Page 89 - Clinical Application of Mechanical Ventilation

Classification of Mechanical Ventilators 55

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Figure 3-3 A bellows drive mechanism for a mechanical ventilator.

waveforms, which are discussed later in this chapter, vary depending on how the
piston is driven.

Bellows Drive Mechanism

Ventilators may also use a bellows to compress the gas for delivery to the patient
(Figure 3-3). A bellows may be compressed by a spring, a weight, or by gas pressure
if it is in a sealed chamber. A one-way valve admits gas to the bellows expanding
the bellows. When it is compressed, the one-way valve closes, causing gas delivery
to the patient.

Microprocessor-Controlled Pneumatic
Drive Mechanism

Although technically both pistons and bellows are pneumatic systems, a separate
classification is required for the newer ventilators that use proportional solenoid
valves and microprocessor controls. Current generation ventilators use programmed
algorithms in the microprocessors to open and close the solenoid valves to mimic
virtually any flow or pressure wave pattern.
This is called a microprocessor-controlled pneumatic drive mechanism. Fur-
pneumatic drive mechanism:
Operation of a ventilator with pres- thermore, with advances in clinical medicine, the microprocessors can be repro-
surized gas as a power source. grammed to deliver new patterns that may not yet be described in the literature.
Ventilator manufacturers, using microprocessors and the associated proportional
solenoid valves, have greater flexibility in designing and updating ventilator
technology.

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