Blood pressure effects of acute high-altitude exposure. A systematic review and a meta-analysis

Abstract

Several studies have suggested that acute exposure to high altitude (HA) and the associated hypoxia may increase blood pressure (BP). This is relevant considering the need to inform large numbers of people who travel to HA for leisure or work about the potential impact of this condition on their cardiovascular health. However, the results have not always been consistent, and it is not clear whether there is any relationship between the altitude of exposure and the magnitude of BP changes.

The aim of this study was to perform a systematic review and meta-analysis of studies addressing this issue.

Methods

Electronic databases (PubMed, EMBASE, Cochrane) were searched using the following combination of keywords: [[altitude OR hypoxia] AND blood pressure] AND humans. Studies in adult lowlanders were included if they reported BP data before and during exposure to an altitude of ≥2000 m asl for at least 24 hours and no more than 28 days. Changes in conventional or ambulatory BP between the two conditions were the main outcomes. Two reviewers conducted the assessment; any disagreements were discussed with a third investigator. The meta-analysis was stratified by altitude and duration of HA exposure. The protocol was registered in the PROSPERO registry.

Results

The initial search yielded 24,485 records. After review, 41 and 38 studies were included in the meta-analysis for conventional systolic (S) and diastolic (D) BP, respectively, and 4 studies were included for 24-hour ambulatory BP. For all these outcomes, significant (p < 0.001) increases in BP at HA were found: 6.1 mmHg [95% CI: 5.1–7.0] for conventional SBP (heterogeneity I² = 82.5%, p < 0.001), 6.0 mmHg [95% CI: 4.8–7.3] for conventional DBP (I² = 88.8%, p < 0.001); 8.5 mmHg [95% CI: 5.2–11.7] for 24-hour SBP (I² = 93.9%, p < 0.001) and 5.8 mmHg [95% CI: 3.5–8.2] for 24-hour DBP (I² = 90.9%, p < 0.001). In the analysis stratified by altitude, there was a significant interaction between altitude and BP increase for both office SBP and DBP (p < 0.001), with the largest BP increases observed at altitudes >5500 m. A U-shaped interaction with exposure duration was observed for office SBP (p = 0.038).

Conclusions

To our knowledge, this is the first meta-analysis on the effects of acute exposure to HA on BP. A significant increase in conventional and 24-hour SBP and DBP was found, with considerable heterogeneity in the magnitude of the observed increase between studies. Very high exposure altitudes were associated with a more pronounced BP increase. The clinical significance of these BP increases, especially in high-risk patients, remains to be defined.