Repeated remote ischaemic preconditioning can prevent acute mountain sickness after rapid ascent to a high altitude

Abstract

ABSTRACT Background This study assessed the effectiveness of 4 different repeated remote ischaemic preconditioning (RIPC) protocols varying in duration and frequency for preventing acute mountain sickness (AMS) after rapid ascent to high altitude. Methods In a randomized but not blinded design, participants were assigned to receive either of the four RIPC treatments at low altitude (Group A, once daily for 1 week; Group B, twice daily for 1 week; Group C, once daily for 4 weeks; and Group D, twice daily for 4 weeks) or control (no specific sham treatment). Participants were then flown to a high altitude (3650 m). The primary outcome was the incidence and severity of AMS evaluated by the Lake Louise score (LLS) after arrival; vital signs were collected simultaneously. Results A total of 250 participants (50 per group; mean age 38.56 ± 0.76 years) were included. The overall AMS incidence was 26.4%. A total of 20 AMS cases (40%) occurred in the control group, 15 cases (30%) both in the RIPC A and RIPC B groups (RR 1.3; 95%CI 0.8-2.3; χ2 = 1.099; p = 0.29), and 8 cases (16%) both in the RIPC C and D groups (RR 2.5; 95%CI 1.2 - 5.2; χ2 = 7.143, p < 0.01), with significantly lower LLSs in the RIPC C and D groups (F = 6.51, p < 0.001). The scores of gastrointestinal symptoms (F = 7.42, p < 0.001) and dizziness (F = 9.82, p < 0.001) but not headache (F = 0.60, p > 0.05) were lower in the RIPC groups compared to control. The blood oxygen saturation level (SpO2) decreased less in the RIPC B, C and D groups compared to control after arrival at a high altitude (F = 11.42, p < 0.001). The number of RIPC treatments received was moderately correlated with SpO2 (R = 0.38, p < 0.001), and SpO2 was moderately inversely correlated with the LLS (R = –0.48, p < 0.001). Conclusion This study demonstrated that a four-week RIPC intervention but not a one-week regimen reduced AMS incidence and severity; however, a placebo effect might have contributed to these results.