The Effect of Positive End-Expiratory Pressure on Lung Micromechanics Assessed by Synchrotron Radiation Computed Tomography in an Animal Model of ARDS.

Gaetano Scaramuzzo,Mariangela Pellegrini,Sam Bayat,Liisa Porra,João Batista Borges,Angela Principia Tannoia,Anders Larsson,Andrea Marzullo,Savino Derosa,Alberto Bravin,Ludovic Broche,Gaetano Perchiazzi

doi:10.3390/jcm8081117

Abstract

Modern ventilatory strategies are based on the assumption that lung terminal airspaces act as isotropic balloons that progressively accommodate gas. Phase contrast synchrotron radiation computed tomography (PCSRCT) has recently challenged this concept, showing that in healthy lungs, deflation mechanisms are based on the sequential de-recruitment of airspaces. Using PCSRCT scans in an animal model of acute respiratory distress syndrome (ARDS), this study examined whether the numerosity (ASnum) and dimension (ASdim) of lung airspaces change during a deflation maneuver at decreasing levels of positive end-expiratory pressure (PEEP) at 12, 9, 6, 3, and 0 cmH2O. Deflation was associated with significant reduction of ASdim both in the whole lung section (passing from from 13.1 ± 2.0 at PEEP 12 to 7.6 ± 4.2 voxels at PEEP 0) and in single concentric regions of interest (ROIs). However, the regression between applied PEEP and ASnum was significant in the whole slice (ranging from 188 ± 52 at PEEP 12 to 146.4 ± 96.7 at PEEP 0) but not in the single ROIs. This mechanism of deflation in which reduction of ASdim is predominant, differs from the one observed in healthy conditions, suggesting that the peculiar alveolar micromechanics of ARDS might play a role in the deflation process.

Highlights

The prognosis of patients suffering from acute respiratory distress syndrome (ARDS) has improved [1] with the introduction of protective mechanical ventilation in clinical practice [2], ventilator-induced lung injury (VILI) [3] can amplify local and systemic inflammatory responses and worsen the clinical course
Researchers have already used computed tomography (CT) to demonstrate that, in healthy lungs [9], multiple asynchronous events of alveolar recruitment and inflation occur through the whole inspiratory portion of the pressure–volume curve [10]
A Servo-I ventilator (Maquet, Solna, Sweden) was used to provide baseline mechanical ventilation that was delivered in pressure control mode, with a positive end-expiratory pressure (PEEP) of 3 cmH2O and a set pressure titrated to obtain a tidal volume (TV) of 6 mL/kg; the I:E ratio was 1:2; the FIO2 = 0.6

Summary

Introduction

The prognosis of patients suffering from acute respiratory distress syndrome (ARDS) has improved [1] with the introduction of protective mechanical ventilation in clinical practice [2], ventilator-induced lung injury (VILI) [3] can amplify local and systemic inflammatory responses and worsen the clinical course. It is commonly believed that the macroscopic lung change in volume derives from the isotropic inflation of the single alveoli [5,6], where changes in alveolar dimensions derive from the uniform scaling of all dimensions [7] but how alveoli behave microscopically is still only partially understood. In this respect, the present researchers recently observed [8] that in healthy lungs, airspaces reacted to deflation by changing their number more than their dimension. Animal models have revealed how, during inspiration, groups of alveoli expand while others contract [10,11,12]

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Methods

Conclusion