Heterogeneous activity of pulmonary vagal receptors during high-frequency oscillation ventilation

The purpose of the study was to examine the response of vagal pulmonary slowly adapting stretch receptors (SAR) to high-frequency oscillation ventilation (HFO) in rabbits by analyzing the afferent activity recorded in vagal single-fiber preparations. The vagal afferent activity was recorded during short runs of HFO with a stroke volume of 2-3 ml/kg applied at oscillation frequencies (fosc) of 5, 10, 15, 20, and 25 Hz and each frequency at three levels of mean airway pressure (P(aw)), namely, 1, 3, and 8 cm H2O. The receptor discharge rates during HFO were compared with those during quiet spontaneous breathing as well as during static lung inflations and deflations. The majority of SAR was stimulated by HFO, however, the SAR discharge patterns during HFO were less homogeneous than during static lung inflations. The heterogeneity of SAR responses to HFO became pronounced with increasing P(aw) and fosc. From the results, we conclude that HFO elicits heterogeneous discharge patterns of SAR, but the previously reported heterogeneity of responses of rapidly adapting receptors was even greater. This heterogeneity of vagal activity is probably the result of heterogeneous mechanical conditions within the lungs during HFO and may, in turn, give rise to the various types of respiratory reflex responses to HFO.