Breath-by-breath respiratory timing and volume control during periodic breathing.

We examined the control of respiratory pattern during non-rapid-eye-movement sleep-related periodic breathing (PB) in adults, with and without hypoxia. We analyzed 186 cycles of PB from 18 epochs occurring in eight subjects; the mean (+/- SD) cycle duration was 30.8 +/- 8.4 s. Significant oscillations occurred in inspired tidal volume (VT), inspiratory duration (TI), mean inspired flow, inspired minute ventilation, and expiratory duration (TE) (P less than 0.005). For each epoch of PB, moving cross-correlation (MCC) functions were employed to describe the time-dependent intervariable relationships between 1) TI vs. TE, 2) VT vs. TE, and 3) VT vs. breath duration (TT) as synchronization, a strong and consistent intervariable correlation; relative coordination (RC), a weaker interaction characterized by an unstable MCC function oscillating at a subharmonic of the PB frequency; or as independence, with no statistical evidence of interaction. Fourteen epochs showed RC between TI and TE, 11 and 12 of which also showed RC between VT and TE, and VT and TT, respectively. In 4 epochs negative synchronization was exhibited by all three variable pairs. In no case were the oscillations between any pair of variables independent. The modes of coupling between variables were not correlated to O2 saturation, end-tidal CO2 levels, or inspired O2 level. We conclude that during sleep-related PB a nonrandom but weak coupling usually exists between TI and TE, VT and TE, and VT and TT.(ABSTRACT TRUNCATED AT 250 WORDS)