Effects of environment light during sleep on autonomic functions of heart rate and breathing

Abstract

Purpose

Poor sleep hygiene including sleeping in the daytime or with the lights on at night is discovered during the assessment of many sleep disorders including sleep apnea. The aim of this study was to investigate whether environmental light affected autonomic control of heart rate, sleep-disordered breathing (SDB), and/or breathing patterning.

Methods

Seventeen non-obese healthy volunteers without witnessed snoring and apneas were recruited. Studies were performed at home using a type 3 portable monitor combined with actigraphy for sleep-wake timing, using a randomly assigned, crossover between dark, or 1,000 lx of fluorescent lighting environment. The outcomes were low-frequency power divided by high-frequency power (LF/HF ratio) in the analysis of heart rate variability, the apnea-hypopnea index (AHI), and ventilatory pattern variability before and after sleep onset between environments.

Results

The LF/HF ratio and AHI were both significantly higher in light as compared to dark. Before sleep onset, the coefficient of variation (CV) for breath-to-breath tidal volume representing breathing irregularity tended to be higher in light than in dark environment. The CV values for tidal volume after sleep onset were significantly decreased compared with before sleep onset in both sleep environments. Mutual information of the ventilatory pattern was significantly lower before sleep onset than after sleep onset, only in the light environment.

Conclusions

Sleeping in the light has effects like that of a stressor as it is associated with neuroexcitation, SDB, and resting breathing irregularity in healthy volunteers. These findings may be relevant to many sleep disorders associated with poor sleep hygiene.

Appendix

Mutual information

Mutual Information (MI) is a measure of the statistical dependence between two time series, or two collections of points from a data set, that can arise from both linear and nonlinear sources [Shannon, C.E. and Weaver, W. (1949). The mathematical theory of communication. University of Illinois Press, Urbana, Illinois.]. The Mutual Information between a given time series x(t) and its time-shifted version x(t + τ) is computed from the joint probability distribution of x(t) and x(t + τ) where τ represents a time lag. The joint probability distribution is defined as P[x(t), x(t + τ)] where P[x(t)] and P[x(t + τ)] are the marginal distributions of the original and time-shifted time series, respectively. The mutual information (MI) can be computed as follows:

$$ MI\left[x(t),x\left(t+\tau \right)\right]={\displaystyle \sum_i{\displaystyle \sum_jP\left[{x}_i(t),{x}_j\left(t+\tau \right)\right] \log}\left[\frac{P\left[{x}_i(t),{x}_j\left(t+\tau \right)\right]}{P\left[{x}_i(t)\right]\cdot P\left[{x}_j\left(t+\tau \right)\right]}\right]} $$

Because the breathing pattern over long time periods is strongly periodic, we computed MI for τ values from one sample (adjacent points separated by 100 ms) to 1 cycle length. MI tends to decrease quickly as τ is increased from a lag of one and then becomes more uniform at higher time lags, and the average MI of a given epoch was quantified excluding small lags as defined by the first minimum of the MI function.