PULMONARY-FUNCTION AND CARDIOPULMONARY INTERACTIONS AT MICROGRAVITY

During short-lasting microgravity the weights of surrounding organs ar e eliminated, and the lungs attain a slightly reduced volume. Long-ter m microgravity may lead to deconditioning of respiratory muscles. The distribution of ventilation becomes more homogeneous but not completel y so. Indirect estimates of the perfusion distribution point to a redu ction of gross interregional differences but a maintained intraregiona l inhomogeneity. The gas/blood interface becomes more effective, as sh own by an improved diffusion capacity. Thus, data on lung function in man at microgravity confirm that gravity is an important determinant o f the distributions of ventilation and perfusion in the lung. However, both for ventilation and perfusion, significant inhomogeneities of di stribution persist also in the weightless state, showing that non-grav ity-related factors also play important roles. It could be speculated that more homogeneous mechanical properties of the lung tissues surrou nding the heart contribute to facilitate cardiac diastolic function in microgravity.