Assessment of Effects of Carbon Dioxide Exposure on Sleep Stability in Insomnia Using the Envelope Analysis

Abstract

Objectives: Insomnia is a common sleep disorder, and various strategies have been explored for its treatment. One of the methods involves the administration of carbon dioxide (CO<sub>2</sub>) at bedtime, as the CO<sub>2</sub> increment exerts a sedative effect on the central nervous system. We aimed to assess the effect of CO<sub>2</sub> on sleep quality in patients with insomnia using the coefficient of variation of the envelope (CVE) analysis, a novel analytical method. Methods: In this randomized, double-blind, sham-controlled crossover trial, 24 adults with sleeping difficulties underwent level 1 polysomnography. Two interventions involved exposure to either 2% low-concentration CO<sub>2</sub> gas or room air. CVE analysis was performed to assess the stability of the delta band. Morphological variations in delta waves can be quantitatively monitored using the envelope analysis, which assesses the effect of manipulations on sleep that may otherwise elude detection. Results: Exposure to CO<sub>2</sub> improved the total sleep time (TST) (<i>p</i>=0.010) and total arousal index (TAI) (<i>p</i>=0.011). The CVE analysis showed a distinct distribution between the experimental and sham-controlled groups. Moreover, correlations between the TST and CVE (r=0.41) and those between the TAI and CVE (r=0.40) were observed. Conclusions: This study is the first to evaluate the effects of CO<sub>2</sub> exposure on sleep stability in patients with insomnia. The CVE analysis implies the possibility of sleep stabilization by CO<sub>2</sub> administration and suggests a link between enhanced sleep maintenance and sleep stability.