IJCS | Volume 32, Nº6, November / December 2019

619 Table 4 - Values obtained at the ABPM in the 3 groups of patients (January to December / 2016) - Analysis of variance ANOVA Group 1 (n = 902)* Group 2 (n = 186) † Group 3 (n = 716) ‡ Age .477 .172 .501 MASBP .000 .738 .000 MADBP .013 .476 .012 MRSBP .552 .265 .402 MRDBP .485 .119 .496 MAX SBP .003 .727 .001 MIN SBP .053 .553 .006 24HMSBP .002 .610 .000 24HMDBP .073 .202 .081 Systolic dipping .006 .151 .020 Diastolic dipping .204 .377 .337 Maximum temperature .000 .000 .000 Minimum temperature .000 .000 .000 Mean temperature .000 .000 .000 Relative air humidity .000 .000 .000 ABPM: ambulatory blood pressure monitoring; MASBP/MADBP: mean awake systolic and diastolic blood pressure; MRSBP/ MRDBP: mean resting systolic and diastolic blood pressure; MAX SBP/MIN SBP: maximum and minimum systolic blood pressure; 24HMSBP/24HMDBP: 24H mean systolic and diastolic blood pressure; (*) total group of patients; (†) group of patients taking antihypertensive medications; (‡) group of patients without antihypertensive medications. Escosteguy et al. Temperature variation in blood pressure Int J Cardiovasc Sci. 2019;32(6):615-622 Original Article pressure levels are strongly and inversely associated with external temperature and suggest that seasonal variations in blood pressure should be considered in the patients’ assessment. In another study, carried out in a rural area of China, in which more than 57,000 individuals between 30 and 79 years old participated, Su et al., 19 also concluded that a lower external temperature is strongly associated with higher mean arterial pressure and the prevalence of hypertension, as well as poorer control of hypertension, and that this factor should be considered when performing population studies of hypertension. Yang et al., 20 in a sample of 23,000 Chinese individuals with a history of cardiovascular disease, showed that there is an increase in blood pressure and cardiovascular mortality in winter. They concluded that careful monitoring and a more aggressive treatment are needed to decrease blood pressure during the cold months and reduce mortality from cardiovascular causes in high-risk individuals. Lewington et al., 21 and Wang et al., 22 carried out surveys with population samples of more than 500,000 and 430,000 individuals, respectively, with the first study sample consisting of individuals from several Chinese rural regions, and the second one of patients from a university hospital linked toZhejiangUniversity (Zhejiang University School of Medicine). The authors of both studies also concluded that a low external temperature increases blood pressure levels, and similarly, suggest that the seasonal variation in blood pressure should be considered in the patients’ clinical assessment. In an American study, Amoah et al., 5 recently investigated the seasonal variation of blood pressure monitoring but correlated the control of blood pressure levels with the use of electronic equipment in the different climatic seasons, and concluded this control is performed cyclically, being higher during the winter period. However, they did not report the results of this variation in absolute numbers of blood pressure. In Brazil, there have been some studies that associated seasonal temperature variation with gestational hypertension, 4,23 symptoms of stroke, 24,25 respiratory diseases, 26 epistaxis 27 and others that investigated the association between climate andmortality fromdifferent diseases in elderly individuals. 28 Only one study 29 approached the subject, when it investigated the effect of water temperature on cardiovascular responses: heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) during exercise at different temperatures (29° C, 33° C and 37° C). The authors found a HR increase and DBP decrease at 37º C; they did not find a significant effect on SBP. At the end, they suggest that, when therapeutic swimming pools are used for water-walking exercises, the choice of the water temperature should be considered as a way to decrease cardiovascular stress. Studies that are similar to the present work, assessing the temperature seasonal variation in association to blood pressure behavior, were not found. This fact indicates the need for further investigations, since studies with large population bases, such as the Chinese studies, have shown that temperature variation does in fact influence blood pressure behavior.