OYONO-ENGUÉLLÉ, S., D. LE GALLAIS, A. LONSDORFER, C. DAH, H. FREUND, P. BOGUI, and J. LONSDORFER. Cardiorespiratory and metabolic responses to exercise in HbSC sickle cell patients. Med. Sci. Sports Exerc., Vol. 32, No. 4, pp. 725–731, 2000.
Purpose: Relative to healthy control individuals with normal hemoglobin (Hb), patients carrying the double heterozygous form of sickle cell disease (HbSC) display an impaired oxygen transport capacity. The present study was undertaken to determine the influence of the decreased oxygen availability associated with the presence of HbSC on the cardiorespiratory and metabolic responses to endurance exercise.
Methods: Eleven black men affected by the double heterozygous form of the sickle cell disease (HbSC group) and seven healthy subjects with normal Hb (HbAA group) of the same ethnic origin submitted successively to an incremental exercise test to exhaustion on a cycle ergometer for the determination of their maximal tolerated power and to a 20-min endurance exercise.
Results: The HbSC had a significantly lower exercise tolerance than the HbAA. During the endurance exercise, they exhibited furthermore significantly lower V̇O2, V̇CO2, and minute ventilation V̇E than the HbAA. Despite the fact that the HbSC exercised at a significantly lower mean absolute work rate than the HbAA, except for the ventilatory equivalent for CO2 (V̇E/V̇CO2), which was higher (P < 0.001) in the HbSC group, the other parameters recorded during the 20-min endurance exercise (heart rate, arterial PaO2, PaCO2, pH, lactate, and V̇E/V̇O2, the ventilatory equivalent for O2) and during the subsequent recovery (blood lactate) were similar for both groups.
Conclusion: The study underscores the importance of considering relative work rate as well as absolute work rate to arrive at a correct interpretation of exercise and recovery data. The results give evidence that the modifications of homeostasis brought into play by exercise were shifted toward distinctly lower absolute work rates in HbSC patients.
Sickle cell diseases are among the most common of genetic diseases, affecting millions of people worldwide. They are the result of a single mutation in the globin gene causing the substitution of valine for glutamic acid at position 6 in the β-subunit of the tetrameric hemoglobin (Hb) molecule. The immediate consequence of this substitution is that the resulting HbS polymerizes in the deoxygenated form. The clinical manifestations associated with this mutation such as anemia and hemolytic events are particularly severe in individuals homozygous for HbSS. They are less pronounced for patients carrying the double heterozygous form HbSC, because the presence of HbC (a further hemoglobinopathy caused by the substitution of lysine for glutamic acid in the β-subunit of Hb) dilutes the deoxygenated HbS in the red blood cells. Nevertheless, as mentioned by Lonsdorfer et al. (20), relative to healthy control subjects with normal HbAA, patients with HbSC show a decreased oxygen transport capacity. The presence of HbSC has a limiting effect on maximal oxygen consumption and muscular exercise tolerance and also promotes an earlier rise of the blood lactate concentrations associated with impaired abilities to exchange and remove lactate during graded exercise (11).
The square wave endurance exercise test (SWEET) is a particular type of exercise in which 1 min periods of very heavy work termed “peaks” alternate with 4-min periods of moderate work termed “base levels” (12–14). This type of exercise mimics the sequence usually encountered in team sports, and the periods of moderate exercise may be viewed as phases of active recovery. Based on the similarity with interval training (except for active recovery during the SWEET versus passive recovery during interval training), several authors have used the SWEET protocol to successfully train healthy subjects (14,22) as well as patients (15,23). It has also been used by Le Gallais et al. (19) for the comparison of the changes in cardiorespiratory and metabolic parameters among sickle cell trait carriers (HbAS) and healthy subjects (HbAA).
The present study was undertaken to investigate the effect of the lowered oxygen transport capacity associated with the disease on the time courses of arterial blood lactate concentrations during and after the SWEET protocol. A second aim was to extend the description of the changes in cardiorespiratory and metabolic parameters induced by this type of exercise which is not yet commonly used (16) and to seek differences between HbAA and HbSC subjects.