Fig. 7
Determinants of brain curve (RCO/min/PaCO2), ventilation curve (V’E/PaCO2) and metabolic hyperbola during unsupported spontaneous breathing (SB) and mechanical ventilation (MV). MV modifies the equation of motion by applying pressure (Paw) to the lungs, which acts in conjunction with the pressure generated by the inspiratory muscles (PmusI). During mechanical ventilation respiratory rate (Fr) may differ from the frequency of the electrical bursts (outputs) due to patient–ventilator dyssynchrony (i.e., ineffective efforts). Paw may change (curved arrows) Ers (recruitment/derecruitment/overdistension), Rrs (airway opening/closure) and PEE (dynamic hyperinflation). Notice that tidal volume (VT) depends on a complex interaction of variables (Modifiers) determining brain curve, ventilation curve and metabolic hyperbola. RCO: respiratory centers output; Pmus: respiratory muscles pressure (inspiratory and expiratory); Ers: respiratory system elastance; Rrs: respiratory system resistance; PEE: elastic recoil pressure of respiratory system at end-expiration; V’: flow; ΔV: volume above end-expiratory lung volume; V’E: minute ventilation; V’CO2: CO2 production; VD/VT: physiological dead space to tidal volume ratio; PaCO2: partial pressure of arterial CO2; PaO2: partial pressure of arterial O2