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Cardio-Pulmonary Module 19 October 2009 Jude Eric L. Cinco, MD HEMODYNAMICS Objectives: To discuss the basic physiology of the cardiovascular system o Specifically, hemodynamics I. The Cardiovascular System: Primary function: To deliver blood to the tissues, providing essential nutrients to the cells for metabolism and removing waste products from the cells. Others: Regulation of arterial blood pressure Delivery of regulatory hormones from the endocrine glands to their sites of action if target tissues Regulation of body temperature Homeostatic adjustments to altered physiologic states II. 1. 2. 3. 4. 5. The Cardiac Cycle Atrial systole: when the atrium contracts Isovolumetric ventricular contraction Ventricular ejection Isovolumetric ventricular relaxation Ventricular filling ***check Slide 14 of lecture powerpoint for diagram*** III. Cardiovascular Physiology systemic circulation: left heart and the systemic arteries, capillaries, and veins −The left ventricle pumps blood to all organs of the body except the lungs. pulmonary circulation: right heart and the pulmonary arteries, capillaries, and veins −The right ventricle pumps blood to the lungs. cardiac output: the rate at which blood is pumped from either ventricle *left Cardiac Output is always equal to right Cardiac Output. * If you decrease heart rate, CO will fall. ***check Slide 15 of lecture powerpoint for diagram*** Group 2 Araño, Escobillo, Peña, Ronquillo, Yu Page 1 of 11 BATCH 2014 HEMODYNAMICS IV. Circuitry 1. Oxygenated blood fills the left ventricle. Blood that has been oxygenated in the lungs returns to the left atrium via the pulmonary vein. This blood then flows from the left atrium to the left ventricle through the mitral valve (the AV valve of the left heart). * Where do you expect to find the lowest possible oxygen saturation in the circulatory system? Just before it enters the lungs – in the pulmonary artery. 2. Blood is ejected from the left ventricle into the aorta. Blood leaves the left ventricle through the aortic valve (the semilunar valve of the left side of the heart), which is located between the left ventricle and the aorta. When the left ventricle contracts, the pressure in the ventricle increases, causing the aortic valve to open and blood to be ejected forcefully into the aorta. Blood then flows through the arterial system, driven by the pressure created by contraction of the left ventricle. 3. Cardiac output is distributed among various organs. via sets of parallel arteries: o 15% of the cardiac output is delivered to the brain o 5% is delivered to the heart o 25% is delivered to the kidneys and so forth total systemic blood flow equals the cardiac output. percentage distribution of cardiac output is not fixed. three major mechanisms change blood flow to an organ system: a. CO remains constant, blood flow is redistributed via selective alteration of arteriolar resistance. b. CO increases or decreases, but percentage distribution of blood flow is kept constant. c. a combination of the first two mechanisms * not all organ systems receive same amount of CO; there is a priority. All organ systems are NOT perfused equally. CO is a constant. Arteriolar resistance alters CO, not the heart. Group 2 Araño, Escobillo, Peña, Ronquillo, Yu 4. Blood flow from the organs is collected in the veins. blood leaving the organs is venous blood and contains waste products from metabolism, such as carbon dioxide (CO2). mixed venous blood is collected in veins of increasing size and finally in the largest vein, the vena cava. the vena cava carries blood to the right heart. 5. Venous return to the right atrium. the right atrium fills with blood (venous return.) In the steady state, venous return to the right atrium equals cardiac output from the left ventricle. 6. Mixed venous blood fills the right ventricle. Mixed venous blood flows from the right atrium to the right ventricle through the AV valve in the right heart, the tricuspid valve. * Mixed venous blood that has returned from all tissues and mixed in the right atrium. Mixed venous blood is taken from the pulmonary artery. 7. Blood is ejected from the right ventricle into the pulmonary artery. The RV contracts and blood is ejected through the pulmonic valve (the semilunar valve of the right side of the heart) into the pulmonary artery, which carries blood to the lungs. In the capillary beds of the lungs, oxygen (O2) is added to the blood from alveolar gas, and CO 2 is removed from the blood and added to the alveolar gas. Thus, the blood leaving the lungs has more O 2 and less CO2 than the blood that entered the lungs. Note that the cardiac output ejected from the right ventricle is identical to the cardiac output that was ejected from the left ventricle. 