On the use of the alveolar capsule technique to study bronchoconstriction

Using the alveolar capsule technique, we studied the time courses of respiratory mechanical parameters at various sites on the lung surface during bronchoconstriction. Six mongrel dogs were anesthetized, tracheostomized, paralyzed and artificially ventilated (12-25 ml/kg, 19-22 breaths/min). Sternotomy was performed and alveolar capsules were glued to various parts of the lungs. Tracheal pressure and flow and alveolar pressure were measured continuously for 25 min after i.v. bolus injections 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 were obtained with our recursive least-squares estimator (Lauzon and Bates, J. Appl. Physiol., 1159-1165, 1991). We found that the time courses of the parameters of most capsules were initially uniform but quickly diverged as bronchoconstriction developed. Also, we found that the differences in time course of mechanics between alveolar regions either developed randomly with step-like features presumably reflecting intermittent opening and closing of the airways leading to the various alveolar capsules, or in a progressive dose-dependant manner, possibly reflecting a gradual but structurally pre-set pattern of bronchoconstriction, or with a combination of these two patterns. We explain our results in terms of inhomogeneous mechanical properties of the lungs and examine some artifacts introduced by the alveolar pressure measurement technique.