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Study Title and Description

Sex differences in the hemodynamic responses to mental stress: Effect of 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 Sex differences in the hemodynamic responses to mental stress: Effect of caffeine consumption.
Author NH Farag,AS Vincent,BS McKey,M Al'Absi,TL Whitsett,WR Lovallo,
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 purpose of this study was to explore the effect of caffeine on hemodynamic responses to stress in healthy young 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) Healthy volunteers (25 men and 22 women) ages 21–35 years were recruited from the community. All participants were normotensive (BP<135/85) at screening, nonsmokers, nonobese (BMI<30), and in good health by self-report and routine physical exam. Participants were excluded if they had current or past evidence of heart disease, liver or renal disease, diabetes, severe asthma, or cerebrovascular disease. All participants regularly consumed 50–700 mg/day of caffeine by structured report and indicated no intolerance to caffeine. Participants were free of nonprescription medication during the time they were enrolled in the study. Women were free from oral contraceptives and were not pregnant, as determined by urine pregnancy test. Study Design The primary study design was a 4-week randomized, placebo-controlled, double-blind, crossover trial of caffeine versus placebo effects on cardiovascular and endocrine function. The development of tolerance and its effect on cardiovascular hemodynamics have been reported elsewhere [NOTE: Farag et al. (2005); Lovallo et al. (2004).] Data reported here examine the effect of caffeine (250 mg) versus placebo on the responses to mental stress following 5 days of placebo home maintenance. This allowed us to compare stress responses following acute administration of placebo versus caffeine after 5 days of caffeine washout. Caffeine Dosing and Compliance Home maintenance placebo was supplied in bottles of identical gelatin capsules (College of Pharmacy, University of Oklahoma, Oklahoma City) containing lactose. Test-day challenge doses were supplied in identical-appearing capsules containing either lactose or lactose mixed with 250 mg of USP caffeine (Gallipot, St. Paul, MN). Compliance with home dosing of placebo was assessed by capsule counts, by caffeine assay of saliva specimens collected at home each day at 7:00 p.m. (Salivette® , Starstedt, Germany), and from a saliva specimen collected on testing days upon entering the laboratory. Participants found to be noncompliant by any of these criteria were dropped and replaced (n = 3). Laboratory Protocol The laboratory protocol included the following activities: breakfast, instrumentation for impedance cardiography measures (60 min), a rest period (20 min), predrug impedance and BP baseline (10 min), capsule, postdrug response (60 min), mental stress (30 min), and recovery (40 min). The mental stressor consisted of a reaction time task in alternation with mental arithmetic. BP was measured every 3 min during screenings and test sessions using a Dinamap 845 oscillometric vital signs monitor (Criticon, Talahassee, FL). Impedance Cardiography Thoracic impedance measurements were carried out using a commercial impedance cardiograph system (Minnesota Impedance Cardiograph Model 304B, Minneapolis, MN) and a microcomputer. Impedance waveforms and electrocardiograms were ensemble averaged and data were extracted by proprietary software (Waveshell Software, Center for Biomedical Engineering, Research Triangle Institute, Research Triangle Park, NC) on an IBM-compatible computer. The following dependent variables were then derived for further analysis: systolic BP, diastolic BP, HR, and stroke volume. The following variables were then calculated: cardiac output = stroke volume x heart rate, and total peripheral resistance = mean arterial pressure x 80/cardiac output). To account for differences in body size, body surface area was used to calculate stroke index (SI; stroke index = stroke volume/body surface area), cardiac index (CI; cardiac index = cardiac output/body surface area), and total peripheral resistance index (TPRI; total peripheral resistance index = mean arterial pressure/cardiac index) x 80), which were used in the analysis. Data Reduction and Statistical Analysis Ensemble averaged impedance waveforms were taken over 1-min intervals during all periods of the protocol. These values were then averaged across the 10-min baseline, 40–60 min after caffeine response, 30 min stress, and 40 min recovery. Blood pressures were averaged over the same time periods. The data were analyzed in three stages, with the first two stages reported previously (Farag et al., 2005). In the third stage, we compared stress responses in men and women during placebo versus caffeine exposure conditions. Data were analyzed using multivariate repeated measures analysis of variance (MANOVA), Student's t test, and Pearson's r. Significant interactions from the MANOVA were followed by simple effects tests. All tests were two-tailed, and statistical significance was set at α = 0.05. The data were analyzed using SPSS (SPSS for Windows, rel. 10.1.0, SPSS Chicago, IL).
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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 index (TPRI)
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List additional health endpoints (separately).4 Cardiac Index (CI)
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List additional health endpoints (separately).5 Stroke Index (SI)
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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 Thoracic impedance measurements were carried out using a commercial impedance cardiograph system (Minnesota Impedance Cardiograph Model 304B, Minneapolis, MN) 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 (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) Habitual caffeine consumption; menstrual cycle phase
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What conflicts of interest were reported? No information provided
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Refid 16916429
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What were the sources of funding? This work was supported by NHLBI grant HL32050 and NIRR grant M01-RR14467 from the National Institutes of Health, Bethesda, Maryland, USA.
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Results & Comparisons

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