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Study Title and Description

The effect of caffeine on the cardiovascular responses to head-up tilt.



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 The effect of caffeine on the cardiovascular responses to head-up tilt.
Author NM Berry,CA Rickards,DG Newman,
Country
Year 2003
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 aimed to determine the effect of caffeine consumption on cardiovascular responses to head-up tilt.
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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) Subjects Subjects were recruited from the general public and from the RMIT University staff and student population. The subject pool consisted of 16 people (10 men and 6 women) with a mean age of 22 +/- 4.8 yr. Subjects were randomly allocated into two groups, caffeine (5 men and 4 women) or placebo (5 men and 2 women). Subjects were all untrained, non-smoking, regular caffeine consumers who were not taking any prescription medication, including oral contraceptives. All female subjects were tested in the follicular phase of the menstrual cycle. No statistically significant differences were observed between the caffeine and placebo groups for age (23.2 +/- 5.7 yr vs. 22.3 +/- 3.6 yr), height (172.6 +/- 8.9 cm vs. 175.9 +/- 11.4 cm), weight (77.5 +/- 16.2 kg vs. 80.6 +/- 17.7 kg), and average daily caffeine consumption (176.5 +/- 211.9 mg/d vs. 112 +/- 136.8 mg/d) as derived from the caffeine consumption surveys completed by all subjects. Caffeine reference quantities used in the questionnaire were based on values presented in Fredholm et al. Instrumentation and Data Acquisition The Aerospace Physiology Laboratory’s manually operated tilt table (constructed by the Technical Services Unit at RMIT University) was used to provide the orthostatic challenge. All BP and heart rate recordings were made noninvasively via a Portapres BP monitor (TNO-TPD Biomedical Instrumentation, Amsterdam, The Netherlands). The Portapres was interfaced with an eight-channel MacLab digital chart recording system (ADInstruments, Castle Hill, NSW, Australia). MacLab Chart (v.4.0) was used for data capture and analysis. Caffeine (96.5% purity, Merck, Germany) or placebo made of Polycose® glucose polymers (Ross Products Division, Abbott Laboratories, Columbus, OH) were administered in capsule form. Each capsule contained 2.5 mg/kg body mass (BM) of either caffeine or placebo. Two capsules were given daily resulting in a total daily dose of 5mg/kg BM. In the caffeine group, the mean caffeine dose per subject was 387.4 =/- 81.2 mg/d. Experimental Protocol The experimental protocol was a double blind study in which subjects were given either caffeine or placebo. Each subject was exposed to a total of three _75° HUTs. The first HUT acted as the pre-treatment control tilt (Control), the second followed an acute dose of caffeine or placebo (Acute) and the third followed a 7-d period of regular consumption of either caffeine or placebo (Chronic). Three days prior to the first tilt each subject began a period of total abstinence from all caffeinated products. Subjects were asked to avoid consumption of items from a list of caffeinated products provided to them pre-test. In addition, subjects were fasted for 4 h prior to presentation to the laboratory for standardization purposes. On the first presentation to the laboratory, subjects were exposed to the Control and Acute HUTs. Subjects rested in a supine position until cardiovascular parameters stabilized. Once stable, a 3-min rest period occurred during which data acquisition commenced. Subjects were instructed not to talk or move during this time. After 3 min, subjects were tilted to an angle of +75° for 2 min. After the 2-min tilt period, subjects were returned to the supine position. After the Control tilt, subjects were rested in a seated position off the tilt table. Two capsules, which contained a combined dose of 5 mg/kg BM of either caffeine or placebo, were then consumed. Subjects were rested for a 60-min period prior to the Acute tilt. During this time, subjects remained quietly seated. After the rest period, the acute tilt was conducted following the same rest/tilt protocol as the control tilt. Prior to leaving the laboratory on the first visit, all subjects were instructed to take two capsules daily, one at 10 a.m. and one at 3 p.m. for the next 7 d. Subjects were advised to consume no caffeine, other than what was given to them, during this period. Seven days after the Acute tilt the subjects were instructed to consume the 10 a.m. capsule only and return to the laboratory approximately 2 h later. On arrival in the laboratory the Chronic tilt was conducted following the same rest/tilt protocol as the Control tilt. Statistical Analysis The following cardiovascular variables were measured in each subject for the duration of the rest and tilt periods: heart rate (HR), systolic BP (SBP), diastolic BP (DBP), and mean arterial pressure (MAP). MAP was calculated according to the formula, MAP = DBP + 1/3(SBP - DBP). The final 30 s of rest and the first 30 s of tilt were analyzed. These data were divided into a resting period (R) and a tilt period (T), with the last 5 sec of rest subtracted due to the potential effects of anticipation of being tilted. Thus, R consisted of the remaining 25 s of resting data. T consisted of the 30 s immediately after tilting to the +75° head-up position. To determine the effect of tilt within each group (caffeine and placebo), averaged values for R, and T for each cardiovascular parameter (HR, SBP, DBP, MAP) were compared. In order to compare the dynamic response to tilt between groups, the average deviation between R and T was used, which was calculated by subtracting the average R value from each T value over the 30 s tilt period. All of these deviation values were then tabulated and averaged for each variable and compared in terms of magnitude and direction. Repeated measures analysis of variance (ANOVA) was used to compare within group (caffeine or placebo) differences, and a one-way ANOVA was used to determine between group (caffeine and placebo) differences. An alpha level of p < 0.05 was considered significant at the 95% confidence interval for all effects. All data were tabulated and imported into SPSS for Windows (v. 10.1) for statistical analysis. All data were reported as mean +/- SEM.
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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) Blood pressure (SBP, DBP, and MAP [calculated])
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List additional health endpoints (separately). 2 Heart rate
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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 All BP and heart rate recordings were made noninvasively via a Portapres BP monitor (TNO-TPD Biomedical Instrumentation, Amsterdam, The Netherlands).
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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.) Placebo control
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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 12862326
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What were the sources of funding? No information provided
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Results & Comparisons

No Results found.