Sinoaortic contribution to ventilatory control in exercising dogs

The role of the sinoaortic reflexes in the regulation of ventilation during exercise was evaluated in seven awake dogs prepared with chronic tracheostomies and arterial catheters. Each dog ran on a treadmill at several work loads before and after sinoaortic denervation and served as its own control. Minute ventilation in the sinoaortic denervated state was significantly reduced from intact values by 10-40% at the mild and moderate levels of exercise [O2 uptake (VO2) = 30-50 ml . kg-1 . min-1] mainly as a result of a lowering respiratory frequency. At higher work loads (VO2 = 70-80 ml . kg-1 . min-1) minute ventilation was similar in the intact and denervated states, but the pattern of ventilation was altered with a higher frequency and a lower tidal volume in the denervated state. The rise in ventilation toward a stable plateau was slower at all work loads in the denervated than in the intact state. After sinoaortic denervation, arterial PCO2(PaCO2) levels were significantly elevated above intact PaCO2 levels during both the preexercise period and the steady state at all exercise levels. These results suggest that the sinoaortic reflexes contribute to both the control of ventilation and the pattern of breathing during mild and heavy levels of exercise in the conscious dog.