PROGRESSIVE CHANGES IN AIRWAY-RESISTANCE DURING SLEEP

Ventilation (V) decreases during sleep while upper airway resistance ( UAR) increases. A number of studies have suggested that. in normal hea lthy individuals tile changes in the two variables are reciprocal. Oth er findings, however, suggest that the relationship between ii and UAR may change as non-rapid-eye-movement (NREM) sleep progresses such tha t most of the change in ii occurs early during the sleep period, where as the most marked changes in UAR occur later during established NREM sleep. However, no study has examined the progressive development of c hanges in both V and UAR over the NREM sleep period. This study examin ed V and UAR over one NREM sleep period in two groups of healthy young male subjects: a ''slow-wave sleep (SWS) group'' (n = 8) in which the subjects obtained the full range of NREM sleep stages from wakefulnes s to stage 4 NREM sleep and a ''no-SWS group'' (n = 5) in which the su bjects did not attain SWS but spent a prolonged period in stage 2 NREM sleep that was repeatedly interrupted by arousals. Results showed tha t the most marked changes in ii occurred Early during the sleep period in association with relatively small increases in UAR. Once NREM slee p became established, further attenuation of V was minimal despite mar ked and progressive increases in UAR. The progressive increase in UAR occurred in association with increasing delta (0.4- to 3.0-Hz) electro encephalographic activity and did not occur in the no-SWS group. We in terpret these findings to indicate that factors in addition to UAR con tribute to the reduction in V early in sleep onset, whereas later, dur ing NREM sleep, compensatory mechanisms are activated to allow for mai ntenance of V in the context of larger increases in UAR.