Time-dependent recruitment effects in ventilated healthy and lung-injured rats: "recruitment-memory"

We investigated the sustained effects of recruitment manoeuvres in terms of "recruitment memory" in healthy and lung injured rats. 46 ventilated rats were allocated to either the control (sham) or the lavage group. Two consecutive low-flow manoeuvres were performed before sham/lavage and hourly during a 2-h-observation period. The slopes of the inspiratory limbs of the two resulting pressure-volume loops were translated into compliance-volume curves. The difference between the two compliance curves was smaller after lavage (root-mean-square deviation: 0.065 ml/cm H2O control group, 0.038 ml/cm H2O lavage group; p<0.05) and stayed small during the whole experiment. In the control group, the deviation was small after sham manoeuvre but increased throughout the experiment. Compliance gain after recruitment was higher in the control group (0.1 ml/cm H2O) compared to the lavage group (0.02 ml/cm H2O, p<0.05). We conclude that lung lavage led to alveolar collapse not susceptible to recruitment manoeuvres. On the contrary in healthy lungs recruitment manoeuvres led to persistent lung recruitment which we interpret as recruitment memory.