Theory of operation
Puritan Bennett™ 700 Series Ventilator System Service Manual
10070389 Rev. A
2-69
Figure 2-57. Breath triggering and breath delivery parameters
2.6.3 Gas delivery to the patient
After the breath is triggered, the piston moves forward, expelling the cylinder’s contents.
(See Figure 2-57).
In a PSV breath, the piston’s speed, force, and size of excursion are determined by the
patient’s demands and ventilator settings. (See Figure 2-58). In a VCV breath, the piston’s
velocity is determined by the PEAK FLOW setting with flow added to compensate for piston/
cylinder leak and compliance. In a PCV breath, the piston’s velocity is determined by the RISE
TIME FACTOR and INSP IRATORY PRESSURE settings. On the 760 Ventilator, delivered volume
is displayed during PSV and PCV breaths, and is calculated based on piston/cylinder
displacement, minus losses due to cylinder leak, tubing compliance, and piston/cylinder
compliance.
In a VCV breath, the patient receives a square flow waveform. The piston velocity waveform
for a VCV breath, however, shows a slight ramp. This is because the increasing cylinder
pressure creates a greater leak in the cylinder, requiring additional leak compensation. In a
PCV breath, the flow waveform is determined by the selected INSPIRATORY PRESSURE and
RISE TIME FACTOR settings (as cylinder pressure increases, the leak and required
compensation also increase).
Gas flows through the inspiration manifold to the ventilator outlet. Throughout breath
delivery, the inspiration gas pilots the exhalation valve closed.
P
e
P
cyl
P
e
P
cyl
P
cyl
P
e
0 L/min
Trigger flow
PEEP = 10 cmH
2
O
≈
-150 L/min
7-00131
Piston
velocity
Exhalation
solenoid
Piston
retraction
Breath
trigger
Breath delivery
Exhalation valve closed
Peak in
flow to get
pressure up
Summary of Contents for Puritan Bennett 700 Series
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