A B S T R A C T The interrelationships of arterial oxygen flow rate index, oxygen binding by hemoglobin, and oxygen consumption have been examined in patients with acute myocardial infarction. Proportional extraction of oxygen increased in close association with decreasing oxygen flow rate, and hence, whole body oxygen consumption was constant over nearly a threefold variation in arterial oxygen flow rate. A reduction in hemoglobin-oxygen affinity at in vivo conditions of pH, PCo2 and temperature also occurred in proportion to the reduction in arterial oxygen flow rate. Therefore, the increased proportional removal of oxygen from arterial blood at low oxygen flow rates, required to maintain oxygen consumption, may have been facilitated by the reduced affinity of hemoglobin for oxygen at in vivo conditions. However, the decrease in affinity did not appear to explain more than 30-40%0 of the increased extraction.Respiratory alkalosis was a frequent occurrence in these patients and 2,3-diphosphoglycerate was positively associated with blood pH as well as with the time-averaged proportion of deoxyhemoglobin in arterial and venous blood.Hemoglobin-oxygen affinity measured at standard conditions and the mixed venous oxygen saturation were equally good indicators of reduced arterial oxygen flow rate in patients without shock. However, Svro2 is more easily measured and is a more useful indicator of reduced oxygen flow rate, since its relationship to oxygen flow appears to be independent of affinity changes and time.

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Serum inorganic phosphorous was decreased significantly on the third postoperative day following cardiac surgery in 18 patients initially studied. Reduced plasma inorganic phosphate has been shown to cause a reduced concentration of red cell organic phosphates, an important determinant of hemoglobin-oxygen affinity. Therefore, 10 consecutive patients were studied to determine if reduced 2,3-diphosphoglycerate (DPG) and adenosine triphosphate (ATP) concentration and increased hemoglobin-oxygen affinity accompanied the fall in serum inorganic phosphate concentration. A significant fall in 2,3-DPG and an increase in hemoglobin-oxygen affinity was present in red cells of patients studied on the first postoperative day. A reduction in red cell ATP was also present and persisted for 5 days during which time red cell 2,3-DPG returned to levels which were in excess of preoperative values. The reduction in serum inorganic phosphorous followed the reduction in red cell 2,3-DPG and correlated with the reduction in ATP. The latter changes may indicate the diversion of glucose and more specifically 1,3-DPG into the Rapoport-Leubering pathway away from ATP generation at the phosphoglycerate kinase step and the utilization of plasma inorganic phosphate for 2,3-DPG resynthesis. Neither the transfusion of stored blood nor the effect of cardiopulmonary bypass fully explained the reduction in red cell 2,3-DPG and the inefficiency of hemoglobin function postoperatively. Further studies in postsurgical patients are needed to clarify the cause of the changes observed since they are potentially deleterious, especially in the subject with compromised cardiovascular and pulmonary function.

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