Decreased Affinity of Blood for Oxygen in Patients with Low-Output Heart Failure

Oxygen affinity of blood was measured in 16 patients (nonsmokers) without anemia and with clinical evidence of low cardiac output. Of these patients, 12 were catheterized and showed an arteriovenous oxygen concentration difference across the lungs greater than 5 ml/100 ml. The partial pressure of oxygen required to half-saturate their blood with oxygen (P50) averaged 29.4 mm Hg (SD ± 1.9). Blood from normal subjects (nonsmokers) had an average P50 of 27.3 mm Hg (SD ± 0.9). The decreased oxygen affinity found in blood of patients with low levels of cardiac output is considered as a compensatory adjustment to poor tissue blood flow, promoting the diffusion of oxygen from blood in tissue capillaries to intracellular sites of utilizaton.