You are an athletic trainer who is working with someone planning to run a marathon. Your trainee tells you to give him a workout that will make his heart 'beat faster than ever before.' What do you tell him about the effects of too rapid a heart rate?

Video transcript

Hi, everyone. Let's take a look at this practice problem together. After consuming an excessive amount of caffeinated beverages, mark experienced palpitations. What could be its repercussions for the heart. The answer options are a, it can increase the demand for carbon dioxide. B it can decrease the amount of blood pumped by the heart C. It can increase cardiac output and D all of the above. So caffeine is a stimulant and it can cause palpitations. Now, palpitations are rapid, strong, irregular heartbeats. So how do the palpitations affect the heart? Let's review the answer options option. A increased demand for carbon dioxide. So the increased demand would actually be for oxygen, not carbon dioxide. With the faster heart rate, more blood is pumped and the cardiac muscle cells will have a larger oxygen demand. So that is why option A is incorrect. Option C is also incorrect. Now, let's talk through this option. C states that there would be an increase in cardiac output and there would actually be a decrease in cardiac output. Mark has an increased heart rate which means that the heart is contracting more frequently. So we have an increased heart rate. The heart is beating more frequently and there is less time in between the contractions. That means that there is less time for ventricular feeling when there's less blood in the ventricles during contraction. This affects and decreases the overall stroke volume. And remember stroke volume is part of the equation to calculate cardiac output. Remember that the equation for cardiac output is that cardiac output equals heart rate, time stroke volume. Or if we use the abbreviation co equals hr multiplied by SV. So decreasing the stroke volume will decrease the cardiac output. So option C is incorrect. The correct answer is option B, remember we have the increased heart rate which will decrease the amount of time for ventricular filling. And that means that there is a decreased amount of blood that can be pumped. So the correct answer is option B it can decrease the amount of blood pumped by the heart. All right, everyone. I hope you found this helpful and I'll see you soon for the next practice problem.