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BIOC33/34 Lec 7.docx

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Biological Sciences
Stephen Reid

BIOC34 Lec 7. Jan 27, 2014  Starling curves, heart failure and sympathetic activity o This diagram is showing 3 starling curves and is relating the starling relationship when there is failure of the heart o Normal SV in green o No sympathetic stimulation (red) o Increase of contractility of ventricles when sympathetic stimulation is added (blue) o When the heart fails, SV is going to go down and in this example, to achieve a normal SV, need a higher EDV when the heart is failing and when adding sympathetic stimulation, it can improve the function of the heart and get SV close to a normal level with EDV  Heart failure o Heart failure: any reduction in the heart’s function that prevents it from maintaining adequate cardiac output o Heart fails for a number of reasons - primary reason is when there is a heart attack  Causes of Heart Failure  1. Heart attack (myocardial infarction) - when one of the coronary arteries gets blocked o There are many little blood vessels going to every region of the heart o If a coronary artery gets blocked, get a region of dead tissue; this tissue will not pump. If in left ventricle, left ventricle will be compromised  2. High BP; stenosis of the aorta o Problems with the valves (AV or semilunar) o E.g. stenosis - valve does not open wide enough  Anarrow valve/opening leads to a long-term problem of heart function  With a small bicuspid valve, if it doesn’t open properly, left ventricle has to work harder to get blood through the opening  When the heart works harder, one side will grow (hypertrophy) and it loses its compliance, ability to stretch and ability to contract o Anything leading the heart to overwork will cause it to grow and it will not be able to pump properly o EDV goes down, and SV and CO go down  3. Third degree heart block o No transmission from atria to ventricles o Could get a decreased HR - if heart rate is decreasing, over time, get excess filling time and increases in EDV o Over time, stretching will occur and heart will lose ability to contract o Over time get chronic filling o (symptoms of heart disease - will not be asked on exams. Just there for interest)  4. Left heart failure o Starts to become rare occurrence where there is no equal amounts of blood flow through systemic and pulmonary circuit o Under normal conditions, do not get mismatch of blood flow o When the heart fails, this is one of the times one can get mismatches in blood flow - depends on where the failure is o If left ventricle is damaged, can start to get a back flow or build-up of pressure coming from the lungs and leading into the left side of the heart  If it is not pumping blood properly out of aorta, get a build-up of blood in the pulmonary veins returning from the lungs into the left side of the heart - can lead to increases in pressure leading to a build-up of pressure in the lung capillaries  Problematic because the pressure in the lungs is low because blood vessels in the lungs are very delicate o If start to get a build-up of pressure in the pulmonary vein, the build-up of pressure helps force fluid from blood vessels across capillaries walls into the lungs - get build-up in the lungs o Problematic because build-up of fluid increases the diffusion distance for oxygen coming from lung tissue into blood and CO2 moving out of blood into lungs - serves as a barrier against gas diffusion o Also has another problematic effect - build-up of fluid in the lungs helps increase surface tension - tension between fluid layer and lung tissue - prevents lungs from expanding properly o Under normal circumstances, lungs are covered in pulmonary surf-actin which helps reduce fluid-lung interactions and reduces surface tension o Fluid in the lungs is bad because it prevents gas diffusion and prevents lungs from expanding o Initial problem with left heart failure - build-up of pressure in the lungs and fluid forced into the lungs  edema  Left heart failure o Since left ventricle is no longer pumping blood normally, BP in systemic circuit decreases - do not have normal SV, CO therefore there is a reduction in BP o When this happens, fluid retention in the kidneys tries to attempt to restore BP by producing less urine - retain water from kidneys keeping it in the blood and EC fluid o In cardiovascular system, most of the volume of blood is found in the vena system - when kidneys retain fluid and get increase in blood volume, this is stored in the vena system o Get attack on the lungs from the other side - build-up of fluid in the vena system  increase in pressure on right side of circuit and heart and increases pressure on pulmonary artery caused by this fluid back up. This causes a build-up of pressure in the pulmonary artery  Intense pressure coming into lungs - serves as a driving force to push fluid out of blood vessels across capillaries and into lung tissue (alveoli) o Get a build-up of pressure because left side is not pumping properly and get a build-up of pressure because of fluid build-up in vena system - fluid builds up on both sides  Congestive heart failure • Have a congestion on both the venous side and arterial side - blood flow is congested because it is not flowing through the aorta  Left and