Understanding Systemic Blood Pressure Mechanics

Okay, so now moving on to section 7 of chapter 19, we're going to talk about blood pressure, but specifically our systemic blood pressure. So we're talking about blood flow from our heart to our tissues throughout our body. So what generates the blood flow is the pumping action of the heart, which we talked about in chapter 18. But the pressure results when the flow is actually opposed by resistance. So the higher the resistance, the higher the pressure. Systemic pressure is always going to be the highest closest to the heart, so highest in our aorta, and then it's going to decline along its pathway. So highest in the aorta, the blood pressure is going to decrease as it enters into our capillary bed and then decrease even further once it hits our veins. So highest pressures in our arteries, lowest pressure is going to be in our veins. However, the steepest drop in pressure is going to be occurring in our arterioles themselves because they have the greatest resistance to blood flow. When we're talking about arterial blood pressure, what the blood pressure is in our arteries is going to be the result of two different things. One is elasticity. So also we'll talk about compliance and distensibility in a little bit. The elasticity of the arteries that are closest to the heart. How elastic are they? The second thing that can affect blood pressure is how much blood is actually being forced into those arteries, so the volume of the blood. And we talked a little bit about the volume when we're talking about the stroke volume, so the amount of blood that's actually pumped out of the ventricles into either the pulmonary trunk or to the aorta. Blood pressure closest to the heart is going to be pulsatile, meaning it's not a steady blood pressure. It's going to be high and low, depending whether we just went through ventricular contraction or ventricular relaxation phase. So it's going to rise and fall with each heartbeat. So just like we talked about systole and diastole, we also can talk about the blood pressures that are associated with these two phases. So systole, we're talking about ventricular contraction. and diastole was ventricular relaxation. So when we're talking about the systolic pressure, we're talking about the pressure exerted in the aorta during ventricular contraction. And if we're specifically referring to the pressure in the aorta, then we're specifically referring to our left ventricle because that's the ventricle of the heart that's responsible for pushing the blood into the aorta itself. The average pressure is about 120 millimeters of mercury in an average normal adult. The diastolic pressure is going to be the lowest aortic pressure, and that would occur when our heart is at rest, so during ventricular relaxation. So if you've ever had your blood pressure taken or you know the standard or typical blood pressure that they look at or that they reference is 120 over 80. And it's actually millimeters of mercury. So what they're referring to is the systolic pressure or the pressure in our aorta at ventricular contraction. That would be the numerator portion of our blood pressure. And then our denominator portion of our blood pressure represents the diastolic pressure, which is typically around 70 to 80 millimeters of mercury. And that would represent ventricular relaxation. So we also have something called the pulse pressure, and this is the difference between the systolic and diastolic pressure. So if we wanted to take our average 120 over 80 blood pressure and determine the pulse pressure, we would just take 120, which is the systolic, and subtract the diastolic pressure, which is 80, and we would be left with 40 millimeters of mercury as our pulse pressure. And pulse, if we ever were to take our pulse, there's several different pulse points that we have on our body. But the pulse just represents the throbbing of the arteries due to the difference in the pulse pressures. And we can feel these under our skin in certain places. So this is just a pressure graft in relation to our blood vessels. So if we're looking at our aorta, we would expect it to be the highest because remember, blood pressure is going to decline as it travels through our body systemically. And our highest blood pressure would be around 180, or I'm sorry, 120. And then our lowest blood pressure would be around 80 millimeters of mercury. And because it can fluctuate and range anywhere between 80 and 120, depending on what state our ventricle is in, we say that it's pulsatile. So that's what that was meaning. So the aortic pressure is going to fluctuate with each heartbeat. And we'll talk about how we have to calculate the mean arterial pressure in order. to figure out what the pressure is going into our capillaries. So again, pulsatile, if we're talking about our arteries, so our aorta, arteries, and arterioles. As we approach the capillaries, it's not really pulsatile anymore. We have one uniform blood pressure because we're further away from the heart. Also notice how much lower the blood pressure is in our capillaries. relative to our aorta. So the steepest decline in pressure was our arterioles. So then we continue to decrease our blood pressure as we travel through our venules, veins, and eventually our vena cava, which is going to bring the blood back into our right atrium. So like I mentioned, the main arterial pressure, that's going to be the pressure that actually propels the blood into tissues. We cannot just take the average of the diastolic and systolic pressures in order to find the mean arterial pressure. Why? Because our heart spends more time in diastole. So it spends more time relaxing in its relaxation phase than it does during systole or the contraction phase. So we can't just do a simple average. So we have to calculate what's called the mean arterial pressure. And we take our mean arterial pressure. basically is calculated by adding the diastolic pressure plus one-third of the pulse pressure. So for example, if we have a mean arterial pressure and we're trying to find the diastolic plus one-third of the pulse pressure, we have to know what the original blood pressure was. So if we were still working with our 120 over 80, we calculated our pulse pressure previously, but it's also shown here from you. Pulse pressure is equal