Temporal effect of applied pressures on observed alveolar recruitment

Introduction

Lung recruitment has been hypothesized to be an important component of protective ventilatory strategy in acute respiratory distress syndrome. Determination of optimal recruitment strategies is limited by uncertainty regarding the relationship between time, pressure, and recruitment at the alveolar level. In this study, we assessed the temporal characteristics of alveolar recruitment.

Methods

Rats were subjected to saline lavage lung injury. In vivo microscopy identified five separate alveolar sacs for which individual recruitment pressures (RP) were determined by increasing the continuous positive airway pressure (CPAP). The time to recruitment was recorded upon application of three pressures for a maximum of 120 s: RP, RP – 1 cmH₂O, and RP – 2 cmH₂O. Volume history was normalized before each pressure application.

Results

No recruitment was observed in the 2-min time period with a pressure of RP – 2 cmH₂O. The time to recruitment was significantly shorter with application of RP vs RP – 1 cmH₂O (Fig. 1). Significance was determined by a one-tailed, paired t test, P < 0.03.

Figure 1

(abstract P102)

Conclusions

We were able to directly observe recruitment behavior that exhibited sensitivity around a critical opening pressure with marked changes in time to recruitment with small changes in pressure. This suggests that very small differences in the airway pressures (as small as 1 cmH₂O in this study) may have dramatic alterations in lung recruitment.