How does exercise increase the efficiency of the heart yet...
...using stimulant drugs causes negative, sometimes even fatal, effects on it (the heart) ?
When you run/cycle/jog/swim you're making your heart beat hard and fast... how is it different than someone who takes a stimulant drug like cocaine, ADHD medicine, speed, meth etc (infrequently). Don't they also make your heart beat harder and faster than normal? Why doesn't your heart get a 'workout' then also?
Posted Apr 12, 2015, 12:24 AM UTC
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I can weigh in a little bit with my pharmacy education but probably not as in depth as a doc or someone with more anatomy/physiology knowledge. And to tell you the truth I don't really know how it gets stronger, but I can tell you why there's a difference in harm between drugs and exercise.
So first off your heart NEEDS oxygen to survive. When oxygen demand exceeds supply then cells die. When your heart rate increases from drugs or exercise you heart will demand more oxygen to survive. Blood is carrying oxygen all around your body and it has to make it back to the heart to supply it with what it needs.
The problem with drugs is that some of them work directly on the blood vessels also as vasoconstrictors, meaning they tighten your blood vessels and make it more difficult for blood to flow through them. So now the drug is working on the heart to make it beat faster and demand more oxygen but it's also constricting your blood vessels to make the blood flow back to the heart more difficult. That's going to cause oxygen demand to exceed supply and lead to cell death, noted by chest pain (ischemia) which can lead to infarction (a heart attack). With chronic drug use too the constant high heart rate can also cause ventricular hypertrophy (thickening) which makes it more difficult for the heart to expand and contract (heart failure)
Cocaine is a little more interesting however! It works by speeding up the heart, strongly constricting the blood vessels, but it also works as a sodium channel blocker. You know when you go to the dentist and they give you Novacaine and your mouth gets all numb? Cocaine works identically to that but it gets in your blood and works on your heart. It can numb the heart in the same way and lead to ventricular arrhythmias which are very lethal. Most drugs won't cause heart problems with the occasional use (I'm not saying use them!) but cocaines heart problems can really happen to anyone at anytime.
With exercise though you don't get that severe vasoconstriction like you do with the drugs. You do get that increase in oxygen demand, but your blood vessels won't constrict as much so the supply can meet the demand. There's also been some research that aerobic exercise upregulates something in your blood vessels called "epithelial nitric oxide synthetase" which will create nitric oxide which is a very strong vasodilator. So now blood can flow through the vessels much easier since they are more open. In really piss poor terms, your heart kind of just gets use to it working harder as long as it isn't becoming damaged. I suck, I'm sorry.
Feel free to ask anything else! And anyone that knows more than me please jump in!
Thanks for the lengthy reply. To jump on your term 'vasodialator' - aren't asthmatics' inhalers also vasodialators? So can using a drug like the ones in an inhaler can help the flow of oxygen getting to heart or is that an oversimplification?
You are on the right track with that! I'll try and break it down as simply!
Blood vessels contain "alpha receptors" and "beta receptors".
If you activate the alpha receptors then your vessels will constrict.
If you activate your beta receptors they will dilate. Your lungs also contain these beta receptors which is what helps the airways open up.
Most asthma inhalers (albuterol, salmeterol) work by activating your beta receptors. But it is a very small dose and you inhale it so not much of the drug will reach your blood stream, but some of it definitely does! So theoretically the small portion of the dose that does get into your bloodstream should help open up those blood vessels too! I've actually never thought of it like that though so thanks for an interesting question haha. Most of the beneficial effects are going to be from allowing your airways to take in more oxygen and supply the heart though.
To come full circle then, is it possible vasodilator drugs mixed with stimulants give your heart "exercise" without the negative effects?
Not u/Pharmastuff but I want to say that sounds reasonable if not risky.
Haha I actually got thinking the same question as I was writing up my other replies. To tell you the truth I have no idea! I guess it might work. Mechanistically it makes sense! But it doesn't always work like that when we try it in the body.
I can't really say for sure if your heart is getting "exercise", but a vasodilator would definitely keep your blood pressure lowered which would significantly reduce the risk of heart problems.
Inhaled medications have a more targeted effect. Most of the medication is absorbed right in the respiratory tract, although small portions do enter systemic circulation.
Medications used to treat asthma include corticosteroids and bronchodilators. In a way, you could say that they are "vasodilators", but I agree that that is a bit of an over simplification. These drugs, such as albuterol, bind to the receptors in the smooth muscles of the airway, and exert their effects there. Albuterol is more of a rescue inhaler because of its quick response, and that is dilating the bronchial vessels to increase the effectiveness of breathing and thus tissue perfusion of oxygen. Corticosteroids are the drug class of choice for asthmatics, as they decrease the inflammation asthmatics experience during an allergic response.
Vasodilators help keep blood pressure within normal limits for someone with hypertension already. However, if they are given to people with a normal blood pressure, they can cause the blood pressure to drop too low which is problematic. All antihypertensives have a vasodilating effect, but they also can act as a blood thinner and diuretic, albeit to a lesser degree. There are periodic labs that need to be drawn when taking these medications, specifically electrolytes. A decrease in any of the electrolytes (but especially sodium and potassium, which effect the heart muscle) can cause imbalances that can have serious negative effects on the heart.
So basically, all medications can cause desired and not so desired effects, a "trade off", if you will. You can't get one without the other, although the severity can differ greatly. This depends a lot on how the individual metabolizes the drug(s), which is a little different for everyone.
Great answer! Just something to add: when heart rate rises the heart has to "save" time somewhere during it's cycle of diastole (relaxation) and systole (constriction). It does this mostly by reducing the diastolic phase. Unfortunately this is also the phase during which the ventricles are filled with blood again.
Therefore, once you reach a certain threshold (ca. 180/min according to my physiology professor) the volume the heart pumps per minute actually goes down again as the ventricles do no get filled enough. If you press the heart to hard (pun intended) and the heart rate is too high this can lead problems. I assume while the body regulates itself to prevent this drugs might push you over that line. Just a guess though.