Page 88 - Clinical Application of Mechanical Ventilation

54 Chapter 3

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Figure 3-1 A schematic diagram of a rotary-driven piston drive mechanism for a mechanical
ventilator.

microprocessors and proportional solenoid valves allow these newer ventilators to
solenoid valves: A valve controlled
by an electronic switching device produce a variety of user-selected inspiratory flow or pressure patterns. An under-
that is used to regulate the specific standing of the different drive mechanisms will allow you to apply a ventilator more
functions of a ventilator.
effectively in the clinical environment. Primary drive mechanisms include pistons,
bellows, and pneumatic circuits.

Piston Drive Mechanism

An electrically driven piston with an inspiratory one-way valve can be used to gen-
erate a pressure gradient to drive a ventilator (Figure 3-1). During the backstroke
of the piston, gas enters the cylinder through the one-way valve. When the piston
travels in the opposite direction, a second one-way valve opens, delivering the com-
pressed gas to the patient.
Pistons are usually electrically powered. However, they may be rotary- or
linear-driven. Figure 3-2 compares a linear-driven and rotary-driven piston. Output

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Figure 3-2 A comparison between (A) a rotary-driven piston and (B) a linear-driven piston
drive mechanism for a mechanical ventilator.

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