Transduction properties of tracheal stretch receptors.

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Abstract
Using single fiber vagal afferent recording, the behavior of slowly adapting stretch receptors located in an isolated, in situ, segment of the trachea in dogs was studied. Responses to positive and negative steady and oscillating transmural pressures were investigated. Of the receptors studied, 78% were tonically active at resting tracheal volume; 90% showed a more pronounced response to positive than to negative transmural pressures. During pressure oscillations, the majority of the receptors had a higher discharge frequency at any given pressure during the ascending phase of the pressure wave than at the same pressure under static conditions. During most of the ensuing descent of pressure toward zero the discharge frequency was lower than the corresponding static value. Discharge frequency led transmural pressure. With increasing frequency of oscillation the differences from the static responses increased (dP/dt sensitivity), especially during the ascending limb of the pressure oscillation (rectifying behavior). In a small number of receptors, discharge frequency lagged behind transmural pressure or was in phase with it (no loop pattern). In 3 cases the same receptor exhibited dP/dt sensitivity during positive pressure oscillations but discharge frequency lagged behind pressure during negative oscillations. The lack of dP/dt sensitivity exhibited under negative pressure conditions apparently does not represent an intrinsic property of these receptors but reflects some aspect of their mechanical arrangement whithin the airway wall. These patterns of response are discussed in terms of intrinsic and extrinsic characteristics of the receptors. The physiological implications of stretch receptor behavior are also considered.