Exercise with hypoventilation induces lower muscle oxygenation and higher blood lactate concentration: role of hypoxia and hypercapnia
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Eight men performed three series of 5-min exercise on a cycle ergometer at 65% of normoxic maximal O2 consumption in four conditions: (1) voluntary hypoventilation (VH) in normoxia (VH0.21), (2) VH in hyperoxia (inducing hypercapnia) (inspired oxygen fraction [FIO2] = 0.29; VH0.29), (3) normal breathing (NB) in hypoxia (FIO2 = 0.157; NB0.157), (4) NB in normoxia (NB0.21). Using near-infrared spectroscopy, changes in concentration of oxy-(Δ[O2Hb]) and deoxyhemoglobin (Δ[HHb]) were measured in the vastus lateralis muscle. Δ[O2Hb − HHb] and Δ[O2Hb + HHb] were calculated and used as oxygenation index and change in regional blood volume, respectively. Earlobe blood samples were taken throughout the exercise. Both VH0.21 and NB0.157 induced a severe and similar hypoxemia (arterial oxygen saturation [SaO2] < 88%) whereas SaO2 remained above 94% and was not different between VH0.29 and NB0.21. Arterialized O2 and CO2 pressures as well as P50 were higher and pH lower in VH0.21 than in NB0.157, and in VH0.29 than in NB0.21. Δ[O2Hb] and Δ[O2Hb − HHb] were lower and Δ[HHb] higher at the end of each series in both VH0.21 and NB0.157 than in NB0.21 and VH0.29. There was no difference in Δ[O2Hb + HHb] between testing conditions. [La] in VH0.21 was greater than both in NB0.21 and VH0.29 but not different from NB0.157. This study demonstrated that exercise with VH induced a lower tissue oxygenation and a higher [La] than exercise with NB. This was caused by a severe arterial O2 desaturation induced by both hypoxic and hypercapnic effects.