Ventilation and gas exchange during phasic hindlimb exercise in the dog.

To investigate the importance of the major neural afferent component from the exercising extremities in exercise hyperpnea, rhythmic contraction of hindlimb muscles was produced in the dog, by electrically stimulating the peripheral cut ends of the sciatic and femoral nerves, bilaterally, for 4- to 5-min periods. VE, VCO2, and VO2 were computed breath-by-breath and PaCO2 was monitored continuously with an indwelling arterial electrode. During exercise, VO2 and VCO2 were approximately doubled in the steady state, rising with t1/2 of 25 +/- 2 and 35 +/- 4 s, respectively. VE increased within five breaths after exercise onset, and thereafter rose to a steady state with a t1/2 of 37 +/- 5 s. Mean PaCO2 increased transiently within the 1st min of stimulation but was not significantly different from control in the steady state. We conclude that the major neural afferent component from the contracting muscles is not an obligatory requirement for normal ventilatory response in the steady state of phasic exercise.