Background Obstructive sleep apnoea (OSA) is the most common sleep disorder and a significant risk factor for cardiovascular disease. In addition, heart rate is an important predictor of hypertension and a risk factor for cardiovascular morbidity and mortality. We hypothesised that changes of nocturnal heart rate in OSA are associated with changes in blood pressure following commencement of continuous positive airway pressure (CPAP) therapy.
Methods A total of 1848 nocturnal pulse oximetries (two consecutive nights) were screened to identify patients with OSA in a tertiary referral centre for sleep disorders. Demographics and pulse oximetry data were recorded at baseline. To assess nocturnal changes heart rate (HR) was compared between the first hour and the last hour of the night-time recording. In patients who were diagnosed with OSA, we further recorded daytime sleepiness, blood pressure, and body weight at three months and one year follow up.
Results Out of all the screened pulse oximetries, a complete dataset of 58 patients with OSA (mean 4% ODI 28.9 (3.3) h-1, 36 males, age 49.4 (1.2) years, weight 109.7 (3.6) kg) and 57 without OSA (mean 4% ODI 2.0 (0.1) h-1, 34 males, age 46.4 (1.7) years, weight 95.0 (7.0) kg P was identified. Pulse rise index, mean HR, and HR of the first and last hour of recording were higher in the OSA group (p<0.0001), whilst oxygen saturation was lower in the OSA group (p<0.0001). Reduction in nocturnal HR vs mean SpO2 (r=–0.39, p<0.01), mean nocturnal HR vs mean SpO2 (r=–0.4, p<0.01) and average HR vs systolic blood pressure (r=–0.42, p<0.05) correlated inversely (Figure).
Conclusion Nocturnal HR is higher in OSA patients than in control subjects likely because of an enhanced sympathetic activation. Changes in nocturnal HR of OSA patients established on CPAP at one year follow up predict changes in systolic but not in diastolic blood pressure or body weight.