Pulmonary arterial and right atrial pressure, cardiac output, lung volumes, blood gases, VD/VT ratio and alveoloarterial oxygen tension gradient were measured in 21 subjects with pulmonary hypertension due to recurrent pulmonary emboli. The mean pressure in pulmonary artery ranged from 19.5 to 97.0 mm Hg. Respiratory examination revealed normal spirometry and slight hypoxemia associated with an increase in alveoloarterial oxygen tension gradient. Lung transfer factor for CO was measured in nine patients; it was either normal or slightly reduced. Hyperventilation was found in the majority of patients already at rest. Pulmonary hypertension was believed to be the most important cause of alveolar hyperventilation in these patients. Total ventilation and VD/VT ratio were measured in 22 normal subjects at rest and during exercise, both with and without unilateral pulmonary artery occlusion. At rest, pulmonary artery occlusion did not lead to any change in total ventilation; during exercise, a 30-percent increase in total ventilation was observed with pulmonary artery occlusion. Pulmonary artery occlusion led to an increase in functional dead space only in those subjects in whom the tidal volume exceeded 700 ml. Whether this increase in tidal volume was associated with exercise or not did not make any difference. In patients with recurrent pulmonary embolism, the value of functional dead space was also higher only in subjects breathing with higher tidal volumes. It seems, therefore, that in the patients the same principle of unmasking the alveolar dead space by the increase in tidal volume can be demonstrated as in the model experiments with pulmonary artery occlusion

Keywords:
Pulmonary embolism, Arterial oxygen tension, Respiratory dead space, Pulmonary artery occlusion
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© 1973 S. Karger AG, Basel
1973
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