Apnea Detection Device

Abstract

A device for providing continuous monitoring of a human breathing and heart rate wherein a fluid-tight mattress is located in contact with the human and produces pressure signals in response to the breathing and heart rate. A pressure transducer is provided for interpreting the pressure signals for application to an electronic circuit for visual or audible recognition of the signals.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to monitoring devices for maintaining a continuous surveillance of certain vital body movements and, more particularly, to a device for monitoring the breathing and heart rate of infants.

Periodic breathing, called apnea, is a respiratory difficulty particularly prevalent in premature infants where the infant experiences a temporary stoppage of breathing and, unless the condition is detected immediately and preventive steps taken, the lack of continued circulation to the brain may result in serious damage.

Although the periodic breathing will sometimes correct itself without assistance to the infant's respiratory system, it is extremely important that some monitor be provided to continuously ascertain the breathing and heart rate of infants, in order to alert hospital personnel to prolonged conditions of apnea so that the proper measures may be quickly taken to restore continuous, uninterrupted breathing. A further need for such apnea monitoring equipment is shown by the unpredictability of an apneac condition, whereas the periodic breathing or stoppage may occur at any time and even immediately after a continued surveilance where no symptoms are evident.

Prior to the present invention, various devices have been devised to afford continuous breathing and heart monitoring; however, in general, these devices have relied upon some physical attachment of electrodes or detectors upon the infant's body and, therefore, have been susceptible to dislodgement through gross body movements of the infant, or during movements of the infant by attending personnel, and a false apnea condition and alarm are experienced.

In addition, such prior art devices have often required an electrical connection in some manner between the infant and the monitoring equipment, thereby presenting a potential electrical hazard.

It is thus an object of the present invention to provide a highly sensitive breathing and heart rate monitor which is continuously capable of detecting apnea conditions in an infant.

It is another object of this invention to provide a sensitive breathing and heart rate monitor wherein no physical attachment of any kind is necessary to the infant being monitored.

It is a still further object to provide a continuous breathing and heart rate monitor where all sensing means associated with the infant are pneumatically operated, whereby no electrical connections are utilized.

The aforementioned objects are all achieved by the provision of a fluid-tight mattress for placement beneath an infant, wherein the changes in pressure within the mattress due to the breathing and heart rate of the infant, are converted by a highly sensitive transducer to an electrical signal which may be used for indicating or recording the sensed function.

A specific embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings, forming a part of the specification, wherein:

FIG. 1 is a schematic drawing of the overall invention;

FIG. 2 is a schematic drawing of an alternate mattress suitable for use in the invention;

FIG. 3 is a schematic diagram showing the electronic circuitry, in block form, which may be used with the present invention.

Referring now to FIG. 1, there is shown a schematic diagram of the overall apnea monitoring system. The system includes a fluid-tight flexible pad 10, adaptable for placement beneath an infant. The pad 10 may contain a resilient porous material for support and comfort of the infant and which allows the free circulation of fluid within the outer non-porous covering.

A pop-off valve 12, the purpose and function of which will be later explained, communicates with the interior of the pad 10 through flexible tubing 14. A transducer 16 is provided and which also is in fluid communication with the interior of pad 10 by means of flexible tubing 18, pop-off valve 12, and tubing 14. The transducer is of the pressure-sensitive type which is adapted to sense a change in pressure and thereafter experience a predetermined change in electrical characteristics in response to the sensed pressure change.

As may now be seen, any pressure fluctuations occurring in the pad 10 are directly transmitted to the transducer 16 where they are sensed and hereafter converted and transmitted as electrical signals. The transducer 16 must be capable of detecting minute pressure changes due to the respiration and heart beat of an infant resting upon the pad 10; however, such transducers are commercially available having the required sensitivity.

The transducer used must be extremely sensitive to pressure variations as the pressure signals experienced from the movement of infants are extremely minute. As an example, the present invention has been utilized to monitor the breathing rate of premature infants weighing less than about 3 pounds, and it is found that the pressure signals from the fluid-tight mattress are in the order of from about 0.05 to 0.08 cm of water. These signals were readily detectable by a pressure transducer.

For infants weighing more than about three pounds, a transducer is easily capable of detecting both the breathing rate as well as the heart rate of the infant.

The transducer, therefore, must be capable of distinguishing pressure signals of minute magnitude and alter its characteristics in order to provide a sufficient alteration for sensing by a later fluidic or electronic circuit.

