Influence of surfactant on the activity of slowly adapting stretch receptors in the lung.

Since surfactant has a major role in lung mechanics, this study was designed to determine whether it influences afferent neural feedback to the brainstem. Rats were anaesthetised, paralysed, artificially ventilated and unilaterally vagotomised before recording neural action potentials responding to ventilation stroke (NAPvS) from single units of slowly adapting receptors. The mean (+/-SEM) NAPvs decreased by 7.4% (+/-2.3%) at post-instillation of Tween-20 (a commercial surfactant previously employed in pulmonary studies) from their pre-instillation levels, whereas, by contrast, NAPvs increased by 12.4% (+/-2.3%) at post-instillation of saline--a significant finding (P=0.029). These changes support the concept that surfactant influences afferent neural feedback to the brainstem from mechanoreceptors in the lung, with implications to surfactant deficiency in respiratory control disorders.