Page 355 - Clinical Application of Mechanical Ventilation

Ventilator Waveform Analysis 321

Figure 11-8 presents one of the mandatory volume- and pressure-time waveforms
presented in Figure 11-7. The computations in Table 11-2 show the volume delivered
by the CFW for each 0.25 sec unit of time under the CFW, and the volume deliv-
ered for the inspiratory time elapsed throughout inspiration (1.0 sec). Table 11-3
shows the volume computations and volume waveform, which mathematically dem-
onstrates that the volume rises linearly during constant-flow ventilation. As shown
(Figure 11-8) During
constant flow ventilation, in Table 11-4, the patient’s C equals 0.04166 L/cm H O. As shown, once C is
2
LT
LT
the volume and pressure rise known, the equation for C can be rearranged, and P can be calculated and plot-
linearly with the inspiratory LT ALV
time. ted for any number of time units throughout inspiration, assuming that static C
LT
remains constant, and the volume delivered for the time periods elapsed is known.

0.833

0.625

V (L)
0.417

0.208

0 0.25 0.5 0.75 1.0
Time (sec)

40

30 P ALV

25
P (cm H 2 O) 20

15

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0 0.25 0.5 0.75 1.0
Time (sec)
Figure 11-8 The volume- and pressure-time waveforms during constant flow ventilation
show the steady increase of volume and pressure as inspiratory time progresses.

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