WO2000033735A9

WO2000033735A9 - Ambulatory apnea screening device

Info

Publication number: WO2000033735A9
Application number: PCT/US1999/029244
Authority: WO
Inventors: Richard P Allen; David T Krausman
Original assignee: Individual Monitoring Systems
Priority date: 1998-12-10
Filing date: 1999-12-10
Publication date: 2001-04-12
Also published as: WO2000033735A1; US6142950A; AU2171500A

Abstract

A method (1) for evaluating an ambulatory subject for sleep apnea, comprises the steps of: (a) locating (2) on the subject's upper lip an airflow sensor (11) that is connected with a miniature, recording unit which has: (i) signal conditioning and filtering circuitry (12) to yield required levels of airflow sensor signal fidelity, (ii) a programmable controller (13) having an analog to digital converter (15), an integrated recorder (14), a data display means (16), and firmware that analyzes the airflow sensor signal, (iii) a mini jack (17) connected to the recorder that connects with a smart cable to control data flow between the recorder and an external computer (18), (b) using (3) this unit to sample at prescribed time intervals the sensor data which effectively quantifies the temporal variation of the subject's inspiration and expiration airflow, (c) time stamping and storing (4) this sampled data in the integrated recorder, (d) using (5a, 5b) the firmware to identify, count and cause the display of the number of apnea events identified as occurring per a specified period of time, and (e) using (6) an external computer (18) with application software to analyze and display the data for further evaluation of sleep apnea events.

Description

9 DESCRIPTION

10 π

12 AMBULATORY APNEA SCREENING DEVICE 13 14

15 TECHNICAL FIELD 6 7 The present invention generally relates to physiological monitoring devices. Mores particularly, this invention relates to a screening device and method for monitoring the9 occurrence of sleep disorder breathing events (e.g., decreases of upper respiratory0 airflow lasting more than ten seconds) in a fully ambulatory subject. 1 2 BACKGROUND ART 3 4 The diagnosis of a patient's sleep disorders often involves the analysis of the5 patient's sleep-related events, such as sleep disordered breathing. Such breathing disorders6 may involve pauses in breathing. These are defined by the American Sleep Disorder7 Association and the American Sleep Apnea Association as being sleep "apnea" if the pause8 lasts ten or more seconds, with these being further identified as: (1) Central Apnea -9 cessation of airflow (upper airway - oral and nasal) and respiratory effort (amplitude of0 chest movement during breathing); (2) Obstructive Apnea - cessation of airflow withi continuation of respiratory effort; and (3) Hypopnea - decrease in airflow from baseline2 (typically one-third to one-half or more) with continuation of normal or decreased levels of respiratory effort. These events lead to decreased blood oxygenation and thus to disruption of sleep. Such events are often analyzed by the use of polysomnography (PSG), the monitoring and recording over an extended period of time of the temporal variations in the amplitude of the patient's sleep-impacted, physiological parameters, including: heart rate, 1 eye blink activity, upper respiratory airflow, thorax and abdomen respiration efforts, the

2 blood's oxygen saturation level, electroencephalograms (EEG; electrical activity of the

3 brain), electro-oculogram (EOG; electrical activity related to movement of the eyes), and

4 electromyograms (EMG; electrical activity of a muscle)

5 FIG. 1 displays portions of PSG computer tracings for three distinct, thirty-second

6 intervals. Each of these printouts, showing the outputs from four of the system's sensors

7 (i.e., upper respiratory airflow, thorax and abdomen respiration effort, and thorax activity).,

8 illustrates temporal variations which are representative of the sleep-related apnea events

9 defined above: FIG. 1 A - Central Apnea, where the airflow sensor shows a marked lo cessation of airflow which lasted ten or more seconds, with cessation of respiratory effort π indicated by the thorax and abdomen sensors; FIG. IB - Obstructive Apnea, where the

12 airflow signal ceases for ten or more seconds, but the thorax and abdomen sensors show no

13 reduction in respiratory efforts; and FIG. 1 C - Hypopnea, where airflow decreases by one-

14 third or more for ten or more seconds and respiratory efforts are also significantly is decreased.

