Impaired oxygen kinetics in beta-thalassaemia major patients
Beta-thalassaemia major (TM) affects oxygen flow and utilization and reduces patients’ exercise capacity. The aim of this study was to assess phase I and phase II oxygen kinetics during submaximal exercise test in thalassaemics and make possible considerations about the pathophysiology of the energy-producing mechanisms and their expected exercise limitation. Methods:
Twelve TM patients with no clinical evidence of cardiac or respiratory disease and 10 healthy subjects performed incremental, symptom-limited cardiopulmonary exercise testing (CPET) and submaximal, constant workload CPET. Oxygen uptake (Vo2), carbon dioxide output and ventilation were measured breath-by-breath. Results:
Peak Vo2 was reduced in TM patients (22.3 ± 7.4 vs. 28.8 ± 4.8 mL kg−1 min−1, P < 0.05) as was anaerobic threshold (13.1 ± 2.7 vs. 17.4 ± 2.6 mL kg−1 min−1, P = 0.002). There was no difference in oxygen cost of work at peak exercise (11.7 ± 1.9 vs. 12.6 ± 1.9 mL min−1 W−1 for patients and controls respectively, P = ns). Phase I duration was similar in TM patients and controls (24.6 ± 7.3 vs. 23.3 ± 6.6 s respectively, P = ns) whereas phase II time constant in patients was significantly prolonged (42.8 ± 12.0 vs. 32.0 ± 9.8 s, P < 0.05). Conclusion:
TM patients present prolonged phase II on-transient oxygen kinetics during submaximal, constant workload exercise, compared with healthy controls, possibly suggesting a slower rate of high energy phosphate production and utilization and reduced oxidative capacity of myocytes; the latter could also account for their significantly limited exercise tolerance.
Document Type: Research Article
Affiliations: 1: Pulmonary & Critical Care Medicine Department, Cardiopulmonary Exercise Testing and Rehabilitation Laboratory, “Evgenidio” Hospital, National and Kapodistrian University of Athens, Athens, Greece 2: 1st Department of Pediatrics, National and Kapodistrian University of Athens, Medical School, Athens, Greece 3: 1st Department of Internal Medicine, National and Kapodistrian University of Athens, Medical School, “Laiko” Hospital, Athens, Greece
Publication date: 2009-07-01