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Laboratory and Animal Investigations: ArticlesThe Effects of Applied vs Auto-PEEP on Local Lung Unit Pressure and Volume in a Four-Unit Lung Model
Section snippets
Lung Model
We developed a four-unit lung model from two training test lungs (model 1600 Dual Adult, Michigan Instruments Inc, Grand Rapids, Mich) connected in parallel (Fig 1). For each of the four lung units, compliance was established by varying the application point of springs along the sides of each unit, while resistance was varied by using endotracheal tube segments of different diameters. Resistance to gas flow for each of the lung units was estimated from the measured resistance of each resistor,
Lung Unit EEP
The EEP of lung units and the total system PEEP are listed in Table 2 for each of the three PEEP levels evaluated. Figure 2 shows the change in pressure vs time of the model trachea and of each lung unit during both 1:3 and 3:1 ventilation. Equal levels of total system PEEP were established for both 1:3 and 3:1 I:E ratio settings during all trials. None of the three trials at the 1:3 I:E ratio produced differences between total system PEEP and the EEP in any of the four lung units. At the 12 cm
Discussion
The effects of auto-PEEP on the distribution of local lung unit EEP and the distribution of EELV are different from those established by applied PEEP. With applied PEEP, local lung unit EEP is equal to the level of PEEP applied at the trachea, whereas with auto-PEEP, large variations in EEP developed both between lung units and between the trachea and specific lung units. Those lung units with the highest compliance, the greatest resistance (slow lung units), or both develop the highest level
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Supported in part by grants from the Puritan-Bennett Corporation and the Newport Company.
revision accepted February 16.