Phrenic and vagal nerve activities during spontaneous respiration and positive-pressure ventilation

Afferent vagal nerve activity from stretch-receptors in the lung and efferent phrenic nerve activity were recorded during spontaneous respiration and during positive-pressure ventilation with three different types of ventilators. During spontaneous respiration the efferent phrenic nerve activity slightly preceded the afferent vagal nerve activity. Volume-controlled ventilation did not alter the phrenic nerve activity when the ventilation was set at a rate equal to that during spontaneous respiration, but afferent vagal volleys increased in duration. At higher frequencies of insufflation spontaneous inspiration was inhibited. An increase in afferent vagal nerve activity and a concomitant slight decrease in efferent phrenic nerve activity were obtained during animal triggered pressure-controlled ventilation. High-frequency positive-pressure ventilation (HFPPV) gave rise to basal, non-grouped activity in vagal afferents, causing inhibition of inspiration. During HFPPV, spontaneous respiration can take place on activation of other afferents to the respiratory centre. Clinical aspects of respirator treatment from a neurophysiological standpoint are discussed.