16 PSG monitoring activities are expensive as they are typically conducted in clinical

17 settings by trained PSG technicians who utilize expensive monitoring equipment having is multiple sensors that are tethered to a centralized recording system and power supply.

19 More recently, a number of portable recording systems for diagnosing sleep

20 disorders have been marketed. These systems range from multi-channel, PSG-style systems 2i to much simpler units that monitor only one or more of the possible physiological

22 parameters of interest. However, these multi-channel, portable systems remain technically

23 complex, expensive and usually require trained PSG technicians to supervise their use.

24 All of the current, portable sleep testing systems share common, less-than-desirable

25 features: (1) their use is expensive, since the equipment itself is expensive and a technician

26 usually must be involved for its set-up and disconnection, plus the data collected must be

27 subjectively analyzed by highly trained, sleep professionals, and (2) the PSG systems are

28 bedside portable, but their use requires patients to be outfitted with an array of tethered

29 electrode wires and sensors for connection to bulky body monitors or table-top consoles;

30 thus, their size and weight does not allow the patient to be ambulatory, which can be i essential for diagnosing patients' problems such as excessive sleepiness, or in the evaluation Less expensive alternatives, with capabilities for unattended, ambulatory use, are needed for assisting with the diagnosis of patients suffering from sleep disorders. For example, an inexpensive preliminary screening device, that provides information as to which patients might benefit the most from complete PSG testing, could contribute greatly by effectively expanding the audience to whom PSG testing would be available. Recognizing the need for an improved apparatus or method for diagnosing of the sleep disorders of a fully ambulatory subject, it is therefore a general object of the present invention to provide a novel method and ambulatory, non-tethered apnea screening device to meet such needs.

l DISCLOSURE OF INVENTION

2

3 The present invention is generally directed to satisfying the needs set forth above

4 and the problems identified with prior portable, sleep testing systems. The problems

5 associated with the expense of PSG testing thereby limiting the number of patients who

6 are assessed for sleep disorders and the non-ambulatory nature of such testing are

7 resolved by the present invention.

8 In accordance with one preferred embodiment of the present invention, the foregoing need can be satisfied by providing a method for evaluating a fully ambulatoryo subject for sleep apnea, comprising the steps of: (1) locating, on or near the subject'si upper lip and in proximity to the nostrils and mouth, a multi-element airflow sensor2 assembly that measures both nasal and oral airflow, with these airflow being physically3 and electrically combined, this sensor assembly being connected with a miniature, self-4 contained, recording unit which has: (a) signal conditioning and filtering circuitry tos yield required levels of airflow sensor signal fidelity, (b) a programmable controller6 having an analog to digital converter, an integrated recorder, a data display means, and7 firmware that analyzes the airflow sensor signal, (2) using this unit to sample ats prescribed time intervals the sensor data which effectively quantifies the temporal9 variation of the subject's combined oral and nasal airflow, (3) time stamping and0 storing this sampled data in the integrated recorder, (4) using the firmware to identify,i count and cause the display of the number of apnea events identified as occurring per a2 specified period of time. 3 In another preferred embodiment, the present invention is seen to take the form of4 a non-tethered, apnea screening device. It comprises: (1) an upper airways sensing5 assembly located so as to measure the subject's inspiration and expiration activity, (2)6 a miniature, self-contained, recording unit integrated with the sensor, this recording7 unit having: (a) signal conditioning and filtering circuitry to yield required levels of8 signal fidelity, (b) a programmable controller connected to the sensor and circuitry, (c)9 an analog to digital converter, (d) an integrated recorder, and (e) a data display means0 connected to the controller, wherein the programmable controller has firmware thati analyzes the upper airways inspiration and expiration signal to identify, count, and display in the display means the number of occurrences of specifically defined apnea events. In another preferred embodiment, the non-tethered, apnea screening device further comprises: (3) a control switch connected to the controller which allows the display means to recall and display the number of apnea events counted for each of the consecutive, specified periods of time that comprise the total period over which the upper ventilating measurements were recorded, and to reset the controller to begin again to count apnea events when the switch remains depressed beyond a specified period of time, (4) a mini jack connected to the controller, and (5) a smart cable that connects with the mini jack to control data flow between the recorder and an external computer, wherein the external computer has application software which is used to analyze and display the temporal variations in the upper airways data for the purpose of evaluating the ambulatory subject for sleep apnea. Other objects and advantages of this invention will become readily apparent as the invention is better understood by reference to the accompanying drawings and the detailed description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 displays partial-PSG computer tracings for three distinct, thirty-second intervals, each of which illustrate a different form of a "sleep apnea" event: 1 A - Central Apnea, IB - Obstructive Apnea, and 1C - Hypopnea. FIG. 2 is a schematic flow diagram which depicts a method in accordance with a preferred embodiment of the present invention. FIG 3 is a schematic flow diagram of an embodiment of the present invention. FIG. 4 is a diagram that shows the placement of an embodiment of the present invention on the head of a to-be-tested subject. FIG. 5 is a schematic circuit diagram for the embodiment shown in FIG. 3.

