Cardiorespiratory and oxygenation responses in iron-deficient anemic women during whole-body exercise under moderate hypoxia.

Purpose: Integrated physiological responses during maximal whole-body exercise, such as cycling, under additive hypoxemia (anemia + hypoxia) are not adequately studied. Therefore, we investigated cardiovascular, muscular and cerebral oxygenation responses in chronic mildly iron-deficient and control women under normoxic and moderate hypoxic conditions during maximal whole-body exercise.

Methods: In a randomized and counterbalanced order, 16 females performed incremental exercise to exhaustion under normoxia (N; FIO₂:20.94%) and hypoxia (H; FIO₂:13.6%). The participants were divided into two groups matched for age and anthropometric characteristics, but intentionally varying in [Hb] (p < 0.001) and V̇O_2max (p < 0.01); iron-deficient (A; n = 8; [Hb]:11.3 ± 0.4 g/dl; V̇O_2max:37.3 ± 2.8 ml/kg/min) and healthy controls (C; n = 8; [Hb]:13.3 ± 0.4 g/dl; V̇O_2max:40.8 ± 1.9 ml/kg/min).

Results: During exercise in hypoxia compared to normoxia, the A exhibited greater decrement in V̇O_2max (5.0%; p = 0.02) and peak power output (5.4%; p = 0.004) than C. Maximal mean arterial pressure was reduced (p < 0.05) due to lower total peripheral resistance (p < 0.05) and unchanged maximal cardiac output (p > 0.05). Enhanced O₂ utilization under H was observed only in C, based on ΔHHb (p < 0.05). Cerebral oxygenation was reduced linearly with CaO₂ (r = 0.95, p < 0.001).

Conclusion: Collectively, moderate hypoxia induced greater reduction of V̇O_2max, peak power output and cerebral oxygenation leading to exercise intolerance in A compared to C. These responses were accompanied by an inability of skeletal muscle to increase O₂ utilization at maximal effort in H and by a failure of the cardiovascular system to compensate and counteract convective and diffusion limitations during maximal whole-body exercise in anemic women.