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Study Title and Description

Hemodynamic mechanisms underlying the incomplete tolerance to caffeine's pressor effects.



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 Hemodynamic mechanisms underlying the incomplete tolerance to caffeine's pressor effects.
Author NH Farag,AS Vincent,BS McKey,TL Whitsett,WR Lovallo,
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)? In this study, we aimed to identify the hemodynamic mechanisms underlying our previous findings of an incomplete tolerance to caffeine’s pressor effects in a sample of healthy adult men and women.
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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) A total of 43 healthy men and women aged 21 to 35 years were studied in a 4-week, placebo-controlled, double-blind, randomized, crossover trial of caffeine’s tolerance effects on BP and hemodynamic responses to fixed challenge doses. They regularly consumed caffeine 50 to 700 mg/day by structured report and used no medications with cardiovascular or metabolic effects. Subjects were instructed to eliminate all caffeine from their diets during the 4 weeks of the study. Each study week consisted of 5 maintenance days with placebo or caffeine self-administration at home [NOTE 300 or 600 mg/day]. Day 6 consisted of a laboratory protocol with placebo or caffeine challenges [NOTE: 500 mg/day]. During the laboratory protocol, pre-drug impedance and BP baseline (10 minutes) and postdrug responses (60 minutes) were measured. BP was measured every 3 minutes during screenings and test sessions using a Dinamap 845 oscillometric vital signs monitor (Criticon, Tallahassee, Florida). Thoracic impedance measurements were carried out using a commercial impedance cardiograph system (Minnesota Impedance Cardiograph model 304B, Minneapolis, Minnesota) and a microcomputer. The following dependent variables were then derived for further analysis: systolic and diastolic BP, heart rate, and stroke volume, using the equation of Kubicek et al. Then, body surface area was used in calculating the following variables to account for differences in body build: stroke index, cardiac index, and total peripheral resistance index. BP and impedance data measured at baseline and 40 to 60 minutes after caffeine challenge were averaged. Two multivariate repeated-measures analyses of variance were performed. The first was a 4-week, within-subjects model in which BP and hemodynamic responses to caffeine (after caffeine - baseline) were tested across the placebo-placebo (PP), placebo-caffeine (PC), caffeine 300 mg/day (C300), and caffeine 600 mg/day (C600) weeks. The second multivariate analysis of variance repeated this analysis adding a grouping variable based on tolerance formation (2 groups: high and low tolerance). Significant interactions were followed with pairwise comparisons using Holm’s sequential Bonferroni procedure to control family-wise error at the alpha <0.05 level. Additionally, examination of differences in hemodynamic variables for each week from that seen on the PP week were performed using Student’s t tests. Data were analyzed using SPSS for Windows version 10.1.0 (SPSS, Inc., Chicago, Illinois).
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How many outcome-specific endpoints are evaluated? 5
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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 Total peripheral resistance
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List additional health endpoints (separately).4 Cardiac index
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List additional health endpoints (separately).5 Stroke index
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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 BP was measured using a Dinamap 845 oscillometric vital signs monitor (Criticon, Tallahassee, Florida). Thoracic impedance measurements were carried out using a commercial impedance cardiograph system (Minnesota Impedance Cardiograph model 304B, Minneapolis, Minnesota) and a microcomputer
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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) Gender
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What conflicts of interest were reported? No information provided
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Refid 15904654
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What were the sources of funding? This work was supported by Grant HL32050 from National Heart, Lung, and Blood Institute and Grant M01-RR14467 from the National Center for Research Resources and the National Institutes of Health, Bethesda, Maryland.
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