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Study Title and Description

Nonlinear dynamics of blood pressure variability after caffeine consumption.



Key Questions Addressed
1 For [population], is caffeine intake above [exposure dose], compared to intakes [exposure dose] or less, associated with adverse effects on cardiovascular outcomes?
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Primary Publication Information
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TitleData
Title Nonlinear dynamics of blood pressure variability after caffeine consumption.
Author TG Papaioannou,C Vlachopoulos,N Ioakeimidis,N Alexopoulos,C Stefanadis,
Country
Year 2006
Numbers

Secondary Publication Information
There are currently no secondary publications defined for this study.


Extraction Form: Cardiovascular Design
Design Details
Question... Follow Up Answer Follow-up Answer
What outcome is being evaluated in this paper? Cardiovascular
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What is the objective of the study (as reported by the authors)? The aim of this study was to investigate the effect of caffeine on indices expressing the complex and chaotic nonlinear characteristics of BP variability.
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Provide a general description of the methods as reported by the authors. Information should be extracted based on relevance to the SR (i.e., caffeine related methods) Fourteen healthy subjects consumed 240 mg of caffeine or placebo orally according to a randomized, double-blind, crossover design. In all cases, caffeine and placebo were administered at approximately the same time (i.e., 8:00 to 10:00 AM). Continuous radial pressure waveforms were recorded by applanation tonometry. A high fidelity micromanometer-tipped probe was used (Millar Instruments, Houston, TX). Each recording (>30 seconds) consisted of measurements in the supine position at baseline and at 30, 60, 90 and 120 minutes following ingestion of placebo or caffeine. All measurements were obtained after an overnight fast and were performed in a quiet, air-conditioned room after a 15-minute resting period. The same well-trained operator performed all measurements, thus eliminating inter-observer variability. Nonlinear Analysis of BP Variability Approximate entropy (ApEn): ApEn (m,r ) of a time series measures the logarithmic frequency with which vectors with m components that are close (i.e., within resolution r) remain close when increasing the number of vector components by one. Small values of ApEn indicate regularity, and large values imply substantial fluctuations or irregularity in a time series. The input values m =2 and r =20% of the standard deviation of the BP data sets were used in accordance with previous findings with good statistical validity. Detrended fluctuation analysis (DFA): DFA was used to quantify the fractal correlation properties of the BP data by estimating the scaling (self-similarity) exponent α. DFA is a modified root mean square analysis of a random walk. Values of α between 0.5 and 1 indicate persistent long-range correlations, such that small and large BP values are more likely to alternate. For α >1, correlations exist but not in a power-low form. An α alue of 1.5 indicates Brownian noise. More than 30 continuous BP waveforms were acquired resulting in the recording of >6000 pressure values. Both ApEn and α were calculated by analyzing all the acquired BP values. Statistical Analysis Analysis of variance (ANOVA) for repeated measurements was performed to detect significant changes in the measured variables after caffeine or placebo consumption. Comparison of the variables’ responses between the caffeine and placebo sessions was performed using a 2 [drug] x 5 [time] general linear model, namely (caffeine vs placebo) x (baseline, 30, 60, 90, 120 minutes). The significance of the interaction term between caffeine and placebo was tested. A Bonferroni-corrected Student’s t-test for multiple comparisons was used to evaluate changes over time for the placebo and caffeine sessions. A two-tailed, paired Student’s t-test was applied to assess differences in baseline values between the two sessions. Data are presented as mean ± standard error of the mean (SEM). Probability levels <0.05 were considered statistically significant.
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How many outcome-specific endpoints are evaluated? 3
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What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately) Blood pressure (SBP and DBP)
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List additional health endpoints (separately). 2 Heart rate
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List additional health endpoints (separately).3 BP Variability (approximate entropy [ApEn] and detrended fluctuation analysis [DFA], expressed as exponent α)
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List additional health endpoints (separately).4
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List additional health endpoints (separately).5
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List additional health endpoints (separately).6
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Clinical, physiological, other Physiological
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What is the study design? Controlled Trial
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Randomized or Non-Randomized? RCT
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What were the diagnostics or methods used to measure the outcome? Objective
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Optional: Name of Method or short description Continuous radial pressure waveforms were recorded by applanation tonometry. A high fidelity micromanometer-tipped probe was used (Millar Instruments, Houston, TX).
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Caffeine (general) Caffeine (general)
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Coffee, Chocolate, energy drink, gum, medicine/supplement, soda, tea, other?
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Measured or self reported? Measured
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Children, adolescents, adults, or pregnant included? Adults
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What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.) Subjects served as their own controls (baseline and placebo)
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What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models.  Copy from methods) None
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What conflicts of interest were reported? No information provided
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Refid 16809403
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What were the sources of funding? No information provided
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Results & Comparisons

No Results found.