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Hypertension Does Not Alter the Increase in Cardiac Baroreflex Sensitivity Caused by Moderate Cold Exposure.

ABSTRACT: Exposure to cold increases blood pressure and may contribute to higher wintertime cardiovascular morbidity and mortality in hypertensive people, but the mechanisms are not well-established. While hypertension does not alter responses of vagally-mediated heart rate variability to cold, it is not known how hypertension modifies baroreflex sensitivity (BRS) and blood pressure variability during cold exposure. Our study assessed this among untreated hypertensive men during short-term exposure comparable to habitual winter time circumstances in subarctic areas. We conducted a population-based recruitment of 24 untreated hypertensive and 17 men without hypertension (age 55-65 years) who underwent a whole-body cold exposure (-10°C, wind 3 m/s, winter clothes, 15 min, standing). Electrocardiogram and continuous blood pressure were measured to compute spectral powers of systolic blood pressure and heart rate variability at low (0.04-0.15 Hz) and high frequency (0.15-0.4 Hz) and spontaneous BRS at low frequency (LF). Comparable increases in BRS were detected in hypertensive men, from 2.6 (2.0, 4.2) to 3.8 (2.5, 5.1) ms/mmHg [median (interquartile range)], and in control group, from 4.3 (2.7, 5.0) to 4.4 (3.1, 7.1) ms/mmHg. Instead, larger increase (p < 0.05) in LF blood pressure variability was observed in control group; response as median (interquartile range): 8 (2, 14) mmHg(2), compared with hypertensive group [0 (-13, 20) mmHg(2)]. Untreated hypertension does not disturb cardiovascular protective mechanisms during moderate cold exposure commonly occurring in everyday life. Blunted response of the estimate of peripheral sympathetic modulation may indicate higher tonic sympathetic activity and decreased sympathetic responsiveness to cold in hypertension.

SUBMITTER: Hintsala HE

PROVIDER: S-EPMC4889607 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Hypertension Does Not Alter the Increase in Cardiac Baroreflex Sensitivity Caused by Moderate Cold Exposure.

Hintsala Heidi E HE Kiviniemi Antti M AM Tulppo Mikko P MP Helakari Heta H Rintamäki Hannu H Mäntysaari Matti M Herzig Karl-Heinz KH Keinänen-Kiukaanniemi Sirkka S Jaakkola Jouni J K JJ Ikäheimo Tiina M TM

Frontiers in physiology 20160602

Exposure to cold increases blood pressure and may contribute to higher wintertime cardiovascular morbidity and mortality in hypertensive people, but the mechanisms are not well-established. While hypertension does not alter responses of vagally-mediated heart rate variability to cold, it is not known how hypertension modifies baroreflex sensitivity (BRS) and blood pressure variability during cold exposure. Our study assessed this among untreated hypertensive men during short-term exposure compar ...[more]

PMID: 27313543

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Project description:Interests about the fine underpinnings of cardiovascular beat-by-beat variability have historical roots. Over the last decades, various aspects of the relationships between arterial pressure and heart period were taken as a proxy of the baroreflex in physiology and medicine, stimulating the interest of investigators in several interconnected scientific fields, in particular, bioengineering, neurophysiology, and clinical medicine. Studies of the overall system facilitated the emergence of a simplified negative (vagal) feedback model of the baroreflex and overshadowed the simultaneous interaction with excitatory, sympathetic positive-feedback mechanisms that would, however, better suit the model of a "paired antagonistic (parasympathetic/sympathetic) innervation of the internal organs." From the bioengineering side, the simplicity of obtaining the series of subsequent RR intervals stimulated the analysis of beat-by-beat variations, providing a multitude of heart rate variability (HRV) indices considered as proxies of the underlying sympatho-vagal balance, and participating to the management of several important clinical conditions, such as hypertension. In this context, advanced statistical methods, used in an integrated manner and controlling for age and gender biases, might help shed new light on the relationship between cardiac baroreflex, assessed by the frequency domain index ?, and the HRV indices with the varying of systolic arterial pressure (SAP) levels. The focus is also on a novel unitary Autonomic Nervous System Index (ANSI) built as a synthesis of HRV considering its three most informative proxies [RR, RR variance, and the rest-stand difference in the normalized power of low-frequency (LF) variability component]. Data from a relatively large set of healthy subjects (n = 1154) with a broad range of SAP [from normal (n Nt = 778) to elevated (n Ht = 232)] show that, e.g., ? and ANSI significantly correlate overall (r = 0.523, p < 0.001), and that this correlation is lower in hypertensives (r = 0.444, p < 0.001) and higher in pre-hypertensives (r = 0.618, p < 0.001) than in normotensives (r = 0.5, p < 0.001). That suggests the existence of curvilinear "umbrella" patterns that might better describe the effects of the SAP states on the relationships between baroreflex and HRV. By a mix of robust, non-parametric and resampling statistical techniques, we give empirical support to this study hypothesis and show that the pre-hypertensive group results at the apex/bottom in most of the studied trends.

