Mecholyl aerosolized in the surrounding lung increases the resistance of the collateral pathways.

Collateral ventilation allows gas exchange in pulmonary units distal to an airway obstruction. Regional control of this airflow may be possible because smooth muscle exists in the wall of collateral pathways. Evidence of an intrasegmental cholinergic control of these pathways has been previously shown. We performed this study to investigate the possible control of collateral ventilation by cholinergic receptors situated in the surrounding lung. By using the wedged catheter technique, we measured collateral resistance before and after aerosolization of methacholine in the lung surrounding the wedged segment: both collateral resistance and the time constant for collateral ventilation increased, providing that a cholinergic stimulation in the surrounding lung can influence collateral pathways. Fast and complete reversibility was obtained after isoproterenol or atropine injection. Collateral obstruction would seem to be due, therefore, to a muscular spasm. The effective compliance of the wedged segment decreased during the spasm induced by mecholyl in the surrounding lung, and could be attributed to an increased interdependence of this segment with surrounding segments. This effect was immediately reversed by intravenous bronchodilators. We conclude that cholinergic receptors on the smooth muscles of the external collateral channels can control collateral ventilation.