Oxygen Uptake Kinetics During Heavy Submaximal Exercise: Effect of Sickle Cell Trait With or Without Alpha-Thalassemia

The role of nitrite in muscle function, susceptibility to contraction injury, and fatigability in sickle cell mice

Sickle cell disease (SCD) patients can have limited exercise capacity and muscle dysfunction characterized by decreased force, atrophy, microvascular abnormalities, fiber distribution changes, and skeletal muscle energetics abnormalities. Growing evidence suggests that in SCD there is alteration in nitric oxide (NO) availability/signaling and that nitrate/nitrite can serve as a NO reservoir and enhance muscle performance. Here, we examined effects of nitrite on muscle strength, exercise capacity, and on contractile properties of fast-(extensor digitorum longus, EDL) and slow-twitch (soleus) muscles in SCD mice. Compared to controls, homozygotes (sickling) had decreased grip strength, impaired wheel running performance, and decreased muscle mass of fast-twitch, but not slow-twitch muscle. Nitrite treatment yielded increases in nitrite plasma levels in controls, heterozygotes, and homozygotes but decreases in muscle nitrite levels in heterozygotes and homozygotes. Regardless of genotype, nitrite yielded increases in grip strength, which were coupled with increases in specific force in EDL, but not in soleus muscle. Further, nitrite increased EDL, but not soleus, fatigability in all genotypes. Conversely, in controls, nitrite decreased, whereas in homozygotes, it increased EDL susceptibility to contraction-induced injury. Interestingly, nitrite yielded no changes in distances ran on the running wheel. These differential effects of nitrite in fast- and slow-twitch muscles suggest that its ergogenic effects would be observed in high-intensity/short exercises as found with grip force increases but no changes on wheel running distances. Further, the differential effects of nitrite in homozygotes and control animals suggests that sickling mice, which have altered NO availability/signaling, handle nitrite differently than do control animals.

Association among sickle cell trait, fitness, and cardiovascular risk factors in CARDIA

The contribution of sickle cell trait (SCT) to racial disparities in cardiopulmonary fitness is not known, despite concerns that SCT is associated with exertion-related sudden death. We evaluated the association of SCT status with cross-sectional and longitudinal changes in fitness and risk for hypertension, diabetes, and metabolic syndrome over the course of 25 years among 1995 African Americans (56% women, 18-30 years old) in the Coronary Artery Risk Development in Young Adults (CARDIA) study. Overall, the prevalence of SCT was 6.8% (136/1995) in CARDIA, and over the course of 25 years, 46% (738/1590), 18% (288/1631), and 40% (645/1,611) of all participants developed hypertension, diabetes, and metabolic syndrome, respectively. Compared with participants without SCT, participants with SCT had similar baseline measures of fitness in cross-section, including exercise duration (535 vs 540 seconds; P = .62), estimated metabolic equivalent of tasks (METs; 11.6 vs 11.7; P = .80), maximum heart rate (174 vs 175 beats/min; P = .41), and heart rate at 2 minutes recovery (44 vs 43 beats/min; P = .28). In our secondary analysis, there was neither an association of SCT status with longitudinal changes in fitness nor an association with development of hypertension, diabetes, or metabolic syndrome after adjustment for sex, baseline age, body mass index, fitness, and physical activity. SCT is not associated with reduced fitness in this longitudinal study of young African American adults, suggesting the increased risk for exertion-related sudden death in SCT carriers is unlikely related to fitness. SCT status also is not an independent risk factor for developing hypertension, diabetes, or metabolic syndrome.

Antioxidant status in haemoglobin E carriers after acute and chronic strenuous exercises

Haemoglobin E (HbE), an unstable haemoglobin, is highly susceptible to oxidative damages. We examined how acute or chronic physiological challenge induced by exercise affects antioxidant response in HbE carriers. Two independent studies were conducted in individuals with HbE trait and paired normal Hb. In study 1, sedentary participants were tested in a graded maximal exercise and blood samples were collected before, immediately after, and 45 minutes after an acute exercise. Our data showed that erythrocyte glutathione peroxidase (GPx) activity failed to recover in HbE carriers after 45 minutes of rest. In study 2, athletes were trained in a 10-week strenuous training and blood samples were collected before and after training period. We found that athletes with HbE carriers showed a larger increase in plasma GPx activity compared to those with normal Hb. These data suggest that HbE carriers could cope with exercise-induced oxidative stress by adjusting endogenous antioxidant markers.

Exploratory study on oxygen consumption on-kinetics during treadmill walking in women with systemic lupus erythematosus

OBJECTIVE

To determine whether oxygen consumption (V o(2)) on-kinetics differed between groups of women with systemic lupus erythematosus (SLE) and sedentary but otherwise healthy controls.

DESIGN

Exploratory case-control study.

SETTING

Medical school exercise physiology laboratory.

PARTICIPANTS

Convenience samples of women with SLE (n=12) and sedentary but otherwise healthy controls (n=10).

INTERVENTION

None.

MAIN OUTCOME MEASURES

V o(2) on-kinetics indices including time to steady state, rate constant, mean response time (MRT), transition constant, and oxygen deficit measured during bouts of treadmill walking at intensities of 3 and 5 metabolic equivalents (METs).

RESULTS

Time to steady state and oxygen deficit were increased and rate constant was decreased in the women with SLE compared with controls. At the 5-MET energy demand, the transition constant was lower and MRT was longer in the women with SLE than in controls. For a similar relative energy expenditure that was slightly lower than the anaerobic threshold, the transition constant was higher in controls than in women with SLE.

