Page 106 - Clinical Application of Mechanical Ventilation

72 Chapter 3

A
70 60 B
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C
D
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Pressure (cm H 2 O) 40 Pressure (cm H 2 O) 40
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Figure 3-18 Four types of pressure waveforms: (A) rectangular; (B) exponential; (C) sinusoidal;
and (D) oscillating.

Pressure Waveforms

Pressure waveforms include rectangular, exponential, sinusoidal, and oscillating
(Figure 3-18). Each of these waveforms would have these characteristic shapes, pro-
viding that pressure is the control variable. The descriptors used to describe each
waveform are based on their respective shapes.
The rectangular waveform is characterized by a nearly instantaneous rise to a peak
pressure value that is held to the start of exhalation. During expiration, the pressure
rapidly drops to baseline.
The exponential waveform is depicted by a more gradual increase in pressure
when compared with the rectangular waveform. This type of waveform is common
in some infant ventilators and has become an option on some adult ventilators. Ven-
tilator settings such as flow and inspiratory time regulate how steep the waveform
sine wave: A graphic presenta- rises toward peak inspiratory pressure.
tion of flow and time that has a The sinusoidal waveform resembles the positive half of a sine wave. Sinusoi-
horizontal “S” appearance.
dal waveforms are characteristically produced by ventilators having a rotary-driven

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