8. Blood flow from the lungs is returned to the heart via the pulmonary vein. Oxygenated blood is returned to the left atrium via the pulmonary vein to begin a new cycle. V. Hemodynamics refers to the principles that govern blood flow in the cardiovascular system. Page 2 of 11 BATCH 2014 HEMODYNAMICS basic principles of physics similar to those applied to the movement of fluids in general. ***See Slides 38-39 for charts*** A. Velocity of Blood Flow rate of displacement of blood per unit time. * Relative to all the arteries and capillaries, the aorta is smallest. *. Aorta – has smallest surface area and largest velocity. *In terms of cross sectional area, there are more in the smaller vessels. Capillaries contain the largest cross sectional area (surface area). Sample Problem: V = Q/A V = Velocity of blood flow (cm/sec) Q = Flow (mL/sec) A = Cross-sectional area (cm2) Group 2 Velocity of blood flow (v) is linear velocity and is expressed in units of distance per unit time (e.g., cm/sec). Flow (Q) is volume flow per unit time and is expressed in units of volume per unit time (e.g., mL/sec). Area (A) is the cross-sectional area of a blood vessel (e.g., aorta) or a group of blood vessels (e.g., all of the capillaries). Area is calculated as A = πr2, where r is the radius of a single blood vessel (e.g., aorta) or the total radius of a group of blood vessels (e.g., all of the capillaries). Araño, Escobillo, Peña, Ronquillo, Yu The smallest vessel represents the aorta, the medium-sized vessel represents all of the arteries, and the largest vessel represents all of the capillaries. A man has a cardiac output of 5.5 L/min. The diameter of his aorta is estimated to be 20 mm, and the total surface area of his systemic capillaries is estimated to be 2500 cm2. What is the velocity of blood flow in the aorta relative to the velocity of blood flow in the capillaries? Solution: Page 3 of 11 BATCH 2014 HEMODYNAMICS Hence, velocity in the aorta is 800-fold that in the capillaries (1752 cm/min in the aorta compared with 2.2 cm/min in the capillaries). * Blood loss due to stabbing in the aorta would be due to high velocity. The resistance of the entire systemic vasculature (a.k.a. systemic vascular resistance). TPR can be measured with the flow, pressure, and resistance relationship by substituting cardiac output for flow (Q) and the difference in pressure between the aorta and the vena cava for ΔP. R = ΔP/Q Sample Problem: B. Relationships between blood flow, pressure and Resistance Blood flow through a blood vessel or a series of blood vessels is determined by two factors: the pressure difference between the two ends of the vessel (the inlet and the outlet) and the resistance of the vessel to blood flow. The pressure difference is the driving force for blood flow, and the resistance is an impediment to flow. The relationship is analogous to the relationship of current (I), voltage (ΔV), and resistance (R) in electrical circuits, as expressed by Ohm's law Ohm's law ΔV = I × R or I = ΔV/R The equation for blood flow is expressed as follows: Renal blood flow is measured by placing a flow meter on a woman's left renal artery. Simultaneously, pressure probes are inserted in her left renal artery and left renal vein to measure pressure. Renal blood flow measured by the flow meter is 500 mL/min. The pressure probes measure renal arterial pressure as 100 mm Hg, and renal venous pressure as 10 mm Hg. What is the vascular resistance of the left kidney in this woman? Solution: R = P/Q = (Pressure in renal artery – Pressure in renal vein)/ renal blood flow = (100 mmHg – 10 mmHg) / 500 mL / min = 90 mmHg / 500 mL / min = 0.18 mm Hg/mL/min Q = ΔP/R Q = Flow (mL/min) ΔP = Pressure difference (mm Hg) R = Resistance (mm Hg/mL/min) The direction of blood flow is always from high to low pressure. Increasing resistance (e.g., by vasoconstriction) decreases flow, and decreasing resistance (e.g., by vasodilation) increases flow. The major mechanism for changing blood flow in the cardiovascular system is by changing the resistance of blood vessels, particularly the arterioles. In order to maintain a constant flow of blood, given the area changes, the velocity has to adapt Blood flow is directly proportional to pressure, and inversely proportional to resistance. Total peripheral resistance dictated by ohms law. Unit is mm / Hg / mL / minute. C. Group 2 Total Peripheral Resistance Araño, Escobillo, Peña, Ronquillo, Yu D. Resistance