Ana B. Peinado1,2, Blair D. Johnson1, Jennifer L. Taylor1, and Michael J. Joyner1.
We tested the hypothesis that the carotid body chemoreceptors (CB) contribute to ventilatory control during steady-state exercise. Six men completed two randomized bouts of cycling exercise at 65% VO2max for up to 2 hours during an IV infusion of dopamine (D; 2 µg/kg/min) to acutely inactivate the CB, or a saline infusion (S). Expired gases were analyzed at baseline, resting-infusion, and during exercise (25%, 50%, 75% and 100% of total exercise time). A hypoxic ventilatory response (HVR) test was performed after exercise during the infusion condition. Subjects were classified as responders (RS; n=3) if their HVR was lower during D vs. S (1.03 ± 0.6 vs. 2.14 ± 0.4 L/min/%SaO2). In RS, partial pressure of end-tidal CO2 had a greater delta from baseline at 75% (2.9 ± 2.1 vs. 1.1 ± 1.9 mmHg) and 100% (0.9 ± 3.4 vs. -0.3 ±3.3 mmHg) during D than S, and the increase in oxygen uptake at 100% was greater during D vs. S (34.7 ± 2.6 vs. 33.0 ± 2.6 mL/min/kg). In RS, there were no differences in the changes from baseline for ventilation (VE), VE/VCO2, respiratory rate, tidal volume, and respiratory exchange ratio between conditions. In the non-responders group, there were no differences between D and S in any variables. When the data was pooled, HVR accounted for 37% of the variance in VE at 100%. Despite evidence that CB chemosensitivity was blunted, the CB appear to play a minor role in controlling ventilation during steady state exercise.
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