Control of ventilation during graded exercise in the dog

We analyzed the time courses of the V̇e, Vt, and f responses to graded levels of exercise produced by increases in treadmill speed at preset inclines in 207 experiments on 15 tracheostomized dogs. At the onset of work, V̇e increased with 1-2 respiratory cycles (V̇e_fast), and then either remained constant, or decreased. Following this time delay (TD), V̇e rose more slowly (V̇e_slow) to attain a stable plateau (Dejours). The amplitude of V̇e_fast, Vt and f during the TD were independent of the work load. However, the duration of the TD and the amplitude of the component meating V̇e_slow were workload dependent. The V̇e_fast and the V̇e during the TD are the major components of the total V̇e response at low work levels ( V ̇_O2 = 30-40 ml · min^-1 · kg^-1) and are mediated primarily by increased f, whereas, at higher V̇_O2 (70-90 ml · min^-1 · kg^-1), V̇e_slow is mediated largely by increased Vt and this component is engaged earlier to make a greater contribution to the total V̇e response. In the conscious dog, the total V̇e response to exercise appears to be comprised of both neural and humoral components when thermal stress is minimal.