Research article
Contribution of opening and closing of lung units to lung hysteresis

https://doi.org/10.1016/0034-5687(95)00055-0Get rights and content

Abstract

The recruitment and derecruitment of lung units is one explanation of the hysteresis observed in an excised lung during inflation and deflation. A simplified model has been proposed in which the recruitment-derecruitment process is a function of end-expiratory pressure (Frazer, D.G., K.C. Weber and G.N. Franz, Respir. Physiol. 61: 277–288, 1985). The object of this study was to test this model with three experimental procedures. During the first set of experiments, progressively larger pressure-volume (Pl-Vl) loops were recorded with end-expiratory pressure held at either −5 cmH2O, where all lung units are assumed to be closed, or +5 cmH2O, where all recruited lung units are assumed to be open. In the first case hysteresis is maximal, in the second, minimal. The difference in hysteresis is presumed to arise from the recruitment-derecruitment process. In the second set of experiments, excised lungs are slowly inflated and then deflated at a constant rate while constant-amplitude sinusoidal volume oscillations are superimposed. The end-expiratory pressure of the superimposed loops gradually rose as the lung was inflated and fell as the lung was deflated. Hysteresis was minimal when end-expiratory pressure was above 4 ± 1 cmH2O even as peak-to-peak loop pressure greatly varied. This supports the notion of an end-expiratory pressure dependent mechanism of recruitment/derecruitment. During the third set of experiments lungs were inflated to either 50%, 75%, or 100% TLC. Volumes of air were then withdrawn and replaced so that the initial volume was restored in sinusoidal fashion as the amplitude of the volume excursions increased. For Pl-Vl loops with end-expiratory pressures between +4 and −2 cmH2O, pressure amplitudes rose and the hysteresis index (loop area/tidal volume) increased, regardless of the initial lung volume. These results are consistent with the previously described model of Frazer et al. (1985) which assumed that Pl-Vl curves can be divided into an ‘opening’ region, an ‘open’ region and a ‘closing’ region and that the demarcation of these regions depends on transpulmonary pressure, specifically end-expiratory pressure, and to a much lesser degree on lung volume.

References (24)

  • B.D. Daly et al.

    Dynamic alveolar mechanics as studied by video microscopy

    Respir. Physiol.

    (1975)
  • J. Davis et al.

    Assessment of closure of lung units based on the pressure-volume curve

    J. Physiol. (London)

    (1975)
  • Cited by (34)

    • A minimal model of lung mechanics and model-based markers for optimizing ventilator treatment in ARDS patients

      2009, Computer Methods and Programs in Biomedicine
      Citation Excerpt :

      This result suggests that recruitment and derecruitment is the dominant cause of volume change, rather than isotropic “balloon like”, expansion of alveoli as had been traditionally thought, which is discussed in [16]. This elastic expansion hypothesis is also utilized by a variety of other clinical studies [18–26,8,13,14,9], and is in contrast to the in vivo and clinically observed, more discrete open–closed behaviour employed here. A modelled lung unit has 2 possible states at a given pressure: (1) recruited and (2) derecruited.

    View all citing articles on Scopus
    View full text