Response of roosters to resistive loads at constant chemical drive to breathe.

This study investigated the role of mechanoreceptors in the respiratory responses to resistive loading in roosters. Adult roosters were unidirectionally ventilated (maintaining a constant chemical drive to breathe). Electrical circuits assessed the respiratory muscle pressure (Pmus) and controlled the relationship between Pmus and the respiratory volume changes. Respiratory volume changes similar to those achieved by flow-resistive unloading or loading were produced by the circuits, imposing a 'virtual' resistance (Rv). When Rv was doubled (decreased rate of volume change, n = 6), tidal volume (VT, measured by whole body plethysmography) decreased significantly (28%), while thoracic volume (VRIP, measured by respiratory inductance plethysmography) did not change. When RV was quadrupled (n = 4) VT and VRIP decreased significantly (53% and 24%, respectively). Changing RV to one half the normal value (n = 5) did not affect these parameters. Inspiratory time and Pmus were not significantly altered at any RV. It is concluded that, at constant chemical drive, mechanoreceptors play a minimal role in maintaining tidal volume during impeded breathing in roosters. Comparative differences which may explain these results are discussed.