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Study Title and Description

Effects of caffeine and high ambient temperature on haemodynamic and body temperature responses to dynamic 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 and high ambient temperature on haemodynamic and body temperature responses to dynamic exercise.
Author CL Stebbins,JW Daniels,W Lewis,
Country
Year 2001
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)? We tested the hypothesis that, in caffeine-naive individuals, this drug increases blood pressure and attenuates FBF and conductance during exercise at a high ambient temperature. Consequently, dissipation of body heat is adversely affected.
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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) The eleven active males (18±40 years of age) selected for this study were free from injury or disease, nonhabitual caffeine users (<50 mg day±1) and nonsmokers. These individuals participated in aerobic exercise training at least 3 days per week. Experimental Design Each subject performed two separate 80-min protocols arranged in a randomized, double blind fashion with placebo and caffeine treatments. On experimental days, each subject reported to the laboratory after a 12-h fast. All subjects abstained from consumption of caffeinated foods and/or beverages for a least 4 days before each session. The first session consisted of a graded maximal exercise test on an electronically braked cycle ergometer (Ergo-metrics 800, SensorMedics, Bilthoven, the Netherlands) to volitional fatigue. Before the remaining two test protocols, each subject was familiarized with the testing equipment. The two test protocols were separated by at least 1 week. Each subject abstained from any form of exercise for 24 h before each test protocol. Immediately on arrival at the laboratory, the subject rested quietly in a chair. Approximately 10 min later, a blood sample was collected for measurement of venous lactate concentrations. The subject was then fitted with a blood pressure cuff and three electrocardiogram leads. Subsequently, resting blood pressure and HR were assessed. Subjects then consumed either a placebo (5 ml water/kg) or caffeine (6 mg/kg) gel capsule and were moved into an environmental chamber where they rested for 40 min at an ambient temperature of 38°C and a relative humidity of 40%. At the 40-min time point, all experimental variables were measured again. At the 45-min time point, each subject exercised at 50% of his predetermined maximal oxygen uptake for 35 min on the bicycle ergometer at a pedalling frequency of 2 g. All variables were assessed again at 15 and 35 min of exercise. Systolic (SBP) and diastolic (DBP) blood pressure were measured in the left arm (by the same investigator in both protocols) using manual auscultation. MAP was calculated as 2/3DBP + 1/3SBP. HR was determined from the ECG tracings by averaging R-R intervals over a time period of 15 s. Data Analysis As peak blood pressure occurred at 15 min of exercise in some subjects and at 35 min in others, the response at these two time points were averaged. Peak HR occurred at 35 min of exercise, so it was not averaged. Results are expressed as mean +/- SEM. Much of our data were skewed and/or had more that one peak. Thus, the assumption was made that they were not normally distributed and a non-parametric analysis was performed. One set of comparisons was made between initial values and those obtained after 40 min of heat exposure for both the placebo and caffeine condition. Another comparison was made between the change in these variables between the placebo and caffeine treatment. A last comparison was made of absolute values of each variable during exercise between caffeine and placebo conditions. All comparisons were made using the Wilcoxon signed rank test. Differences between mean were judged to be significantly different at P<0.05.
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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 (mean arterial pressure [MAP])
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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 Systolic (SBP) and diastolic (DBP) blood pressure were measured in the left arm (by the same investigator in both protocols) using manual auscultation. MAP was calculated as 2/3DBP + 1/3SBP. HR was determined from the ECG tracings by averaging R-R intervals over a time period of 15 s.
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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.) Each study subject received the same treatment and served as their own controls
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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 11576153
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What were the sources of funding? No information provided
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Results & Comparisons

No Results found.