Heart Rate and Contractility – Determinants of Blood Pressure (Nursing)

00:01 So now we know the four parts of blood pressure, and we know how to look and find out the four parts of blood pressure, how to measure them.

00:10 Now let's look at what they mean and how they affect the blood pressure.

00:13 So again, the first is the heart rate.

00:15 Remember, our normal range is about 60-100 beats a minute.

00:20 When your ventricle start to beat faster, meaning your heart rate goes up faster, then your blood pressure will start to increase up to a certain point.

00:29 Once it reaches a certain point, then your ventricles do not fill adequately.

00:34 And you lose that Frank Starling law means you lose that stretch.

00:38 So a fast heart rate affects blood pressure by two ways.

00:42 It doesn't allow the ventricle to fill up enough with enough blood volume.

00:47 And it decreases contractility because you lose that Frank-Starling law that stretch.

00:53 Now, if your heart rate is too slow, basically, you don't have enough cardiac output, because you're not getting enough blood out per minute, because the heart rate is too slow.

01:02 That's going to be under 60.

01:04 Now, what determines how it's too fast and how it's too slow and when you have low blood pressure? It's really patient dependent.

01:10 You may have a patient that has a blood, a heart rate of 130 beats a minute, and their blood pressure may be fine.

01:18 Or then you have another patient that their heart rate is 160 beats per minute, and their blood pressure is really, really low.

01:25 Or vice versa, you may have a patient that's bradycardic and have a heart rate of 35 and they are still maintaining a decent MAP.

01:35 The next patient, you come in that bradycardic might be a heart rate of 45 and they are symptomatic and they've got a blood pressure or a MAP that's under 60.

01:45 So it's really patient dependent when it comes to heart rate.

01:50 The second part of your heart that affects blood pressure is the contractility.

01:55 We know how to look at it, remember? We can visualize our contractility with an echocardiogram.

02:00 But if you don't have a recent echocardiogram, or you're not able to get one, then we can look at it secondarily by our cardiac output/index.

02:08 I want you to remember though, if you have a low cardiac output and index, it doesn't automatically mean your contractility is too low, because there's so many determinants in it.

02:17 The determinants of cardiac output are heart rate, contractility, preload, and afterload.

02:23 So basically, you need to rule out all the three other parts of cardiac output to decide, "My contractility is the issue." So you're the first to look at heart rate and say, "Okay, my heart rate is within normal." and my EKG is normal, then you go to preload and go, "My tank is full, I've got enough fluid volume." Then you look at your afterload with your systemic vascular resistance and, "Hey, I'm between 800 and 1200, that's not affecting my cardiac output." So then you can say, "It's probably my contractility.

02:53 I may need an echocardiogram or start a medication that can increase contractility." So cardiac output, just reviewing remember it's 4-8 L/min.

03:04 And remember, as a heart rate increases, and contractility increases, so does our cardiac output.

03:11 But the heart rate can be too fast where the ventricles don't fill and we don't get that that stretch, which would cause a decrease in cardiac output.

03:19 I want you to look at the picture and see as that left ventricle stretches, and then contracts, that's a visualization of our cardiac output.