Material characterization of ovine lung parenchyma at pressures representing the breathing cycle.

Lung tissue behavior at different physiological pressures has not been well studied. The objectives of this study therefore were to characterize lung tissue at different physiologically relevant pressures within the breathing cycle, quantifying how the tissue deforms, and determining associated shear moduli. We utilized fresh ovine lungs harvested and tested within 8 hours of sacrifice, using spherical indentation and digital image correlation (DIC). Tests were conducted at three different pressures - 0, 4, and 10 cmH2O. Lungs from a total of ten animals were tested. The resulting instantaneous shear modulus, relaxed shear modulus, and shear modulus ratio were used for statistical analyses, via a mixed effect model. The instantaneous shear modulus had trending differences between pressures (0.05 < p < 0.1), however, the relaxed shear modulus did not (p > 0.1). The modulus ratio was considered significantly different, as p < 0.05. When comparing pressurized (4 and 10 cm H20 together) to non-pressurized, both instantaneous and relaxed shear moduli were significantly lower than the ambient pressure state.