to the systolic minus the diastolic, so that would give us a pulse pressure of 40. So we take our 80, which is our diastolic pressure, and then we take one-third of our pulse pressure. So we just take one-third times the 40, and that would give us around 93 millimeters of mercury. You won't have to do any calculations and you don't need a calculator on your exam, but you should understand what the mean arterial pressure represents, which is taking diastolic pressure and adding it to a third of the pulse pressure. And the reason why you have to do that is because of the differences in time spent between diastole and systole. Regardless, our pulse pressure and our mean arterial pressure are both going to decline the further away we get from the heart. So it would always be highest near closest to the heart and then lowest in like our vena cava. So this is just clinical. If we're talking about vital signs, so if we're talking about vital signs, a lot of times if you go to the doctor, they'll take your pulse, your blood pressure, along with your respiratory rate and body temperature. But if you're taking a pulse, this is the locations over here. um where you can take your pulse you do not have to memorize these um maybe for lab you might but not for lecture but the radial pulse is a frequent pulse that's taken um that's the one that's taken at the rent at the wrist and we also have some pressure points which are just areas where the arteries are really close to the body surface um so if you were ever to start bleeding you would actually want to put pressure on one of these pressure points in order to stop blood from flowing and preventing huge amounts of blood loss. So pulse points are also called pressure points. Okay, so measuring blood pressure. Again, you may be doing this in lab. Systemic arterial blood pressure is measured indirectly by eschizoteri methods using a sphygomanometer. So you You've probably had your blood pressure taken or maybe gone to a grocery store and had it taken there. But that's basically where they take a cuff, wrap it around your arm, superior or above your elbow. And the pressure... And the cuff is going to continually increase until it's going to exceed your systolic pressure. And then the pressure is going to release slowly, and it's going to listen for sounds of corticof with a stethoscope. So like I mentioned before, systolic pressure is normally or should be at about 120 millimeters of mercury. And that That represents when the first sounds are heard as the blood starts to kind of spurt through the artery when the pressure starts to be released. The diastolic is normally around 80 millimeters of mercury or should be lower than that. And this pressure is when the sounds disappear because the artery is no longer constricted at all. So that's why it slowly releases the pressure. Okay, capillary blood pressure, we would expect to be much lower than that of our arteries because we're further so far away from our heart. So the range of capillary blood pressure can be anywhere from 35 millimeters of mercury at the beginning of a capillary. to 17 millimeters of mercury at the end of the capillary bed. We want this low blood pressure. It's a good thing because remember, our capillary walls are typically a single layer thick. with cells. So if we had too high of a blood pressure entering these capillary beds, it would rupture our capillaries because they're so thin. Most capillaries, like we talked about before, they're permeable because they have those pores or those fenestrations. So the low pressure forces the filtrate into the interstitial fluid, which is exactly what we wanted to do. Venous blood pressure doesn't really change a lot during the cardiac cycle. It's pretty steady because, again, it's so far away from the heart at this point that when the ventricles contract and relax, it's no longer affecting the pressure that far away. So small pressure gradient, only about 15 millimeters of mercury. One way to tell if you were to ever injure yourself, whether or not you cut a vein or an artery, is looking at the amount of blood that's coming out. So if a vein is cut... Because it's a low pressure blood vessel, your blood will kind of just trickle out very smoothly. If for some reason you cut an artery, because it's under such high pressure, your blood is actually going to spurt out. So if you cut yourself, that's one way to kind of tell. Low pressure is due to the cumulative effects of peripheral resistance. The energy of the blood pressure is lost as heat during each circuit. So in A&P 1, you probably talked about energy conversions. Anytime you convert energy from one form to another, some is always lost as heat. So that's why we have a relatively high body temperature. The low pressure of the venous side does require some adaptations to help with the venous return. So one downside to our veins having such a low blood pressure is how do we get this blood that's at a low blood pressure all the way back to our heart? especially if we're talking about inferior places like our ankles or our feet. We have to have some adaptations to continue to have the blood moving in one direction superiorly to our heart. So a couple of factors help get our blood from our veins back to our right ventricle. One of them is the muscular pump. So our skeletal muscles actually aid in helping move blood back. towards the heart. When our skeletal muscles contract, they squeeze on the veins, pushing the blood forward. And our veins, I don't know if you remember when we were describing the three different types of blood vessels and their characteristics, veins also have valves. So once our skeletal muscle contracts and it pushes the blood forward, the valves prevent it from flowing backwards. Respiratory prompt. So So pressure changes during breathing can also help move blood towards the heart. When we hit the respiratory system, we'll learn more about these pressure changes and their contribution to this. The sympathetic veno constriction. So under sympathetic control, our smooth muscles are going to constrict. And that's also going to help push the blood back toward the heart. So basically, all three of these are capable of increasing. venous return. If they can increase venous return, that also means we've increased our stroke volume and increased our cardiac output.

