# Sleep Posture and Autonomic Nervous System Activity Across Age and Sex in a Clinical Cohort: Analysis of a Nationwide Ambulatory ECG Database

## TL;DR

This study shows that sleep posture affects heart rate variability, a measure of autonomic nervous system activity, and these effects vary by age and sex.

## Contribution

The study identifies sleep posture as a significant and independent factor influencing autonomic nervous system activity during sleep.

## Key findings

- Heart rate was consistently lowest in left lateral posture and highest in right lateral posture across most age groups.
- Posture-specific heart rate variability indices showed consistent differences between left and right lateral postures.
- Sleep posture patterns varied with age and sex in a large clinical cohort.

## Abstract

What are the main findings?
Sleep posture patterns varied with age and sex in a large clinical cohort of over 130,000 individuals undergoing 24-h Holter ECG monitoring.Posture-specific heart rate variability (HRV) indices, including HR, SDRR, HF, LF, VLF, CVHR, and Hsi, showed consistent differences between left and right lateral postures across age and sex groups.

Sleep posture patterns varied with age and sex in a large clinical cohort of over 130,000 individuals undergoing 24-h Holter ECG monitoring.

Posture-specific heart rate variability (HRV) indices, including HR, SDRR, HF, LF, VLF, CVHR, and Hsi, showed consistent differences between left and right lateral postures across age and sex groups.

What is the implication of the main finding?
Sleep posture is a significant and independent factor influencing autonomic nervous system activity and should be considered when interpreting HRV, particularly in clinical populations.Incorporating posture-specific HRV analysis may enhance the physiological relevance and clinical utility of wearable ECG-based sleep monitoring.

Sleep posture is a significant and independent factor influencing autonomic nervous system activity and should be considered when interpreting HRV, particularly in clinical populations.

Incorporating posture-specific HRV analysis may enhance the physiological relevance and clinical utility of wearable ECG-based sleep monitoring.

Sleep posture has received limited attention in studies of autonomic nervous system (ANS) activity during sleep, particularly in clinical populations. We analyzed data from 130,885 individuals (56.1% female) in the Allostatic State Mapping by Ambulatory ECG Repository (ALLSTAR), a nationwide Japanese database of 24 h Holter ECG recordings obtained for clinical purposes. Sleep posture was classified as supine, right lateral, left lateral, or prone using triaxial accelerometer data. Heart rate variability (HRV) indices—including heart rate (HR), standard deviation of RR intervals (SDRR), high-frequency (HF), low-frequency (LF), very low-frequency (VLF) components, cyclic variation in heart rate (CVHR), and HF spectral power concentration index (Hsi)—were calculated for each posture and stratified by age and sex. HR was consistently lowest in the left lateral posture and highest in the right lateral posture across most age groups. Other HRV indices also showed consistent laterality, although the effect sizes were generally small. Posture distribution differed slightly by estimated sleep apnea severity, but the effect size was negligible (η2 = 0.0013). These findings highlight sleep posture as a statistically significant and independent factor influencing ANS activity during sleep, though the magnitude of differences should be interpreted in the context of their clinical relevance.