Intermittent hypoxia exposure at sea level improves functional capacity (6MWT) at high altitude

Abstract

Our primary objective is to observe whether acclimatisation is elicited by the intermittent hypoxic exposure (IHE) protocol. For this, we have utilised performance in a 6-min walk test (6MWT) as a tool to assess physiological responses to high altitude (HA) both in control and IHE-exposed groups, respectively. The study was a prospective cohort study conducted on Indian army volunteers (n = 57) and they were divided into two groups, a control group (CG) and an experimental group (EG). At the sea level, a baseline study was carried out on barometric pressure. IHE was performed at sea level in the normobaric hypoxia chamber (low fraction of inspired oxygen [FiO2], at normal barometric pressure, 740 mmHg), in which the FiO2 of the chamber was artificially decreased using O2-filtering membranes. The oxygen percentage was constantly maintained at 12%-13%. After recording the baseline, the subjects were exposed to a normobaric hypoxia chamber at 12%-13% FiO2 (altitude – equivalent to 4350 m Approx). Heart rate and blood pressure (BP) were recorded with a battery-operated portable BP monitor (OMRON) at both locations. A finger pulse oximeter probe was set on the right index finger to measure the resting oxygen saturation (SpO2) level (Model MU 300). Incidence of acute mountain sickness (AMS) was scored with the help of the standard Lake Louise questionnaire (LLS). Total LLS scores more than >3 (range 0–15) were considered AMS. EG individuals that went through IHE performed better at 6MWT at Stage I (P = 0.03). EG also had better SpO2, levels as compared to CG (P = 0.00) at Stage II (P = 0.03). Furthermore, there was a significant difference in the Borg’s Scale between CG and EG. The Delta SpO2 of EG was better as compared to CG in all stages, albeit not significant (P = 0.07). There was a significant difference between IHE and CG groups, and CG was at an increased risk for lower SpO2 (8.00 [1.21–52.60], P = 0.03). The findings elucidate the benefits of IHE in rapid acclimatisation, and it contributed to better distance covered as shown by 6MWT as well and reduces hypoxic incidents in HA.