The purpose of the pop-off valve 12 is to prevent large changes in pressure from the pad 10, such as those caused by gross bodily movements of the infant, from reaching and affecting the transducer 16. To this purpose, the pop-off valve 12 is provided with a pair of discs 20 and 22 which are adapted to be displaced with respect to their respective seats 24 and 26 to allow fluids to pass freely therethrough.

As shown, the disc 20 is positioned such that a predetermined negative pressure caused by a gross body movement causes a displacement of the disc 20, allowing atmospheric pressure to enter the pop-off valve 12 to equalize the effect of the negative pressures.

The disc 22 is positioned such that a predetermined positive pressure caused by the gross body movement displaces that disc 22 and the excess pressure is exhausted to the atmosphere. Conventional means, such as springs, are provided in order to return the discs 20 and 22 to their proper seated condition after the increase or decrease in pressure has been properly equalized, and also, conventional means may be included for adjusting the sensitivity of response of each of the discs 20 and 22. In the preferred embodiment, it has been found that either weight or spring loaded discs may be suitable and satisfactory results have been achieved where the valves are preset to be displaced from their seats at a predetermined positive or negative pressure of about .+-.0.5 cm water. This value is therefore the largest positive or negative pressure experienced by the pressure transducer.

In addition to limiting the effects of large pressure variations due to gross body movements, the pop-off valve 12 serves to achieve an equilibrium point during the initiation of the system. The compression of the pad 10 due to the initial placement of an infant within an incubator or the like upon pad 10 will cause the disc 22 to be displaced and allow the excess pressure to escape. This venting of excess pressure will continue automatically until an equilibrium point is reached, at which time, the system is closed and small pressure variations; i.e., within .+-.0.5 cm. water will be completely contained within the system and will act upon the transducer 16.

Further, very slow fluctuations in pressure, such as by a gradual temperature change, are bled from the system through orifice 28 in pop-off valve 12, thereby creating a stable base line reading, yet the orifice 28 may be adjusted such that rapid fluctuations caused by the infant's respiration and heart rate are unaffected by its presence. Although the orifice 28 is shown in the preferred embodiment located on pop-off valve 12, the actual placement within the system may vary widely without affecting its operation. The actual size of the orifice 28 also may vary depending on the overall design of the system. Its size governs the frequency response of the system; i.e., where the orifice 28 size is particularly small, relatively slow fluctuations are detected, while a large size orifice may entirely exhaust the same slow fluctuations.

The changes in electrical characteristics of the transducer 16, responsive to pressure fluctuations in the pad 10, are applied to electronic circuitry 30 for performing various functions such as triggering an alarm system at a particular apnea condition or controlling a read-out device which may be under surveilance by attending hospital personnel.

Referring now to FIG. 2, there is shown an alternate flexible pad 10 suitable for use in the apnea detection device. Although a flexible pad 10 of a continuous design, that is, the internal resilient material is dispersed uniformly and uninterrupted throughout the pad 10, is most easily constructed, it also entraps a relatively large quantity of air and thus, the pressure signals may be somewhat attenuated. In FIG. 2, therefore, an embodiment of the flexible pad 10 is disclosed where individual pockets or fingers 32 of resilient material are individually enclosed within a flexible non-porous material, and are spaced such that some portion of the infant will always rest upon one or more of the fingers 32. In this manner, the amount of entrained air is reduced and a less attenuated pressure signal is realized.

Although the fingers 32 are shown in elongated form, they may also be of other configurations, including spherically shaped fluid-tight pockets.

Turning now to FIG. 3, there is shown, in block form, a schematic of a typical electronic circuit 30 utilized in this invention. The individual circuits shown are of generally conventional designs so that only their overall function will be explained. As shown, the circuit 30 is used wherein only one sensed movement is monitored, such as breathing rate, however, a similar electronic circuit may also be used where both breathing rate and heart rate movements are sensed.

Briefly, the flexible pad 10, as previously explained, experiences pressure fluctuations in response to the breathing rate of an infant resting thereon and these pressure changes are transmitted to the transducer 16. The transducer 16, in the preferred embodiment is caused to change its capacitance in response to the pressure variations received, and a detection circuit 32 is provided in order to sense the capacitance changes and transmit the changes in the form of an analog signal for amplification by the amplifier 34.

