Study Preview
Study Title and Description
Effect of caffeine on aortic elastic properties and wave reflection.
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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| Title | Effect of caffeine on aortic elastic properties and wave reflection. |
| Author | C Vlachopoulos,K Hirata,MF O'Rourke, |
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| Year | 2003 |
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Secondary Publication Information
There are currently no secondary publications defined for this study.
Extraction Form: Cardiovascular Design
| Question... Follow Up | Answer | Follow-up Answer | |
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| 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 the present study was to investigate the acute effect of caffeine on both aortic elastic properties and wave reflection in healthy subjects. |
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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 We studied 20 subjects (17 men) aged 50 +/- 16 (range 20 to 70) years; all had normal blood pressure, did not have diabetes, or family history of premature vascular disease. Four subjects were smokers. All but two subjects had no history of hyperlipidemia. They were clinically well and taking no regular cardiovascular medications (except for two who were on lipid-lowering drugs). All subjects were regular caffeine consumers (>100 mg/day). Subjects abstained from caffeine, ethanol, and nicotine for at least 12 h before each session. Study Design The study was carried out using a randomized, placebo-controlled, double-blind, cross-over design. Each subject was studied in the morning on two separate days, one with caffeine and one with placebo, after an overnight fast. Measurements were obtained in a quiet, air-conditioned room. After a 20-min rest period, baseline measurements were taken while the subjects were lying on a bed. After baseline measurements, the subjects took either 250 mg of caffeine (No-Doz, Key Pharmaceuticals, Rhodes) or placebo, and all measurements were repeated at 30, 60, 120 and 180 min after drug intake. For the determination of caffeine concentrations, salivary samples were also obtained at all time points. Evaluation of aortic elastic properties Carotid-femoral pulse wave velocity was calculated from measurements of pulse transit time and the distance travelled between two recording sites [pulse wave velocity = distance (m)/transit time, (s)] using a validated non-invasive device (Complior; Dupont Medical, Pantin, France) which allows online pulse wave recording and automatic calculation of pulse wave velocity. Measurement of wave reflection indices We used a validated, commercially available system (SphygmoCor1 ; AtCor Medical, Sydney, Australia) [25–28to measure wave reflection indices. First, from the radial artery recordings the ensemble-averaged radial pressure waveform is obtained. Then, this is calibrated according to sphygmomanometric systolic and diastolic pressure measured in the brachial artery; subsequently, the mean radial pressure is calculated by digital integration of the waveform. Thereafter, from the radial artery pressure waveform the central (aortic) arterial pressure waveform is derived. This is done with the use of a generalized transfer function, and by assuming that the mean pressure in the aorta is the same as the mean pressure in the radial artery. Augmentation index and augmented pressure of the central waveform were measured as indices of wave reflection. The merging point of the incident and the reflected wave can be identified on the pressure waveform as an inflection point. Augmented pressure (defined as: maximum systolic pressure – pressure at the inflection point) is the pressure added to the incident wave by the returning reflected one. Augmentation index was defined as augmented pressure divided by pulse pressure and expressed as a percentage. Statistical Analysis Data are expressed as the mean +/- SD. P values less than 0.05 were considered statistically significant. Characteristics and resting cardiovascular parameters were compared between the caffeine and placebo sessions using the paired t -test. Repeated-measures analysis of variance (averaged F) was used to detect statistically significant changes over time in variables performing three different analyses (1) within the caffeine, (2) within the placebo session separately, and (3) between the caffeine and the placebo session compositely (= two drugs [caffeine versus placebo] x 5 periods [baseline, 30, 60, 120, 180, min post-drug]); the latter is referred to as drug interaction in the Results section. As regards pulse wave velocity, to detect any possible influence of pressure on the changes observed, comparisons were also made with mean pressure as a covariate. As regards augmentation index, to detect any possible influence of heart rate on the changes observed, comparisons were also made with heart rate as a covariate. Responses between central and peripheral pressures were compared with paired t -test. Data analysis was performed with SPSS software, version 9.0 (Chicago, Illinois, USA). |
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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 (central [aortic] and peripheral [brachial] SBP, DPB, and PP) |
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| List additional health endpoints (separately). 2 | Heart rate |
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| List additional health endpoints (separately).3 | Aortic stiffness (pulse wave velocity) |
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| List additional health endpoints (separately).4 | Wave reflection (augmentation index, augmented pressure) |
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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 | Method for measuring heart rate was not specified in Methods |
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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, then 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) | Mean pressure was a covariate in analysis of pulse wave velocity and heart rate was a covariate in analysis of augmentation index |
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| What conflicts of interest were reported? | No information provided |
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| Refid | 12640250 |
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| What were the sources of funding? | No information provided |
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Results & Comparisons
No Results found.
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