81 O2 TRANSPORT IN CONGENITAL HEART DISEASE

Abstract

The physiology of oxygen delivery was studied in 83 patients (ages ld-16yr) at cardiac catheterization. Oxygen consumption (VO2), arterial and venous blood gases and oxygen saturations (O2 satrange, 41-98%), hemoglobin concentration (Hb), 2, 3 DPG and P50 levels were measured; cardiac output (CO), systemic oxygen transport (SOT), arterial and venous oxygen contents ([art] and [ven]) and the SOT/VO2 ratio (1/extraction coefficient) were calculated. P50 averaged 32 torr, compared to 28 torr in 8 control children. The composite in vivo O2-Hb dissociation curve was broad; PO2's varied from 39-60 torr at 80% O2sat. P50, 2, 3 DPG, Hb and O2 sat varied widely and inconsistently with PO2, [art] and [ven], but resulted in clustering of [art] near 165 ml/L (SD ±23), over a wide range of PO2 and Hb. SOT varied directly with CO (r=0.82 p<.001), but not with [art], PO2 or P50. VO2 varied widely at normal or high levels of SOT, but decreased linearly at SOT levels below 400 ml/min/M2. SOT/VO2 varied inversely with [ven], falling to 2.0 and plateauing below [ven] of 100 ml/L; SOT/VO2 did not correlate with PO2 [art] or P50. These data suggest O2 sat cannot be predicted accurately from measured PO2, but must be measured directly; 2, 3 DPG and P50 fluctuate to stabilize [art]; SOT is determined primarily by CO and limits O2 consumption at low levels of transport; and [ven] is the primary determinant of O2 extraction.