Discussion
In the present study, we identified that children and adolescents with SCA showed reduced functional capacity, quality of life and pulmonary function when compared to their healthy peers. Additionally, the clinical field tests MSWT and 5STS-test proved to be reproducible to assess the functional capacity in these volunteers. As far as we know, this is the first study that includes these tests of functional capacity in the evaluation of individuals with SCA.
Cardiorespiratory morbidity of SAC contributes to functional capacity decreasing.25,26 This can be associated with anthropometric variables such as weight and height that were worse in patients of the SCAG compared to control group.26Several studies have shown that the resting energy expenditure of these patients is up to 20% higher when compared to healthy individuals, this is due to erythropoiesis, increased cardiac work, chronic hemolysis and hypoxia in tissues.22,27,28
Studies have already pointed out the relationship between low hemoglobin and decreased performance in the 6MWT in children with SAC.29,30 The status of chronic anemia and the reduction in hemoglobin transport in the SCAG, may have caused a lower carrying of the oxygen and may have provided worse performance during the tests. In this study, the mean Hb of the SCAG was 8 ± 1g/Dl. The chronic hemolysis may impair the performance in the MSWT for promoting greater fatigue. Additionally, patients with SCA tend to have sedentary behavior due to the chronicity of the disease, which is an important aspect in reducing functional capacity.31,32
Hospital admissions due to cardiopulmonary complications occur due to frequent episodes of acute chest syndrome (ACS) and lower lung function. In SCA, patients tend to have the syndrome of high cardiac output, described as the disease that most increases cardiac output at rest, contributing to the lower performance in activities such as walking fast or running and playing.33 In this study, both groups reached higher values of heart rate (more than 80% of the maximum heart rate), at the peak of the MSWT. However, the patients of the SCAG reached these values with a much shorter distance than the CG, which highlights the aspect of sedentary lifestyle, lower exercise capacity and chronicity of the disease.34,35
Children and adolescents with SCA are exposed to several factors that contribute to the decrease in QOL in the physical and social fields. The results of this study showed a significant difference in all domains of the PedsQl.16, 17 In the physical functioning domain, several studies reported that pain has a greater impact on QoL in patients with SCA, although its intensity is variable and depends on the individual characteristics of each patient. Pain is the main symptom that lead to frequent hospital admissions and higher school absenteeism.42,43,44 Acute or chronic pain affect functional status, which predisposes these children and adolescents to remain at rest and sedentary behavior.25,28,44
The 5STS-test and MSWT showed to be reproducible in SACG. Additionally, we observed an excellent value in the ICC and Bland Altman analysis with a small difference between the measurements and acceptable limits of agreement. Similar results for the MST were observed in pediatric patients with cerebral palsy45 and cystic fibrosis.46 Bohannon et al, described test and retest reliability for 5STS-test from strong to excellent in the ICC analysis for healthy adults.47 This shows that two test (5STS-test and MSWT) should be performed to assess functional capacity in SAC individuals.
The main limitation of the study was the lack of stratification of patients by disease severity; however, the choice was made to select the group with the greatest impairment, so that a greater number of individuals were evaluated.
We conclude that children and adolescents with SCA-HbS-S genotype have reduced functional capacity when compared to their healthy peers, as well as having a worse quality of life and lung function. Additionally, MSWT and 5STS-test proved to be reproducible in this population and can be used as an alternative to evaluate functional capacity.