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Relationship between changes in pulmonary math formula kinetics and autonomic regulation of blood flow



Various regulatory mechanisms of pulmonary oxygen uptake (math formula) 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 math formula 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 math formula, cardiac output (math formula) and RMSSDRR were determined using a mono-exponential model. During heavy-intensity exercise, the phase II τ of math formula 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 math formula τ, with 30% of the rate of this rise in Q explained by the τ of RR and RMSSDRR. No relationship was evident between math formula 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 math formula kinetics during heavy-, but not moderate-, intensity exercise.