Impaired oxygen kinetics in beta-thalassaemia major patients.
OBJECTIVE
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).


CONCLUSIONS
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.
Vasileiadis
I
I
Pulmonary & Critical Care Medicine Department, Cardiopulmonary Exercise Testing and Rehabilitation Laboratory, Evgenidio Hospital, National and Kapodistrian University of Athens, Athens, Greece.
Roditis
P
P
Dimopoulos
S
S
Ladis
V
V
Pangalis
G
G
Aessopos
A
A
Nanas
S
S
D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism; D004452:Echocardiography; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D005319:Fetal Hemoglobin / Q000378:metabolism; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D007700:Kinetics; D008297:Male; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology; D013147:Spirometry; D014797:Vital Capacity / Q000502:physiology; D055815:Young Adult; D017086:beta-Thalassemia / Q000097:blood / Q000503:physiopathology*
D002245:Carbon Dioxide; D005319:Fetal Hemoglobin; D010100:Oxygen