Response of pulmonary stretch receptors to shifts of functional residual capacity

Abstract

The response of slowly adapting pulmonary stretch receptors (PSRs) to sustained elevations of functional residual capacity (FRC) was investigated in spontaneous breathing anesthetized cats. A subatmospheric pressure was produced around the thorax and abdomen to increase FRC by approximately one tidal volume (V T) for up to 60 min. During eupneic breathing the PSR frequency (f PSR) was closely related to changes in transpulmonary pressure (P TP), bu occasionally hysteresis was observed in the f PSR - P TP relationship. Elevation of FRC caused most phasic PSRs to discharge continously for a few breaths before returning to a phasic discharge pattern. During the shift in FRC there were increases in mean f PSR, peak f PSR and PSR firing threshold which were sustained throughout the period of elevated FRC. PSRs that normally showed discharges at FRC similarly increased their mean and peak firing rates. For all PSRs the y-intercept ( f PSR at P TP = 0) of the f PSR - P TP relationship was decreased but the sensitivity of the PSRs as defined by Δf PSR/ΔP TP was not changed until the period of elevated FRC exceeded 30 min. Thereafter, PSR sensitivity tended to decline. There results suggest that PSRs undergo some modification of their discharge parameters during prolonged elevation of FRC.