Fig. 3
From: The future of mechanical ventilation: lessons from the present and the past
Upper box: simplified equation of motion, showing that, at any given moment, the pressure in the respiratory system (P) above the relaxed volume equals the sum of the elastic pressure (elastance of the respiratory system E rs times change in lung volume), plus the pressure needed to move the gases (flow F times airway resistance), plus the pressure (if any) to keep the lung pressure above the atmospheric pressure at end expiration (PEEP). If each of these three components is multiplied by the tidal change in lung volume ∆V, the energy per breath is obtained. If multiplied by the respiratory rate, the corresponding power equation is obtained. 0.098 is the conversion factor from liters/cmH2O to Joules (J). I:E inspiratory–expiratory ratio, PEEP positive end-expiratory pressure, Power rs mechanical power to the respiratory system, RR respiratory rate, ∆V change of volume R aw airways resistances