Heart rate variability in patients with pulmonary vascular disease living permanently at high altitude relocated to low altitude

<bold>Background:</bold> The aim was to investigate how a higher inspired oxygen pressure during a stay at sea level affects heart rate variability (HRV) in patients with pulmonary vascular disease (PVD) - pulmonary arterial (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH). <bold>Methods:</bold> Nocturnal HRV from 5min-segments were assessed in patients with PVD permanently living at high altitude (HA) during one night in Quito (2850 m) and during two nights at sea level (0m, Pedernales). Time domain HRV indices (RMSSD and pRR50, suppressed by parasympathetic blockade) and frequency domain HRV parameters (high frequency, HF, parasympathetic activity; and low frequency, LF, dominance of sympathetic activity) were assessed. <bold>Results:</bold> In 22 patients with PVD living at HA (86% female, age 45.4 ± 11.6 years, SpO2 at 2850 m 90.3 ± 4.6 %, pulmonary vascular resistance 16.0 ± 8.0 WU, mean pulmonary arterial pressure 55 ± 17 mmHg), travelling to sea level resulted in a significant increase in RMSSD, pRR50, LF, HF and a decrease in LF/HF ratio and heart during the night. <bold>Conclusions:</bold> Exposure to sea level resulted in a significant change in HRV in patients with PVD, indicating an increase in parasympathetic activity and shift to sympatho/vagal balance towards lower sympathetic modulation. The relative change in HRV at sea level was more pronounced during the first night.