Modern lung ventilators are able to generate three basic wave forms of flow: squared waveform, descending waveform, and sinusoidal waveform. A square waveform pattern is found on most mechanical ventilators, old and new, and achieves a constant flow.
During the inspiration phase, the flow rate rises to a predetermined level and remains constant, thus giving the appearance of a square wave form. This produces the shortest inspiratory time compared to other flow patterns. A decelerating flow waveform pattern, also known as descending ramp, achieves the highest level of flow at the start of a breath, when patient flow demand is often greatest.