Obstructive sleep-disordered breathing (OSDB) is common in children and is now recognized as having substantial neurocognitive, neurobehavioral, and cardiovascular consequences. There are major limitations in diagnosing OSDB in children, who often do not have discrete apneas or hypopneas that can be diagnosed by measurement of airflow. Instead, children often have long periods with high-resistance breathing where they generate very-low esophageal pressure swings to maintain airflow in the presence of a narrowed airway. Esophageal pressure (Pes) recording is the definitive method to diagnose OSDB, but this measurement is invasive and not widely available. Even without Pes, laboratory polysomnography (PSG) is a complex, burdensome, and costly procedure. Work by two University of Virginia (UVA) physicians, who are part of the proposing team, demonstrated that: (1) high-frequency inspiratory sounds (HFIS) in the frequency range of 2-10 kHz are a marker for the occurrence of OSDB in children;and (2) children generate HFIS when they have a narrowed upper airway during sleep, in which case their upper airway acts as a resonating chamber, completely in agreement with the physics of sound resonance in a cylindrical pipe. It is important to emphasize that these HFIS are different from the low-frequency (<2 kHz) sounds that describe snoring in adults. Barron Associates and UVA propose to develop the SoundTrak system, a low-cost sleep monitor for use in individuals'home environments to noninvasively and ergonomically acquire and analyze HFIS data pertaining to OSDB. The SoundTrak system will unobtrusively collect low- and high-frequency sound data via a microphone and a small portable PC 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 (e.g., a sibling sleeping in the same room, noise from heating, ventilation, and air conditioning systems, etc). Additionally, a commercial wireless wrist-worn finger oximetry system will be included in the Phase I study to investigate the issue of adequacy of ventilation during HFIS events, which can occur with or without oxyhemoglobin desaturation. When HFIS events occur without desaturation, they are frequently not detected by PSG since, in this case, airflow is adequate to maintain ventilation and oxygenation;this is often referred to as the upper airway resistance syndrome (UARS). Being able to distinguish HFIS events with and without desaturation will provide a simple noninvasive method to study whether these events contribute to morbidity in OSDB. Prior studies looking at outcomes for OSDB have been unable to detect the UARS without use of Pes. Recent work by the proposing team demonstrated the feasibility of using HFIS and thoracic monitoring in the sleep laboratory as an alternative to polysomnography for diagnosing OSDB. The central goal of the proposed effort is to demonstrate the viability of in-home HFIS studies in children who are suspected of having OSDB. In particular, traditional overnight laboratory polysomnography, augmented to include esophageal manometry and/or pulse transit time measurement, will be compared with multi-night in-home sleep studies based on an easy-to-use prototype SoundTrak system, and their agreement with respect to a diagnosis of OSDB assessed.
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. Polysomnography may also fail to reproduce patients'usual sleep habits, since the patient is in a new environment and is highly instrumented;as such, home studies using the SoundTrak system are likely to be found to 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. This decision underscores the relevance of the project and the viability of the marketplace.
