Oxygen consumption in children with congenital diseases of the heart

1. An open-circuit method for the measurement of oxygen consumption in children which is suitable for use during cardiac catheterization has been described.

2. Since it has been previously shown that there is no systematic error in this method, the accuracy of the method is described by the random error (i.e. reproducibility). The reproducibility of the method has been determined by the repeated measurement of oxygen consumption in children with congenital diseases of the heart under specified ‘standard’ conditions.

3. A simple method of predicting the oxygen consumption in these children was devised by subjecting the data to a multivariate regression analysis.

4. It is concluded that the accuracy of these predictions, although considerably better than that in the published literature, is not good enough to merit its use in the routine haemodynamic assessment.

Tritiated digoxin. 18. Studies in infants and children

Tritiated digoxin turnover studies were performed in nine children aged 4 days to 7 years. Mean serum turnover time was 32.5 (range 18-48) hours, and the 3-day urine and stool excretion was 55% of the total dose administered. These findings are quite similar to those observed in adults and indicate that the larger doses of digoxin required for digitalization in infants are not accompanied by increased metabolism or excretion but by increased blood levels and presumably increased tissue concentrations of the glycoside.

Arterial oxygen desaturation and intestinal absorption of xylose

Small-bowel absorption was studied using the xylose absorption test in 16 patients with varying degrees of arterial oxygen desaturation due to either congenital heart disease or chronic lung disease. Xylose absorption was decreased in the cases with more severe desaturation. The correlation of xylose absorption with arterial saturation was significant. In nine cases hypoxia was relieved by either oxygen administration or surgery. Repeat testing showed an increase in xylose absorption in every case, the mean increase being 11.7%, which was statistically significant.

Alteration of glucose and insulin metabolism in congenital heart disease

Children with left-to-right shunt, with and without congestive heart failure, were found to have impaired glucose tolerance tests (GTT). In cyanotic children normal levels of glucose were found in association with abnormally high levels of insulin following oral GTT. Several possible mechanisms are proposed to explain the different glucose tolerance alterations: (1) Suppression of insulin release appeared to partially explain the low levels of insulin in congestive heart failure. This suppression may be related to the high levels of circulating norepinephrine found in these patients. (2) Excessive clearance of insulin by the lung may also be responsible for the reduced arterial insulin levels in patients with left-to-right shunt, and underclearance of insulin for the abnormally higher arterial insulin levels in patients with right-to-left shunts in whom a significant amount of venous blood has bypassed the lung. (3) Hypoxia of the pancreas and the liver in cyanotic patients and those with congestive heart failure may explain the reduction of insulin levels in the hepatic vein following i.v. glucose tolerance tests. An excess production of a glucagonlike gastrointestinal factor in cyanotic children may partially explain the abnormally high levels of insulin following oral GTT.

The effects of deoxygenation of adult and fetal hemoglobin on the synthesis of red cell 2,3-diphosphoglycerate and its in vivo consequences

Patients over 1 month of age with arterial oxygen pressures of less than 60 mm Hg were found to have elevated red cell 2,3-diphosphoglycerate (2,3-DPG) levels and blood with a decreased affinity for oxygen. The increase in 2,3-DPG was proportional to the degree of hypoxemia. In patients under 1 month of age this relationship was not observed. Red cells from adults, but not newborns, showed rapid increases in 2,3-DPG when incubated under nitrogen. Adult, but not fetal, deoxyhemoglobin was shown to facilitate in vitro synthesis of 2,3-DPG by binding this organic phosphate and relieving the product inhibition of 2,3-DPG mutase. Throughout a wide range change in oxygen affinity as measured by the P(50) is linear with respect to the 2,3-DPG concentration; a change of 430 mmumoles of 2,3-DPG/ml of red blood corpuscles (RBC) resulting in a change of the P(50) of 1 mm Hg. It appears that the 2,3-DPG of the adult's red cells responds rapidly to metabolic and environmental influences and in turn effects metabolism and the cellular environment. Many of these effects are not shared by the red cells of the newborn.