Abstract
OBJECTIVES: Individuals in high-altitude areas (HAs) have a relatively high prevalence of hypertension. However, only a few studies have reported the out-of-office blood pressure (BP) at HAs. This study aimed to evaluate the differences in ambulatory BP parameters between untreated hypertensives at high and low altitudes and explore the influencing factors. DESIGN: This was a cross-sectional, case-control study. SETTING: Participants were recruited from 15 hospitals in Tibetan HAs and low altitudes in Sichuan Province, Southwest China. PARTICIPANTS: A total of 755 participants were eligible prior to matching, among whom 209 untreated hypertensive patients in each group were matched using 1:1 propensity score matching, with low altitudes/HAs as grouping variables (55.71±10.79 years, 55.7% male). PRIMARY AND SECONDARY OUTCOME MEASURES: The differences in ambulatory BP parameters between untreated hypertensives at high and low altitudes, and the influencing factors. RESULTS: Compared with patients at low altitudes, multivariate linear regression analysis revealed that the 24-hour and night-time diastolic BP (DBP) of patients at HAs increased by 2.16 mm Hg (95% CI 0.12 to 4.19), p=0.04, and 2.89 mm Hg (95% CI 0.49 to 5.30), p=0.02, respectively; the 24-hour and night-time DBP loads increased by 6.40% (95% CI 2.38% to 10.42%), p=0.002 and 4.14% (95% CI 0.23% to 8.05%), p=0.04, respectively. Mediation effect analysis revealed that 22% (95% CI 5.00% to 81.00%), p=0.01 of the increase in night-time DBP was mediated by night-time pulse rate (PR). However, the mediating effect of haemoglobin was relatively weak (5%, p=0.73). CONCLUSION: Compared with patients at low altitudes, with no difference in the risk of 10-year Framingham cardiovascular disease, the night-time DBP of hypertensive patients in HAs was significantly greater, which was mediated through an increased night-time PR. This difference may be related to the increased nocturnal sympathetic excitability in hypertensives at HAs. TRIAL REGISTRATION NUMBER: ChiCTR2200059719.