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Lecture 13

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PHGY 210
Michael Guevara

Sarah Margareta Ibrahim Lecture 13 - Cardiovascular Physiology (Part 7 of 9) (1) Right Heart Wiggers diagram was all for left side of heart. The exact same thing is happening on right side of heart. Whatʼs the difference? First of all everything is on the right and second, instead of seeing big pressures going up 120mmHg it goes up to maybe about 20mmHg because pressures on right are less than pressures on left. Everything is happening a the same time though. You have the same four cycles of the cardiac cycle. (2) Starlingʼs Law of the Heart (Frank-Starling Mechanism) Whatʼs a typical end diastolic volume? About 120 -140. Stroke volume is about 70. This is what youʼre at now. If we could increase this more, when you stretch cardiac muscle it contracts more forcefully so if you increase the EDV, youʼll get a more forceful contraction and youʼll eject more blood (higher stroke volume). You get this curve by doing a bunch of EDV. You get this in exercise. Your cardiac output goes up, your venous return goes up and the atria and ventricles filling goes up and that increase in EDV will generate more force therefore more stroke volume so your cardiac output will go up because of this. Thereʼs a concept called pre-load and this is the state of load on the muscle just before it contract. So if the EDV is bigger, the amount of stretch in the muscle is bigger, prior to contraction the pre-load is bigger. We talked about measurement of pressure in the right atrium before remember? Well one of the reasons we do this is to assess this pre-load. You can make a measurement of volume in ventricle using x-rays or echocardiography or you can just make a measurement of the pressure in the right atrium. If the volume of blood in right atrium is bigger, the pressure is going to be bigger as well and the amount of blood in the ventricle will also be bigger. So you see thereʼs a direct correlation between the pressure in the atrium and the volume of blood in the ventricle. Thatʼs why the pressure in right atrium is measured it to get a measurement of the index of the degree of filling in the ventricle. (3) Valvular Murmurs On Wiggers diagram we had two heart sounds. On some people you hear 3 or 4 heart sounds. Other people have these softer heart sounds called murmurs. You can hear this with stethoscope. Not all murmurs are pathological or physiological. Not always a sign something is wrong with heart. (4) Normal Valves Normal flow of blood through valves: When the valve (any one of the four) is fully open thereʼs a big hole and the blood flows through adn the flow is smooth or laminar so you donʼt hear anything. When the valve closes as it should, if it closes completely, thereʼs no flow - you hear nothing. You have a normal situation. When the valve closes completely, thereʼs no flow. You hear nothing. This is the normal situation. (5) Abnormal valves If you have a valve that is a stenosed valve (it doesnʼt open properly due to calcification or whatever) the blood is going to squirt through this smaller opening at high speed and itʼs going to see that expanse ahead of it so the flow moving through the valve is going to expand because now you have the full size of the atrium or the ventricle or whtever and that creates turbulent flow. That flow will shake the leaflets of the valve or the heart itself and youʼll get a sound. An insufficient valve doesnʼt close properly so you have a small opening there and there will be flow of blood through the valve (in this case, backflow) and youʼll hear a murmur. ▯ 1 Sarah Margareta Ibrahim This is not a physiologic sound itʼs a pathologic sound because something is wrong with the valve. (6) Systemic Arterial Blood Pressure. Youʼre measuring the blood pressure in the arteries! And youʼre measuring it on the left heart (the systemic side of circulation). (7) Arterial Blood Pressure The aortic pressure stays high throughout the resting period in the heart when the ventricular pressure is almost zero. During the ejection phase, you eject a volume of blood (the stroke volume) into the aorta. The aorta is an elastic organ. As you pump blood into the aorta it will stretch. This blood has to go to the arterioles and such where there is a high resistance so it takes time for that blood to flow through that whole system so the pressure there will stay high for some time. There are four different pressures to calculate. The peak pressure is