Exercise Capacity and Biomarkers Among Children and Adolescents With Sickle Cell Disease

BACKGROUND

Sickle cell disease is the most common genetic hemoglobinopathy globally and systemically affects body functioning, decreasing exercise capacity.

OBJECTIVE

To assess exercise capacity through the 6-minute walk test (6MWT) and biomarkers in children and adolescents with sickle cell disease.

MATERIALS AND METHODS

Cross-sectional study involving 20 children and adolescents from Brazil. Demographic and socioeconomic data were obtained. Baseline measurements included biomarkers (red blood cells, hemoglobin, hematocrit, white blood cells, platelets, reticulocytes, lactate dehydrogenase, creatine phosphokinase, C-reactive protein, interleukin 6, and fetal hemoglobin). The following data were obtained before, during, and after the 6MWT: heart rate, blood pressure, and peripheral oxygen saturation.

RESULTS

Eighteen children and adolescents ages 5-14 years old were analyzed, 61.1% boys, 100% black or brown, and 61.1% in primary education, with low household income. The average distance walked in 6MWT was 463.8 (137.7) m, significantly less than the predicted value (P < .001). The distance of 6MWT was associated positively with age (P = .042) and inversely with reticulocyte count (P = .42) and interleukin 6 (P = .00). Age modified the effect of interleukin 6 in younger children (P = .038).

CONCLUSION

Our findings suggest increased baseline levels of biomarkers of hemolysis and inflammation impact on 6MWT performance.

Altered cardiac reserve is a determinant of exercise intolerance in sickle cell anaemia patients

BACKGROUND

The underlying mechanisms of exercise intolerance in sickle cell anaemia (SCA) patients are complex and not yet completely understood. While latent heart failure at rest could be unmasked upon exercise, most previous studies assessed cardiac function at rest. We aimed to investigate exercise cardiovascular reserve as a potential contributor to exercise intolerance in adult SCA patients.

METHODS

In this observational prospective study, we compared prospectively 60 SCA patients (median age 31 years, 60% women) to 20 matched controls. All subjects underwent symptom-limited combined exercise echocardiography and oxygen uptake (VO₂ ) measurements. Differences between arterial and venous oxygen content (C(a-v)O₂ ) were calculated. Cardiac reserve was defined as the absolute change in cardiac index (Ci) from baseline to peak exercise.

RESULTS

Compared to controls, SCA patients demonstrated severe exercise intolerance (median peakVO₂ , 34.3 vs. 19.7 ml/min/kg, respectively, p < .0001). SCA patients displayed heterogeneously increased Ci from rest to peak exercise (median +5.8, range 2.6 to 10.6 L/min/m²) which correlated with peakVO₂ (r = 0.71, p < .0001). In contrast, the C(a-v)O₂ exercise reserve was homogenously reduced and did not correlate with peakVO₂ (r = 0.18, p = .16). While haemoglobin level and C(a-v)O₂ were similar in SCA subgroups, SCA patients in the lower VO₂ tertile had chronotropic incompetence and left ventricular diastolic dysfunction (left atrial peak longitudinal strain was reduced, and both E/e' ratio and left atrial volume index were increased) and were characterized by a reduced cardiac reserve, +5.0[4.2-5.5] compared to +6.7[5.5-7.8] L/min/m² for the rest of the patient cohort, p < .0001.

CONCLUSIONS

Altered cardiac reserve due to chronotropic incompetence and left ventricular diastolic dysfunction seems to be an important determinant of exercise intolerance in adult SCA patients.

Physical Impairment and Function in Children and Adolescents With Sickle Cell Disease: A Systematic Review

OBJECTIVE

To examine physical impairments and physical function in children and adolescents with sickle cell disease (SCD).

DATA SOURCES

PubMed, Embase (embase.com), Cumulative Index to Nursing and Allied Health (EBSCO), Cochrane Central Register of Controlled Trials (Wiley), and Dissertations and Theses (ProQuest) were searched from January 1, 1990, to September 25, 2020. References retrieved were required to include a term for SCD and a term for physical impairments or physical function. Results were limited to articles with children and adolescents and in the English language.

STUDY SELECTION

A total of 3054 nonduplicate articles were independently screened by 2 reviewers, resulting in 240 articles for full-text review. The full-text review, performed by 2 independent reviewers, resulted in 67 articles.

DATA EXTRACTION

Data were extracted from each full text to a custom Excel document by a single reviewer and were verified by a secondary reviewer.

