Page 362 - Clinical Application of Mechanical Ventilation

328 Chapter 11

airway resistance has been changed. A decrease in total C is the only explanation for
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the increase in PIP, which is supported by the increase in peak P ALV at end-inspiration.
The same peak flow, flow pattern, and volume (Area 1 5 Area 2) are being used for
volume delivery in each example. Total C can be estimated by observing the infor-
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mation provided in the graphic comparison and, in this example, it has decreased by
half. The calculated V under the flow curve is 1 L or 1000 mL (1 L/sec 3 1 sec),
T
and total C is 50 mL/cm H O (C 5 1000 mL/20 cm H O) for the first example,
2
LT
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2
versus 25 mL/cm H O (1000 mL/40 cm H O) in the second example.
2
2
EFFECTS OF DESCENDING RAMP FLOW WAVEFORM
DURING VOLUME-CONTROLLED VENTILATION

Time- and Flow-Limited Ventilation

Figure 11-13 demonstrates the changes that occur when the flow pattern on a ven-
tilator is adjusted from a constant to a descending ramp flow waveform (DRFW)
during time-limited ventilation (first example) compared to flow-limited ventilation

Time-Limited Ventilation (Area a = Area b)
80
V (L/min) a b Flow-Limited Ventilation (Area a = Area b)

a

b
1 2 3 4 5 6 7

P (cm H 2 O) 280

TA
40 PIP & Initial P TA Same Initial Peak P for the Same Initial Flow
P TA P TA
Peak P ALV No PIP = Peak P ALV
End-Flow No
P TA
© Cengage Learning 2014

22
1 2 3 4 5 6 7
Time (sec)
Figure 11-13 Changes of dynamic pressure waveforms created by descending ramp flow
during time-limited and flow-limited ventilation.

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