US 3903876 A
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United States Patent 1w] Harris 1 1 Sept. 9, 1975 1 1 RESPIRATION MONITOR  Inventor:
 Assignee: The Board of Trustees of Leland Stanford Junior University, Stanford, Calif.
 Filed: Apr. 10, I974  Appl. No: 459.780
Related US. Application Data  Continuation-impart of Ser. Nov 287.435 Sept. 8.
Thomas R. Harris, Tucson Ariz.
 US. Cl. [ZS/2.08; 73/204; 12X/DIG. 29: 340/279  Int. Cl. a A618 5/08  Field of Search... 128/2 R, 2 C, 2.08. DIG. 17. 128/DIG. 29; 73/204, 213, 205; 340/239. 279
 References Cited UNITED STATES PATENTS 2,831,181 4/1958 Warner 1. 128/2 R 3,081.766 3/1963 Duhsky et a1... 128/208 3.368212 2/1968 Klyec t w a r r 340/239 3,504,542 4/1970 Blevins H 73/205 TRANSDUCER (141 3.577984 5/1971 Levy et a1 128/208 1626.755 12 1971 Rudolph. 73/205 L 163L438 12/1971 Lewinun. 340/240 311431152 2/1972 Beltran 128/208 3.73.5,752 5/1973 Roddcr 4. 128/208 FOREIGN PATENTS OR APPLICATIQNS 121.334 2/1931 Austria .1 128/208 Prinu1r btuml'nerKy1e L. Howell Arlm'nc Agent, or FirmF1ehr, HOhbaCIL Test Albritton & Herbert 1571 ABSTRACT A respiration monitor in which inspired and expired air is directed to flow past one end of a plurality of tubes which have their other ends associated with an air flow transducer. Bidirectional air flow past the one end of the tubes induces unidirectional air flow at the other end which is detected by the transducer to pro vide output signals with each flow movement of air to indicate respiration A monitor is conneeted to the transducer and provides an output alarm when output signals terminate indicating apnea.
4 Claims, 6 Drawing Figures OUTPUT SIGNAL PATENTED 91975 3. 903,876
TRANSDUCER (l4) TRANSDUCER MONITOR ALARM RESPIRATION MONITOR GOVERNMENT GRANT CROSS REFERENCES This is a continuation in part of application Ser. No. 287,435 filed Sept. 8, 1972 now abandoned.
BACKGROUND OF THE INVENTION Commonly used respiration or apnea monitors register transthoracic impedance changes associated with the breathing cycle by way of contact chest electrodes. Alarm is sounded if successive breaths are not taken within a preset time interval. No attempt is made in presently available impedance type monitors to provide alarm for hypoventilation, since impedance changes are very dependent upon the position of the electrodes, the degree of their contact to the skin, the position of the patient. and various intrathoracic events besides tidal air flow.
There is a commercially available monitor respiration system which monitors respiration by translating breathing movement of the patient lying on an air mattress into air displacements from one segment of the air mattress to the other. The air movement is channelled into a manifold and past a heated thermistor (transducer) which is cooled by the air flow and provides an output signal indicative of air flow. A monitor is associated with the transducer and provides an alarm when there is apnea. The advantage of this system over the impedance type monitor is that no electrodes are required. However. the patient is mounted on an air mattress and movements other than breathing may be falsely interpreted by the monitor as respiration.
There have been attempts to use transducers such as thermistors and thermocouples disposed adjacent to the tracheostomy to sense the flow of respiratory air at the mouth ofthe tracheostomy. However, the transducers directly pick up exhaled air which is fully saturated with water vapor and often laden with mucus which interferes with the effectiveness of the transducer. This has been an overwhelming problem in previous attempts to use thermistors to monitor infant respirations.
OBJECTS AND SUMMARY OF THE INVENTION It is a general object of the invention to provide an improved respiration monitor and method.
It is another object of the invention to provide a respiration monitor which is not critically dependent upon the positioning of electrodes.
It is a further object of the invention to provide a respiration monitor which is not sensitive to a patients body movements.
It is still a further object of the present invention to provide a respiration monitor which is not directly in the stream of inspired and expired air.
