Sympathetic arousals during sleep - observations in a cohort of healthy subjects

In peripheral arterial tonometry (PAT) based sleep assessment sympathetic activations can be calculated in addition to respiratory events. However, they do not necessarily represent a respiratory or other pathologic events. The primary aim of this study is to investigate these events in a sleep healthy population and to identify the physiological variation of these events and possible influencing factors.

70 healthy subjects were evaluated. A variety of indices of sympathetic arousal were calculated over a period of six nights using PAT as a diagnostic modality. The present study centered on the pRDI, the PAT activation index (PAI), and various sub-calculations of the PAI, which detects events that follow a specific pattern in the case of increased sympathetic activity. The cohort was divided into two age groups. A mixed model linear regression and a repeated-measures analysis of variance (ANOVA) were implemented to assess the intra- and interindividual variability as well as as the influence of gender, age, day of testing and selected life style parameters.

All indexes of sympathetic activations were found to undergo relevant intraindividual variations in a multi-night-testing. In some subjects the indexes reached values above 100 events/h. Female study participants had a 2.5-fold lower pRDI and also the age of the participants influenced the sympathetic parameters. Day, previous illness, alcohol consumption, or daytime sleep had no effect on the frequency of sympathetic activations.

This study was the first to describe the distribution of sympathetic activations in peripheral arterial tone in a sleep-healthy population. The measures of sympathetic activations were largely stable between individuals. However, there were relevant intraindividual fluctuations in the multi-night measurement. A statistically significant influence of gender and age was found. The presented data could be a possibility to better understand and further investigate sympathetic activations during sleep.