Behavior of slowly adapting stretch receptors in the extrathoracic trachea of the dog.

We have studied the response of 40 slowly adapting stretch receptors located in the extrathoracic trachea to maintained positive and negative pressures together with their behavior during the breathing cycle and inspiratory efforts against closed airways in anesthetized dogs. Like the other tracheal stretch receptors they are located in the smooth muscle of the posterior wall and are stimulated either by inflation or deflation. Most of these receptors are active at zero transmural pressure and increase their response with positive pressure; with negative pressure their resting discharge decreases at first (-5 to -10 cm H2O) and then increases, but it is generally lower than that of the corresponding positive pressure value. As predicted by their static response, the activity of these receptors decreases during inspiration and increases during expiration and therefore it is out of phase with the discharge of the other airway stretch receptors. Their activity is related to the corresponding transmural pressure and therefore to airflow and upper airway resistance. During inspiratory efforts against the closed airways their activity decreases, unlike that of the intrathoracic airway receptors, which retain essentially their FRC activity.