Evaluation of Automatic Analysis of SCSB, Airflow and Oxygen Saturation Signals in Patients with Sleep Related Apneas

We have developed a computerized analysis of respiratory and body movements (static charge sensitive bed [SCSB]), oxygen saturation (pulse oximeter), and airflow (thermistor) for the evaluation of sleep related apneas. The cumulative distribution of oxygen saturation, the number and distribution of desaturation events, and the duration and type of apneas are assessed. Analysis is performed separately during the total recording time and during the time when the patient sleeps on his back. We have compared the automatic analysis with the results obtained on simultaneous daytime polysomnograph naps in 55 subjects (snorers or obstructive sleep apnea syndrome [OSAS] patients). The compressed graphs obtained automatically demonstrated a periodic breathing pattern in all 22 patients who presented sleep-related apneas at polygraphic recording. The cumulative distribution of oxygen saturation was not as steep in the apnea patients as in patients not showing apneas; in 19 of the 22 OSAS patients, the value was outside our normal limits (80 percent of the recording time inside 3.6 percent SaO2 variation band). The apnea index (AI) was 26.4 in manual and 23.3 in automatic analysis. Using the automatic method there were three false negative cases in the analysis of desaturations; in these patients periodic breathing was present in output graphs indicating need for further polygraphic assessment. The duration of apneas in the automatic analysis was shorter than in manual analysis, but the agreement was sufficient for screening purposes (mean error less than 3 s, mean duration of apneas 20.1 s). The automatic method is presently used in clinical routine for screening purposes, for assessment of the severity of the disorder and the type of treatment that a subject may need, in epidemiologic investigation and follow-up of the treatment.