Effect of isoproterenol on peripheral airway pressure-diameter behavior.

Abstract

I radiographically evaluated the pressure-diameter relationships of peripheral airways (average diameter approximately 2 mm at total lung capacity) in a collaterally ventilating lung segment in 22 caudal dog lung lobes. Eleven lobes were studied when freshly excised, and 11 lobes were studied after being rinsed with 0.5% isoproterenol. Airways within the segment (intrasegmental) and a control region of similarly sized airways external to the segment were studied. Radiographs were taken when airway opening pressure (Pao) equaled pressure in the segment (Ps) (homogeneous case) and when Pao was 5, 10, or 15 cmH2O greater than Ps (nonhomogeneous case). Airway diameter was calculated as a fraction of the diameter at Pao = Ps = 25 cmH2O. The response of intrasegmental airways to increases in pressure in the homogeneous case (Ps = Pao) and nonhomogeneous case (Ps > Pao) differed between freshly excised and isoproterenol-rinsed lobes. I conclude that dilating peripheral airways by decreasing bronchomotor tone limits the extent to which they can respond to a regional increase in alveolar pressure.