Cardiorespiratory response to exercise in patients with thalassemia major

The cardiorespiratory response to exercise was examined in 13 patients, 12 to 22 yr of age, who were in stable condition while receiving regular transfusions for thalassemia major. Before transfusion (Hgb, 10.8 g/dl), the patients had reduced peak oxygen consumption for body weight (by 25%, p less than 0.002) in comparison with 20 age- and sex-matched control subjects (Hgb, 13.8 g/dl). The ventilatory equivalent for carbon dioxide was significantly reduced at all work rates, and end-tidal PCO2 was abnormally high (46.3 versus 40.7 mm Hg, p less than 0.001), but ventilatory reserve, as estimated from pulmonary function tests, was normal. Both heart rate and cardiac output (as estimated by the indirect Fick method) were abnormally high during exercise; at an oxygen consumption of 19 ml/min/kg, heart rate was 13% higher (p less than 0.01) and, at 16 ml/min/kg, cardiac output was 28% higher (p less than 0.001) in the patients than in the control subjects. Nine patients were retested 3 to 8 days after transfusion (Hgb, 13.0 g/dl, p50, 26.4 mm Hg). Neither ventilatory nor circulatory abnormalities improved significantly. In patients 12 to 22 yr of age in stable condition with thalassemia major, we conclude: cardiac output, estimated by the CO2 rebreathing method, is high and arteriovenous O2 extraction is low during exercise; the high cardiac output during exercise is associated with hypoventilation; the high cardiac output is independent of short-term changes in hemoglobin concentration associated with transfusion.