Abstract
BACKGROUND: Contrary to adaptive support ventilation (ASV), prolonged totally controlled mechanical ventilation (CMV) results in the absence of diaphragm activity and causes ventilator-induced diaphragmatic dysfunction. Because maintaining respiratory muscles at rest is likely a major cause of ventilator-induced diaphragmatic dysfunction, ASV may prevent its occurrence in comparison with CMV. The aim of our study was to compare the effects of ASV with those of CMV on both in vivo and in vitro diaphragmatic properties.METHODS: Two groups of six anesthetized piglets were ventilated during a 72-h period. Piglets in the CMV group (n = 6) were ventilated without spontaneous ventilation, and piglets in the ASV group (n = 6) were ventilated with spontaneous breaths. Transdiaphragmatic pressure was measured after bilateral, supramaximal transjugular stimulation of the two phrenic nerves. A pressure-frequency curve was drawn after stimulation from 20 to 120 Hz of the phrenic nerves. Diaphragm fiber proportions and mean sectional area were evaluated.RESULTS: After 72 h of ventilation, transdiaphragmatic pressure decreased by 30% of its baseline value in the CMV group, whereas it did not decrease in the ASV group. Although CMV was associated with an atrophy of the diaphragm (evaluated by mean cross-sectional area of both the slow and fast myosin chains), atrophy was not detected in the ASV group.CONCLUSION: Maintaining diaphragmatic contractile activity by using the ASV mode may protect the diaphragm against the deleterious effect of prolonged CMV, as demonstrated both in vitro and in vivo, in healthy piglets.