Observations on the mechanism of hypoxaemia in acute minor pulmonary embolism.

An automated computer analysis of ventilation-perfusion lung scans was used to derive graphical data from lung scans of 11 patients with acute minor pulmonary embolism, free of pre-existing cardiorespiratory disease, and with no evidence of intrapulmonary complication or pleural effusion. In each case the analysis showed the presence of areas of lung, remote from those affected by the pulmonary embolism, that had a pathological disturbance of ventilation-perfusion matching with relative overperfusion. Such a disturbance would cause hypoxaemia. When the extent of the mismatching was calculated in terms of relative blood flow and alveolar ventilation it correlated well with the degree of arterial hypoxaemia. It is proposed that in acute minor pulmonary embolism the development of ventilation-perfusion mismatching in areas of lung unaffected by the embolic event may be an important mechanism of hypoxaemia.