Control of ventilation during graded exercise in the dog

We analyzed the time courses of the VE, 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, VE increased within 1-2 respiratory cycles (VE fast), and then either remained constant, or decreased. Following this time delay (TD), VE rose more slowly (VE slow) to attain a stable plateau (Dejours). The amplitude of VE 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 mediating VE slow were workload dependent. The VE fast and the VE during the TD are the major components of the total VE response at low work levels (VO2 = 30-40 ml . min-1 . kg-1) and are mediated primarily by increased f, whereas, at higher VO2 (70-90 ml . min-1 . kg-1), VE slow is mediated largely by increased VT and this component is engaged earlier to make a greater contribution to the total VE response. In the conscious dog, the total VE response to exercise appears to be comprised of both neural and humoral components when thermal stress is minimal.