Integrated autonomic control of bronchial blood flow and third generation airway dimensions during exercise

Abstract

Neural mechanisms controlling 3rd generation airway blood flow and dimensions were studied in 8 sheep trained to run on a treadmill during moderate exercise O2 uptake 20 ml.kg−1.min−1 for 2 min, 10 min recovery. We measured rapid changes in bronchial blood flow and conductance (Qbr, Cbr), circumference (Circbr) and wall thickness (Thbr), using pulsed‐Doppler flowmetry, transit‐time sonomicrometry, and single crystal sonomicrometry, respectively. At exercise onset Pa rose to 111% (P< 0.05) of resting and HR from 85 b/min to 164 b/min (P< 0.001) before returning in recovery at 5 min. Qbr fell immediately to 91% and to 90% at 1.5 min (P< 0.05), and early in recovery to 84% (P< 0.05) before returning to pre‐exercise levels. Cbr followed a similar pattern (P< 0.05). Circbr fell immediately to 96% (P< 0.001) where it remained for the duration of exercise, and Thbr increased and was sustained during exercise before returning to control levels in recovery. Cholinoceptor block by i.v. methscopolamine bromide modified these responses. Pa rose to 109% of resting (P< 0.01), and HR rose from 120 b/min to 168 b/min (P< 0.001). A minor Qbr and Cbr fall was not significant, and only an immediate transient fall in Circbr was evident (P< 0.01). Thus raised vagal activity dominates the exercise‐induced bronchovascular and airway wall constriction in 3rd generation airways during and after exercise.Funding: Hunter Medical Research Institute