ABC | Volume 110, Nº2, February 2018

Original Article Casali et al Short & very short-term blood pressure variability Arq Bras Cardiol. 2018; 110(2):157-165 In controls, correlations between very short- and short-term BP variability were present with FBPM data at rest and after the standing-up maneuver, but only when daytime data were included. This probably occurs because both methods are evaluating BP signals in similar situations, as 24h-ABPMprovides data obtained mostly during routine activities in standing-up position (mean duration of nighttime period ∼ 6.9h). The most significant correlations were those between time-rate index (24h-ABPM) and LF component of BP variability and delta_LF/HF (FBPM); also between the coefficient of variation (24h-ABPM) and between total BPV and the alpha index in all periods that included daytime data. The time-rate index obtained by 24h-ABPM (24-hour or daytime period) in healthy individuals is expected to reflect what the reference standard (FBPM) would show, considering LF component of BP variability and delta_LF/HF. The weak correlations observed between 24h-ABPM and FBPM indices in the diabetic-hypertensive group depict a very different pattern, which is certainly related to their disease. Moreover, therewas no correlation between short-termvariability parameters and delta indices. These correlations are weak even though four times more patients were evaluated, which would show significant correlations if they in fact existed. We cannot exclude that one or both methods employed may provide false results for this specific population once FBPM, for example, depends on attaining good BP signals, and quality of such informationwas not good because of vascular disorders common to this population. 32 Therefore, we do not recommend24h-ABPM to estimate very short‑term BP variability parameters based on short-termvariability indices for diabetic-hypertensive individuals. Currently, the evaluation of BP variability across the several indices that can be obtained from 24h-ABPM or home blood pressure monitoring is not recommended by guidelines, 14,33 for predicting cardiovascular risk, or as additional goal for antihypertensive therapy, because literature has no consensus on these issues. 4,14,34,35 It is possible that evidence available is not strong enough to support this use because the tools used are not so reliable. We suggest that equations derived from the 24h-ABPM measurement for non-diabetic subjects would be useful for risk prediction, but not for diabetic-hypertensive patients. It is unknown, though, whether this pattern occurs in hypertensive‑only populations. The use of BP variability reduction as a new target to explore in further intervention trials related to hypertension should only be considered after this information is validated. Considering the high prevalence of autonomic neuropathy in diabetes, 36,37 and characteristic changes of this complication detected in the diabetic-hypertensive group (circadian behavior differences, lower spontaneous baroreflex sensitivity, HR variability and lower responses to stand-up in the LF/HF ratio vs. controls), we attributed to this complication some of the differences observed in other indices between groups. The standing-up maneuver is usually applied to induce sympathetic activation in very short‑term BP variability evaluation, and in fact it induced the expected cardiac autonomic response for many indices in controls, but not for most of them in diabetic-hypertensive individuals. Taking clinical characteristics of diabetic-hypertensive subjects into account and bearing in mind that the sample studied was obtained from a tertiary center, many patients were not adequately monitored (BP and metabolic control), indicating a high-risk group. Perhaps in this high-risk population, variability found in 24h-ABPM or other home BP evaluation methods may not successfully qualify higher cardiovascular risk beyond absolute systolic or diastolic BP, as previously described. 34,38 Also, the age differences found could, at least partially, overestimate the differences between groups, and therefore configure a limitation of this study. Conclusions In summary, short-term BP variability measured by time‑rate index, standard deviation or coefficient of variation in 24h-ABPM are correlated with LF component BPV and delta_LF/HF obtained from FBPM in nondiabetic individuals. Such findings should be evaluated in further cohort studies adequately designed for this purpose, also seeking relations with hard outcomes. This correlation was not well established in diabetic-hypertensive subjects. Some indices obtained from FBPM for diabetic subjects are promising tools for the diagnosis of diabetic autonomic neuropathy. Considering a standard reference for the diagnosis of autonomic neuropathy, these indices and cutoff values should be evaluated in further studies adequately designed for this purpose. Author contributions Conception and design of the research and Analysis and interpretation of the data: Casali KR, Schaan B, Montano N, Massierer D, Neto FMF, Teló G, Ledur PS, Reinheimer M, Sbruzzi G, Gus M; Acquisition of data: Casali KR, Schaan B, Montano N, Massierer D, Teló G, Ledur PS, Reinheimer M, Sbruzzi G, Gus M; Statistical analysis: Casali KR, Teló G, Gus M; Obtaining financing: Schaan B, Gus M; Writing of the manuscript: Casali KR; Critical revision of the manuscript for intellectual content: Schaan B, Montano N, Massierer D, Neto FMF, Teló G, Ledur PS, Reinheimer M, Sbruzzi G, Gus M. Potential Conflict of Interest No potential conflict of interest relevant to this article was reported. Sources of Funding This study was funded by CNPq and FIPE (Hospital de Clínicas de Porto Alegre). Study Association This study is not associatedwith any thesis or dissertationwork. Ethics approval and consent to participate This study was approved by the Ethics Committee of the Hospital de Clínicas de Porto Alegre (RS) and Instituto de Cardiologia do Rio Grande do Sul / Fundação Universitária de Cardiologia under the protocol number 0469.0.001.000‑08 and 4313/09. 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. 163