Obstructive sleep-disordered breathing (OSDB) is common in both children and adults and is recognized as having substantial health-related consequences at all ages. Laboratory polysomnography (PSG) is the gold standard for diagnosing OSDB, but the procedure is not without problems. Polysomnographic studies are complex, invasive, expensive, not universally available, and require an overnight stay in a sleep laboratory. Additionally, conventional signals used to detect air ow, especially oral air ow, are qualitative, making it difficult to precisely quantify OSDB. Furthermore, in children, discrete apneas or hypopneas are often not present; instead, there are long periods with high-e ort/high-resistance breathing requiring very low esophageal pressures to generate air ow in a narrowed airway. This high-resistance breathing is difficult to detect using conventional PSG. Published research by the proposing team has demonstrated that: (1) high-frequency inspiratory sounds (HFIS) in the frequency range of 2-10 kHz are a marker for the occurrence of OSDB; and (2) HFIS are generated when the upper airway is narrowed during sleep and acts as a resonant chamber (in agreement with the physics of sound resonance in a cylindrical pipe). It is emphasized that these HFIS are different from the low-frequency (< 2 kHz) sounds that describe typical snoring. HFIS intensity can be analyzed quantitatively to determine the degree of airway narrowing and the pressure gradient across the airway. Barron Associates and the University of Virginia (UVA) are developing the SoundTrak system, a low-cost sleep monitor for use in individuals' home environments to noninvasively, ergonomically, and automatically acquire and analyze HFIS data pertaining to OSDB. The SoundTrak system will collect low- and high-frequency sound data via a microphone and a small, highly-portable computing base station. Breathing movements will be measured using a wireless thoracic band, enabling inspirations to be detected and the patient's sleep sounds to be discriminated from other sources. The thoracic band will also collect wireless electrocardiogram (ECG), body posture, activity, and skin temperature data, and relay that information in real time to the SoundTrak base station. The SoundTrak system will include a pulse oximeter to report oxygen saturation levels, which are often helpful to, and expected by, physicians assessing OSDB. The SoundTrak system will provide many advantages over currently available home sleep monitoring technologies, as is described herein. The Phase I effort, along with other recent, published work by the proposing team, demonstrated the feasibility of using HFIS and thoracic monitoring as an alternative to PSG for diagnosing OSDB. The central goal of the proposed e ort is to demonstrate the viability of in-home HFIS studies in 20 children and 80 adults. Traditional overnight laboratory PSG will be compared with in-home sleep studies based on the easy-to-use, noninvasive Phase II prototype SoundTrak system.
Products resulting from this research have strong potential to provide a more accurate and cost-effective alternative to traditional polysomnography studies performed in sleep laboratories worldwide. PSG may also fail to reproduce patients' usual sleep habits, since the patient must sleep in a new environment while being highly instrumented; as such, home studies using the SoundTrak system may provide more representative data for diagnosing OSDB. Medicare recently announced that it will cover in-home sleep diagnostics, including those using the apnea/hypopnea index as their main criterion, a decision that underscores the relevance of the project and its viability in the marketplace.
