Author(s): MACDONALD, T., SHEPLEY, B.R.2, YACOUB, L.2, KENNEY, J.N.2, MAIER, L.E.3, GIBBONS, T.D.4, GASHO, C.5, MACLEOD, D.B.6, SMITH, K.J.7, BAIN, A.R.2, TYMKO, M.M.1, Institution: UNIVERSITY OF GUELPH , Country: CANADA, Abstract-ID: 2666

INTRODUCTION:
Acid-base regulation plays a central role in exercise physiology, inducing changes in ventilation, buffering capacity, and the development of fatigue during endurance and high-intensity exercise. Hypobaric hypoxia (i.e. high altitude) elicits a hypoxic ventilatory response, the magnitude of which may be sex dependent (1). The hypoxic ventilatory response attenuates the decline of arterial oxygen (PaO2), but also reduces the partial pressure of arterial carbon dioxide (PaCO2), resulting in respiratory-induced alkalosis. Eventually, the alkalosis is corrected by renal bicarbonate (HCO3-) excretion to return pH near low-altitude values. Therefore, the purpose of this study was to characterize differences in acid-base balance between males and females at sea-level and during high altitude acclimatization. It was hypothesized that both males and females would demonstrate respiratory alkalosis at high altitude, with males exhibiting a larger reduction in PaCO2 and greater increase in pH, consistent with a stronger hypoxic ventilatory response.
METHODS:
Eighteen healthy lowlanders (9 male, 9 female), all living below 500 m were studied at sea level (Guelph, ON, Canada; 340 m) and again between days 3-7 at high-altitude (Barcroft Research Station; 3,800 m). Arterial (brachial) blood samples were taken at rest and analyzed immediately for blood gases and pH (Radiometer ABL90 Flex) Two-way repeated measures ANOVAs were used to assess condition and sex effects.
RESULTS:
At high-altitude, pH was elevated in both males and females compared to sea-level (7.42±0.01 to 7.47±0.01 and 7.42±0.02 to 7.45±0.01, respectively; p<0.01); however, this response was augmented in males (p=0.04). PaCO₂ decreased with high-altitude exposure in males and females (38.9±2.1 to 29.1±3.0 and 35.7±1.7 to 29.3±1.3 respectively; p<0.01), due to an increase in alveolar ventilation at high-altitude this response was exacerbated in males compared to females (p<0.01 and p=0.02, respectively). Similarly, PaO₂ was reduced at high-altitude in both males and females (91.8±6.8 to 55.9±6.1 and 101.0±4.3 to 53.7±4.0 respectively; p<0.01), and this reduction was more pronounced in females compared to males (p<0.01). There was a metabolic compensation via increased [HCO₃⁻] excretion at high-altitude in response to the respiratory alkalosis (p<0.01). The magnitude of [HCO₃⁻] excretion in response to high-altitude was similar between males and females (p=0.52). However, [HCO₃⁻] was elevated in males at both sea-level and high-altitude compared to females (25.1±0.9 to 23.2±1.2 and 23.9±1.0 to 22.3±0.6, respectively; p=0.01).
CONCLUSION:
These findings demonstrate that there are sex differences in acid-base regulation in response to 4-8 days of high-altitude acclimatization. Males exhibited a greater alkalosis and larger reductions in PaCO2, consistent with an augmented ventilatory response, whereas females experienced a greater decline in PaO2.
1 Raberin, A., Burtscher, J., Citherlet, T. Sports Med 2024 54:271–287