Schematic illustration of pressure waveforms for common modes of mechanical ventilation. In volume control there is a “ramp up” pressure waveform with a square wave flow waveform. Note the inspiratory and expiratory phases of the flow waveform. Volume-controlled ventilation is a time-cycled, volume-limited, and volume-cycled mode of ventilation. In pressure control, the pressure waveform is a square wave, whereas the inspiratory flow is exponentially increasing. Pressure-controlled ventilation is time-cycled, pressure-limited, and time-cycled. In pressure support, note the small downward deflection in the pressure wave followed by a square wave of pressure support. When the flow decreases to a threshold value, pressure support is terminated.