Effects of positional changes on alveolar dynamics and respiratory mechanics in rats with and without acute lung injury.

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Lung protective mechanical ventilation is a hallmark of modern anesthesia and intensive care and has been shown to significantly reduce morbidity and mortality in both, lung healthy and injured patients. Beside the use of low tidal volumes, positional therapy has been shown to be associated with beneficial effects.Respiratory resistance and compliance as well as blood gas analysis are routinely used at the bedside but provide only limited information about the regional distribution of ventilation and perfusion. Moreover, imaging modalities such as CT and MRI provide information about the global structure of the lung, but there is limited knowledge about the alveolar dynamic, neither in healthy nor in injured lungs. It is assumed that especially in injured lungs at low pressure, alveoli in gravitationally dependent areas collapse, but this could not be proven by any imaging modality so far. In this proposal, the effects of mechanical ventilation on the structure and function of alveolar tissue will be imaged in vivo in lung healthy and rats with surfactant depletion induced acute lung injury. We will image the same areas of the lung in both, prone and supine position. Presumable there will be changes in alveolar structure and dynamic within the same lung region based on the gravitationally position. Especially in the injured lung, we assume that alveoli will be on average smaller and partly liquid filled.Ventilation parameters such as airway and tissue resistance and compliance will be measured simultaneously with the imaging of alveolar structures and correlated to them. From the combination of alveolar dynamics and lung elasticity, we hope to gain a better understanding for the physiological and pathophysiological processes during mechanical ventilation. Our results will hopefully help the clinician at the bedside to better interpret global lung functional measurements and help to better understand and maybe improve lung protective mechanical ventilation strategies to further reduce morbidity and mortality of mechanically ventilated patients.