ABC | Volume 110, Nº6, June 2018

Original Article Marui et al Blood pressure variables in Duchenne muscular dystrophy Arq Bras Cardiol. 2018; 110(6):551-557 among those children? The mdx mouse develops X-linked recessive muscular dystrophy ( locus Xp21 ) and does not express dystrophin. Although it does not show intense fibrosis and fatty tissue accumulation in muscles, it is considered the most appropriate animal model of DMD. A mechanistic study with those mice has shown that the absence of dystrophin interferes with nitric oxide (NO)-dependent vascular dilatation. When submitted to pressure variations, the vessel showed no adaptation. Because the endothelium is essential for the arteries to adapt to chronic changes in blood flow, in the long run that deficiency might affect the flow-induced vascular remodeling, with consequence to vascular resistence. 26 Other studies have shown an abnormal sympathetic neurovascular control in dystrophin-deficient muscle, which is evidenced during physical exercise, when sympathetic vasoconstriction is normally absent in active muscles, due to the action of local vasodilating substances, such as NO. 27,28 The neuronal deficiency of NO sintase, which is reduced in the absence of dystrophin, seems to be the major cause of vasoregulation deficiencies. However, the vascular tone modulation can also be hindered by dystrophin deficiency in arterial smooth muscle cells. Dystrophin is usually expressed in the tunica media of blood vessels, being absent in the vessels of mdx mice. 29,30 Considering those findings, we might explain the high number of individuals with DMD and BP changes in our study. Another aspect that can be related to endothelial change is the absence or attenuation of ND in those children. Duchenne muscular dystrophy is usually accompanied by changes in the respiratory pattern during sleep, such as obstructive sleep apnea (OSA), causing deleterious effects to the cardiovascular system. In addition, excessive sympathetic activity occurs in OSA, which can contribute to the lack of decrease in BP levels during the night. Study limitations Because DMD is a rare disease, our study can be considered a potential generator of hypotheses. It is worth noting the lack of standardization for ABPM use for children. Thus, we followed the AHA recommendation, which was based on expert opinions. However, such data need to be validated in further studies, with a greater sample power. In addition, it is worth noting the difficulties in measuring the height of the children, because many of them were wheelchair-bound. Thus, we used the historical height, reported by the parents or legal guardians. Another limitation of our study was the patients’ stratification based on age groups, by use of convenience sampling, because of the low incidence of DMD. Because of the difficulty of conducting randomized clinical trials in the pediatric population, the recommendations used were based on expert opinions. Conclusion The analysis of BP variables, obtained mainly from ABPM, is a useful tool to identify patients with DMD at higher risk. Considering the cardiovascular changes of those patients, the early identification of BP changes would allow the appropriate and specific therapeutic intervention. In addition, we suggest the regular and multidisciplinary follow-up of those patients to identify their BP changes, ensuring improvement in their life expectancy and comfort. Author contributions Conception and design of the research: Marui FRRH, Povoa RMS; Acquisition of data: Marui FRRH, Thalenberg JM; Analysis and interpretation of the data: Marui FRRH, Bianco HT, Oliveira ASB, Povoa RMS; Statistical analysis: Marui FRRH, Bianco HT, Palmeira NGF, Povoa RMS; Obtaining financing: Marui FRRH, Povoa RMS; Writing of the manuscript: Marui FRRH, Bombig MTN, Povoa FF, Izar MCO, Fonseca FAH, Povoa RMS; Critical revision of the manuscript for intellectual content: Bianco HT, Bombig MTN, Palmeira NGF, Thalenberg JM, Povoa FF, Izar MCO, Fonseca FAH, Povoa RMS. Potential Conflict of Interest No potential conflict of interest relevant to this article was reported. Sources of Funding This study was funded by CNPq. Study Association This article is part of the thesis of Doctoral submitted by Fabiane R. R. H. Marui, fromUniversidade Federal de São Paulo. Ethics approval and consent to participate This study was approved by the Ethics Committee of the Universidade Federal de São Paulo (UNIFESP) under the protocol number CEP 0199/10, 05/21/10. All the procedures in this study were in accordance with the 1975 Helsinki Declaration, updated in 2013. Informed consent was obtained from all participants included in the study. 555