Effect of sleep stages on measurements of passive respiratory mechanics ininfants with bronchiolitis

The measurement of passive respiratory mechanics by the single-breath occlu sion technique is one of the more frequently used tests of infant lung func tion. Measurements are routinely done under chloral hydrate sedation, and a possible influence of sleep stages on these measurements has not been eval uated so far. We combined the assessment of passive respiratory mechanics w ith sleep stage monitoring in 44 infants and toddlers with mild to moderate ly severe bronchiolitis. In 31 infants, only nonrapid eye movement (NREM) s leep was recorded. In 13 patients who showed both NREM and rapid eye moveme nt (REM) sleep, compliance of the respiratory system was significantly lowe r during REM than NREM sleep (73.2 +/- 19.7 vs. 81.2 +/- 21.3 mL/kPa, P = 0 .0007), while resistance remained essentially unchanged. This finding was e xplained by an unchanged airway opening pressure in combination with a sign ificantly decreased extrapolated volume. As tidal volume did not change fro m NREM to REM, this indicates reduced dynamic elevation of lung volume duri ng REM sleep and thus supports previous observations of decreased lung volu me in this sleep stage. From a practical perspective, these findings argue for the monitoring of sleep stage during measurements of passive respirator y mechanics. thereby increasing the complexity of these measurements signif icantly. (C) 1999 Wiley-Liss, Inc.