ON THE USE OF THE ALVEOLAR CAPSULE TECHNIQUE TO STUDY BRONCHOCONSTRICTION

Using the alveolar capsule technique, we studied the time courses of r espiratory mechanical parameters at various sites on the lung surface during bronchoconstriction. Six mongrel dogs were anesthetized, trache ostomized, paralyzed and artificially ventilated (12-25 ml/kg, 19-22 b reaths/min). Sternotomy was performed and alveolar capsules were glued to various parts of the lungs. Tracheal pressure and flow and alveola r pressure were measured continuously for 25 min after i.v. bolus inje ctions of histamine (0, 0.05, 0.5, 5.0, 50.0 mg). The challenges were spaced 1 h apart. Estimates of lung tissue resistance and elastance we re obtained with our recursive least-squares estimator (Lauzon and Bat es, J. Appl. Physiol., 1159-1165, 1991). We found that the time course s of the parameters of most capsules were initially uniform but quickl y diverged as bronchoconstriction developed. Also, we found that the d ifferences in time course of mechanics between alveolar regions either developed randomly with step-like features presumably reflecting inte rmittent opening and closing of the airways leading to the various alv eolar capsules, or in a progressive dose-dependant manner, possibly re flecting a gradual but structurally pre-set pattern of bronchoconstric tion, or with a combination of these two patterns. We explain our resu lts in terms of inhomogeneous mechanical properties of the lungs and e xamine some artifacts introduced by the alveolar pressure measurement technique.