Differential effects of waking from non-rapid eye movement versus rapid eye movement sleep on cardiovascular activity.

The occurrence of cardiovascular events increases in the morning, and while the mechanism responsible is yet to be determined, possible contributors include surges in sympathetic activity and concurrent rises in blood pressure (BP). This study tested the hypothesis that the increase in sympathetic dominance and the surge in BP were greater when waking spontaneously from Stage 2 sleep compared with waking from rapid eye movement (REM) sleep. Twenty healthy young adults had overnight polysomnography, including electrocardiogram measurements. Spectral analysis of heart rate variability (HRV) was conducted on 2-min blocks of stable data selected from the last 30 min of sleep and during 30 min of resting wakefulness (supine) immediately following sleep. Outputs included absolute low frequency (LF) and high frequency (HF) power, the LF/HF ratio, heart rate (HR) and BP. To investigate the effect of waking from Stage 2 or REM sleep on HRV and BP responses, two-way analyses of variance (anovas) (Stage 2 versus REM) with repeated measures (sleep versus morning wakefulness) were performed. It was found that waking from Stage 2 sleep was associated with significant increases in HR (P = 0.002) and BP (P < 0.001), as well as a tendency towards an increase in the LF/HF ratio (P = 0.08), whereas measurements during REM sleep and subsequent wakefulness were similar (P > 0.05). The greater increase in BP and HR when waking from Stage 2 sleep compared with REM sleep suggests that in vulnerable populations, waking from Stage 2 sleep could be an adjunct risk factor of cardiovascular events during the morning period.