Ischemia potentiates the reflex bronchodilation evoked by static muscular contraction in dogs

In eleven anesthetized dogs, we found that static contraction of hindlimb muscles that were freely perfused decreased total lung resistance by 0.7 ± 0.1 cm H₂O·L^-1·sec, whereas static contraction of the same muscles rendered ischemic decreased total lung resistance by 1.5±0.4 cm H₂O·L^-1·sec (P < 0.025). In ten other dogs, we found that static contraction of freely perfused hindlimb muscles decreased total lung resistance by 0.9 ± 0.2 cm H₂O·L^-1·sec, whereas dynamic contraction of the same freely perfused muscles decreased total lung resistance by 1.1 ± 0.3 cm H₂O·L^-1·sec. The difference in the magnitudes of the bronchodilator responses of the two modes of contraction was not significant (P > 0.05). We conclude that a mismatch between blood supply and demand in working skeletal muscle increases the reflex bronchodilator response to static contraction. We also conclude that dynamic contraction evokes a reflex bronchodilation equivalent to that evoked by static contraction provided that the tension produced by the two modes of contraction are equal.