DATA SYNTHESIS

The studies identified in this systematic review offer evidence that children and adolescents with SCD demonstrate physical impairments and physical function limitations compared with control participants as noted by varying percentages in deficits up to 19%-58% in muscle and bone composition and/or symptoms, muscle strength, cardiopulmonary function, motor performance, physical activity, and physical function domains of quality of life questionnaires.

CONCLUSIONS

Children and adolescents with SCD present with physical impairments and physical function limitations. Scientists and clinicians should consider developing collaborative standards to define and objectively measure physical impairment and function in this population to comprehensively examine the underlying factors that contribute to physical impairments and function.

Safety of maximal cardiopulmonary exercise testing in individuals with sickle cell disease: a systematic review

OBJECTIVE

We evaluated the safety of maximal cardiopulmonary exercise testing (CPET) in individuals with sickle cell disease (SCD). Maximal CPET using gas exchange analysis is the gold standard for measuring cardiopulmonary fitness in the laboratory, yet its safety in the SCD population is unclear.

DESIGN

Systematic review.

DATA SOURCES

Systematic search of Medline (PubMed), EMBASE, Cochrane, ClinicalTrials.gov and professional society websites for all published studies and abstracts through December 2020.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Two reviewers independently extracted data of interest from studies that assessed safety outcomes of maximal CPET in children and adults with SCD. A modified version of the Newcastle-Ottawa Scale was used to assess for risk of bias in studies included.

RESULTS

In total, 24 studies met inclusion/exclusion criteria. Adverse events were reported separately or as part of study results in 36 (3.8%) of 939 participants with SCD undergoing maximal CPET in studies included. Most adverse events were related to transient ischaemic changes on ECG monitoring or oxygen desaturation during testing, which did not result in arrhythmias or other complications. Only 4 (0.43%) of 939 participants experienced pain events due to maximal CPET.

CONCLUSION

Maximal CPET appears to be a safe testing modality in children and adults with SCD and can be used to better understand the physiological basis of reduced exercise capacity and guide exercise prescription in this population. Some studies did not focus on reporting adverse events related to exercise testing or failed to mention safety monitoring, which contributed to risk of bias.

Physiological Evaluation for Endurance Exercise Prescription in Sickle Cell Disease

PURPOSE

Although strenuous exercise may expose sickle cell disease (SCD) patients to risks of vaso-occlusive crisis, evidence suggests that regular endurance exercise may be beneficial. This study aimed to test (i) the safety and usefulness of a submaximal incremental exercise in evaluating physical ability of SCD patients and identify a marker for the management of endurance exercise and (ii) the feasibility of endurance exercise sessions in SCD patients.

METHODS

Twenty adults with SCD (12 men and 8 women) performed a submaximal incremental exercise used to determine the first lactate threshold (LT1) and stopped as soon as blood lactate concentration ([lactate]b) reached ≥4 mmol·L. Fifteen of those patients (8 men and 7 women) also performed three 30-min endurance exercise sessions at ~2.5 mmol·L of [lactate]b on separate occasions.

RESULTS

LT1 occurred at 47 ± 3 and 33 ± 3 W for men and women, respectively, demonstrating the extreme deconditioning and, thus, low physical ability of adult SCD patients. During endurance exercise, peripheral oxygen saturation and [lactate]b most often remained stable and within acceptable ranges.

CONCLUSIONS

The proposed strategy of submaximal incremental exercise allowed safe determination of LT1, an important parameter of patients' physical ability. The study also demonstrated the feasibility and safety of individually tailored endurance exercises at ~2.5 mmol·L of [lactate]b. These latter results suggest that endurance training programs may be considered for adult SCD patients and that the method proposed here may be helpful in that regard.

Exercise Testing of Adolescents and Young Adults With Sickle Cell Disease: Perceptual Responses and the Gas Exchange Threshold

For individuals with sickle cell disease (SCD), mild to moderate exercise is advised, but self-regulation of these intensities is difficult. To regulate intensity, one SCD recommendation is to stop exercising at the first perception of fatigue. However, perceived effort and affect (how one feels) are perceptual cues that are commonly used to guide exercise intensity. This study (a) examined perceived effort, affect, and fatigue in relation to metabolic state (gas exchange) in adolescents and young adults (AYAs) with SCD, (b) explored guidelines AYAs use to self-regulate exercise, and (c) compared perceived effort and affect at gas exchange threshold (GET) with healthy counterparts. Twenty-two AYAs with SCD completed an incremental cycle test. Perceived effort, affect, and fatigue were assessed every 2 minutes. A mixed-effects linear model was conducted to model changes in effort, affect, and fatigue across time. Mean scores of effort and affect at GET were compared with published data of healthy counterparts. Participants were queried about self-regulation exercise strategies. Findings indicated that both perceived fatigue and effort at GET was lower than expected. Perceived effort was lower (p < .0001), and perceived affect was significantly higher (p = .0009) than healthy counterparts. Interviews revealed that most participants (95%) do not stop exercising until fatigue is moderate to severe, and many (73%) do not stop until symptoms are severe (chest tightness, blurry vision). Nurses should review guidelines for safe exercise with AYAs with SCD. Exercise training may be beneficial to AYAs with SCD for learning how to interpret bodily responses to exercise to improve self-regulation.

