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Study Title and Description

Effects of caffeine on linear and nonlinear measures of heart rate variability before and after exercise.



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 Effects of caffeine on linear and nonlinear measures of heart rate variability before and after exercise.
Author VK Yeragani,S Krishnan,HJ Engels,R Gretebeck,
Country
Year 2005
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)? This study sought to examine the effects of caffeine on HR variability measures before and during progressive exercise.
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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) Participants were 6 normal males (29 +/- 7 years) (mean +/-SD) and 5 normal females (23 +/- 7 years). Their ages ranged from 18 to 43 years. Each participant was healthy and did not have any risk factors for cardiac illness. They also were not taking any medications known to affect autonomic function. All participants were normotensive nonsmokers, and anyone who reported to be caffeine sensitive was not included in the study. As a group, our participants represented relatively caffeine-naıve, low-level caffeine-intake subjects. The participants were familiarized with the cycle ergometer and exercise-testing protocol. Throughout the test, resting-rate (R-R) intervals (interbeat intervals) were monitored using a Polar HR monitor. An elastic band with electrodes was placed around the participant’s chest. The Polar software program recorded R-R intervals throughout the duration of the test to an accuracy of 1 ms (digitized signal at 1000 Hz). Anhydrous caffeine (Firma Caesar & Loretz, Hilden, Germany) was used as the caffeine source. Prior to oral administration, 5-mg/kg body weight anhydrous caffeine was dissolved in 250 ml of caffeine-free diet cola. The placebo drink was the same caf feine-free diet soda without the added caffeine. All testing was done in the morning following an overnight fast. In addition, subjects were asked to abstain from caffeine containing products for 24 hr prior to each experimental test to allow for the elimination of any dietary caffeine from the body. After arrival in the laboratory, participants were given caffeine or placebo solution and then rested in the laboratory until the start of data collection 60 min later, unless they had to use the restroom. To make the analyses simpler, we used the baseline data for 128 s prior to the exercise test and 128 s of data 5 min after exercise, at which time most HR segments were stationary and data were available for these subjects for analyses. The HR (bpm) time series were sampled at 4 Hz. Spectral Analysis HR series (128 s at 4 Hz. 512 points) was subjected to spectral analyses, and the power spectrum was computed with the Blackman Tukey method. The powers were integrated in bands of the LF and HF regions. Approximate Entropy (APEN) There are two input parameters that should be set prior to the analysis: m, the run length, and r, the filter level. From previous reports, a value of 2 for m and 0.2 times the SD of the time series of HR for r give reliable results. APEN is derived from the correlation integral, which is the number of points in the signal closer than distance r to the "i"th point when embedded in m-dimensional space. APEN was calculated for all 128 s of data sampled at 4 Hz for pre- and post-placebo and caffeine conditions. Statistical Analysis We used the BMDP statistical package (Berkeley, CA) for all analyses. We used two-way ANOVAs for repeated measures with caffeine versus placebo as one repeated measure and pre- and post-exercise as the other repeated measure. Significant effects were followed up by paired t tests for post hoc comparisons. All tests were two-tailed, and a probability value of .025 was accepted as significant as we performed two post hoc t tests.
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How many outcome-specific endpoints are evaluated? 2
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What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately) Heart rate
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List additional health endpoints (separately). 2 Heart rate variability (total power, LF power, HF power, LF/HF ratio, HR APEN)
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List additional health endpoints (separately).3
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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 Resting-rate (R-R) intervals (inter-beat intervals) were monitored using a Polar HR monitor
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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 (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 15965989
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What were the sources of funding? No information provided
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Results & Comparisons

No Results found.