So here we have an example problem that says, blood is flowing from point A to point B at a constant rate. Then a physiological change causes the resistance to blood flow between the two points to decrease. And then the problem asks, what will happen to the rate of blood flow? We've got these three potential answer options down below that say that it will increase, it will decrease, or it will remain the same. Now, in order to solve this problem, I've gone ahead and drawn a little sketch just to help us better visualize the scenario. Notice that I've drawn a blood vessel right here and indicated where point A is and where point B is. Again, the problem tells us that blood is flowing from point A to point B at a constant rate, but then there's some kind of physiological change that occurs that causes the resistance to blood flow between the two points to decrease. Now recall from our previous lesson videos that the resistance refers to any opposition to the blood flow or how difficult it is for blood to flow through the cardiovascular system. It's a measure of the amount of friction that the blood encounters as it travels through the cardiovascular system. Recall that the greater the resistance is, the lower the blood flow will be. So there is an inverse relationship between the two. Notice that this problem mentions that there is a decrease in the resistance, which means there is less opposition to the blood flow, and that will make it easier for the blood to flow through the cardiovascular system between the two points. And so what that means is that the blood flow is going to increase if there's a decrease in the resistance. So that means that we can indicate that answer option A, it will increase, is the correct answer to what will happen to the rate of blood flow. So we can indicate that A here is correct, and these other options are not correct.
Now another approach that we could have taken to solving this problem is remembering the equation that we introduced in our last lesson video that relates the important hemodynamics variables, which recall are blood flow, blood pressure gradient, and resistance. Recall that the equation is that blood flow, or F, is equal to the blood pressure gradient, or ∆P, divided by the resistance, or R. The problem tells us that the resistance between the two points is decreasing, so the value of R is going down. And, of course, because the resistance is in the denominator, that causes this entire value here, which is the blood flow, to increase. Now, we could also use some random numbers here to help us better understand how this equation could have worked. Let's say that for the blood pressure, we used a value of 2, and for the resistance, we also used a value of 2. And, of course, 2 divided by 2 is 1, so that would make the blood flow 1. Now let's imagine that this was the case, initially before the physiological change. Now after the physiological change, there was a decrease in the resistance, which is the R value in the bottom. So, let's make it 1 this time. The blood pressure difference we'll say is the same, just 2. And so, 21 is going to be 2. That shows that when the resistance decreases, as you see here, that causes the value of the blood flow to increase, which, again, validates that answer option A is correct. So, hopefully, this was helpful for you all, and that concludes this example. I'll see you all in our next video.