Effects of tidal volume stretch on airway constriction in vivo

Tidal stresses are thought to be involved in maintaining airway patency in vivo. The present study examined the effects of normal stresses exerted by the lung parenchyma during tidal ventilation on recovery from agonist-induc ed airway constriction. In seven anesthetized dogs, one lung was selectivel y ventilated with a Univent endotracheal tube (Vitaid, Lewiston, NY). Airwa y tone was increased either transiently (intravenous bolus) or continuously (intravenous infusion) with methacholine (MCh). During one-lung ventilatio n, changes in the airway size of both lungs were measured for up to 40 min during recovery from constriction by using high-resolution computed tomogra phy. After recovery to baseline, the alternate lung was ventilated, and the protocol was repeated. The absence of tidal stresses led to an attenuated recovery from either transient or steady-state airway constriction. The eff ectiveness or lack thereof of normal tidal stress in stabilizing airway siz e may be one factor that contributes to the lack of reversal with tidal bre athing and deep inspiration seen in asthmatic subjects.