It is a further object of the present invention to provide a respiration monitor in which the inspired and ex* pircd air is indirectly monitored.
The foregoing and other objects of the invention are achieved by a monitor in which one or more tubes have one end adjacent the flow of inspired and expired air from the patient with the other end disposed adjacent a transducer which senses air flow and provides an output signal. The flow of expired and inspired air past the one end induces a flow of air in the tubes, which flow of air causes air to flow past the transducer thereby providing an indication of respiration.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a plan view of a respiration monitor and transducer associated with a tracheostomy tube.
FIG. 2 is an enlarged view of a tracheostomy tube.
FIG. 3 is a plan view of a detachable clip-on type device for mounting on a tracheostomy tube.
FIG. 4 shows an adapter for the device of FIG. 3 for mounting on a tracheostomy tube.
FIG. 5 is a plan view ofa respiration monitor adapted for use with an endotracheal tube.
FIG. 6 is a block diagram of the electronic circuitry associated with the transducer.
DESCRIPTION OF PREFERRED EMBODIMENT The respiration monitor, FIG. 1, comprises a manifold 11 including one or more flexible connector tubes 12 having one end projecting into the manifold opening 13 and in communication with a transducer 14. Manifold opening 13 is vented to the atmosphere. The trans ducer is adapted to sense air flow and may comprise, for example, a heated thermistor as will be presently described. The other ends of the tubes I2 are received by adapter 16 which includes passages I7, FIGS. I and 2, communicating with the inside of the tubes 12 with the end of the passages 17 lying in the air stream which flows in the inner cannula 18 of a tracheostomy tube 19, having a generally constant cross section, at a substantially right angle to the air stream. The passages 17 are substantially at a common cross section of tracheostomy tube 19.
During inspiration and expiration of air through the cannula 18, air rushes to and from the tracheostomy cannula past the adapter passages 17. The bidirectional flow of air in cannula 18 sets up a suction effect in the passages 17 which draws clean air unidirectionally into the tubes 12 through manifold opening 13, past the transducer 14. It is observed that a self-cleaning effect is incorporated. The fresh air flowing from the manifold 11 through connector tubes 12 tends to clear the connector tubes 12 of moisture and mucus.
If mucus does build up to the point where it partially occuludes the inner cannula 18 or adapter passages 17, the output from the transducer 14 drops or stops because the suction effect is reduced or stopped due to reduced respiration or apnea. As a consequence, air flow past the transducer 14 or thermistor falls below a critical threshold The monitor associated with the transducer 14, to be presently described, sounds or gives an alarm. Thus, the attendant receives a warning to clear the tracheostomy tube 19 before it gets totally blocked. This is an advantage over the other types of respiration monitors in which an alarm is sounded only when breathing or movement of the patient has ceased altogether. It should be noted that the transducer 14 is out of the line of respiratory airflow and is therefore always free of fouling by mucus or other matter introduced into the respiratory airflow.
The transducer I4 may be a heated thermistor which is part of a commercially available thermistor type apnea alarm such as that used in connection with air mattresses responsive to movements of air such as that described in U.S. Pat. No. 3,63 I ,438. The thermistor is preheated by a constant current provide by a battery. The thermistor, in turn, generates voltage changes when it is cooled by movement of air through the connector tubes 12. These voltage changes are amplified to operate an electric trigger circuit which discharges a capacitor that is constantly being charged at a set rate and will activate the alarm if allowed to go uninterrupted to full charge. A suitable thermistor and monitor is sold by Codman and Shurtliff, Inc. of Randolph, Mass.
Rather than providing a tracheostomy tube 19 with a permanently fixed adapter, there may be provided a clip-on type adapter for mounting on the inner cannula base 20 of the tracheostomy tube 19. Such an adapter structure is shown in FIGS. 3 and 4. It consists ofa clip member 21 which is spring-loaded by spring 22 and which is adapted to encircle the base 20 on the end of the tracheostomy tube 19. With the clip 21 applied to base 20 on the end of the tracheostomy tube 19, tubes 23 attached to the top of the clip 21 are disposed adjacent to the inner cannula l8 and inspiration and expiration of the air flowing past the ends of the tubes 23 in duces movement of air in the tubes 23 which, in turn, induces movement of air in the connector tubes 12 and associated manifold 13. The air movement in manifold 13 causes an output from transducer 14 as heretofore described.
