Response of tracheal slowly adapting stretch receptors to longitudinal forces

During breathing and various respiratory maneuvers the trachea sustains significant longitudinal stresses which could be sensed by its mechanoreceptors. In this study we have measured the longitudinal motion and elongation of the trachea in supine, anesthetized dogs during quiet breathing and with occlusion of the upper airways and recorded the response of tracheal stretch receptors in each of the two conditions. The respiratory modulation of intrathoracic tracheal stretch receptors is essentially absent during airway occlusion when the elongation of the trachea becomes greater than in a quiet breath. We have also measured the response of tracheal stretch receptors to transmural pressure at different tracheal length, both statically and dynamically. When the trachea is elongated the receptors decreased their activity at higher positive pressures and remained unaffected with lower distending pressures, at zero transmural pressure and with collapsing pressures. These results indicate that the longitudinal forces applied to the trachea are not capable of changing the transducing properties of its stretch receptors over most of its pressure-volume range, only toward its TLC position their response appear to become attenuated.