Relationship between changes in pulmonary V ˙ O 2 kinetics and autonomic regulation of blood flow

Various regulatory mechanisms of pulmonary oxygen uptake ( V ˙ O 2 ) kinetics have been postulated. The purpose of this study was to investigate the relationship between vagal withdrawal, measured using RMSSDRR , the root mean square of successive differences in cardiac interval ( RR ) kinetics, a mediator of oxygen delivery, andV ˙ O 2kinetics. Forty‐nine healthy adults (23 ± 3 years; 72 ± 13 kg; 1.80 ± 0.08 m) performed multiple repeat transitions to moderate‐ and heavy‐intensity exercise. Electrocardiography, impedance cardiography, and pulmonary gas exchange parameters were measured throughout; time domain measures of heart rate variability were subsequently derived. The parameters describing the dynamic response ofV ˙ O 2 , cardiac output ( Q ˙ ) and RMSSDRR were determined using a mono‐exponential model. During heavy‐intensity exercise, the phase II τ ofV ˙ O 2was significantly correlated with the τ of RR ( r  = 0.36, P  < 0.05), Q ( r  = 0.67, P  < 0.05), and RMSSDRR ( r  = 0.38, P  < 0.05). The τ describing the rise in Q explained 47% of the variation inV ˙ O 2τ, with 30% of the rate of this rise in Q explained by the τ of RR and RMSSDRR . No relationship was evident betweenV ˙ O 2kinetics and those of Q , RR , or RMSSDRR during moderate exercise. Vagal withdrawal kinetics support the concept of a centrally mediated oxygen delivery limitation partly regulatingV ˙ O 2kinetics during heavy‐, but not moderate‐, intensity exercise.