l BEST MODE FOR CARRYING OUT THE INVENTION

2

3 Referring again to FIG 1 and the previously given definitions for a central

4 apnea, obstructive apnea and hypopnea, it can be noted that knowledge of a patient's

5 respiration effort (amplitude of the physical movement of the chest) is not required to

6 identify an "apnea" event — such knowledge is only needed to distinguish between the

7 various types of apnea events (e g , central or obstructive apnea) This suggests the

8 possibility of developing an apnea detection apparatus and an apnea detection method

9 by monitoring only a patient's upper respiratory airflow o Validation of such an apnea detection method was accomplished through an 1 SBIR research contract (#N43-NS-5-2328) from the National Institute of Neurological2 Disorder and Stroke Seven patients with symptoms of sleep disordered breathing3 were tested in a clinical setting Each subject in seven separate, all-night sleep studies4 was fitted with four non-tethered, portable recorders including the present inventions containing an oral/nasal airflow sensor placed on or near the upper lip 6 Two other recorders configured as chest-belt units were placed about the chest7 for separately monitoring the respiration effort of the thorax and the respiration efforts of the abdomen These units used piezoelectric sensors that measured the expansion9 and contraction of the chest belts A forth chest-belt monitor recorded thorax 0 movement activity using a piezoelectric sensor Additionally, each patient was fittedi with a standard array of sensors and electrodes to provide a PSG recording on a2 polygraph recorder 3 After the night's sleep, data from the non-tethered recorders was downloaded4 to an external computer, compared to the PSG polygraph tracings and scored by a5 Diplomat of the American Board of Sleep Disorders Medicine The Diplomat reviewed6 both the displayed computer records and the polygraph records The sleep apnea7 events, determined by computer display and analysis of the monitor's data, showed8 excellent correlations with those from the visually scored polysomnogram (PSG) The9 data shown in FIG 1 is from these sleep studies and was recorded using the non-0 tethered, portable recorders 1 The above described method of monitoring respiratory ventilation via upper2 airflow presents a less complex alternative to standard PSG testing and has been 1 shown to provide sufficient information for the detection and counting of apnea events.

2 In effect, this study's data demonstrated that using the upper respiratory ventilation

3 function alone is a useful method for screening apnea and a means for assessing

4 treatment effects or changes in the patient's breathing disorder during sleep.

5 Referring now to the drawings wherein are shown preferred embodiments and

6 wherein like reference numerals designate like elements throughout, there is shown in FIG.

