Respiratory syncytial virus infection reinforces reflex apnea in young lambs.

To evaluate the effect of respiratory syncytial virus (RSV) infection on reflex apnea elicited by application of water on the laryngeal mucosa, 11 healthy, term lambs were chronically instrumented at 2 wk of age. Six lambs were inoculated with bovine RSV, and five lambs were mock-infected. The lambs were studied awake and unsedated before and 4, 8, 14, and 21 d after infection. RSV infection was associated with slight rhinorrhea and with moderately increased tracheal mucous discharge. There was an average increase of 0.5 degrees C in body temperature. Arterial pH, PO2, and PCO2 remained within the normal range. The ventilatory response to laryngeal chemostimulation measured as the percentage of decrease in ventilation from control was significantly (p less than 0.05) larger among the infected animals when compared with controls on d 4 and 8. There were no differences in indices of respiratory drive (airway occlusion pressure and mean inspiratory flow), ventilatory response to hypoxia (0.10 fraction of inspired O2), or hypercarbia (0.03 fraction of inspired O2). We speculate that RSV infection alters the sensitivity of the laryngeal chemoreceptors so that a prolonged or even fatal apnea may result from stimulation of these receptors. These results may be relevant to the pathogenesis of sudden infant death syndrome associated with RSV infection.