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Confounding Factors in the Analysis of the Relationship between Aortic Arch Calcification with a Non-Dipper Blood Pressure Pattern

Aorta, Thoracic; Calcification; Blood Pressure; Prevalence Ratio; Thorax/radiography

Dear Editor,

We read the following article with great interest: “Aortic Arch Calcification on Routine Chest Radiography is Strongly and Independently Associated with Non-Dipper Blood Pressure Pattern”. In this study, the aim was to evaluate a possible relationship between aortic arch calcification on chest radiographs and the non-dipper blood pressure pattern. Altogether, 406 patients were analyzed and divided into two groups: dipper and non-dipper. Approximately 261 (64%) patients presented the pattern of non-dipper blood pressure, against 145 (36%) with dipper blood pressure. It was found that the non-dipper group presented a higher prevalence of aortic arch calcification (70% vs. 33%, p<0.0001).

In the multivariate analysis of the study, the outcome of interest is whether the participant belongs to the non-dipper group from a dichotomous variable. As this is a cross-sectional design and not a case-control design, since the independent variables are not retrospective and there is no pairing of the groups, the most indicated analysis strategy would be Poisson or Cox regression. Unlike logistic regression that has Odds Ratio (OR) as a measure of effect, Poisson and Cox regression estimate the Prevalence Ratio (PR), whose application is more appropriate to the design. OR and PR will only be similar when the outcomes are infrequent (<10%).11. Coutinho Leticia M S, Scazufca Marcia, Menezes Paulo R. Métodos para estimar razão de prevalência em estudos de corte transversal. Rev Saúde Pública.2020;42(6):992-8.

The use of OR in this study brings potential bias due to the high prevalence of the outcome (PADV), making the point estimate over dimensional and its confidence interval more dilated. This condition of analysis brings doubts for variables such as age, body mass index, left ventricular mass index, triglycerides and the glomerular filtration rate which has very borderline confidence intervals (OR~1). It is very likely that calcification is associated with PADV, but not alone and/or to a lesser extent.22. Lopes JM. Rate or proportional epidemiological measures? J Orthop Sport Phys Ther. 2018;48(8):669–71.

Nearly 59 (22.6%) of the patients in the non-dipper group and 25 (17.2%) in the dipper group were diabetics. The researchers did not indicate what kind of diabetes the patients had in the non-dipper group and whether or not these patients were insulin resistant (IR). It is known that IR leads to high plasma levels of insulin and that it acts at the level of hypothalamic receptors of the central nervous system (CNS), leading to an increase in sympathomimetic flow.33. Mancia G., Grassi G. The Autonomic Nervous System and Hypertension. Circ Res. 2014;114(11):804-14. , 44. Young CN, Deo SH, Chaudhary K, Thyfault JP, Fadel PJ. Insulin enhances the gain of arterial baroreflex control of muscle sympathetic nerve activity in humans. J J Physiol. 2010 Sept 16;588:3593-603. This way, there is a predominance of sympathetic activity. Several studies have shown that sympathetic activation is directly proportional to the severity of hypertension. Thus, in the most severe forms of hypertension, the sympathomimetic flow is more prominent.33. Mancia G., Grassi G. The Autonomic Nervous System and Hypertension. Circ Res. 2014;114(11):804-14. The authors could have evaluated the real influence of IR on diabetics of the non-dipper group in order to identify the real action of diabetes, avoiding a confounding factor, because it is not possible to state whether such patients had the pattern of non-dipper pressure due to IR or other factors.

Another important consideration is that the study does not mention some limitations of Ambulatory Blood Pressure Monitoring (ABPM), considering that the patients’ sleep quality was not evaluated. It is known that low quality of sleep associated with the level of discomfort related to the method can significantly interfere with nightly blood pressure drop. Besides, patients with arrhythmia were not excluded from the study, such as atrial fibrillation, atrial flutter and frequent ventricular extrasystoles.55. Nobre F, Mion Jr. D, Gomes MAM, Barbosa ECD, Rodrigues CIS, Neves MFT et al. 6ª Diretrizes de Monitorização Ambulatorial da Pressão Arterial e 4ª Diretrizes de Monitorização Residencial da Pressão Arterial. Arq Bras Cardiol. 2018;110(5 Supl 1):1-29. Thus, the correlation between calcification in the aortic arch and the non-dipper pattern assessed by ABPM could also be important confounding factors.

Referências

  • 1
    Coutinho Leticia M S, Scazufca Marcia, Menezes Paulo R. Métodos para estimar razão de prevalência em estudos de corte transversal. Rev Saúde Pública.2020;42(6):992-8.
  • 2
    Lopes JM. Rate or proportional epidemiological measures? J Orthop Sport Phys Ther. 2018;48(8):669–71.
  • 3
    Mancia G., Grassi G. The Autonomic Nervous System and Hypertension. Circ Res. 2014;114(11):804-14.
  • 4
    Young CN, Deo SH, Chaudhary K, Thyfault JP, Fadel PJ. Insulin enhances the gain of arterial baroreflex control of muscle sympathetic nerve activity in humans. J J Physiol. 2010 Sept 16;588:3593-603.
  • 5
    Nobre F, Mion Jr. D, Gomes MAM, Barbosa ECD, Rodrigues CIS, Neves MFT et al. 6ª Diretrizes de Monitorização Ambulatorial da Pressão Arterial e 4ª Diretrizes de Monitorização Residencial da Pressão Arterial. Arq Bras Cardiol. 2018;110(5 Supl 1):1-29.

Publication Dates

  • Publication in this collection
    03 Feb 2021
  • Date of issue
    Jan 2021

History

  • Received
    08 July 2020
  • Reviewed
    25 Aug 2020
  • Accepted
    25 Aug 2020
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