7 2 a schematic flow diagram which depicts a method in accordance with a preferred

8 embodiment of the present invention for evaluating a fully ambulatory subject for sleep

9 apnea. lo In this embodiment the method 1 is seen to comprise the steps of: (1) locating 2 on π the subject's upper lip an airflow sensor that is connected with a miniature, recording

12 unit, this unit having signal conditioning and filtering circuitry to yield required levels

13 of airflow sensor signal fidelity, a programmable controller with an analog to digital

14 converter, an integrated recorder and a data display means, with the programmable is controller having firmware that allows the unit to identify, count and record the

16 number of occurrences of sleep apnea events, (2) using 3 the unit to sample at

17 prescribed time intervals sensor data that quantifies the temporal variation of the is subject's airflow, (3) time stamping and storing 4 the sampled data in unit's recorder,

19 (4) using 5a the firmware to identify, count and record in the unit's recorder the

20 number of occurrences of sleep apnea events, and (5) using 5b the display means to 2i visually communicate the number of apnea events identified by the firmware as

22 occurring per a specified period of time, typically an hour.

23 The versatility of the display means may be enhanced by providing the controller

24 with a control switch that allows the display means to recall and display the number of

25 apnea events counted for each of the consecutive, specified periods of time that

26 comprise the total period over which the airflow measurements were recorded, and to

27 reset the controller to begin again to count apnea events when the switch remains

28 depressed beyond a specified period of time, typically about five seconds.

29 In another embodiment of the present invention, the above method further

30 comprises the step of using 6 an external computer with application software to i analyze and display the temporal variations in recorded data for the purpose of further 2 evaluating the ambulatory subject for sleep apnea. This capability is provided by 1 providing the unit with a mini jack that connects with a smart cable to control data

2 flow between the unit and an external computer.

3 In another preferred embodiment, the present invention is seen to take the form of a

4 non-tethered, apnea screening device 10. A general overview of this embodiment is

5 shown in FIG. 3 which provides a schematic block diagram of the device. It is a battery

6 operated device that comprises: (a) an airflow sensor 11 with appropriate signal

7 conditioning and filtering circuitry 12 to yield required levels of signal fidelity, thus

8 providing sensor output data that quantifies the temporal variations in the subject's

9 upper respiratory airflow, (b) a programmable controller 13 with embedded ιo programmable read only memory (PROM) to store control firmware including π appropriate algorithms to identify, count and record the number of occurrences of

12 specifically defined apnea events, while also compensating for drift in the amplitude of

13 said sensor's airflow data, (c) memory 14 for storing time-stamped data, (d) an analog

14 to digital converter 15 to sample sensor output data at prescribed time intervals, and is (e) a data display means 16. FIG. 4 illustrates the placement of the present invention on a

16 patient.

17 In another embodiment of the present invention, the non-tethered, apnea

1 screening device further includes a mini jack 17 which allows connection to a smart

19 cable for downloading the recorded data to an external computer system 18. This

20 system has application software to analyze and display the temporal variations in the 2i recorded data for the purpose of further evaluating the ambulatory subject for sleep

22 apnea.

23 In another embodiment of the present invention, the non-tethered, apnea

24 screening device further includes a control switch 19 that allows the display means 16

25 to recall and display the number of apnea events counted for each of the consecutive,

26 specified periods of time that comprise the total period over which the airflow

27 measurements were recorded, and to reset the controller 13 to begin again to count

28 apnea events when the switch 19 remains depressed beyond a specified period of time,

29 typically about five seconds.

30 In a preferred embodiment of the present invention, the schematic circuit 3i diagram for the device is illustrated in FIG. 5. i Appropriate hardware for use in this recorder unit includes (a) an ultra-low

2 power CMOS microprocessor controller (Microchip PIC16C74) for timing and system

3 control, (b) programmable memory, (c) signal conditioning and filtering circuitry, (d)

4 an 8 bit, analog to digital (A/D) converter for digitizing the analog signal, (e) 512K

5 bytes or greater of SRAM, EEPROM or FLASH memory for storing the digitized

6 signal, and (f) a LCD readout with a LCD driver chip Support components and

7 circuit chips are of surface mount technology (SMT)

