Validation of Air Storage System for Hypoxia Exposure During Exercise

Norberto, Matheus S., João Victor G. Torini, Matheus S. Firmino, and Marcelo Papoti. Validation of air storage system for hypoxia exposure during exercise. High Alt Med Biol. 00:000-000, 2024.-Considering the importance of optimizing normobaric hypoxia exposure (i.e., higher delivery capacity), the current study aims to validate a hypoxic air storage system. The study has a cross-over, one-blind randomized design. The air storage is composed of a piping system that directs hypoxic air from a hypoxia generator into nylon bags. Sixteen men (age, 25.4 ± 4.8 years; height, 174.9 ± 9.4 cm; weight, 77.1 ± 17.2 kg) performed three incremental treadmill tests until exhaustion on different days. For test-retest, the subjects repeated two tests in similar hypoxia conditions (H1 and H2; fraction of inspired O₂ [F_IO₂] = ∼0.13; reliability analysis), and one time in normoxia (F_IO₂ = ∼0.20; condition comparison). Subjects' performance, blood lactate concentration ([La^-]), arterial oxygen saturation (SpO₂), oxygen consumption (VO₂), heart rate (HR), and several respiratory-derived variables were evaluated. A comparison was made between the rest, moderate intensity, and exhaustion stages. All variables were compared using the Friedman test with Durbin-Conover post hoc (p < 0.05). The hypoxia test-retest showed no statistical differences for any variable. Time analysis showed similar behavior for SpO₂, HR, and cardiorespiratory variables (p < 0.01) for both conditions. The mean F_IO₂ at rest and during the incremental treadmill test was higher for normoxia (20.6 ± 0.2%) than for H1 (13.8 ± 0.8%) and H2 (13.7 ± 0.3%) (p < 0.001). The VO₂ response was higher in normoxia than during hypoxia exposure at moderate intensity (Normoxia = 43.1 ± 8.1; H1 = 38.7 ± 5.7; H2 = 35.8 ± 8.8 ml.kg^-1.min^-1) and at the exhaustion stage (Normoxia = 52.7 ± 12.5; H1 = 41.9 ± 8.8; H2 = 40.5 ± 8.9 ml.kg^-1.min^-1) (p < 0.01). SpO₂ and HR showed excellent intraclass correlation coefficient (ICC) during all moments, whereas VO₂, SpO₂, ratio between ventilation and CO₂ production (V_E/V_CO2), ratio between oxygen consumption and ventilation (V_E/V_O2), and HR showed moderate or good ICC and coefficient of variation <9% during hypoxia test-retest exercises. Thus, the air storage system showed validity for its application and reliability in the measurements associated.