Effects of graded exercise on bronchial blood flow and airway dimensions in sheep

Our aim was to define exercise stimulus‐response relationships for airway blood supply and dimensions. They are vital for postulates concerning reflex factors which underlie asthma syndromes of exercise. Ewes between 35 and 40 kg had pulsed Doppler transducers on the bronchial artery, and transit‐time plus single crystal sonomicrometers on the left main bronchus. These recorded bronchial blood flow (Q br ), conductance (C br ), bronchial circumference (Circ br ) and wall thickness (Th br ). In Protocol 1 (P1), four sheep ran continuous speeds of 1min duration, namely, 0.8, 1.6, 2.2, 1.6 and 0.8 mph (moderate exercise), followed by 10 min recovery. In P2, four sheep ran at constant 4 mph (strenuous exercise). In P3, one sheep ran separate protocols each of 3 min at 2.2, 4.4 and 6 mph (severe exercise). In P1, effects were directly related to exercise effort. At highest speed Q br and C br fell (to 83% and 75%; both P<0.001). Circ br fell to 96% (P=0.02), and Th br thinned. In P2 and P3 effects were greater than for P1, and the exercise stimulus‐response relationship was near linear (4.4mph: C br to 43%, Circ br to 93%; 6.6mph: C br 25%, Circ br 82%). There was no recovery hyperaemia, but there was residual bronchoconstriction. The exercise stimulus‐response relationships for sheep C br and Circ br are near linear, inverse and functionally constrictor.