8 This signal conditioning and filtering circuitry includes a high gain amplifier

9 whose circuitry is adjusted to provide a band pass of about 0 15 to 0 80 hertz in ordero to measure the expected low frequency range of airflow associated with respiration,i while filtering out the higher frequency ranges 2 The 8 bit A/D converter of the present invention is set to sample the sensor3 output signal at ten data points per second For these low frequency signals, this4 sampling rate yields good representation and detail for the sensor's analog signal Fors a recording unit having 512K bytes of RAM storage and at this sampling frequency,6 there is fourteen hours of recording time Standard digital sampling techniques are7 employed to record the airflow signal s For monitoring the upper airway breathing of a subject, extensive bench tests9 were conducted on pressure, thermistor and thermocouple sensors 0 Thermocouples were found to be very stable and repeatable while thermistori output and sensitivity output varied greatly from unit to unit The advantage of2 thermocouples are that they are self generating (i e , two dissimilar metals generate an3 output voltage when connected together at a junction), the output signal changes in4 proportion to inspired and expired air (cooling and heating) as it passes across the5 junction element Thermocouples are very low impedance devices and exhibit more6 stable and predictable properties than do thermistors which tended to produce a static7 sensitive environment resulting from artifact distortion 8 Combined nasal and oral airflow may be measured with a commercially-9 available, airflow sensor 11 of the thermocouple type, such a Pro-Tech cannula style,0 Model No 1242, nasal/oral airflow sensor or the Rochester Electro-Medical Noi 602640 sensor assembly The Rochester unit is made of medical grade silicone tubing 1 that is fully flexible to fit a variety of facial shapes. This design eliminates the need for

2 taping, allows for simple easy adjustment and the soft tubing adds to patient comfort.

3 An adjustable elastic strap 20 is attached to the sensor assembly and worn

4 around the back of the head for good stability and comfort. The strap also serves as a holding platform for attachment of the recorder unit which is attached at cheek level on

6 one side of the face. Although the recorder unit may be a small, flat wafer (i.e., about

7 1.5 x 1.9 x 0.4 inches, with soft rounded corners), frontal positioning of the unit was

8 determined to be the most unobtrusive since attachment behind the head would be

9 uncomfortable and might interfere with sleep. A short lead (i.e., 1 -2 inches) betweeno the sensor and the recorder unit is firmly attached to the strap (i.e., no tethered wires).i Pressure sensors provide another alternative means for making the necessary2 airflow measurement. For example, a standard oxygen nasal cannula, similar to a Sure3 Flow unit #33801 (B & F Medical), connected to a solid-state air pressure transducer,4 such as a Fuijikura type PSM-002KPG (Servoflo Corporation), can be substituted fors the thermocouple (or thermistor) sensor to measure upper airway breathing. Air6 pressure has the advantage of producing a more stable signal even if the nasal cannula (soft plastic air tube) placed about the upper lip and near the nostrils is displaced ors moves during sleep. The nares placed cannula is typically routed about the patient's9 ears, then under the chin and held in place by a lanyard style fastener. The cannula is0 then connected to a pressure transducer contained in the monitoring unit. Thisi combination detects the pressure fluctuations caused by inspiration and expiration,2 with the signal's contour being basically proportional to the subject's airflow. 3 The device's recorder unit is uniquely configured to report apnea events4 (including both apneas and hypopneas) occurring per hour for apnea screening5 purposes. This recorder is outfitted with a visual readout and special firmware for6 counting apnea events. 7 This firmware employs an algorithm that finds the maximum and minimum signal levels in a preset time epoch (usually 5 seconds), effectively capturing the high9 and low points of a single breath with varying DC offsets. A potential apnea begins0 when a 'max-min" point falls below a specified threshold and ends when it rises abovei the same threshold. The threshold is set in terms of a percentage, for example, 50%, 1 of a "baseline amplitude" (DC level). This is the average "max-min" value determined

2 at the start of the record.

