Effect of fast ascent, acclimatization and re-exposure to 5050m on cerebral autoregulation in lowlanders. A prospective cohort study

Abstract

<b>Background:</b> Cerebrovascular autoregulation (CA) is essential for brain function in high altitude (HA) workers exposed to hypoxia. Effects of acute, continued and repeated HA exposure on CA are unknown. <b>Methods:</b> 18 healthy lowlanders (11 women), age 24±4y, were studied at 520m and during 2 HA sojourns of 7d each, separated by 7d recovery at 520 m, similar to real-life work shifts. During HA sojourns, participants stayed 4-8h/d at 5050m and slept at 2900m. Cerebral autoregulation was assessed by transcranial Doppler ultrasound of the middle cerebral artery and continuous blood pressure monitoring by finger photoplethysmography. The cerebral autoregulation index (ARI) was computed as: relative change in peak blood flow velocity (ΔMCAv, %)/change in mean blood pressure (ΔMAP, %) in response to standing up from sitting. Higher ARI indicate more impaired CA. <b>Results:</b> At 520m, mean(95%CI) ΔMCAv was -13%(-19 to -7), ΔMAP -26%(-41 to -10); mean±SE ARI was 0.58±0.63Δ%/Δ%. On Day1 at 5050m, ARI rose to 3.29±0.70Δ%/Δ%, but fell back with 5d acclimatization to 1.44±0.65Δ%/Δ%, P&lt;0.05 both changes. ARI increased less with re-exposure to 5050m, Day1, i.e., 1.22±0.70Δ%/Δ%, P&lt;0.05 vs. Day1, 1st ascent. <b>Conclusions:</b> Acute HA exposure impairs CA, but CA improves within a few days of acclimatization. Repeated exposure to HA after low-altitude recovery promotes a mitigated ARI response suggesting some retention of acclimatization. The findings are relevant for designing HA work schedules.