Effect of tidal volume and frequency on airway responsiveness in mechanically ventilated rabbits

Shen, X., S. J. Gunst, and R. S. Tepper. Effect oftidal volume and frequency on airway responsiveness in mechanically ventilated rabbits. J. Appl. Physiol.83(4): 1202-1208, 1997.We evaluated the effects of the rate andvolume of tidal ventilation on airway resistance (Raw) duringintravenous methacholine (MCh) challenge in mechanically ventilatedrabbits. Five rabbits were challenged at tidal volumes of 5, 10, and 20 ml/kg at a frequency of 15 breaths/min and also under static conditions(0 ml/kg tidal volume). Four rabbits were subjected to MCh challenge atfrequencies of 6 and 30 breaths/min with a tidal volume of 10 ml/kg andalso under static conditions. In both groups, the increase in Raw with MCh challenge was significantly greater under static conditions thanduring tidal ventilation at any frequency or volume. Increases in thevolume or frequency of tidal ventilation resulted in significant decreases in Raw in response to MCh. We conclude that tidal breathing suppresses airway responsiveness in rabbits in vivo. The suppression ofnarrowing in response to MCh increases as the magnitude of the volumeor the frequency of the tidal oscillations is increased. Our findingssuggest that the effect of lung volume changes on airway responsivenessin vivo is primarily related to the stretch of airway smooth muscle.