3 To compensate for varying signal amplitudes as might be caused by minor

4 displacements of the airflow sensor, an adaptive threshold algorithm is applied. This

5 involves slowly adjusting the baseline amplitude throughout the recording while

6 maintaining a fixed percentage of this baseline as the threshold. Means used to adjust this baseline include a 3dB/octave low-pass filter with a time constant of typically three

8 minutes. Alternatively, a more sophisticated adaptive threshold algorithm uses a

9 "stack" (first in - first out list) which holds all the max-min points for an "adaptiveo period," typically a few minutes. For every time-step, a new max-min point is pushedi onto the stack displaying the oldest. Then, periodically (typically every 10-15 seconds)2 the stack is sorted and the max-min value at a certain percentile (typically, the 80th) is3 taken to be the new adaptive baseline. From this, new percentage thresholds are4 derived. The device's firmware was written in Assembly Language code using assembler6 software for the PIC Microchip. This program was initially burned into the electrically7 programmable/erasable read only memory (EPROM) in the PIC 16C74 s microprocessor. After the program was finalized, a one-time programmable (OTP)9 memory PIC Microchip replaced the EPROM. 0 The smart cable for use with this recorder consists of a miniplug 17 at one endi for connection to the recorder and a DB9 connector at the computer end. A very2 small SMT circuit board is contained within the DB9 shell and populated with an RS-3 232 UART chip to establish data communications between the recorder and the4 computer. Power is taken from the computer's serial port. Application software5 manages the data transfer and formats the data into a convenient file structure. 6 Because of the signal fidelity achieved with the present invention, it is possible to use an external computer to further analyze the airflow data recorded using the8 present invention. 9 Although the foregoing disclosure relates to preferred embodiments of the 0 invention, it is understood that these details have been given for the purposes of clarificationi only. Various changes and modifications of the invention will be apparent, to one having ordinary skill in the art, without departing from the spirit and scope of the invention as hereinafter set forth in the claims

Claims

l CLAIMS

2

3 We claim

4 1 A method (1) for evaluating a fully ambulatory subject for sleep apnea,

5 comprising the steps of

6 locating (2) on the subject's upper lip an airflow sensor (11) that is connected

7 with a miniature, recording unit, said unit having signal conditioning and filtering

8 circuitry (12) to yield required levels of airflow sensor signal fidelity, a programmable controller (13) with an analog to digital converter (15), an integrated recorder (14) and lo a data display means (16), wherein said programmable controller (12) having firmware ιι that analyzes said signal,

12 using (3) said unit to sample at prescribed time intervals sensor data that

13 quantifies the temporal variation of the subject's airflow,

14 time stamping and storing (4) said sampled data in said integrated recorder

1 (14),

16 using (5a) said firmware to identify, count and record in said integrated

17 recorder (14) the number of occurrences of specifically defined apnea events, and is using (5b) said display means (16) to visually communicate the number of

19 apnea events identified by said firmware as occurring per a specified period of time

20 2 A method for evaluating a fully ambulatory subject for sleep apnea, as recited 2i in claim 1, wherein

22 said controller (13) having a control switch (19) that allows said display means

23 (16) to recall and display the number of apnea events counted for each of the

24 consecutive, specified periods of time that comprise the total period over which said 5 airflow measurements were recorded, and to reset said controller (13) to begin again

26 to count apnea events when said switch (19) remains depressed beyond a specified

27 period of time

28 3 A method (1) for evaluating a fully ambulatory subject for sleep apnea, as 9 recited in claim 1, further comprising the steps 0 providing said unit with a mini jack (17) that connects with a smart cable to i control data flow between said recorder and an external computer (18), and 1 using (6) said external computer (18) with application software to analyze and

