system in accordance with claim 4, together with means operative at any time that the oximeter detects a predetermined oxygen concentration less than 100 percent of saturation to generate a second signal, and means to utilize said second signal to immediately increase the rate of oxygen supply to the user to relieve the detected oxygen deficiency.

6. A system in accordance with claim 4, together with means for adjusting the time period between successive operations of the said oxygen supply rate reducing means.

7. A system for regulating the rate of oxygen supply for closed system breathing in such manner as to avoid either under or over saturation of the user's blood with oxygen, comprising in combination, first regulatory means designed to determine a relatively low, constant rate of oxygen supply useful for gradually relieving a condition of supersaturation of oxygen in the user's blood, second regulatory means arranged to determine a variable rate of oxygen supply in accordance with the user's demand for oxygen from time to time, a third regulatory means designed to determine a constant rate of oxygen supply greater in magnitude than any rate determined by either said first or said second regulatory means for rapidly making up any oxygen deficiency in the user's blood, an optical oximeter arranged to continuously monitor the user's blood, time interval measuring means, sample interval timing means for initiating a measurement of degree of supersaturation of oxygen in the blood, means actuated by said sample interval timing means to energize said first regulatory means, and to start a time measurement in said time interval measuring means, means operable by said oximeter upon detection of less than 100 percent oxygen saturation in the user's blood to terminate a time interval measurement by said time interval measuring means and to disable said first regulatory means, means controlled by said time interval measuring means for adjusting the said second regulatory means, to determine an oxygen supply rate inversely proportional to the time interval so measured and to energize said second regulatory means, and means operable by said oximeter upon detection of an oxygen deficiency in the user's blood to enable said third regulatory means while at the same disabling both said first and second regulatory means, to relieve said oxygen deficiency at any time regardless of the operation of the remainder of the system.

8. The method of controlling the oxygen concentration in a breathing mixture for supplying a user, comprising the steps of measuring supersaturation of oxygen in the blood stream of the user by establishing the time required for an anoxic mixture to reduce oxygen content at said blood stream below saturation, generating a control signal determined by said time, and using the said control signal to adjust the oxygen concentration in the said breathing mixture in relation to the degree of supersaturation measured.

9. The method of measuring the degree of oxygen supersaturation in the blood stream with the aid of an oximeter of a type that can detect oxygen concentration up to 100 percent of saturation, which method comprises the steps of temporarily supplying to the lungs a breathing mixture having a constant oxygen deficiency, using the oximeter to continuously monitor the state of the blood and to give a signal when the blood stream is reduced from whatever degree of supersaturation existed when the oxygen-deficient mixture was first supplied to a condition of substantially 100 percent saturation, and measuring the time elapsed from the time at which the oxygen-deficient mixture was first supplied until the 100 percent saturation signal is generated by the oximeter, whereby the elapsed time is a measure of the original degree of supersaturation of the blood stream.

10. The method in accordance with claim 9, together with the further step of generating a control signal inversely proportional to the said elapsed time, and utilizing the said control signal for decreasing the supply rate of oxygen to the lungs in proportion to the measured degree of supersaturation.