Arousal, EEG spectral power and pulse transit time in UARS and mild OSAS subjects

Upper airway resistance syndrome (UARS) and obstructive sleep apnea syndrome (OSAS) are associated with arousals and autonomic activation. Pulse transit time (PTT) has been used to recognize transient arousals. We examined the accuracy of PTT to recognize arousals, and the relationship between PTT deflection and visual and non-visual arousals.

Ten UARS and 10 mild OSAS subjects were studied via polysomnography including measurement of esophageal pressure. Electroencephalogram (EEG) spectral power was obtained from central leads. Seven types of events were identified, depending upon the presence or absence of: a sleep-related respiratory event (SRRE), i.e. apnea, hypopnea, and abnormal breathing effort; a PTT signal; or a visually scored arousal (>1.5s).

One thousand four hundred forty-six events were identified in 20 subjects. Fifty-nine percent of all SRREs were associated with a PTT signal and a visual EEG arousal. Nineteen percent of SRREs had no EEG arousals at their termination, and 7.4% had no associated PTT signal. Delta power was significantly increased when non-visual EEG arousals were scored. The time delay for PTT was determined by the presence or absence of EEG arousal. The sensitivity of PTT to recognize EEG arousal was 90.4% and the specificity was 16.8%. The sensitivity and specificity of PTT to recognize SRRE was 90.7 and 21.9%, respectively.

These results preclude the use of PTT by itself. SRREs induce an activation with positive PTT response but without arousal in 14% of cases. This PTT response, however, is much slower than that occurring with arousal. UARS and mild OSAS do not respond in the same way to SRREs, particularly during rapid eye movement sleep.