Characterisation of the acute hypoxic response using breathing variability parameters: A pilot study in humans

Abstract

Purpose: We aimed to investigate respiratory rate variability (RRV) and tidal volume (V_t) variability during exposure to normobaric hypoxia (i.e., reduction in the fraction of inspired oxygen - FiO₂), and the association of the changes in RRV and V_t variability with the changes in pulse oxygen saturation (SpO₂).

Methods: Thirty healthy human participants (15 females) were exposed to: (1) 15-min normoxia, (2) 10-min hypoxia simulating 2200 m, (3) 10-min hypoxia simulating 4000 m, (4) 10-min hypoxia simulating 5000 m, (5) 15-min recovery in normoxia. Linear regression modelling was applied with SpO₂ (dependent variable) and the changes in RRV and V_t variability (independent variables), controlling for FiO₂, age, sex, changes in heart rate (HR), changes in HR variability (HRV), and changes in minute ventilation (V_E).

Results: When modelling breathing parameter variability as root-mean-square standard deviation (RMSSD), a significant independent association of the changes in RRV with the changes in SpO₂ was found (B = -4.3e-04, 95% CI = -8.3e-04/-2.1e-05, p = 0.04). The changes in V_t variability showed no significant association with the changes in SpO₂ (B = -1.6, 95% CI = -5.5/2.4, p = 0.42). When modelling parameters variability as SD, a significant independent association of the changes in RRV with the changes in SpO₂ was found (B = -8.2e-04, 95% CI = -1.5e-03/-9.4e-05, p = 0.03). The changes in V_t variability showed no significant association with the changes in SpO₂ (B=1.4, 95% CI = -5.8/8.6, p = 0.69).

Conclusion: Higher RRV is independently associated with lower SpO₂ during acute hypoxic exposure, while V_t variability parameters are not. Therefore, RRV may be a potentially interesting parameter to characterize individual responses to acute hypoxia.

Keywords: Acute hypoxic response; Normobaric hypoxia; Respiratory variability; Tidal volume.