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Keywords:

  • heart rate variability;
  • inline image kinetics;
  • oxygen delivery;
  • cardiac output

Various regulatory mechanisms of pulmonary oxygen uptake (inline image) 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, and inline image kinetics. 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 of inline image, cardiac output (inline image) and RMSSDRR were determined using a mono-exponential model. During heavy-intensity exercise, the phase II τ of inline image was 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 in inline image τ, with 30% of the rate of this rise in Q explained by the τ of RR and RMSSDRR. No relationship was evident between inline image kinetics and those of Q, RR, or RMSSDRR during moderate exercise. Vagal withdrawal kinetics support the concept of a centrally mediated oxygen delivery limitation partly regulating inline image kinetics during heavy-, but not moderate-, intensity exercise.