Spontaneous breathing intensity is related with the severity of ventilator-induced diaphragmatic dysfunction

Purpose: To determine whether there is a certain relationship between spontaneous breathing intensity and the severity of ventilator-induced diaphragmatic dysfunction (VIDD) and which spontaneous breathing intensity could effectively prevent VIDD. Materials and Methods: Sixty Sprague-Dawley rats were randomly assigned to one of the following: 1) absolute spontaneous breathing (100%SB); 2) 80% of spontaneous breathing intensity (80%SB); 3) 60% of spontaneous breathing intensity (60%SB); 4) 40% of spontaneous breathing intensity (40%SB); 5) 20% of spontaneous breathing intensity (20%SB); or 6) absolute CMV (0%SB). After 24 hours of respective mechanical ventilation, we carried out the following measurements on diaphragm specimens: transdiaphragmatic pressure (Pdi), Pdi max, diaphragmatic tetanic force (in vivo and in vitro), active calpain and casepase-3 levels, myofiber cross-sectional area (CSA). Results: With the decrease of the spontaneous breathing intensity, Pdi, Pdi max, in vivo and in vitro diaphragmatic tetanic force decreased, active calpain and casepase-3 levels increased, and myofiber CSA reduced. Compared to the intensity with 100% SB, those with less than 60%-80% SB resulted in a significant decrease in Pdi, Pdi max, in vivo and in vitro diaphragmatic tetanic force, those with less than 20% SB resulted in a significant increase in active calpain and casepase-3 levels, and those with less than 80% SB resulted in a significant decrease in myofiber CSA. Conclusions: There is a significant negative correlation between spontaneous breathing intensity and VIDD; preserving spontaneous breathing with the intensity of more than 60%-80% may be helpful to prevent VIDD.