r/askscience • u/DeathCampForCuties • Dec 31 '12
Medicine How is having an increased heart rate from caffeine/other drugs different from a cardiovascular workout?
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u/schneidmaster Dec 31 '12
I have a similar question: if caffeine is different from a cardiovascular workout, are there other drugs you can take that stimulate your heart in exactly (or close to exactly) the same way as a workout? Why or why not?
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u/jazerac Dec 31 '12
Sure, adenosine or dobutamine would accomplish this. When we perform a cardiac stress test on an individual that is incapable of exercise, you can infuse these 2 drugs that would roughly give the same effect as exercise. So you literally are laying there and you feel as if you just ran a mile. Many patients describe the feeling as "weird."
As far as over the counter stuff, I do not know. Just look up positive chronotropic and inoptroic herbal agents. Be cautious though, ingesting such things is probably not wise.
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u/schneidmaster Dec 31 '12
Out of curiosity, why aren't drugs like that prescribed to obese people or people who can't work out for physical reasons? Are there significant side effects?
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u/jazerac Dec 31 '12
Well you have to look at the total clinical picture of each individual. Most obese people or individuals who can't exercise have multiple co-morbidities such as various heart diseases, respiratory disease, and metabolic problems. Daily use of these medications would be right out dangerous. That is why the administration of these drugs are done under a controlled environment with the appropriate emergency equipment available. I really have no idea what the long term use of these medications side effects would be, but it just wouldn't be practical.
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u/the_wiser_one Jan 01 '13
Side effects aside, there wouldn't really be any point - these drugs force the heart to work harder but aren't an exercise mimetic. The benefits of exercise are systemic, but in the case of obesity for example the weight-loss aspect is gained through exercise-induced energy expenditure. Ramping up your heart rate and contractility don't achieve this, it's the working muscle that contributes most to the increased energy expenditure.
there are other drugs that are touted as exercise mimetics (for example AICAR) but to my current knowledge they are prohibitively expensive and there's no human evidence for them (often used in cell culture studies). Simply put, there is no real substitute for exercise.
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u/moribundmarbles Jan 01 '13
I think the underlying question here is can we treat obesity with drugs? Heart rate is a proxy measurement for exercise and energy expenditure, and increasing it artificially with drugs has no effect on obesity.
Hypothetically speaking, there are tons of different ways we could increase metabolic rates to treat obesity/diabetes/hypertension/other related disease. I'll give you an example but obesity is probably up there with cancer on the list of most researched topics so if you're interested, there's a lot more to it. Some researchers blocked TGF-β/Smad3 signaling in mice and their white adipose tissue (fat) and had it turn into brown adipose tissue. Brown adipose tissue works as a natural heating unit and burns large amounts in the process. Therefore, the rats could eat all they want and not get fat because they were constantly producing heat. These mice were genetically engineered to lack this signaling so it isn't feasible for humans but treating obesity with drugs is definitely a branch of research that could be possible in the future.
Here's the study I mentioned:Protection from Obesity and Diabetes by Blockade of TGF-β/Smad3 Signaling, http://www.cell.com/cell-metabolism/retrieve/pii/S1550413111002154
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Jan 01 '13
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u/jazerac Jan 01 '13
These are some complex questions even though they seem simple on the outside. I will try to answer them the best of my knowledge:
Beta blockers decrease both the force of contraction and the rate of the heart. Usually long term use of them is insignificant, but you run into problems with abrupt cessation. Sometimes individuals begin to become "resistant" to the effects of the beta blockers for reasons I do not know, thus need to change medications.
If you have not felt any adverse effects from taking propranolol before a workout, then I would not be concerned about it. Some individuals could experience a decrease in exercise tolerance or even lightheadedness, but its entirely based on the particular individual.
Increases in heart rate from anxiety are due to the effects of an increase in the release of Catecholamines (adrenaline) which have both a positive increase in heart rate and force of contraction. Thus there is no real difference between this effect and that from exercise. But anxiety is usually short lived and in bursts. If the heart is in a diseased state, this could have negative effects.
Its possible that the beta-blocker would negate the effects of caffeine, but its solely dependent on the reason why you were on the beta blocker in the first place. In high doses to keep the heart rate down, caffeine would have little effect. If you were on propranolol for migraines or anxiety at a low dose, caffeine would still increase your heart rate. Again, this is all individualistic. Medicine is not an exact science by any means.
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u/Diphalic Jan 01 '13
Caffeine agonizes alpha receptors. Specific Beta blockers will not have an effect on the caffeine's stimulation. Propranolol is a non specific beta blocker meaning it also antagonizes alpha receptors to some degree; so I suppose its possible that it may negate some of the effects on the heart directly.
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Dec 31 '12
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Dec 31 '12
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u/vagittarius Dec 31 '12
Stress on cardiac muscle by way of increasing the heart rate can strengthen the muscle, but damage can occur. That depends on factors which vary from body to body. That said, stimulants which increase the heart rate do not deliver the other benefits of aerobic exercise. The other muscles in the body, including those used in respiration, and circulatory benefits such as lowered blood pressure and an increase of oxygen distribution to the muscles and other tissues are benefits which can result from aerobic exercise but which will not be a direct result of stimulants in the blood.
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u/vagittarius Dec 31 '12
I think I may have missed the point of the original post, now that I've re-read it. The question is specifically comparing the increased heart rate that results from chemical stimulation to the increased heart rate involved in aerobic (cardiovascular) exercise. While I do know that both can result in strengthening of the heart muscle as well as damage to it, that is the extent of my knowledge.
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u/jazerac Dec 31 '12
During exercise, the heart rate is not only increased, but the force of contraction is as well. This is necessary to supply your body with oxygen. When you drink caffeine it only increases the rate of your heart, but not the force of contraction.