Objective: Validated automated oscillometric sphygmomanometers have been recommended by clinical guidelines to replace mercury sphygmomanometers. No studies have been conducted to evaluate whether these validated devices designed for use at normal altitude are also suitable at high altitudes.
Methods: In Dangxiong County in Tibet, 4300 m above sea level, two trained cardiologists used standardized protocols to measure the blood pressure (BP) of 129 adults aged between 19 and 69 years three times in a quiet room. The electronic sphygmomanometer was connected to the mercury sphygmomanometer by a 'Y,' or a three-way air-control valve, and the electronic device providing the pressure. This allowed simultaneous and blinded BP measurements with both instruments.
Results: The mean systolic BP measured by the electronic sphygmomanometer (124.67 ± 20.39 mmHg) was significantly higher than the BP reported by the mercury device (118.91 ± 20.56 mmHg; P < 0.001), whereas the diastolic BP measured by electronic (76.54 ± 12.63 mmHg) and mercury (76.95 ± 13.86 mmHg) sphygmomanometers showed no significant difference (P = 0.228). There was a strong linear relationship between readings from the two instruments, with correlation coefficients for systolic and diastolic BP of 0.97 and 0.96, respectively. Bland-Altman plots showed a general consistency between the two instruments for both systolic and diastolic BP. The systolic BP values, calibrated by subtracting the mean difference, were not inferior to those obtained from linear regression equations.
Conclusion: This first explorative study conducted at a high altitude demonstrated that the electronic sphygmomanometer can provide an accurate direct measurement of diastolic BP; however, a simple calibration is required for systolic BP.