Heart Rate Variability Analysis in Obstructive Sleep Apnoea Patients with Daytime Sleepiness.

STUDY OBJECTIVES: Recent studies suggest sleepy patients with OSA are at higher risk for incident cardiovascular disease. This study assessed cardiac autonomic function in sleepy versus non-sleepy patients with obstructive sleep apnoea (OSA) using heart rate variability (HRV) analysis. We hypothesised that HRV profiles of sleepy patients would indicate higher cardiovascular risk.

METHODS: Electrocardiograms (ECG) derived from polysomnograms (PSG) collected by the Sydney Sleep Biobank were used to study HRV in groups of sleepy (ESS≥10) and non-sleepy OSA patients (ESS<10). HRV parameters were averaged across available ECG signal during N2 sleep.

RESULTS: A total of 421 patients were evaluated, with mean age of 54 (14) years, body mass index (BMI) of 33 (9) kg/m2, apnoea hypopnoea index (AHI) of 21 (28) events/h and, 66% male. The sleepy group consisted of 119 patients, and the non-sleepy group 302 patients. Sleepy patients exhibited lower HRV values for: root mean square successive difference (RMSSD, p= 0.028); total power (TP, p= 0.031); absolute low frequency (LF, p= 0.045); and high frequency (HF, p= 0.010) power compared to Non-Sleepy patients. Sleepy patients with moderate to severe OSA exhibited lower HRV values for: (RMSSD, p= 0.045; TP, p= 0.052) ; absolute LF (p= 0.051); and HF power (p= 0.025). There were no differences in other time and frequency domain HRV markers.

CONCLUSIONS: This study shows a trend towards parasympathetic withdrawal in sleepy OSA patients, particularly in moderate to severe cases, lending mechanistic support to the link between the sleepy phenotype and CVD risk in OSA.