The Effects of Obstructive Sleep Apnea on Autonomic Function during Steady-State Exercise

Abstract

Obstructive sleep apnea (OSA) is a disorder that significantly disrupts autonomic function, and is a mechanism for an increased risk for hypertension and cardiovascular disease seen with OSA. Heart rate variability (HRV) is an easy, non-invasive way to assess autonomic function. To date, diminished HRV has been shown at rest in OSA but not during steady-state exercise. PURPOSE: To assess HRV at rest and during submaximal exercise in OSA patients versus a non-OSA control group. METHODS: Subjects were classified as OSA (n=10) or non-OSA (n=16) based on results from an at-home sleep assessment. Measures of body composition, physical activity, and HRV were recorded at rest in each subject. Subjects completed a 5 minute walking trial at light intensity (35% of predicted VO2 Reserve) and at vigorous intensity (70%). Heart rate, blood pressure, time-domain and frequency-domain HRV variables were collected. Time-domain measures include the standard deviation of all NN or RR intervals (SDNN) and the square root of the mean of the sum of squares of differences between adjacent NN intervals (RMSSD). SDNN represents a general picture of HRV. Frequency-domain measures include total power, low frequency (LF), high frequency (HF), and the LF-HF ratio. Total power is the variance of NN intervals over the time period analyzed. LF represents parasympathetic and sympathetic activity; HF represents parasympathetic activity. The LF-HF ratio is the relationship between low and high frequency activity. HRV variables not normally distributed were log transformed before statistical analysis. RESULTS: Physical activity and body composition did not differ between groups. At rest, the OSA group had lower SDNN (OSA: 1.57 ± 0.31, CON: 1.85 ± 0.29; P = 0.027), RMSSD (OSA: 1.37 ± 0.27, CON: 1.78 ± 0.37; P = 0.006), and Total Power (OSA: 3.26 ± 0.65, CON: 3.79 ± 0.57; P = 0.041). A lower LF-HF ratio was found in the OSA group compared to the control group during exercise (Light = OSA: 2.25 ± 0.44, CON: 2.51 ± 0.45; Vigorous = OSA: 2.03 ± 0.45, CON: 2.34 ± 0.39; P = 0.048). CONCLUSION: A unique finding of this study was evidence for a lack of parasympathetic withdrawal during exercise in the OSA group. OSA may lead to altered autonomic function during steady-state exercise due to sympathetic dominance and a blunted parasympathetic response.