So highest in the aorta, the blood pressure is going to decrease as it enters into our capillary bed and then decrease even further once it hits our veins. So highest pressures in our arteries, lowest pressure is going to be in our veins. However, the steepest drop in pressure is going to be occurring in our arterioles themselves because they have the greatest resistance to blood flow.

When we're talking about arterial blood pressure, what the blood pressure is in our arteries is going to be the result of two different things. One is elasticity. So also we'll talk about compliance and distensibility in a little bit. The elasticity of the arteries that are closest to the heart. How elastic are they?

The second thing that can affect blood pressure is how much blood is actually being forced into those arteries, so the volume of the blood. And we talked a little bit about the volume when we're talking about the stroke volume, so the amount of blood that's actually pumped out of the ventricles into either the pulmonary trunk or to the aorta. Blood pressure closest to the heart is going to be pulsatile, meaning it's not a steady blood pressure.

It's going to be high and low, depending whether we just went through ventricular contraction or ventricular relaxation phase. So it's going to rise and fall with each heartbeat. So just like we talked about systole and diastole, we also can talk about the blood pressures that are associated with these two phases.

So systole, we're talking about ventricular contraction. and diastole was ventricular relaxation. So when we're talking about the systolic pressure, we're talking about the pressure exerted in the aorta during ventricular contraction. And if we're specifically referring to the pressure in the aorta, then we're specifically referring to our left ventricle because that's the ventricle of the heart that's responsible for pushing the blood into the aorta itself.

The average pressure is about 120 millimeters of mercury in an average normal adult. The diastolic pressure is going to be the lowest aortic pressure, and that would occur when our heart is at rest, so during ventricular relaxation. So if you've ever had your blood pressure taken or you know the standard or typical blood pressure that they look at or that they reference is 120 over 80. And it's actually millimeters of mercury.

