Increased Right Ventricular Cardiac Output to Left Ventricular Cardiac Output Ratio in High-Altitude Residents Without Pulmonary Hypertension: An Echocardiography Study.

Right ventricular cardiac output to left ventricular cardiac output (RVCO/LVCO) ratio in high-altitude residents had not been well characterized. The purpose of this study was to investigate the normal reference range for RVCO/LVCO ratio among high-altitude residents without pulmonary hypertension. Between October 2024 and June 2025, 88 consecutive high-altitude (?4000 meters above sea level) residents without pulmonary hypertension were enrolled in this study. RVCO/LVCO ratio was quantified by transthoracic echocardiography. The difference of RVCO/LVCO ratio between high-altitude residents and low-altitude residents were compared. High-altitude residents display significantly larger right atrium, right ventricle, and pulmonary artery dimensions than low-altitude residents, with slightly thickened right ventricular free walls but slightly smaller tricuspid annular plane systolic excursion (p<0.05). RVCO, right ventricular cardiac index, and the RVCO/LVCO ratio (1.15 [0.97-1.38] vs. 0.97 [0.91-1.05], p<0.0001) was significantly greater in high-altitude residents than in low-altitude residents, but left heart size, LVCO and left ventricular cardiac index show no significant differences between groups (p>0.05). There was a negative correlation between the RVCO/LVCO ratio and altitude (r = 0.298, p < 0.0001). The regression equation was y = 8.2083 - 0.001726x, where x represents altitude and y represents the RVCO/LVCO ratio. The increased RVCO/LVCO ratio observed in high-altitude residents without pulmonary hypertension suggests that adaptive cardiac changes may be mediated by hypoxia-driven hemodynamic compensatory adjustments. These findings make RVCO/LVCO ratio a crucial indicator for detecting plateau physiological adaptation and pathological conditions in high-altitude hypoxic environments.