Systolic Blood Pressure and Acute High Altitude Exposure: Which Relationship?

Abstract

INTRODUCTION

Exposure to high altitude (HA) is associated with hypobaric hypoxia, a physiological condition that may induce significant cardiovascular adaptations, including changes in systolic blood pressure (SBP). Although several studies have investigated the effect of acute HA exposure on SBP, their findings remain heterogeneous, and the magnitude of SBP changes appears to vary across different settings and populations. In particular, the shape of the relationship between altitude and SBP have not yet been clearly established.

AIM

The primary aim of this meta-analysis was to investigate the relationship between altitude levels and the SBP changes.

METHODS

We searched PubMed, Embase, and the Cochrane Library to identify studies published up to February 28, 2025, using the search terms “(altitude OR hypoxia) AND blood pressure AND humans”. We included studies enrolling adults (>18 years) permanently living below 1000 m above sea level (lowlanders), who were assessed both at sea level and during acute exposure to high altitude (>2500 m above sea level). Eligible studies reported conventional SBP as a continuous outcome before and during high-altitude exposure (or the corresponding mean difference) and provided a measure of variability for the SBP values. To investigate the relationship between SBP changes (related to sea level) and altitude, we applied the one-stage dose–response meta-analysis proposed by Orsini and Crippa, restricted to studies including at least two different high-altitude exposure levels. We additionally explored the altitude–SBP relationship using a more flexible multilevel mixed-effects meta-regression model, including all available SBP measurements. Within both approaches, we evaluated linear and restricted cubic splines and compared their goodness of fit using the Akaike Information Criterion (AIC).

RESULTS

We included 10 studies that reported SBP measurements at two or more high-altitude levels, whereas 31 reported a single SBP measurement during high-altitude exposure. In the dose–response meta-analysis, the restricted cubic spline model with knots at the 5th, 50th, and 95th percentiles appeared to fit the available data slightly better than the alternative models (AIC = 461.62), suggesting a non-linear relationship between altitude and SBP, with larger SBP increases observed at higher altitude levels. Consistent findings were observed in the multilevel mixed-effects meta-regression, where the same spline specification achieved the lowest AIC (512.39) and showed a similar pattern of progressively larger SBP increases with increasing altitude.

CONCLUSIONS

Our preliminary analyses suggest a possible non-linear relationship between altitude and SBP, with a tendency toward greater SBP increases at higher altitudes. Although both modelling approaches showed broadly consistent results, the existence and location of a potential threshold point remain uncertain. The clinical relevance of these BP increases, particularly in individuals at high cardiovascular risk, remains to be established.