Chest, Vol 87, 293-302, Copyright © 1985 by American College of Chest Physicians

ARTICLES

Impact of profound reductions of PaO2 on O2 transport and utilization in congenital heart disease

J Theodore, ED Robin, CM Burke, SW Jamieson, A Van Kessel, D Rubin, EB Stinson and NE Shumway

A group of eight adult patients with congenital cyanotic heart disease (CCHD) with PaO2 values of less than 32 mm Hg at rest and/or exercise were studied. Four of the patients were re-studied after heart-lung transplantation and restoration of PaO2 to normal values. All eight patients showed increased red cell counts (polycythemia), whereas frankly elevated hemoglobin concentrations were found in only one patient. There was no impressive change in the affinity of hemoglobin for O2 as compared to normal subjects. Blood lactate concentrations were normal at rest before transplantation, rose very modestly during moderate exercise, and were normal following transplantation indicating that the concept of anaerobic threshold is not valid in the present group of patients. Cardiac index was not elevated in the pretransplantation period, indicating that an elevated cardiac output is not an essential adaptive mechanism for dealing with hypoxia. In the pre-transplant period, O2 consumption was elevated as compared to normal values and almost doubled during exercise despite a further decline in PaO2 and SaO2; this establishes that the rate of mitochondrial O2 utilization is maintained despite profound reduction in PaO2. These patients are capable of moderate exercise and normal brain function despite severe hypoxia and the absence or attenuation of various adaptive mechanisms for dealing with hypoxia. Further study of the specifics of O2 transport and utilization in similar patients should prove rewarding.