Effects of hemodilution on O2 transport in high-altitude polycythemia.

A native of the Peruvian Andes (4,250 m) was studied before and after isovolemic hemodilution of the hematocrit from 62 to 42%. O2 transport was studied with newly developed catheters in the radial and pulmonary arteries. These catheters allowed continuous measurement of arteriovenous O2 content and intermittent cardiac output by thermodilution. During exercise tests, breath-by-breath gas exchange measurements also allowed cardiac output to be calculated by the O2-Fick technique. A complex series of interrelated physiological changes occurred in response to hemodilution. These included increased ventilation, increased arterial and mixed venous PO2, increased cardiac output (both heart rate and stroke volume), and improved ventilation-flow match. The general improvement in symptoms that followed hemodilution correlated well with increased anaerobic threshold and mixed venous PO2 during exercise.

Normal whole blood Bohr effect in Peruvian natives of high altitude.

Measurements of whole blood O2 affinity were made with an automatic technique that allowed recording of O2 saturation continuously over a range of PO2 of 1 to 150 torr at constant pH and PCO2 with fresh samples of blood obtained from 5 natives of high altitude at Morococha, Peru (altitude, 4540 m). The results were not significantly different from those obtained with controls living at sea level with regard to the dlog P50/dpH slope at constant PCO2 or at constant base excess. Both results also agree with previous studies with normal sea-level blood. Thus earlier claims of an increased Bohr in Peruvian high-altitude natives is not supported.

Simulation of continuous blood O2 equilibrium curve over physiological pH, DPG, and Pco2 range.

We analyzed 56 O2 equilibrium curves of fresh human blood, each from 0 to 150 Torr Po2. The data were collected over ranges of values for the 2,3-diphosphoglyceric acid-to-hemoglobin concentration ratio [DPG]/[Hb] of 0.2-2.7, for pH of 7.0-7.8, and for Pco2 of 7-70 Torr. Each curve was characterized according to the Adair scheme for the stepwise oxygenation of Hb, and the resulting constants (a1, a2, a3, a4) were analyzed to allow the simulation of the entire O2 equilibrium curve under any conditions of [DPG]/[Hb], pH, and Pco2 in the specified range. This analysis provides a powerful tool to study the affinity of Hb for O2 within the red blood cell and to predict the shape of the O2 equilibrium curve in various physiological and pathological states. Other attempts to predict blood O2 affinity have considered only P50 (the Po2 at one-half saturation with O2) or have provided too little data for continuous simulations.