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.

Cardiorespiratory pathogenesis of sickle cell disease in a mouse model

The nature and development of cardiorespiratory impairments associated with sickle cell disease are poorly understood. Given that the mechanisms of these impairments cannot be addressed adequately in clinical studies, we characterized cardiorespiratory pathophysiology from birth to maturity in the sickle cell disease SAD mouse model. We identified two critical phases of respiratory dysfunction in SAD mice; the first prior to weaning and the second in adulthood. At postnatal day 3, 43% of SAD mice showed marked apneas, anemia, and pulmonary vascular congestion typical of acute chest syndrome; none of these mice survived to maturity. The remaining SAD mice had mild lung histological changes in room air with an altered respiratory pattern, seizures, and a high rate of death in response to hypoxia. Approximately half the SAD mice that survived to adulthood had an identifiable respiratory phenotype including baseline tachypnea at 7–8 months of age, restrictive lung disease, pulmonary hypertension, cardiac enlargement, lower total lung capacity, and pulmonary vascular congestion. All adult SAD mice demonstrated impairments in exercise capacity and response to hypoxia, with a more severe phenotype in the tachypneic mice. The model revealed distinguishable subgroups of SAD mice with cardiorespiratory pathophysiology mimicking the complications of human sickle cell disease.

Cognitive and behavior deficits in sickle cell mice are associated with profound neuropathologic changes in hippocampus and cerebellum

Strokes are perhaps the most serious complications of sickle cell disease (SCD) and by the fifth decade occur in approximately 25% of patients. While most patients do not develop strokes, mounting evidence indicates that even without brain abnormalities on imaging studies, SCD patients can present profound neurocognitive dysfunction. We sought to evaluate the neurocognitive behavior profile of humanized SCD mice (Townes, BERK) and to identify hematologic and neuropathologic abnormalities associated with the behavioral alterations observed in these mice. Heterozygous and homozygous Townes mice displayed severe cognitive deficits shown by significant delays in spatial learning compared to controls. Homozygous Townes also had increased depression- and anxiety-like behaviors as well as reduced performance on voluntary wheel running compared to controls. Behavior deficits observed in Townes were also seen in BERKs. Interestingly, most deficits in homozygotes were observed in older mice and were associated with worsening anemia. Further, neuropathologic abnormalities including the presence of large bands of dark/pyknotic (shrunken) neurons in CA1 and CA3 fields of hippocampus and evidence of neuronal dropout in cerebellum were present in homozygotes but not control Townes. These observations suggest that cognitive and behavioral deficits in SCD mice mirror those described in SCD patients and that aging, anemia, and profound neuropathologic changes in hippocampus and cerebellum are possible biologic correlates of those deficits. These findings support using SCD mice for studies of cognitive deficits in SCD and point to vulnerable brain areas with susceptibility to neuronal injury in SCD and to mechanisms that potentially underlie those deficits.

Longitudinal differences in aerobic capacity between children with sickle cell anemia and matched controls

BACKGROUND

The purpose of this study was to compare longitudinal trajectories of maximal aerobic capacity in children with sickle cell anemia (SCA) and matched healthy controls, and explore whether these trajectories were associated with selected physiologic variables.

PROCEDURE

Children with SCA (n = 33) and healthy controls (n = 30) matched at baseline for race, sex, Tanner stage, height, and weight completed three consecutive annual fitness assessments (VO2peak ). Data were compared between the groups at each time point and within groups over time. Change in VO2peak between the two groups over time was assessed using a linear mixed model with age, sex, fat-free mass (FFM), Tanner stage, and hemoglobin (Hgb) concentration as covariates.