2 display the temporal variations in said data for the purpose of evaluating the

3 ambulatory subject for sleep apnea

4 4 A method (1) for evaluating a fully ambulatory subject for sleep apnea, as

5 recited in claim 2, further comprising the steps

6 providing said unit with a mini jack (17) that connects with a smart cable to

7 control data flow between said recorder and an external computer (18), and

8 using (6) said external computer (18) with application software to analyze and

9 display the temporal variations in said data for the purpose of evaluating theo ambulatory subject for sleep apnea i 5 A method (1) for evaluating a fully ambulatory subject for sleep apnea, as2 recited in claim 1, wherein 3 said firmware having an algorithm that finds the maximum and minimum signal4 levels in a preset time epoch, computes the difference between said signal levels ands defines an apnea event as occurring when said signal level difference falls below and6 stays below a specified threshold for a prescribed period of time, 7 said threshold being set in terms of a percentage of the average over a specified8 number of time epochs of the difference between said signal levels 9 6 A method (1) for evaluating a fully ambulatory subject for sleep apnea, as0 recited in claim A, wherein i said firmware having an algorithm that finds the maximum and minimum signal2 levels in a preset time epoch, computes the difference between said signal levels and3 defines an apnea event as occurring when said signal level difference falls below and4 stays below a specified threshold for a prescribed period of time, 5 said threshold being set in terms of a percentage of the average over a specified6 number of time epochs of the difference between said signal levels 7 7 A device (10) for evaluating a fully ambulatory subject for sleep apnea, said8 device comprising 9 an airflow sensor (11) located so as to measure the subject's airflow, 0 a miniature, recording unit connected to said sensor, said unit having signali conditioning and filtering circuitry (12) to yield required levels of signal fidelity, a2 programmable controller (13) connected to said sensor (11) and circuitry (12), said 1 controller (13) connected to and controlling both an analog to digital converter (15)

2 and an integrated recorder (14), and a data display means (14) connected to said

3 controller (13),

4 wherein said programmable controller (13) having firmware that analyzes said

5 signal to identify, count, record in said integrated recorder (14), and display in said

6 display means (16) the number of occurrences of specifically defined apnea events

7 8 A device (10) for evaluating a fully ambulatory subject for sleep apnea, as

8 recited in claim 7, said device further comprising

9 a control switch (19) connected to said controller (13) that allows said displayo means (16) to recall and display the number of apnea events counted for each of thei consecutive, specified periods of time that comprise the total period over which said airflow measurements were recorded, and to reset said controller (13) to begin again3 to count apnea events when said switch (19) remains depressed beyond a specified4 period of time 5 9 A device (10) for evaluating a fully ambulatory subject for sleep apnea, as6 recited in claim 7, said device further comprising 7 a mini jack (17) connected to said recorder (14), s wherein said jack (17) connects with an external smart cable to control data9 flow between said recorder and an external computer (18), 0 wherein said external computer (18) having application software to analyze andi display the temporal variations in said data for the purpose of evaluating the 2 ambulatory subject for sleep apnea 3 10 A device (10) for evaluating a fully ambulatory subject for sleep apnea, as4 recited in claim 7, said device further comprising 5 a mini jack (17) connected to said recorder, 6 a smart cable that connects with said mini jack (17) to control data flow7 between said recorder (14) and an external computer (18), 8 wherein said external computer (18) having application software to analyze and9 display the temporal variations in said data for the purpose of evaluating the 0 ambulatory subject for sleep apnea i 11 A device (10) for evaluating a fully ambulatory subject for sleep apnea, as2 recited in claim 7, wherein 1 said firmware having an algorithm that finds the maximum and minimum signal

2 levels in a preset time epoch, computes the difference between said signal levels and

3 defines an apnea event as occurring when said signal level difference falls below and

4 stays below a specified threshold for a prescribed period of time,

5 said threshold being set in terms of a percentage of the average over a specified

