Blood-Gas Changes and Pulmonary Hemodynamics following Acute

Arterial and mixed venous oxygen tensions were measured in 24 patients following acute myocardial infarction while they were breathing air and 100 % oxygen. Total venous admixture and the right-to-left shunt during 100 % oxygen breathing were cal-culated. These data were related to the pulmonary arterial diastolic pressure, the cardiac index, and the central blood volume. Patients with myocardial infarction that was not complicated by congestive failure had blood gases, pulmonary shunts, and pulmonary arterial diastolic pressures com-parable to control patients who were at rest in bed. When congestive failure complicated myocardial infarction, arterial blood oxygen tension was lower, pulmonary shunting was increased, and the pulmonary arterial diastolic pressure was elevated. Cardiac index and central blood volume were usually normal. The present data quantitate the contribution of anatomic shunting to the hypoxemia observed in myocardial infarction. Hypoxemia and increased anatomic shunting are closely correlated to the degree of elevation of pulmonary arterial diastolic pressure. The interrelationships of arterial hypoxemia, venous admixture, arterial-alveolar oxygen gradient, and pulmonary arterial diastolic pressure suggest that pulmonary venous congestion is an important determinant of the hypoxemia and shunting observed in patients with acute myocardial infarction. Additional Indexing Words: Pulmonary arterial diastolic pressure Right-to-left shunt in lung Oxygen breathing IN THE PAST 5 years, arterial hypoxemia abnor has been recognized as a common occur- heart rence during the first few days of hospitaliza- normc tion after acute myocardial infarction.1-10 nisms Recently, the magnitude of the hypoxemia has cardia been related to the clinical condition of the in a patient.10 Arterial oxygen tension is most studi