Pulmonary afferent activity during high-frequency ventilation at constant mean lung volume.

We recorded the responses of 21 slowly adapting pulmonary stretch receptors (PSRs) and 8 rapidly adapting pulmonary stretch receptors (RARs) from the vagi of anesthetized open-chest dogs to high-frequency ventilation (HFV) at 15 Hz, at constant mean end-expiratory lung volume, and constant end-tidal PCO2. HFV applied in this way has been shown to prolong expiration. The responses of pulmonary afferents during HFV at constant mean volume have not been described. In the present experiments, receptor discharge during HFV was compared with that during the end-expiratory pause of normal-frequency ventilation. Average PSR discharge increased when HFV was applied, although not all PSRs exhibited increases. RARs were generally silent during normal and high-frequency ventilation at functional residual capacity and above. However, at low lung volumes, RAR discharge increased greatly when HFV was applied. We conclude that PSR discharge is increased during HFV in the absence of increased lung volume and that increases in PSR discharge during HFV are sufficient to explain the reflex that prolongs expiration in dogs.