Effects of Between- and Within-Subject Variability on Autonomic Cardiorespiratory Activity during Sleep and Their Limitations on Sleep Staging: A Multilevel Analysis

Table 7

Proportion of variance explained (PVE, %) accounted for by different effects for the six cardiorespiratory parameters analyzed in this study.

Effect	Respiratory parameters		Cardiac parameters
	BR	SDBR	HR	SDNN	LF	HF
Overall between-subject effect
Demographic effect	3.55%	1.37%	3.36%	13.69%	0.63%	3.70%
Centering (physiological) effect	55.26%	26.23%	77.95%	39.06%	28.63%	26.41%
Between-subject time effect	2.74%	2.72%	2.67%	2.00%	1.87%	1.58%
Between-subject physiological effect	5.03%	7.62%	2.27%	3.91%	3.49%	3.44%
Overall within-subject effect
Within-subject time effect	0.01%	0.37%	1.32%	0.42%	0.16%	0.14%
Within-subject physiological effect	33.39%	61.69%	12.43%	40.87%	65.04%	64.54%
Cross-interaction effect
Demographic-related time effect	0.02%	Ne	Ne	0.06%	0.18%	0.19%

Note: ln, natural logarithm; Ne, no effect. For each cardiorespiratory parameter, the sum of PVEs from all the effects is 100%, representing the total variance for that parameter. The centering effect reflected some between-subject physiological variability (at the overnight mean level) that was assumed to be independent of sleep stage composition over the entire night.