Project description:BackgroundThe diagnosis of hypertension is often preceded by cardiac structural abnormalities. Thus, we assessed whether high-sensitivity cardiac troponin T (hs-cTnT), a marker of subclinical myocardial damage, can identify individuals at risk for hypertension or left ventricular hypertrophy.Methods and resultsWe studied 6516 Atherosclerosis Risk in Communities (ARIC) Study participants who were free of prevalent hypertension and cardiovascular disease at baseline (1990-1992). We examined the association of baseline hs-cTnT categories with incident diagnosed hypertension (defined by self-report of a diagnosis or medication use during a maximum of 19.9 years of follow-up) and with incident visit-based hypertension (defined by self-report, medication use, or measured blood pressure >140/90 mm Hg over 6 years). Relative to hs-cTnT <5 ng/L, adjusted hazard ratios for incident diagnosed hypertension were 1.16 (95% confidence interval, 1.08-1.25) for individuals with hs-cTnT of 5 to 8 ng/L, 1.29 (95% confidence interval, 1.14-1.47) for hs-cTnT of 9 to 13 ng/L, and 1.31 (95% confidence interval, 1.07-1.61) for hs-cTnT ≥14 ng/L (P for trend <0.001). Associations were stronger for incident visit-based hypertension. These associations were driven by higher relative hazard in normotensive people (compared with those with prehypertension; P for interaction=0.001). Baseline hs-cTnT was also strongly associated with incident left ventricular hypertrophy by electrocardiography over 6 years (eg, adjusted hazard ratio, 5.19 [95% confidence interval, 1.49-18.08] for hs-cTnT ≥14 versus <5 ng/L). Findings were not appreciably changed after accounting for competing deaths or adjusting for baseline blood pressure levels or N-terminal probrain natriuretic peptide.ConclusionsIn an ambulatory population with no history of cardiovascular disease, hs-cTnT was associated with incident hypertension and risk of left ventricular hypertrophy. Further research is needed to determine whether hs-cTnT can identify people who may benefit from ambulatory blood pressure monitoring or hypertension prevention lifestyle strategies.

Project description:Spontaneous baroreflex sensitivity (BRS) is a widely used tool for the quantification of the cardiovascular regulation. Numerous groups use the xBRS method, which calculates the cross-correlation between the systolic beat-to-beat blood pressure and the R-R interval (resampled at 1 Hz) in a 10 s sliding window, with 0-5 s delays for the interval. The delay with the highest correlation is selected and, if significant, the quotient of the standard deviations of the R-R intervals and the systolic blood pressures is recorded as the corresponding xBRS value. In this paper we test the hypothesis that the xBRS method quantifies the causal interactions of spontaneous BRS from non-invasive measurements at rest. We use the term spontaneous BRS in the sense of the sensitivity curve is calculated from non-interventional, i.e., spontaneous, baroreceptor activity. This study includes retrospective analysis of 1828 measurements containing ECG as well as continues blood pressure under resting conditions. Our results show a high correlation between the heart rate - systolic blood pressure variability (HRV/BPV) quotient and the xBRS (r = 0.94, p < 0.001). For a deeper understanding we conducted two surrogate analyses by substituting the systolic blood pressure by its reversed time series. These showed that the xBRS method was not able to quantify causal relationships between the two signals. It was not possible to distinguish between random and baroreflex controlled sequences. It appears xBRS rather determines the HRV/BPV quotient. We conclude that the xBRS method has a potentially large bias in characterizing the capacity of the arterial baroreflex under resting conditions. During slow breathing, estimates for xBRS are significantly increased, which clearly shows that measurements at rest only involve limited baroreflex activity, but does neither challenge, nor show the full range of the arterial baroreflex regulatory capacity. We show that xBRS is exclusively dominated by the heart rate to systolic blood pressure ratio (r = 0.965, p < 0.001). Further investigations should focus on additional autonomous testing procedures such as slow breathing or orthostatic testing to provide a basis for a non-invasive evaluation of baroreflex sensitivity.

Dataset Information

Hypertension Does Not Alter the Increase in Cardiac Baroreflex Sensitivity Caused by Moderate Cold Exposure.

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Hypertension Does Not Alter the Increase in Cardiac Baroreflex Sensitivity Caused by Moderate Cold Exposure.

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