This amplified analog signal may then be applied to a known circuit such as a Schmitt trigger, where the analog signal is converted to a digital signal by a preselected analog range.

The Schmitt trigger 36 is a generally known electrical circuit which is adapted to tripper a digital pulse when an analog signal of a predetermined signal amplitude is reached, and continue to transmit the constant digital pulse until the analog signal thereafter falls below a predetermined cut-off strength.

A respiration indicator 38 receives the digital signal from the Schmitt trigger 36 and provides a visual monitoring read-out means such as by a meter or digital read-out. At this point, therefore, hospital personnel may have a continuous visual indication of the breathing rate of the infant.

An apnea alarm 40 is also provided for an audible sound to warn of severe apnea conditions and the alarm 40 receives a signal from the Schmitt trigger 36 through a time delay 42. The purpose of the intermediate time delay 42 is to introduce a predetermined delay before an audible sound is triggered. The length of predetermined delay is chosen in order that small stoppages in breathing rate, i.e., less than 3 second delay do not sound the audible alarm, as often times, the infant will experience short delays in breathing followed immediately by a return to a normal breathing rate. The time delay 42 serves to eliminate the short, or normal breathing interruptions and only trigger the audible alarm where the breathing rate has slowed or even ceased for a predetermined amount of time, at which point, the attending hospital personnel are warned of the severe apnea condition so that the necessary steps may be taken. The circuit may also provide for silencing the alarm once breathing has again resumed.

A conventional test circuit 44 may also be included in order to afford continuous assurance that the alarm 40 is in proper working condition.

There is thus provided an apnea alarm system for continuous monitoring of the respiratory and heart rate of infants through a resilient fluid-tight pad adapted to underlie the infant and which transmits pressure variations to a highly sensitive pressure transducer. Large pressure variations normally introduced through gross body movements of the infant are automatically filtered out of the pressure signal to the transducer while long continuous pressure changes are stabilized at a desired zero metering point. The pressure transducer thereafter undergoes a variation in capacitance in response to the pressure variation, which is detected, amplified, and applied to known visual as well as audible monitoring systems.

Claims

I claim:

1. A breathing monitor for continuously detecting movement of a living infant, comprising a flexible air-tight resilient mattress, adapted to underlie and support said infant, the interior of said mattress containing air volumes which in response to bodily movement of the infant on said mattress are compressed and exhibit relative pressure fluctuations with respect to the ambient atmosphere; means communicating with said mattress interior for receiving said pressure fluctuations and converting said pressure fluctuations into a recognizable signal; and non-closeable bleed means connected continuously between said mattress interior and ambient atmosphere to enable bleeding of relatively slow pressure fluctuations from said interior.

2. A breathing monitor for continuously detecting movement of a living infant, comprising a flexible air-tight resilient mattress adapted to underlie and support said infant, the interior of said mattress containing air volumes which in response to bodily movements of the infant on said mattress are compressed and exhibit pressure fluctuations; valve means communicating with said mattress interior for receiving said pressure fluctuations, said valve means being adapted to filter out pressure fluctuations above and below a predetermined pressure range; and means connected for receiving the remaining filtered pressure fluctuations from said valve means and converting said filtered pressure fluctuations into a recognizable signal.

3. A breathing monitor as defined in claim 2 wherein said valve means comprises a chamber, said chamber having an inlet and an outlet, a first check valve means in said chamber adapted to open said chamber to ambient atmosphere at a predetermined positive pressure within said chamber, a second check valve means in said chamber adapted to open said chamber to ambient atmosphere at a predetermined negative pressure within said chamber.

4. A breathing monitor as defined in claim 3 wherein said predetermined positive pressure within said chamber is about 0.50 cm water and said predetermined negative pressure within said chamber is about 0.50 cm water.

5. A breathing monitor as defined in claim 3 wherein said chamber has an orifice adapted to bleed slow changes in pressure within said chamber to the ambient atmosphere.

6. A method of monitoring the breathing and heart rate related movements of an infant, comprising the steps of:

positioning an air-tight pad underlying and supporting the infant to be monitored,

maintaining the interior of said pad at about ambient atmospheric pressure,

sensing pressure variations in the pad resulting from movements of the infant,

receiving the sensed variations and filtering out gross pressure variations above and below a predetermined pressure range,

monitoring the filtered pressure variations and converting the filtered variations to a recognizable signal.