PETCO2 in Women at Sea‐Level and Upon Acute Exposure to a Normobaric Hypoxic Environment Simulating 3,500 m

Abstract

While prior work (Muza, J. Appl. Physiol. 91: 2001) suggests that women and men have similar responses to high altitude, no studies have attempted to develop gender specific predictive values for end‐tidal CO2 (EtCO2) in a normobaric hypoxic (NH) environment simulating acute exposure to an altitude of 3,500 m based on sea‐level (SL) EtCO2 values. As part of a larger study examining individual variability upon acute exposure to NH, EtCO2, heart rate (HR), and respiratory rate (RR) were measured in 107 subjects at sea level (SL) who, no sooner than two days later, entered a normobaric hypoxia chamber at approximating O2 partial pressures equivalent to those found at 3,500 m.METHODSParticipants in this IRB‐approved study included: 63 informed volunteer female subjects (56 Treatment [NH]: 20.5±1.5 yr.; 165.8±6.9 cm; 63.011.1 kg; 22.93.3 BMI; 7 SHAM: 20.31.1 yr; 167.56.2 cm; 57.26.2 kg; 20.46.4 BMI); 44 informed volunteer male subjects (35 Treatment [NH]: 20.31.3 yr; 178.26.8 cm; 77.414.0 kg; 24.23.2 BMI; and 9 SHAM: 20.71.0 yr; 179.87.8 cm; 73.310.0 kg; 22.73.1 BMI). All subjects were tested at SL then again 2+ days later after entering a NH (FiO2=13.55%) chamber where EtCO2, HR, and RR were measured after 30 minutes of rest.RESULTSBonferroni t‐tests revealed no difference in female or male EtCO2 between the SL and SHAM conditions while, as expected, there was a difference (P≤0.05) in EtCO2 between the SL and NH conditions in the female treatment group (37±3 vs. 36±3 mmHg) and the male treatment group (39±3 vs. 37±2 mmHg). RR and HR remained unchanged in the female and male groups in all conditions.CONCLUSIONSUsing the following algorithm, we were able to predict EtCO2 in female subjects at the P 0.001 level of confidence [Actual vs. Predictive (EtCO2 at FiO2 = 13.55%) Y = 86.394 – 0.221X1‐ 0.541X2 (Where Y = EtCO2_HYPO, X1 = RR_NH, X2 = SpO2_NH, R2 = 0.520, P<0.001] while the predictive value of the male data was not significant (R2 = 0.099, P = 0.187). Therefore, female responsiveness to acute exposure to simulated altitude may be greater than that of male peers.Support or Funding Information: The Chuo University Oversea Research Program, The Doug Morton/Marilyn Brown Endowment for Biomedical Research, The Foundation for Aging Studies and Exercise Science Research, and The Borgenicht Program