Nongravitational perfusion distribution

There also appears to be a non-homogeneous distribution of perfusion in non-gravitational planes, i.e. in the medial-lateral and apical-basal directions in the supine position. Thus more perfusion in central parts of the lung than in the periphery has been found during mechanical ventilation in the anesthetized dog, and a redistribution of blood flow towards the lateral and basal borders has been observed during ventilation with positive end-expiratory pressure. More recent studies of the perfusion distribution in an awake healthy man using single-photon-emission CT (see below) suggest a maximum blood flow in the middle of the lung, although different results and opinions have also been presented ( H..u.g,h.e.s,..1.991.). It has been proposed that the decreasing blood flow towards the periphery of the lung is due to the increasing length of the pulmonary arterial vessels which increases the resistance to blood flow. Blood flow has also been fitted to a fractal model with the provocative conclusion that gravity is only a minor determinant of blood flow distribution in the lung. However, full agreement has not been reached on either the degree of non-gravitational inhomogeneity of perfusion or possible mechanisms behind such inhomogeneity.

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