Fig. 5

Brain curve (red line), unsupported (dashed black line) and supported with PS (green line) ventilation curves early in the course of critical illness of the patient of Fig. 4. Point 1: desired PaCO₂ by respiratory centers; Point 2: theoretical PaCO₂ during unsupported spontaneous breathing; Point 3: actual PaCO₂ with PS during stable breathing (steady state); Point 4: RCO/min corresponding to desired V’_E with unsupported spontaneous breathing; Point 5: RCO/min corresponding to desired V’_E with PS ventilation; Notice the unmet demands without (difference in ventilation between points 2 and 4), and with PS (difference in ventilation between points 3 and 5). PS: pressure support; RCO/min: respiratory centers output per min; V’E: minute ventilation