Obstructive sleep apnea syndrome (OSAS) is a major public health problem. The golden reference for diagnosing OSAS is the sleep-laboratory based polysomnography (PSG). However, screening of population for OSAS may be practical and cost efficient only through ambulatory home recordings. In this work we aimed to design, construct and evaluate a novel ambulatory device for these recordings. The device was designed to record breathing movements, nasal and oral flow, position, snore, blood oxygen saturation and heart rate. The first part of clinical evaluation was done by recording 19 patients simultaneously with the novel device and with clinical reference instrumentation at a sleep laboratory. In the simultaneous recordings, no statistically significant difference was detected in the apnea-hypopnea index. All patients were correctly diagnosed, as compared to the reference instrumentation, with the novel ambulatory device. The second part of clinical evaluation was conducted through 323 ambulatory home recordings of which 275 (193 males and 82 females) were of diagnostically acceptable quality. A total of 106 and 169 recordings were successfully conducted with the novel device and a commercial ambulatory device, respectively. Both devices showed similar diagnostic capability in detecting sleep apnea. The novel device was found clinically applicable, technically reliable and sensitive for the diagnostics of OSAS.
Sleep apnea Home recording Ambulatory Polysomnography Digital signal processing
The air pressure from the nasal prongs is brought to the pressure sensor chamber via a small plastics tube (a). The pressure is sensed by a piezo electric transducer and the signal is amplified and filtered before the analogue-to-digital converter. The changes in temperature due to inspiration and expiration are detected with three oro-nasal thermistors (b). The thermistors are biased and the signal is amplified and filtered before digitizing. Thorax and abdominal movements are detected with custom-made double strain gauges (c). The weak signals obtained from the strain gauges are strongly amplified and then band-pass filtered before analogue-to-digital conversion. Snoring sounds (air pressure levels) are detected with a DC biased electret microphone (d). Two operational amplifiers generate virtual grounds midway between a single power supply for the analog electronics (e). With custom made resistive (from zero to infinity) jumpers to connectors J1 – J3 the gains of the last amplifiers can be adjusted. (EPS 506 kb)