RESULTS

At baseline, children with SCA had significantly lower Hgb concentration (8.9 vs. 13.7 g/dL, P < 0.001) and relative VO2peak (24.2 vs. 27.9 ml/kg/min, P = 0.006) than healthy controls. Over time, children with SCA had smaller increases than healthy controls in VO2peak (-0.1 and +4.9 ml/kg/min, P < 0.001), Tanner stage at year 2 (15% and 66% Tanner 4, P < 0.001), and FFM (+4.0 and +6.8 kg, P = 0.02). Changes in Hgb concentration did not differ between groups (+0.03 and +0.09 g/dL, P = 1.0). After adjusting for age, sex, Tanner stage, FFM, and Hgb concentration the differences in change in VO2peak over time remained significant (P < 0.001).

CONCLUSION

Children with SCA demonstrate lower relative VO2peak compared to healthy children and the difference increases over time. The difference in VO2peak trajectories between the two groups during puberty remains significant after adjusting for age, sex, FFM, Tanner stage, and Hgb concentration.

Reduced fitness and abnormal cardiopulmonary responses to maximal exercise testing in children and young adults with sickle cell anemia

Physiologic contributors to reduced exercise capacity in individuals with sickle cell anemia (SCA) are not well understood. The objective of this study was to characterize the cardiopulmonary response to maximal cardiopulmonary exercise testing (CPET) and determine factors associated with reduced exercise capacity among children and young adults with SCA. A cross-sectional cohort of 60 children and young adults (mean 15.1 ± 3.4 years) with hemoglobin SS or S/β(0) thalassemia and 30 matched controls (mean 14.6 ± 3.5 years) without SCA or sickle cell trait underwent maximal CPET by a graded, symptom-limited cycle ergometry protocol with breath-by-breath, gas exchange analysis. Compared to controls without SCA, subjects with SCA demonstrated significantly lower peak VO2 (26.9 ± 6.9 vs. 37.0 ± 9.2 mL/kg/min, P < 0.001). Subjects demonstrated slower oxygen uptake (ΔVO2/ΔWR, 9 ± 2 vs. 12 ± 2 mL/min/watt, P < 0.001) and lower oxygen pulse (ΔVO2/ΔHR, 12 ± 4 vs. 20 ± 7 mL/beat, P < 0.001) as well as reduced oxygen uptake efficiency (ΔVE/ΔVO2, 42 ± 8 vs. 32 ± 5, P < 0.001) and ventilation efficiency (ΔVE/ΔVCO2, 30.3 ± 3.7 vs. 27.3 ± 2.5, P < 0.001) during CPET. Peak VO2 remained significantly lower in subjects with SCA after adjusting for age, sex, body mass index (BMI), and hemoglobin, which were independent predictors of peak VO2 for subjects with SCA. In the largest study to date using maximal CPET in SCA, we demonstrate that children and young adults with SCA have reduced exercise capacity attributable to factors independent of anemia. Complex derangements in gas exchange and oxygen uptake during maximal exercise are common in this population.

Reduced forced expiratory flow but not increased exhaled nitric oxide or airway responsiveness to methacholine characterises paediatric sickle cell airway disease

BACKGROUND

Asthma and airway hyper-responsiveness are reportedly more common in children with sickle cell disease (SCD).

AIM

To determine airway responsiveness, airway inflammation and clinical features of asthma in SCD.

METHODS

A prospective, single-centre study of 50 SCD children without overt pulmonary vascular disease and 50 controls. Exhaled nitric oxide (FeNO) and total serum IgE were measured and spirometry and methacholine challenge were performed. The methacholine dose-response slope (DRS) was calculated.

RESULTS

Doctor diagnosis of asthma was made in 7 (14%) SCD versus 12 (24%) control subjects (p=0.203). FeNO levels were similar in SCD and controls (p=0.250), and were higher in those with atopy and an asthma diagnosis (OR 4.33, 95% CI 1.7 to 11.1; p<0.05). zFEV1 (p=0.002) and zFEV1/FVC (p=0.003) but not zFVC (p=0.098) were lower in SCD versus controls. DRS was higher in those with asthma (p=0.006) but not in SCD versus controls (p=0.403). DRS correlated with FeNO and blood eosinophil count in controls but not SCD. In SCD, DRS was higher in those admitted to hospital with respiratory symptoms (n=27) versus those never admitted (n=23) (p=0.046). DRS was similar in those with at least one acute chest syndrome episode (n=12) versus those with none (n=35) (p=0.247).

CONCLUSIONS

SCD children have airflow obstruction despite having minimal evidence of pulmonary vascular disease. Airflow obstruction is not associated with increased methacholine sensitivity or eosinophilic inflammation, at least as judged by FeNO. Airflow obstruction in SCD does not appear to be related to childhood eosinophilic asthma, but its pathophysiology remains ill understood.