Cardiorespiratory Response to Exercise in Patients with Thalassemia Major

Abstract

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 < 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 < 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 consumpton of 19 ml/min/kg, heart rate was 13% higher (p < 0.01) and, at 16 ml/min/kg, cardiac output was 28% higher (p < 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: (1) cardiac output, estimated by the CO2 rebreathing method, is high and arteriovenous O2 extraction is low during exercise; (2) the high cardiac output during exercise is associated with hypoventilation; (3) the high cardiac output is independent of short-term changes in hemoglobin concentration associated with transfusion.