6 number of time epochs of the difference between said signal levels

7 12 A device (10) for evaluating a fully ambulatory subject for sleep apnea, as

8 recited in claim 8, wherein

9 said firmware having an algorithm that finds the maximum and minimum signalo levels in a preset time epoch, computes the difference between said signal levels andi defines an apnea event as occurring when said signal level difference falls below and2 stays below a specified threshold for a prescribed period of time, 3 said threshold being set in terms of a percentage of the average over a specified4 number of time epochs of the difference between said signal levels s 13 A device (10) for evaluating a fully ambulatory subject for sleep apnea, as6 recited in claim 9, wherein 7 said firmware having an algorithm that finds the maximum and minimum signals levels in a preset time epoch, computes the difference between said signal levels and9 defines an apnea event as occurring when said signal level difference falls below and0 stays below a specified threshold for a prescribed period of time, i said threshold being set in terms of a percentage of the average over a specified2 number of time epochs of the difference between said signal levels 3 14 A device (10) for evaluating a fully ambulatory subject for sleep apnea, as4 recited in claim 10, wherein 5 said firmware having an algorithm that finds the maximum and minimum signal6 levels in a preset time epoch, computes the difference between said signal levels and7 defines an apnea event as occurring when said signal level difference falls below and8 stays below a specified threshold for a prescribed period of time, 9 said threshold being set in terms of a percentage of the average over a specified0 number of time epochs of the difference between said signal levels i 15 A device (10) for evaluating a fully ambulatory subject for sleep apnea, said2 device comprising 1 an airflow sensor (11) located so as to measure the subject's airflow,

2 a miniature, recording unit integrated with said sensor, said unit having signal

3 conditioning and filtering circuitry (12) to yield required levels of signal fidelity, a

4 programmable controller (13) connected to said sensor (11) and circuitry (12), said

5 controller (13) connected to and controlling both an analog to digital converter (15)

6 and an integrated recorder (14), and a data display means (16) connected to said

7 controller, wherein said programmable controller (13) having firmware that analyzes said signal to identify, count, and display in said display means the number of occurrenceso of specifically defined apnea events. i 16. A device (10) for evaluating a fully ambulatory subject for sleep apnea, as2 recited in claim 15, said device further comprising: 3 a control switch (19) connected to said controller (13) that allows said display4 means (16) to recall and display the number of apnea events counted for each of thes consecutive, specified periods of time that comprise the total period over which said6 airflow measurements were recorded, and to reset said controller (13) to begin again7 to count apnea events when said switch (19) remains depressed beyond a specifieds period of time. 9 17. A device (10) for evaluating a fully ambulatory subject for sleep apnea, as0 recited in claim 15, said device further comprising: i a mini jack (17) connected to said recorder, 2 wherein said jack (17) connects with an external smart cable to control data3 flow between said recorder and an external computer (18), 4 wherein said external computer (18) having application software to analyze and5 display the temporal variations in said data for the purpose of evaluating the 6 ambulatory subject for sleep apnea. 7 18. A device (10) for evaluating a fully ambulatory subject for sleep apnea, as8 recited in claim 15, said device further comprising: 9 a mini jack (17) connected to said recorder, 0 a smart cable that connects with said mini jack (17) to control data flowi between said recorder (14) and an external computer (18), wherein said external computer (18) having application software to analyze and display the temporal variations in said data for the purpose of evaluating the ambulatory subject for sleep apnea. 19. A device (10) for evaluating a fully ambulatory subject for sleep apnea, as recited in claim 15, wherein: said firmware having an algorithm that finds the maximum and minimum signal levels in a preset time epoch, computes the difference between said signal levels and defines an apnea event as occurring when said signal level difference falls below and stays below a specified threshold for a prescribed period of time, said threshold being set in terms of a percentage of the average over a specified number of time epochs of the difference between said signal levels. 20. A device (10) for evaluating a fully ambulatory subject for sleep apnea, as recited in claim 17, wherein: said firmware having an algorithm that finds the maximum and minimum signal levels in a preset time epoch, computes the difference between said signal levels and defines an apnea event as occurring when said signal level difference falls below and stays below a specified threshold for a prescribed period of time, said threshold being set in terms of a percentage of the average over a specified number of time epochs of the difference between said signal levels.