SleepStrip Sleep Apnea Tester

SleepStrip® Device Description

The SleepStrip is intended for use in monitoring nasal and oral airflow. It is generally indicated for use by physicians to screen patients to determine the need for further clinical evaluation by polysomnography based on their SleepStrip score. SleepStrip is specifically indicated to obtain a quantitative measure of respiratory airflow, which correlates with the Apnea Hypopnea Index (AHI). SleepStrip is intended for use with adult users during an overnight sleep, i.e., less than 24 hours.

The readout of the SleepStrip indicates sleep apnea severity in 4 categories, based on the number of apnea and hypopnea episodes combined that the patient experiences per hour at the duration of the test. While both SleepStrip readout and AHI are derived from very similar the terms differ. AHI is measured using sleep lab instrumentation and additional means (not only thermosensors) and is used for diagnostic purposes, while the Strip readout is obtained only by thermosensors and used only for screening and not diagnostic purposes.

The SleepStrip is a disposable screening device. The device is manufactured from a standard Kapton® film with two wide wings and a bridge (see Figure 1 below) on which electronic circuitry is printed that connects the components of the system. The SleepStrip is placed on the patients upper lip under the nose for one night sleep only. Its primary components are: (1) Three thermosensors (two for sensing nasal and one for oral-airflow); (2) An adhesive that covers the back of the devices wings; (3) A tape that covers the back of the devices bridge; (4) A CPU and its firmware; (5) A digital electro-chemical display; comprising elements that change from silver to dark gray; (6) A red LED; and (7) A battery. Below is a brief description of the primary components of the device:

1. SleepStrip Thermosensors: The thermosensors are standard negative temperature coefficient thermistors, soldered to the copper traces on the base film on its protrusions, and potted with heat conductive epoxy adhesive (see Fig. 1). They sense and provide a temperature signal to the CPU. They sense the temperature difference between colder inhaled the warmer exhaled airflow because the inhaled one is at room temperature while the exhaled airflow is at body temperature, which is warmer. Negative Temperature Coefficient means that the thermistors resistance increases when temperature decreases, and vise versa. These changes in the resistance are translated into an electric signal measured by the CPU. The CPU detects a pause in breathing (apnea) when it does not sense a change in temperatures over a period of 10-sec. A decrease in the level of breathing (hypopnea) is detected when the difference in temperatures between the inhaled and exhaled airflow is lower than the normal breathing as has been determined during the calibration period of the device (in the first 20-min of its wearing). The device cannot determine whether the patient is asleep or not.
2. Adhesive and tape: The SleepStrips wings are covered by a double sided medical grade foam adhesive that is used to separate the wings from the face as well as to provide a biocompatible adhesive. A surgical paper tape covers the bridge in order to prevent its adherence to the face.
3. The SleepStrip readout display: The device display consists of a digital seven segment display, which is silvery in the new device, and which presents a single digit in dark gray 30 minutes after the end of the study. The readout displays a single digit from 0 to 3 or the letter E. For description of the display indications please see "SleepStrip Physician instructions for use"
4. The SleepStrip CPU and its firmware: The device includes a CPU, which uses software (as firmware) for data collection (at 10Hz rate), analysis and display. The SleepStrips CPU analyzes the data to determine the average breathing pattern and any deviations, which may indicate an apnea or hypopnea. The algorithm calculates the average respiration temperature swing peak to peak value, and each new respiration cycle peak to peak value is compared to that average value. After each cycle, the CPU decides whether to include the value in the running average calculations, or to take other action using the following logic:
   • If the new value is less than 50% of the average - start a 10-sec "low respiration" timer. This timer counts the duration of the "Hypopnea", and adds a count to the total event counter if 10-sec pass and no new valid respiration cycle is detected.
   • If the new value is less than 10% of the average start a 10-sec "no respiration" timer. This timer counts the duration of the "Apnea", and adds a count to the total event counter if 10-sec pass and no new valid respiration cycle is detected.
   • In case of a more than 120-sec apnea, the CPU determines that the SleepStrip was removed from the face as the end of the study. It calculates the appropriate readout and starts the display activation sequence which takes about 30 minutes to complete.
   The SleepStrip readout score, together with additional indices, such as sleep questionnaires, physical measurements and patients own subjective feeling, may be used by the physician when determining whether the patient will be referred to a sleep lab or take the watchful waiting strategy.
5. A red LED: The device has a red LED (a standard electronic component), which is used to indicate to the user that the device is properly positioned on the face and is functioning properly. At the end of the test, the LED indicates that enough data was accumulated and is being processed for display.
6. A battery: The SleepStrip uses a standard miniature 3V lithium battery as a power supply for the duration of the test.

Operation of the device is conducted in the following way: When the user is ready to go to bed, he or she first washes his or her face with soap and water and dries it thoroughly. Then, the SleepStrip is removed from its package and both nose sensor prongs are folded forward. Afterwards, the green activation sticker must be applied on the display. This both activates the device as indicated by the LED lighting up, and also prepares the display for writing at the end of the study. The paper covers from the adhesive backing on both sides are removed, and (standing in front of a mirror), the SleepStrip is attached to the users face, above the upper lip just under the nose. The user should make sure the nose sensor prongs point away from the face, and do not go into the nose, but sit beneath the nostrils. The SleepStrips bridge should not be too tight on the upper lip. Looking into a mirror, the user breathes softly alternately through the nose and the mouth. The LED on the right side of the SleepStrip should blink red once each time a breath is exhaled. If it is not blinking, the SleepStrip should be repositioned so that air from both nose and mouth passes over the prongs. The SleepStrip should be readjusted until each breath causes a blink from both the nose, and separately the mouth. If the user can not produce this response, the device is defective and should be replaced.

After about 20 minutes, the blinking light will stop. The user should try to fall asleep on his/her back to assure a more precise reading. Also, the user is advised to sleep at least 5 hours so that the SleepStrip can gather enough data. The SleepStrip will display the letter E for Error and invalidate the test in case the device has not been in use for a minimum of 4 hours. In the morning, the user simply peels off the SleepStrip form his face. After a few minutes the LED will turn ON indicating that the end of the study was detected, and that the display is being activated. This process takes about 30 minutes, and the green sticker should not be removed from the display sooner or the readout will be difficult or impossible to read.

Figure 1: