Effect of voluntary hyperventilation with supplemental CO2 on pulmonary O2 uptake and leg blood flow kinetics during moderate-intensity exercise

New findings center dot What is the central question of this study? Voluntary hyperventilation that induces hypocapnic alkalosis (HYPO) is associated with slowed adaptation of O-2 uptake and leg blood flow during moderate exercise; however, it is unknown whether hypocapnia, alkalosis and/or the hyperventilation manoeuvre is related to these observations. center dot What is the main finding and its importance? We included a condition with the same work of breathing as HYPO, but the fall in CO2 was prevented by the addition of higher CO2 to the inspirate (normocapnia). This condition demonstrated that hypocapnia/alkalosis was responsible for the slower leg blood flow response; however, the act of hyperventilation itself also had a role to play in the slower O-2 uptake kinetics. Pulmonary O-2 uptake ((V) over dot(O2P)) and leg blood flow (LBF) kinetics were examined at the onset of moderate-intensity exercise, during hyperventilation with and without associated hypocapnic alkalosis. Seven male subjects (25 +/- 6 years old; mean +/- SD) performed alternate-leg kneeextension exercise from baseline to moderate-intensity exercise (80% of estimated lactate threshold) and completed four to six repetitions for each of the following three conditions: (i) control [CON; end-tidal partial pressure of CO2 (P-ET,(CO2)) similar to 40 mmHg], i. e. normal breathing with normal inspired CO2 (0.03%); (ii) hypocapnia (HYPO; P-ET,P-CO2 similar to 20 mmHg), i. e. sustained hyperventilation with normal inspired CO2 (0.03%); and (iii) normocapnia (NORMO; P-ET,P-CO2 similar to 40 mmHg), i.e. sustained hyperventilation with elevated inspired CO2 (similar to 5%). The. (V)over dot(O2P) was measured breath by breath usingmass spectrometry and a volume turbine. Femoral artery mean blood velocity was measured by Doppler ultrasound, and LBF was calculated from femoral artery diameter and mean blood velocity. Phase 2 (V)over dot(O2P) kinetics (tau(V)over dot(O2P)) was different (P < 0.05) amongst all three conditions (CON, 19 +/- 7 s; HYPO, 43 +/- 17 s; and NORMO, 30 +/- 8 s), while LBF kinetics (tLBF) was slower (P < 0.05) in HYPO (31 +/- 9s) compared with both CON (19 +/- 3 s) and NORMO (20 +/- 6 s). Similar to previous findings, HYPO was associated with slower. (V) over dot(O2P) and LBF kinetics compared with CON. In the present study, preventing the fall in end-tidal P-CO2 (NORMO) restored LBF kinetics, but not. (V) over dot(O2P) kinetics, which remained ` slowed' relative to CON. These data suggest that the hyperventilation manoeuvre itself (i.e. independent of induced hypocapnic alkalosis) may contribute to the slower. (V) over dot(O2P) kinetics observed during HYPO.