Page 394 - Clinical Application of Mechanical Ventilation

360 Chapter 11

800

600 PIP
Peak P ALV
Volume (mL) 400 P AO

200
P TA
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10 20 25 30 40 50 60
Assist Breath Pressure (cm H 2 O)

Figure 11-38 Characteristics of a pressure-volume loop. The dotted line within the loop is
the peak alveolar pressure (P ALV or plateau pressure). The transairway pressure (P TA or flow resistive
pressure) is the difference between the P AO and P ALV .

Effects of Lung-Thorax Compliance on PVL
(Figure 11-38) This
pressure-volume loop shows
that the lung-thorax compli- Figure 11-39 shows a control breath; there is no negative pressure to trigger the
ance (C LT ) remains unchanged
because the P ALV rises linearly mechanical breath. This PVL illustrates how a reduction in C causes the loop
LT
with increases in volume. to move down and to the right (i.e., toward the pressure axis). The increase in

800
P ALV(1) PIP (1) P ALV(2) PIP (2)

600
Volume (mL) 400 P TA P TA

200

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10 20 30 40 50 60
Pressure (cm H O)
2
Figure 11-39 The effects of lung-thorax compliance (C LT ) on the pressure-volume loop
during volume-controlled, constant flow ventilation. A decreased C LT shifts the curve toward the
pressure axis.

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