Beta Blockers and Asthma

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

How would you like it if you were to have two serious medical problems? And how would you like it if the medication for one interfered with the medication for the other? Learn how this might be the case on this lesson on beta-blockers and asthma.

Treating Two Problems

It's bad enough if you have one disorder, right? If you have a heart condition, that's really serious! What's even more dangerous is when you have a lung condition on top of the heart condition. Both are bad enough, but two at the same time can pose multiple problems. One of these problems involves the use of beta blockers to treat cardiovascular conditions in people with asthma.

This lesson ties these concepts together for you.

What Is Asthma?

Asthma is a type of chronic airway disorder. By chronic, this means it is a long-term disorder. There are many parts and aspects to asthma. For example, a person with asthma will have a cough and difficulty breathing. The reasons for these and other asthma-related problems are many, but this lesson's main need is for you to remember this: one part of asthma involves bronchospasms.

Bronchospasms are the involuntary and sudden contractions of the smooth muscles around the airways of the lungs, airways called bronchi and bronchioles. These smooth muscles control the expansion and contraction of the airways. In asthma, a bronchospasm leads to the contraction (constriction) or narrowing of the airways, which makes it difficult to breathe. Thus, people with asthma use bronchodilators to help dilate (expand) or open up the airways.

What Are Beta-Blockers?

That's all you need to know about asthma for now. Just for a second, let's skip over to understanding a bit about beta-blockers before tying the latter in with asthma. Beta blockers are medications that block the effects of a hormone called epinephrine. Epinephrine lands on beta receptors to exert its effects. The two main beta receptors are beta-1 receptors, located on the heart, and beta-2 receptors, located on the smooth muscles of the airways (among many other places).

When epinephrine stimulates beta-1 receptors, the heart beats faster and works harder. So, we want to block beta-1 receptors in conditions like heart failure.

The Relationships Between Beta Blockers & Asthma

And here is where we tie in asthma to our beta blockers. Not all beta blockers are created equal. Some beta blockers are cardioselective, which means they (for the most part) block beta-1 receptors only. In other words, they only affect the heart. Other beta blockers are non-cardioselective. This means they block both the beta-1 (heart) and beta-2 (lung) receptors. This may pose a problem for people with asthma.

See, when epinephrine lands on beta-2 receptors in the lungs, it causes the airways of our lungs to expand. But if we give a person a non-cardioselective beta blocker, this medication will stop epinephrine's effects on the airways. In other words, such a beta blocker will result in the constriction (narrowing) of the airways much like a bronchospasm might. That's bad for people with asthma who already have narrowed airways!

The other, second whammy, is that bronchodilators used to treat asthma, such as albuterol, are beta-2 agonists. In other words they, like epinephrine, land on beta-2 receptors to stimulate the smooth muscles of the airways to relax and thus open up the person's airways to help them breathe easier. But if we give such a person using a bronchodilator a non-cardioselective beta-blocker, we're giving them a medication that literally blocks the potentially life-saving effects of their own bronchodilator!

This is why people being treated for a heart condition by a beta blocker, who also happen to have asthma, are either not given a beta blocker at all, or are given a cardioselective beta blocker only. Of course, just about everything in medicine has a caveat. Remember how you read that cardioselective beta blockers '(for the most part) block beta-1 receptors only'? That phrasing was purposeful. Even some cardioselective (beta-1) blockers lose their selectivity and begin to affect beta-2 receptors at higher doses. In other words, higher doses of cardioselective beta blockers may also lead to a bronchospasm.

Thus, the choice to use or not use even a cardioselective beta-blocker in patients with asthma rests upon multiple factors, such as their ultimate need for a beta blocker, how well-controlled their asthma is, and the length of treatment. Monitoring of the patient's response to the medication is just as critical.

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