right heart failure o Diagram - normal distribution  Most blood in venous system o Left heart failure  Build-up of pressure on both sides  Blood is forced out of capillaries into lung tissues  pulmonary edema o Right heart failure  Get a further congestion in the venous system because normally the right heart is pumping to the lungs - if it is not pumping blood effectively, get a build-up of blood in the venous system. This forces fluid from veins and upstream into systemic tissue • Get a swelling of extremities o Can think of heart failure as on the left or right hand side - both lead to edema (fluid buildup) in lungs or systemic circuit  Heart failure: systolic and diastolic dysfunction o Under normal circumstances, atria are filling passively and the small amounts of atria contraction bring to ventricles o During systole, ventricles are pumping blood out  If there is a systolic dysfunction, get a normal filling of ventricles. Since the ventricles are damaged, they will pump less blood than normal o Can have a diastolic failure - not because ventricles can’t contract but because they are not filling properly with blood during diastole - this happens when the heart muscles becomes enlarged or stiff o Heart contracts generally fine but there is just not as blood in there to be pumped out o Diastolic failure - failure in filling o Systolic failure - failure in pump  Blood flow o When looking at blood flow and BP regulation - need to keep in mind: talk about BP as being the product of CO and TPR. In the circulation as a whole, there is only one BP. BP is overall everywhere. Can reduce BP by reducing the resistance to flow  When talking about BP and TPR - talking about resistance to blood flow in the body as a whole  When looking at blood flow to certain organs, can change the resistance to flow in an organ and alter blood flow to one organ at the expense of another organ  Blood pressure = WHOLE body phenomena  Blood flow = local level; have increase in flow to one organ, decreases to another, but overall, blood flow is still constant; just redirecting blood flow from one region to another  Designed to get blood to a certain organ  Measuring blood flow o Used to put a cuff on leg in a barrel of water, as blood flow increased, blood could not move o More modern way of measuring - in experimental approach, can put BP cuffs around an artery and then cuffs around the artery that measure blood flow directly  Calculating blood flow o Flow = Pressure Gradient / Resistance  = P/R o Calculate as a change in P divided by resistance to blood flow o Change in pressure is in the systemic circuit MAP o Flow = BP/ resistance  In entire body  = TPR o Primary thing affecting resistance to blood flow is the radius of a blood vessel - this is regulated and has enormous effects on resistance and therefore, flow  Different types of blood vessels o Important for regulating resistance and for other functions o As we go through cardiovascular system with blood flowing to heart, arteries tend to be thick, musculature, easily stretch and relaxes back during diastole o Arteries are thick, muscular and highly elastic o Capillaries are very thin; gases move in and out - cite of gas exchange o Veins are easily extendable and can hold lots of volume o Arterioles are important in regulating resistance; covered in rings of smooth muscle that can contract and relax in order to narrow or widen diameter of blood vessel  Blood vessel compliance o Ability of a blood vessel to expand when its filled with an excess of blood is our COMPLIANCE  Ameasure of the capacity of a blood vessel to distend o Distending (transmural) pressure = P (inside) - P (outside) o Compliance = change in V/ change in P o Compliance =  Volume /  (Pin – Pout) o When looking at compliance from POV of blood vessel, it is the P inside vessel - P outside vessel o On arterial side of capillary beds, this P is positive; pushing fluid outside of the blood vessels and into EC space o As blood flows through capillary bed, see that this pressure gradient reverses where the driving force from P POV is to force fluid back into the blood vessels - key concept on kidney function  Take capillary bed as a whole, fluid is forced out on the arterial side and is sucked back in on the venous side  Amount of fluid forced out is not the same as the fluid being sucked back to the heart  Compliance of arteries vs veins o Compliance of veins is (at low pressures) much greater than the compliance in arteries. For any given extending pressure in a vein, there is a much greater change than in the arteries o Relationship of volume to distending pressure is not linear; changes in compliance change as distending pressure (or BP) increases o At low pressures, veins have higher compliances than at high pressures o At higher pressures, compliance decreases but becomes similar to arterial compliance o At very high pressures (near MAP) compliance relationship is the same in arteries and in veins - see tangential slopes that are the same o This has an important practical concept when replacing coronary vessels: at higher pressures, compliance is identical in veins and arteries  Coronary artery bypass graft o If a coronary artery is blocked and needs a replacement, get a portion of the vein from the leg and graft onto aorta to ca
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