the systolic pressure (usually around 120 mmHg). The minimum pressure is diastolic pressure (usually around 80 mmHg). If you subtract the diastolic pressure from the systolic pressure you get the pulse pressure (usually around 40 -> 120-80). The fourth pressure is the mean arterial pressure this is the pressure that you would give a steady pressure to have the same cardiac output. This is the diastolic pressure + ⅓ of the pulse pressure. A typical mean arterial pressure is around 100mmHg. (8) Measurement of Blood Pressure ▯ Direct method or indirect methods (palpitation, auscultation, oscillometry). (9) Direct Method Done. You make an arterial puncture and you take a tube with something that can make a measurement of pressure (manometer) you can put a small plastic tube into artery of patient that will translate pressure into voltage and voltage goes off to a monitor. Thatʼs a direct method. (10) Aneroid Sphygmomanometer Makes a measurement of the pressure of the pulse (the arterial bp). This uses an aneroid gauge (meaning no fluid involved). Thereʼs a cuff, an inflating bulb and an aneroid gauge. The purpose of the bulb is to pump air into the cuff and to decrease the pressure you turn the valve the other way (remember the lab). (11) Aneroid Gauge If you look in aneroid gauge there is a vacuum chamber. The air thatʼs coming in from the cuff is filling that dark space. If thereʼs air up there at a pressure and thereʼs no pressure at the bottom - it will push the bottom down and cause the pointer to move). (12) Mercury Sphygmomanometer Why is bp measured in mmHg? Historical. Instead a vacuum we had a column of mercury at the bottom and we would use the height of the column to make a measure of mercury at that point (you see a gauge in centimeters and mm) and this is the same way that Hales measured his stuff). (13) Method of Palpitation Palpate means to touch. You pump the cuff, increase the pressure. When the pressure in the cuff is higher than the systolic arterial bp, the artery will close. No pulse. Then you turn the needle valve to let the air out of the cuff. (14) Palpitation Graph The pressure in the cuff will fall and fall and fall and at some point, youʼll begin to feel the pulse. This is the systolic BP (that pressure). As the pressure in the cuff falls the pressure in the cuff will become zero. You can only measure the systolic this way. You have to use something else to get diastolic. ▯ 2 Sarah Margareta Ibrahim (15) Stethoscope If you donʼt put the cuff on and itʼs not inflated, you donʼt hear anything (unless youʼve got a problem with your valve - the flow through this artery is laminar). (16) Method of Auscultation Inflate all the way and cut off pulse. When the artery reopens, blood will squirt through and it will generate turbulent flow. (17) Korotkoff Sounds The sounds that you hear due to the turbulent flow are called the Korotkoff sounds. As the pressure in the cuff falls, the artery is still partially occluded so you hear the sounds all the way to the diastolic pressure where the flow becomes laminar. So you only hear the sound when the artery is partially occluded!! (18) Oscillometry If you look at this instrument as youʼre bringing the BP down, before you get to the systolic BP, before you get to hear those sounds, youʼll see that the needle starts to tick. This ticking means that itʼs picking up a pressure which means that there is an oscillation of the pressure in the cuff before you get to the systolic pressure. So in those instruments there is a sensor in the cuff that makes a measurement of the pressure and it converts that into an electrical signal or voltage and sends that into the box. So the instrument inflates the bulb and it raises pressure to a high level and then there are these oscillations before the systolic and it lasts way after as well. It makes a measurement of the fluctuations of the pressure in the cuff as the pressure drops and the computer does some calculations. (19) Why is BP important? Why does BP have to be regulated? BP is important because it generates the perfusion pressure for the organs in the body. BP is tachyregulated so if you lose blood your BP is going to drop but there are control systems in your body that try to keep your BP at a normal level. People with high BP have problems with these systems. (20) Cont. Of 19 Remember arterial pressure and perfusion pressure? Now we know about mean arterial pressure so delta P becomes MAP. Thatʼs why BP is so important because itʼs the guy
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