CONCLUSION

V o(2) on-kinetics was prolonged in women with SLE. The prolongation was concomitant with an increase in oxygen deficit and may underlie performance fatigability in women with SLE.

Skeletal muscle structural and energetic characteristics in subjects with sickle cell trait, α-thalassemia, or dual hemoglobinopathy

Previous studies have shown that subjects with sickle cell trait (SCT), α-thalassemia (α-t), and the dual hemoglobinopathy (SCT/α-t) manifest subtle, albeit significant, differences during exercise. To better understand such differences, we assessed skeletal muscle histomorphological and energetic characteristics in 10 control HbAA subjects (C), 5 subjects with α-t (α-t), 6 SCT carriers (SCT) and 9 SCT carriers with α-t (SCT/α-t). Subjects underwent a muscle biopsy and also performed an incremental maximal exercise and a time to exhaustion test. There were no observable differences in daily energy expenditure, maximal power output (Pmax), or time to exhaustion at 110% Pmax ( Tex) among the groups. Blood lactate concentrations measured at the end of the Tex, muscle fiber type distribution, and mean phosphofructokinase (PFK), lactate dehydrogenase (LDH), β-hydroxyacyl-CoA-dehydrogenase (HAD), and citrate synthase (CS) activities were all similar among the four groups. However, SCT was associated with a lower cytochrome- c oxidase (COx) activity in type IIa fibers ( P < 0.05), and similar trends were observed in fiber types I and IIx. Trends toward lower creatine kinase (CK) activity ( P = 0.0702) and higher surface area of type IIx fibers were observed in SCT ( P = 0.0925). In summary, these findings support most of the previous observations in SCT, such as 1) similar maximal power output and associated maximal oxygen consumption (V̇o2max) values and 2) lower exercise performances during prolonged submaximal exercise. Furthermore, performances during short supramaximal exercise were not different in SCT. Finally, the dual hemoglobinopathy condition does not seem to affect muscle characteristics.

Remodeling of skeletal muscle microvasculature in sickle cell trait and alpha-thalassemia

The influence of sickle cell trait and/or alpha-thalassemia on skeletal muscle microvascular network characteristics was assessed and compared with control subjects [hemoglobin (Hb) AA] in 30 Cameroonian residents [10 HbAA, 5 HbAA alpha-thalassemia (alpha-t), 6 HbAS, and 9 HbASalpha-t] matched for maximal work capacity and daily energy expenditure. Subjects performed an incremental exercise to exhaustion and underwent a muscle biopsy. Muscle fiber type and surface area were not different among groups. However, sickle cell trait (SCT) was associated with lower capillary density (P < 0.05), lower capillary tortuosity (P < 0.001), and enlarged microvessels (P < 0.01). SCT carriers had reduced counts of microvessels <5-microm diameter, but a higher percentage of broader microvessels, i.e., diameter >10 microm (P < 0.05). alpha-Thalassemia seemed to be characterized by a higher capillary tortuosity and unchanged capillary density and diameter. Thus, while SCT is a priori clinically benign, we demonstrate for the first time that significant remodeling of the microvasculature occurs in SCT carriers. These modifications may possibly reflect protective adaptations against hemorheological and microcirculatory dysfunction induced by the presence of HbS. The remodeling of the microvascular network occurs to a lesser extent in alpha-thalassemia. In alpha-thalassemic subjects, increased capillary tortuosity would promote oxygen supply to muscle tissues and might compensate for the lower Hb content often reported in those subjects.

Cardiorespiratory responses during three repeated incremental exercise tests in sickle cell trait carriers

This study investigated the cardioventilatory responses during heavy exercise in sickle cell trait carriers (SCTc) and subjects with normal hemoglobin (control group). Eight SCTc and six control subjects repeated three incremental exercise tests (Iet) separated by 10-min recoveries. Cardioventilatory parameters were analyzed at rest and during the first and third Iet. No significant difference in the ventilatory parameters [notably, maximal oxygen uptake (VO2max) and the ventilatory thresholds] was observed between the two groups. The time course of power output showed a significant difference between the first and third Iet from 80% of VO2max to VO2max (P < 0.05) in both groups. In conclusion, SCTc exhibited normal ventilatory responses during three successive Iet, which strongly suggests that this population, despite the presence of HbS in their red blood cells, is not limited during this type of aerobic exercise.

Effects of progressive and maximal exercise on plasma levels of adhesion molecules in athletes with sickle cell trait with or without α-thalassemia

The aim of the study was to examine the effects of exercise on soluble vascular cell adhesion molecule-1 (sVCAM-1) and intercellular adhesion molecule-1 (sICAM-1) in sickle cell trait (SCT) athletes with or without α-thalassemia. Six athletes with SCT, seven athletes with both SCT and α-thalassemia (SCTAT), and seven control athletes (Cont) performed an incremental and maximal test on cycloergometer. Levels of sICAM-1 and sVCAM-1 were assessed at rest, immediately after the end of exercise, and 1, 2, and 24 h after exercise. Although Cont and SCTAT groups exhibited similar basal plasma levels of inflammatory and adhesion molecules, the SCT group had higher sVCAM-1 basal concentrations. Incremental exercise resulted in a significant increase of sVCAM-1 in all subjects, which remained elevated only in the SCT group during the recovery period. In conclusion, as sVCAM-1 increased with exercise and during the recovery period, our findings support the concept that SCT athletes might be at risk for microcirculatory disturbances and adhesive phenomena developing at rest and several hours after exercise. α-Thalassemia might be considered protective among exercising SCT subjects.