Abstract: Objective To investigate the changes of heart rate variability (HRV) in Tibet patients with high altitude pulmonary hypertension (HAPH) . Methods From November 2018 to March 2019, 120 patients with HAPH in the cardiac care unit of the People's Hospital of Tibet Autonomous Region were selected as observation groups, and 50 patients without organic heart disease served as control groups. Pulmonary artery systolic pressure (PASP) was evaluated by Doppler ehocardiography in patients with PAH, according to which PAH is divided into three groups: mild group PASP: 30 ~ 49 mm Hg (1mmHg = 0.133 kPa); moderate group PASP: 50 ~ 69 mmHg Severity group PASP: ≥70mmHg. A 24-h dynamic electrocardiogram was performed on each group of patients.Heart rate variability index [Time domain : standard deviation of normal RR intervals (SDNN), standard deviation of 5 minutes average normal RR intervals (SDANN) , root mean square of sueeessive difference in RR interval (RMSSD), percentage of RR intervals differing more than 50ms from the preeding one (PNN50), HRVTI is also called triangle index; frequency domain: total power (TP), very low frequency (VLF: 0.03-0.04 Hz), low frequency (LF: 0.04-0.15 Hz) and high frequency (HF: 0.15-0.40 Hz) were measured and compared. Results Compared with the control group, the 24-hour long-range analysis time domain indicators SDNN, SDANN, RMSSD, PNN50, and HRVTI were significantly reduced (P<0.01). Short-term analysis of frequency domain indicators included in total frequency domain (TP), very low frequency (VLF), low frequency (LF), and high frequency (HF). These all showed a significant reduction (P<0.01) . However, LF/HF was the highest in the mild pulmonary hypertension group and the lowest in the moderate pulmonary arterial pressure group, and the difference between the groups was statistically significant. Conclusions The heart rate variability of patients with chronic high altitude pulmonary hypertension in high altitude areas in Tibet is significantly reduced relative to healthy controls. It is significantly negatively correlated with the severity of pulmonary artery pressure.

Key words: high altitude, high altitude pulmonary hypertension, autonomic nervous system, heart rate variability