The effect of clustered versus regular sleep fragmentation on daytime function

Previously, we found that regular sleep fragmentation, similar to that foun d in patients with sleep apnoea/hypopnoea syndrome (SAHS), impairs daytime function. Apnoeas and hypopnoeas occur in groups in patients with REM or po sture related SAHS. Thus, we hypothesised that clustered sleep fragmentatio n would have a similar impact on daytime function as regular sleep fragment ation. We studied 16 subjects over two pairs of 2 nights and 2 days. The fi rst night of each pair was for acclimatisation. On the second night, subjec ts either had their sleep fragmented regularly every 90 s, or fragmented ev ery 30 s for 30 min every 90 min, the remaining 60 min being undisturbed. W e fragmented sleep with tones to produce a minimum 3 s increase in EEG freq uency. During the days following each pair of nights we tested subjects day time function. Total sleep time (TST) and microarousal frequency were simil ar on both study nights. We found significantly less stage 2 (55 SD 4, 62 /- 7%; P = 0.001) and more slow wave sleep (21 SD 3, 12 +/- 6%; P < 0.001) on the clustered night. Mean sleep onset latency was similar on MSLT (clust ered 10 SD 5, regular 9 +/- 4 min; P = 0.7) and MWT (clustered 32 SD 7, reg ular 30 +/- 7 min; P = 0.2). There was no difference in subjects mood or co gnitive function after either study night. These results suggest that altho ugh there is more slow wave sleep (SWS) on the clustered night, similar num bers of sleep fragmenting events produced similar daytime function whether the events were evenly spaced or clustered.