Airway Pressure Contour

Consistent with Equation 1, simple inspection of the airway pressure contour in a ventilator-dependent patient can provide useful information on the activity of a patient's respiratory muscles. With a given inspiratory flow waveform, any deviation from the relaxed configuration indicates active contraction of a patient's inspiratory muscles (Figure 2). The work performed by the patient can be quantified as the difference in area between the actual versus the relaxed airway pressure contour plotted against either time or volume (48, 49, 53). A patient actively contributes to the total work of breathing (WOB), either intentionally or unintentionally, whenever his or her ventilatory demands exceed the inspiratory flow rate setting on the ventila-tor—a phenomenon called flow deprivation. Some modern ventilators have the capability of detecting such an occurrence with their operational software and can compensate for it.

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