Apparatus of the type just described is especially suitable for monitoring infants with chronic tracheostomies where continual supervision is needed due to the high incidence of complications. The most frequent complication is total occlusion of the inner cannula l8. Supervision is required both day and night and one is reluctant to leave the children unattended even for the shortest periods of time knowing how quickly a mucus plug can totally obstruct the narrow fixed airway and suffocate the child. The system of the present invention provides direct detection of respiratory air movement and gives advance warning to partial as well as total occlusion of the tracheostomy tube 19.
The indirect monitoring system of the present invention is also suitable for use with endotracheal tubes still in place in patients recovering from anesthesia. The system consists of a spring-loaded clip 31, FIG. 5, which is adapted to clip onto the endotracheal tube 32 to dispose tubes 33 in the air stream flowing in passage 34 whereby to induce air flow in connector tubes 12.
Referring to FIG. 6, a complete system is shown in which a transducer 36, which may be a heated thermistor, as just described. or may consist of a thermocouple or other air flow sensing means, is connected to a monitor 37 which monitors the signal and provides an output when air flow is slowed down or stopped indicating a complication. The monitor 17 activates an alarm 38 to warn the nurse or parent of the complication.
Thus, it can be seen that there has been provided an improved respiration monitor which remotely senses flow of inspired and expired air along a flow path and which is especially adapted for use with infants. The monitor operates by using the flow of inspired and expired air to induce the flow of air in connector tubes associated with a transducer. The remote sensing avoids major problems encountered in previous attempts to use transducers to directly monitor infant respiration. The system avoids the problems of other prior art systems by eliminating the complications of affixing electrodes, and eliminating false indications due to body movement.
1. A respiration monitor for remotely sensing flow of inspired and expired air along a respiratory air flow path comprising, a plurality of tubes having open ends, means connected to one end of each of said tubes for holding each of said one ends adjacent the respiratory air flow path so that inspired and expired air flows across said one end of each of said tubes to induce air flow into said tubes from their other ends, means vented to the atmosphere attached to said other ends of each of said plurality of tubes, a transducer mounted within said means vented to the atmosphere adjacent to said other ends and providing an output signal responsive to temperature change induced by cooling air flow, whereby the flow of air into said tubes from the atmosphere causes said transducer to produce said output signal, said output signal thereby being indicative of respiratory air flow relative to a critical threshold.
2. A respiration monitor for use with a tracheostomy tube through which passes an inspired and expired air stream, comprising first and second connector tubes having open ends, adapter means for detachable mounting on the end of the tracheostomy tube, said adapter means being connected to said first and second connector tubes for orienting said connector tubes adjacent the end of the tracheostomy tube when mounted thereon, so that said connector tubes have their axes at substantially a right angle with respect to the air stream, whereby air flow across said open ends adjacent the end of the tracheostomy tube induces unidirectional air flow into said connector tubes from their other ends, a transducer having an output responsive to temperature change, and means vented to the atmosphere for mounting said other ends of said connector tubes together with said transducer adjacent thereto so that said transducer senses temperature change due to the flow of air into said other ends of said tubes and thereby provides an output signal indicative of respiratory air flow.
3. A respiration monitor as in claim 2 including a monitor connected to receive the output of said transducer for providing an alarm when respiratory air flow falls below a critical threshold.
4. A respiration monitor for use with a patient, comprising a section of air flow path of uniform cross section for conducting inspired and expired air to and from the patient, a manifold in communication with the atmosphere, a plurality of tubes having open ends with one of said open ends connected to and in communication with said section of air flow path and the other of said open ends connected to and in communication with said manifold, and a transducer mounted in said manifold adjacent to said other open ends, said transducer being responsive to cooling induced by air flow and providing an output signal responsive to temperature change, whereby when inspired and expired air flows through said section of air flow path, unidirectional air flow is induced from the atmosphere through said manifold, to flow by said transducer, and through said plurality of tubes toward said section of air flow path, thereby causing the temperature of said transducer to change and said output to be indicative of respiration relative to a critical respiration threshold.