A lower inflection point, an upper inflection (or deflection) point, and respiratory system compliance can be estimated from an inspiratory static pressure-volume (SPV) curve of the respiratory system. Such data are often used to guide selection of positive end-expiratory pressure (PEEP)/tidal volume combinations. Dynamic pressure-volume (DPV) curves obtained during tidal ventilation are effortlessly displayed on modern mechanical ventilator monitors and bear a theoretical but unproven relationship to the more labor-intensive SPV curves. ⋯ The contours of the SPV curve are not reflected by those of the DPV curve in this model of acute lung injury. Therefore, this study indicates that DPV curve should not be used to guide the selection of PEEP/tidal volume combinations. Furthermore, an increase in end-expiratory lung volume occurs during tidal ventilation that is not reflected by the classical SPV curve, suggesting a stable component of lung volume recruitment attributable to tidal ventilation, independent of PEEP.
Inspiratory rise time adjustment during pressure ventilation and inspiration termination criteria adjustment during pressure support ventilation are available on some of the newest mechanical ventilators. Both are designed to improve patient-ventilator synchrony. However, the function of these adjuncts during pressure ventilation on these ventilators has not been evaluated. ⋯ Major differences exist for each ventilator as rise time or inspiration termination criteria are varied and among ventilators at similar settings. Inspiration termination criteria adjustment markedly affects transition to exhalation in the Puritan Bennett 840.