Daytime Ventilatory and Blood Acid–Base Responses During Ascent to 3500 m Are Larger and More Rapid in Females Than Males
Nicole V. Bushfield, Benjamin W. L. MacKenzie, Nicole A. Johnson, Rodion Isakovich, Jamie L. Keess, Nicholas D. J. Strzalkowski, Gustavo Zubieta‐Calleja, Richard J. A. Wilson, Trevor A. DayABSTRACT
With ascent to high altitude (HA), increased ventilation reduces the pressure of P a CO 2 (i.e., hypocapnia), resulting in respiratory alkalosis. A subsequent renal compensation is mediated through reductions in [HCO 3 − ] a , partly‐correcting pH a . High inter‐individual variability exists in ventilation, blood oxygenation, and acid–base responses with ascent to HA, but potential sex differences have not been well‐characterized. We recruited 38 lowland participants (20 M; 18 F) before and after rapid ascent to and residence at 3500 m over 10 days in La Paz, Bolivia. We performed radial arterial blood draws to assess blood oxygenation and acid–base variables before (1100 m), and following ascent to 3500 m both early HA (E‐HA; D2/3) and late HA (L‐HA; D9/10). With E‐HA, all participants had higher calculated V̇ A , and lower P a O 2 and S a O 2 ( p < 0.0001), with subsequent increases in A , [Hb] and C a O 2 L‐HA ( p = 0.0056; p = 0.0003; p = 0.0013). Although females had higher A and P a O 2 than males E‐HA ( p < 0.0001; p = 0.0143), males had higher [Hb] and C a O 2 at 1100 m, at both E‐HA ( p = 0.0008; p = 0.0085) and L‐HA ( p = 0.0007; p = 0.0045). E‐HA, all participants had lower P a CO 2 and [HCO 3 − ] a , and higher pH a than 1100 m ( p < 0.0001; p = 0.0004, p < 0.0001), suggesting respiratory alkalosis and partial renal compensation. L‐HA, P a CO 2 and [HCO 3 − ] a were further reduced ( p = 0.0062; p = 0.0202), with pH a only partly‐compensated ( p = 0.4306). E‐HA, P a CO 2 , [HCO 3 − ] a and pH a were significantly lower in females ( p < 0.0001; p < 0.0001; p = 0.0457), suggesting more complete renal compensation. However, these sex‐differences were not apparent at L‐HA ( p > 0.5341). This is the first clear demonstration of differential ventilatory, oxygenation and acid–base compensation between sexes with rapid ascent to HA.