Pulmonary artery pressure and arterial oxygen saturation in people living at high or low altitude: systematic review and meta-analysis

More than 140 million people are living at high altitude worldwide. An increase of pulmonary artery pressure (PAP) is a hallmark of high-altitude exposure and, if pronounced, may be associated with important morbidity and mortality. Surprisingly, there is little information on the usual PAP in high-altitude populations. We, therefore, conducted a systematic review (MEDLINE and EMBASE) and meta-analysis of studies published (in English or Spanish) between 2000 and 2015 on echocardiographic estimations of PAP and measurements of arterial oxygen saturation in apparently healthy participants from general populations of high-altitude dwellers (>2,500 m). For comparison, we similarly analyzed data published on these variables during the same period for populations living at low altitude. Twelve high-altitude studies comprising 834 participants and 18 low-altitude studies (710 participants) fulfilled the inclusion criteria. All but one high-altitude studies were performed between 3,600 and 4,350 m. The combined mean systolic PAP (right ventricular-to-right atrial pressure gradient) at high altitude [25.3 mmHg, 95% confidence interval (CI) 24.0, 26.7], as expected was significantly (P < 0.001) higher than at low altitude (18.4 mmHg, 95% CI 17.1,19.7), and arterial oxygen saturation was significantly lower (90.4%, 95% CI 89.3, 91.5) than at low altitude (98.1%; 95% CI 97.7, 98.4). These findings indicate that at an altitude where the very large majority of high-altitude populations are living, pulmonary hypertension appears to be rare. The reference values and distributions for PAP and arterial oxygen saturation in apparently healthy high-altitude dwellers provided by this meta-analysis will be useful to future studies on the adjustments to high altitude in humans.