A: Pressure (green) and volume (black)/time curve in airway pressure release ventilation (APRV). Shown in the figure: 2 full mandatory breaths (not triggered by muscle effort), and 2 full spontaneous breaths (triggered by muscle effort, in blue) on the top of the mandatory ones. Muscle pressure (blue): the long arrow represents the T high, and the short one represents the T low of the mandatory breath. B: Flow (black) and volume (green)/time curve in APRV. T high is the start of the inspiratory flow to the start of expiratory flow, T low is the start of expiratory flow to the beginning of the next inspiratory flow. The 2 red intersecting lines are at 50% of the peak expiratory flow.
Comparison of airway pressure release ventilation (APRV) (blue curve) and biphasic positive airway pressure (BIPAP) (black curve). Compared to APRV, BIPAP uses shorter T high, longer T low, and usually higher P low. Despite the differences between their settings, mathematically both can achieve the same mean airway pressure (red line) and same tidal volume (green curve). Blue curves represent APRV, black curves represent BIPAP.
Lung simulator diagram of airway pressure release ventilation (APRV): volume (yellow), lung pressure (white), and flow (orange)/time curve. Time constant (TC) was known and the T low was set to more than 4 TCs. The blue vertical lines represent each TC. Intrinsic PEEP at each TC would be equal to the point intersecting with the pressure curve, or can be calculated as the end-expiratory lung volume divided by respiratory compliance. Notice that at each TC the flow curve did not decay to 36.2% from its previous value, as expected per the mathematical model.
Illustration of the values of the inspiratory and expiratory volume, pressure, and flow in relation to the time constant theory. Each 1 time constant, the volume, pressure and flow change by 63.2% from their previous value.