Analysis of mechanical stresses within the alveolar septa leading to pulmonary edema

Mechanical ventilation has been associated with pulmonary edema in the clinical setting, but the pathophysiological mechanisms of this process have not been clearly defined. Experimental studies have shown that high transpulmonary pressures resulting from ventilation may damage the capillary walls, thereby leading to edema. Knowledge of the stress distribution within the alveolar septa would be an important step in understanding this phenomenon. A newly developed saline-filled alveolar sac model was utilized for analysis of septal stresses in young and aging healthy lungs, in order to examine their vulnerability to pulmonary edema during ventilation. Significant stress concentrations were shown to develop near highly curved regions (small local radii of less than 4 mum in a lung inflated to 80% could be as high as 25 times that of average septal stresses. The combination of elevated stress sites that are formed in the stiffer parenchyma of the aging lung, together with the cyclic loading of ventilation, may explain the gaps and breaks previously observed in pulmonary edema.