So what they're referring to is the systolic pressure or the pressure in our aorta at ventricular contraction. That would be the numerator portion of our blood pressure. And then our denominator portion of our blood pressure represents the diastolic pressure, which is typically around 70 to 80 millimeters of mercury.

And that would represent ventricular relaxation. So we also have something called the pulse pressure, and this is the difference between the systolic and diastolic pressure. So if we wanted to take our average 120 over 80 blood pressure and determine the pulse pressure, we would just take 120, which is the systolic, and subtract the diastolic pressure, which is 80, and we would be left with 40 millimeters of mercury as our pulse pressure. And pulse, if we ever were to take our pulse, there's several different pulse points that we have on our body.

But the pulse just represents the throbbing of the arteries due to the difference in the pulse pressures. And we can feel these under our skin in certain places. So this is just a pressure graft in relation to our blood vessels. So if we're looking at our aorta, we would expect it to be the highest because remember, blood pressure is going to decline as it travels through our body systemically. And our highest blood pressure would be around 180, or I'm sorry, 120. And then our lowest blood pressure would be around 80 millimeters of mercury.

And because it can fluctuate and range anywhere between 80 and 120, depending on what state our ventricle is in, we say that it's pulsatile. So that's what that was meaning. So the aortic pressure is going to fluctuate with each heartbeat. And we'll talk about how we have to calculate the mean arterial pressure in order. to figure out what the pressure is going into our capillaries.

So again, pulsatile, if we're talking about our arteries, so our aorta, arteries, and arterioles. As we approach the capillaries, it's not really pulsatile anymore. We have one uniform blood pressure because we're further away from the heart.

Also notice how much lower the blood pressure is in our capillaries. relative to our aorta. So the steepest decline in pressure was our arterioles. So then we continue to decrease our blood pressure as we travel through our venules, veins, and eventually our vena cava, which is going to bring the blood back into our right atrium.

So like I mentioned, the main arterial pressure, that's going to be the pressure that actually propels the blood into tissues. We cannot just take the average of the diastolic and systolic pressures in order to find the mean arterial pressure. Why?

Because our heart spends more time in diastole. So it spends more time relaxing in its relaxation phase than it does during systole or the contraction phase. So we can't just do a simple average.

So we have to calculate what's called the mean arterial pressure. And we take our mean arterial pressure. basically is calculated by adding the diastolic pressure plus one-third of the pulse pressure. So for example, if we have a mean arterial pressure and we're trying to find the diastolic plus one-third of the pulse pressure, we have to know what the original blood pressure was. So if we were still working with our 120 over 80, we calculated our pulse pressure previously, but it's also shown here from you.

Pulse pressure is equal to the systolic minus the diastolic, so that would give us a pulse pressure of 40. So we take our 80, which is our diastolic pressure, and then we take one-third of our pulse pressure. So we just take one-third times the 40, and that would give us around 93 millimeters of mercury. You won't have to do any calculations and you don't need a calculator on your exam, but you should understand what the mean arterial pressure represents, which is taking diastolic pressure and adding it to a third of the pulse pressure.

And the reason why you have to do that is because of the differences in time spent between diastole and systole. Regardless, our pulse pressure and our mean arterial pressure are both going to decline the further away we get from the heart. So it would always be highest near closest to the heart and then lowest in like our vena cava. So this is just clinical. If we're talking about vital signs, so if we're talking about vital signs, a lot of times if you go to the doctor, they'll take your pulse, your blood pressure, along with your respiratory rate and body temperature.

But if you're taking a pulse, this is the locations over here. um where you can take your pulse you do not have to memorize these um maybe for lab you might but not for lecture but the radial pulse is a frequent pulse that's taken um that's the one that's taken at the rent at the wrist and we also have some pressure points which are just areas where the arteries are really close to the body surface um so if you were ever to start bleeding you would actually want to put pressure on one of these pressure points in order to stop blood from flowing and preventing huge amounts of blood loss. So pulse points are also called pressure points.

