Abstract
The physiological/pathophysiological effects of caffeine on the human cardiovascular system have not been investigated by physiologists and are poorly understood. In a world where caffeinated beverages are evidently the adult’s drug of choice (coffee, energy drinks, soda, tea) investigating their effects on the physiology of the cardiovascular system is of considerable importance. In this experiment, we investigated caffeine, taken orally as a tablet, on reactive hyperemia, a form of local control of blood flow. Young adults between the ages of 18 and 21 years were the experimental subjects. They were instrumented to monitor systemic arterial blood pressure, peripheral blood flow, calculated peripheral vascular resistance, heart rate and an electrocardiogram during a reactive hyperemia maneuver in the absence and presence of caffeine. Caffeine-mediated peripheral vasoconstriction was observed as early as 15 minutes after its consumption. Forty-five minutes later (60 min after consumption of caffeine) peripheral vasoconstriction was so prominent that reactive hyperemia was abolished. This was reflected, in part, as a marked and significant reduction in post-ischemia reactive hyperemia that accompanied a 2.5-fold increase in peripheral vascular resistance (P 0.05). Heart rate was unaffected by caffeine under our experimental conditions. We conclude that caffeine has the ability to inhibit important cardiovascular properties, including reactive hyperemia. If the effects that were seen in a digit are indicative of what caffeine might do in the heart and/or brain, then one has to question the wisdom of regularly consuming caffeine. More experimental physiological and pharmacological investigation is needed.
Highlights
Caffeine is widely used for medical and non-medical purposes
60 minutes after an oral dose of 200 mg caffeine, all subjects experienced a marked and statistically significant reduction in digit blood flow. This was accompanied by the inability of that digit to regulate its blood supply during a brief period of ischemia and reperfusion
Another expression of reactive hyperemia is the duration of the flow response following release of an occlusion; the time it takes for the maximum flow to be achieved
Summary
Caffeine is widely used for medical and non-medical purposes It is most commonly consumed in beverages and as over-the-counter capsules, pills and tablets because consumers believe it boosts their energy, enhances motivation, improves gym performance, and/or reduces disease [3]-[8]. Abuse of bodies and minds by caffeine has become a pastime for many consumers even though there are unanswered questions about its aphysiological effects on the body, especially the brain and cardiovascular system. Since caffeine and other methylxanthines are adenosine receptor inhibitors, adenosine-mediated circulatory regulation in the brain, heart and elsewhere can be dangerously impaired by caffeine [9] [10] [11] [12]
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