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Study Title and Description

Hemodynamic effects of dietary caffeine, sleep restriction, and laboratory stress.



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 effects of dietary caffeine, sleep restriction, and laboratory stress.
Author JE James,ME Gregg,
Country
Year 2004
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 present study sought to characterize the hemodynamic effects induced by three main variables: dietary caffeine, sleep restriction, and laboratory stress. Furthermore, because both caffeine use and sleep pattern may have reciprocal influences on the performance of everyday activities, which may in turn induce psychophysiological stress, the study aimed to examine the combined hemodynamic effects of all three variables. Finally, gender effects were also examined in the present study.
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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 Using the Symptom Substance Questionnaire (James, Bruce, Lader, & Scott, 1989), participants were recruited from among the university student community. A total of 96 healthy volunteers were selected, comprising 54 women and 42 men. All participants reported being habitual caffeine consumers, with intakes ranging from 180 to 668 mg caffeine per day (mean=353mg), the approximate equivalent of 2–7 cups of coffee per day. Participants were normotensive (blood pressure less than 140/90 mmHg), were not taking any prescription medication, and were not consulting a physician for any medical condition at the time of the study. Cigarette smokers and users of oral contraceptive steroids were excluded. Participants ranged in age from17 to 52 years (mean of 19 years), with a body mass index of 18–28 kg/m2 for women and 18–29 kg/m2 for men. Study Design Throughout the study, caffeine and placebo (maize starch) were administered in gelatin capsules. All capsules were visually identical and contained starch alone or caffeine (B. P. anhydrous) plus starch filler. Participants were required to abstain from all caffeine beverages throughout the 4 weeks of the study. Capsules were assigned double-blind to ensure alternating weeks of caffeine and placebo ingestion, with counterbalancing between participants. On the seventh day of each week, participants ingested the first capsule (placebo or caffeine) for that day 30min before they were scheduled to arrive at the laboratory. As such, laboratory measurements were timed to coincide with the period of peak plasma caffeine concentration (i.e., 40–60 min post-ingestion). Dietary Caffeine For purposes of the study, dietary use was operationally defined as the ingestion of caffeine 1.75 mg/kg of body weight (the approximate equivalent of 1.0 to 1.5 cups of coffee) taken three times daily at 09.00, 11.00, and 15.00 for 7 consecutive days. This level and rate of intake approximates the ‘‘average’’ pattern of caffeine consumption for the United States, the United Kingdom, Canada, and Australia, and produces steady-state levels of plasma caffeine concentration within 24 h of commencing regular intake. In addition, because previous research has generally shown that caffeine tolerance plateaus and withdrawal effects abate within 3 to 5 days of continuous use, the present study employed 7 consecutive days of placebo/caffeine intake to achieve stability of responding by the end of each alternating period. Sleep Restriction On sleep-restricted nights, participants retired to bed in their own home at their usual bedtime, but set a bedside alarm to be awakened when they had experienced only 40% of their usual amount of nighttime sleep. Hemodynamic Measurement Beat-to-beat blood pressure and heart rate were measured noninvasively using a Finapres 2300e Continuous NIBP Monitor, Model (Ohmeda, Madison, WI). In addition, Finapres measurements were analyzed using the pulse contour method performed by the ‘‘Modelflow’’ program developed specifically for deriving estimates of cardiac output (CO) and total peripheral resistance (TPR). Hemodynamic Profile In the present study, determinations of hemodynamic profile were obtained from readings taken (a) when participants were sleep restricted versus rested (i.e., usual sleep), (b) during a resting baseline versus performance of psychomotor and cognitive tasks, and (c) when participants were caffeine exposed versus abstinent. Laboratory Stress Laboratory sessions were timed to begin at 08.30, 09.30, 10.30, and 11.30, and individual participants attended at the same time for all four weekly sessions. Two distinctly different laboratory challenges were employed, whereby half of the participants performed a single prolonged task requiring sustained vigilance, the remainder performed a battery of six brief psychomotor and cognitive tests (maze test, simple and complex reaction time tasks, recognition memory, mental arithmetic, and vigilance). Both the vigilance task and the test battery required 15 min to complete, and hemodynamic measurements were conducted continuously during both sets of activities Statistical Analysis The main statistical analyses involved two separate mixed-model ANOVAs performed on each of the five hemodynamic variables of systolic (SBP) and diastolic (DBP) blood pressure, heart rate (HR), CO, and TPR. The first ANOVA was a three-way analysis with one between-groups factor for gender, and two within-subjects factors for the main experimental manipulations of sleep (rested vs. sleep restricted) and caffeine (placebo vs. drug). The second ANOVA was a two-way analysis with a between-groups factor for task type (varied battery vs. sustained vigilance) and a within-subjects factor for period (baseline vs. task).
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How many outcome-specific endpoints are evaluated? 4
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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 Cardiac output
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List additional health endpoints (separately).4 Total peripheral resistance
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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 Beat-to-beat blood pressure and heart rate were measured noninvasively using a Finapres 2300e Continuous NIBP Monitor, Model (Ohmeda, Madison, WI). In addition, Finapres measurements were analyzed using the pulse contour method performed by the ‘‘Modelflow’’ program developed specifically for deriving estimates of cardiac output (CO) and total peripheral resistance (TPR).
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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) Gender, sleep deprivation
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What conflicts of interest were reported? No information provided
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Refid 15563344
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What were the sources of funding? This work was supported by the European Commission Fifth Framework Programme, Grant No. QLK1-CT-2000-00069.
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Results & Comparisons

No Results found.