Hemodynamic response to respiratory tract infections. Studies of total and peripheral blood flow

Plasma volume, cardiac output, and extremity blood flow were measured in 42 patients whose acute respiratory tract infections were due to a variety of viral and bacterial agents. Previously normal subjects and patients with pre-existing diseases were studied. A local increase in upper extremity blood flow and an increase in total cardiac output were the most striking results. The increase in extremity flow occurred with a decrease in vascular resistance. The increased cardiac output was mediated mainly through an increase in the heart rate. Plasma volume showed a tendency to be lower during acute infection. The patients generally had mild hyperventilation and resultant hypocapnia. All patients with hypercapnia had pre-existing lung disease. Hypercapnia did not preclude the usual increased blood flow in response to fever. Five patients who eventually died from the respiratory infections differed from the others in that all had pre-existing lung disease. The peripheral blood flow failed to increase in response to the infection, and carbon dioxide was frequently retained.