Okay, so measuring blood pressure. Again, you may be doing this in lab. Systemic arterial blood pressure is measured indirectly by eschizoteri methods using a sphygomanometer.

So you You've probably had your blood pressure taken or maybe gone to a grocery store and had it taken there. But that's basically where they take a cuff, wrap it around your arm, superior or above your elbow. And the pressure...

And the cuff is going to continually increase until it's going to exceed your systolic pressure. And then the pressure is going to release slowly, and it's going to listen for sounds of corticof with a stethoscope. So like I mentioned before, systolic pressure is normally or should be at about 120 millimeters of mercury.

And that That represents when the first sounds are heard as the blood starts to kind of spurt through the artery when the pressure starts to be released. The diastolic is normally around 80 millimeters of mercury or should be lower than that. And this pressure is when the sounds disappear because the artery is no longer constricted at all. So that's why it slowly releases the pressure.

Okay, capillary blood pressure, we would expect to be much lower than that of our arteries because we're further so far away from our heart. So the range of capillary blood pressure can be anywhere from 35 millimeters of mercury at the beginning of a capillary. to 17 millimeters of mercury at the end of the capillary bed.

We want this low blood pressure. It's a good thing because remember, our capillary walls are typically a single layer thick. with cells.

So if we had too high of a blood pressure entering these capillary beds, it would rupture our capillaries because they're so thin. Most capillaries, like we talked about before, they're permeable because they have those pores or those fenestrations. So the low pressure forces the filtrate into the interstitial fluid, which is exactly what we wanted to do.

Venous blood pressure doesn't really change a lot during the cardiac cycle. It's pretty steady because, again, it's so far away from the heart at this point that when the ventricles contract and relax, it's no longer affecting the pressure that far away. So small pressure gradient, only about 15 millimeters of mercury.

One way to tell if you were to ever injure yourself, whether or not you cut a vein or an artery, is looking at the amount of blood that's coming out. So if a vein is cut... Because it's a low pressure blood vessel, your blood will kind of just trickle out very smoothly. If for some reason you cut an artery, because it's under such high pressure, your blood is actually going to spurt out.

So if you cut yourself, that's one way to kind of tell. Low pressure is due to the cumulative effects of peripheral resistance. The energy of the blood pressure is lost as heat during each circuit. So in A&P 1, you probably talked about energy conversions. Anytime you convert energy from one form to another, some is always lost as heat.

So that's why we have a relatively high body temperature. The low pressure of the venous side does require some adaptations to help with the venous return. So one downside to our veins having such a low blood pressure is how do we get this blood that's at a low blood pressure all the way back to our heart? especially if we're talking about inferior places like our ankles or our feet. We have to have some adaptations to continue to have the blood moving in one direction superiorly to our heart.

So a couple of factors help get our blood from our veins back to our right ventricle. One of them is the muscular pump. So our skeletal muscles actually aid in helping move blood back.

towards the heart. When our skeletal muscles contract, they squeeze on the veins, pushing the blood forward. And our veins, I don't know if you remember when we were describing the three different types of blood vessels and their characteristics, veins also have valves.

So once our skeletal muscle contracts and it pushes the blood forward, the valves prevent it from flowing backwards. Respiratory prompt. So So pressure changes during breathing can also help move blood towards the heart. When we hit the respiratory system, we'll learn more about these pressure changes and their contribution to this.

The sympathetic veno constriction. So under sympathetic control, our smooth muscles are going to constrict. And that's also going to help push the blood back toward the heart.

So basically, all three of these are capable of increasing. venous return. If they can increase venous return, that also means we've increased our stroke volume and increased our cardiac output.

Transcript for:Understanding Systemic Blood Pressure Mechanics

Transcript for:
Understanding Systemic Blood Pressure Mechanics