Study Preview
Study Title and Description
Caffeine decreases exercise-induced myocardial flow reserve.
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 | Caffeine decreases exercise-induced myocardial flow reserve. |
| Author | M Namdar,P Koepfli,R Grathwohl,PT Siegrist,M Klainguti,T Schepis,R Delaloye,CA Wyss,SP Fleischmann,O Gaemperli,PA Kaufmann, |
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| Year | 2006 |
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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)? | We studied the acute effect of caffeine on myocardial blood flow (MBF) at rest and exercise in healthy volunteers at normoxia and during acute exposure to simulated altitude. |
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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) | Study Population Eighteen healthy volunteers (7 women, 11 men) were included in the study. The patients had no history of and low clinical probability for CAD. Normal lipid profiles were found in each individual. All patients were habitual coffee drinkers (at least two cups of coffee per day) but refrained from ingesting caffeinated beverages or food for 36 h before the study. Study Protocol For group 1 (n = 10; mean age, 27 +/- 6 years), with the patient’s feet attached to a bicycle ergometer (model 380 B, Siemens-Elema AG, Bulach, Switzerland), MBF was measured at rest and during supine bicycle exercise-induced hyperemia at normoxia corresponding to 450 m above sea level (i.e., Zurich ground altitude). The MBF measurement was performed immediately after the end of exercise. This was followed by oral intake of a commercially available tablet containing 200 mg caffeine as only active substance (GlaxoSmithKline, Pittsburgh, Pennsylvania). Fifty minutes later, the measurements were repeated using the same protocol used at baseline. Group 2 (n = 8; mean age, 29 +/- 4 years) underwent the same study protocol as group 1 while exposed to a hypoxia simulating an altitude of 4,500 m throughout the study. Heart rate and peripheral arterial oxygen saturation (Sa O2) were recorded with a finger pulse oximeter (Nellcor N-200E, Nellcor Inc., Hayward, California). After achieving a cardiorespiratory steady state as assessed by a steady end-tidal CO2 partial pressure, Sa O2 , and heart rate, positron emission tomography (PET) measurements were performed. During the examination, blood pressure was continuously monitored by a Finapress BP Monitor (BOC Inc., Englewood, Colorado) and recorded at one-minute intervals. The electrocardiogram was monitored continuously throughout the procedure, and a 12-lead electrocardiogram was recorded at baseline and every minute during exercise at each level as well as during five minutes of recovery. Venous blood samples to determine serum caffeine concentration and lipid values were drawn before baseline resting scan and before post-caffeine bicycle exercise. Image Acquisition The MBF was assessed at the PET Center of the University Hospital in Zurich on a GE Advance positron emission tomograph (GE Medical Systems, Milwaukee, Wisconsin). Image Processing The obtained sinograms were corrected for attenuation and reconstructed on a Sun workstation (Sun Microsystems, Mountain View, California) using standard reconstruction algorithms. Coronary Resistance and MFR To account for the variability of coronary driving pressure, the ratio of mean arterial pressure to MBF was calculated as an index of coronary resistance. The MFR was defined as the ratio of MBF during physiologic hyperemia (induced by exercise) to MBF at rest and was calculated for baseline and repeated measurements. Statistical Analysis. Data are reported as mean values +/- standard deviation. Hemodynamic and PET data at rest and during stress were compared using the paired Student t test; p values of < 0.05 were considered to indicate statistical significance. |
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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 (SPB, DPB, MAP) |
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| List additional health endpoints (separately). 2 | Heart rate |
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| List additional health endpoints (separately).3 | Serum cholesterol (TC, LDL, HDL) |
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| List additional health endpoints (separately).4 | Myocardial flow (myocardial blood flow [MBF] and myocardial flow resistance [MFR]) |
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| List additional health endpoints (separately).5 | Coronary resistance |
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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? | NCT |
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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 | Blood pressure was continuously monitored by a Finapress BP Monitor (BOC Inc., Englewood, Colorado) and recorded at one-minute intervals. The electrocardiogram was monitored continuously throughout the procedure, and a 12-lead electrocardiogram was recorded at baseline and every minute during exercise at each level as well as during five minutes of recovery |
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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) |
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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 | 16412869 |
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| What were the sources of funding? | Dr. Kaufmann was supported by a grant from the Swiss National Science Foundation (SNSF-professorship grant no. PP00A-68835 and grant no. 31-68386). |
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Results & Comparisons
No Results found.
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