Clinical Science (2008) 114, 243–249 (Printed in Great Britain) doi:10.1042/CS20070172 243 Continuous positive airway pressure increases heart rate variability in heart failure patients with obstructive sleep apnoea Matthew P. GILMAN * , John S. FLORAS * †, Kengo USUI * ‡, Yasuyuki KANEKO * ‡, Richard S. T. LEUNG * ‡§ and T. Douglas BRADLEY * †‡§ ∗ Sleep and Cardiovascular Physiology Research Laboratories, Mount Sinai Hospital, Toronto, ON, Canada, M5G 1X5, †Toronto General Hospital/University Health Network, Toronto, ON, Canada, M5G 2C4, ‡Toronto Rehabilitation Institute, Toronto, ON, Canada, M5R 1Y8, and §Centre for Sleep Medicine and Circadian Biology, University of Toronto, Toronto, ON, Canada, M5G 2C4 A B S T R A C T Patients with heart failure or OSA (obstructive sleep apnoea) have reduced HF-HRV (high- frequency heart rate variability), indicating reduced cardiac vagal modulation, a marker of poor prognosis. CPAP (continuous positive airway pressure) abolishes OSA in patients with heart failure, but effects on daytime HF-HRV have not been determined. We hypothesized that, in patients with heart failure, treatment of coexisting OSA by CPAP would increase morning HF-HRV. In 19 patients with heart failure (left ventricular ejection fraction < 45 %) and OSA ( 20 apnoeas and hypopnoeas/h of sleep), HF-HRV was quantified before and 1 month after randomization to a control or CPAP-treated group. In the control group (n = 7), there were no changes in HF-HRV over the 1 month study during wakefulness in the morning. In the CPAP-treated group (n = 12) HF-HRV increased significantly during wakefulness in the morning [from 2.43 + − 0.55 to 2.82 + − 0.50 log(ms 2 /Hz); P = 0.002] due to an increase in transfer function between changes in lung volume and changes in HF-HRV (92.37 + − 96.03 to 219.07 + − 177.14 ms/l; P = 0.01). In conclusion, treatment of coexisting OSA by nocturnal CPAP in patients with heart failure increases HF-HRV during morning wakefulness, indicating improved vagal modulation of heart rate. This may contribute to improved prognosis. INTRODUCTION Heart failure affects over 4 million North Americans, and its prevalence is continuing to increase [1] with an annual incidence of half a million [2]. Despite advances in medical therapy, morbidity and mortality remain high. Accordingly, it is important to identify and treat conditions that may contribute to the progression of heart failure. In the last two decades, a growing body of evidence indicates that one such condition may be OSA (obstructive sleep apnoea). Not only does OSA frequently coexist with heart failure [3], but it appears to contribute to a higher mortality rate [4], possibly due to adverse effects on haemodynamics and autonomic cardiovascular regulation [5,6]. The transition from wakefulness to normal sleep is accompanied by increases in cardiac vagal activity and reductions in sympathetic tone [7,8]. However, Key words: continuous positive airway pressure (CPAP), heart failure, heart rate variability (HRV), obstructive sleep apnoea (OSA), vagal modulation. Abbreviations: AHI, apnoea/hypopnoea index; BMI, body mass index; BP, blood pressure; CPAP, continuous positive airway pressure; HF, high frequency; HR, heart rate; HRV, HR variability; LF, low frequency; LV, left ventricular; LVEF, LV ejection fraction; NYHA, New York Heart Association; OSA, obstructive sleep apnoea; Sao 2 , arterial oxygen saturation; VPB, ventricular premature beat. Correspondence: Dr T. Douglas Bradley (email douglas.bradley@utoronto.ca). C  The Authors Journal compilation C  2008 Biochemical Society