to Blood Flow from blood vessels and blood itself The relationship between resistance, blood vessel diameter (or radius), and blood viscosity is described by Poiseuille's equation. Stroke is caused by decreased flow due to increased resistance (not 'pooh-zuls', it is pronounced 'pwah-zweez'') 1. Poiseuille Equation: R = Resistance η = Viscosity of blood ('eta') l = Length of blood vessel r4 = Radius of blood vessel raised to the fourth power resistance to flow is inversely proportional to the fourth power of the radius (r4) of the blood vessel. Page 4 of 11 BATCH 2014 HEMODYNAMICS for example, if the radius of a blood vessel decreases by one half, resistance does not simply increase twofold, it increases by 16-fold (24)! Sample Problem: A man suffers a stroke caused by partial occlusion of his left internal carotid artery. An evaluation of the carotid artery using magnetic resonance imaging (MRI) shows a 75% reduction in its radius. Assuming that blood flow through the left internal carotid artery is 400 mL/min prior to the occlusion, what is blood flow through the artery after the occlusion? Solution: The internal carotid artery is occluded, and its radius is decreased by 75%. Another way of expressing this reduction is to say that the radius is decreased to one-fourth its original size. The first question is How much would resistance increase with 75% occlusion of the artery? The answer is found in the Poiseuille equation. After the occlusion, the radius of the artery is onefourth its original radius; thus, resistance has increased by 1/(1/4)4, or 256-fold. The second question is What would the flow be if resistance were to increase by 256-fold? The answer is found in the flow, pressure, resistance relationship (Q = ΔP/R). Since resistance increased by 256-fold, then flow decreased to 1/256, or 0.0039, or 0.39% of the original value. The flow is 0.39% of 400 mL/min, or 1.56 mL/min. 2. Series and Parallel Resistance The total resistance of the system arranged in series is equal to the sum of the individual resistances Rtotal = Rartery + Rarterioles + Rcapillaries + Rvenules + Rveins The total resistance in a parallel arrangement is less than any of the individual resistances a. Series Resistance illustrated by the arrangement of blood vessels within a given organ. each organ has a major artery and a major vein. within the organ, blood flows from the major artery to smaller arteries, to arterioles, to capillaries, to venules, to veins. arteriolar resistance is the greatest and thus greatly determines the total resistance The arrangement of blood vessels within a given organ is in series b. Parallel Resistance Group 2 Araño, Escobillo, Peña, Ronquillo, Yu Page 5 of 11 BATCH 2014 HEMODYNAMICS illustrated by the distribution of blood flow among the various major arteries branching off the aorta there is parallel simultaneous blood flow through each of the circulations (e.g., renal, cerebral, and coronary). the flow through each organ is a fraction of the total blood flow. with this arrangement there is no loss of pressure in the major arteries and that mean pressure in each major artery will be approximately the same as mean pressure in the aorta. adding a resistance to the circuit causes total resistance to decrease, not to increase. for example: Four resistances, each = 10, are arranged in parallel. total resistance is 2.5 (1/Rtotal = 1/10 + 1/10 + 1/10 + 1/10 = 2.5). if a fifth resistance with a value of 10 is added to the parallel arrangement, the total resistance decreases to 2 (1/Rtotal = 1/10 + 1/10 + 1/10 + 1/10 + 1/10 = 2). Thus if you graft a vessel directly to the aorta, total resistance will decrease. on the other hand, if the resistance of one of the individual vessels in a parallel arrangement increases, then total resistance increases. for example: four blood vessels, each resistance = 10 and with total resistance = 2.5. if one of the four blood vessels is completely occluded, its individual resistance becomes infinite. the total resistance of the parallel arrangement then increases to 3.333 (1/Rtotal = 1/10 + 1/10 + 1/10 + 1/∞). Turbulent Flow E. Laminar and Turbulent Flow Laminar Flow The length of the arrows shows the approximate velocity of blood flow. Laminar blood flow has a parabolic profile, with velocity lowest at the vessel wall and highest in the center of the stream. Turbulent blood flow exhibits axial and radial flow. Group 2 Araño, Escobillo, Peña, Ronquillo, Yu Ideally, blood flow in the CV system is laminar, or streamlined. In laminar flow, there is a parabolic profile of velocity within a blood vessel, with the velocity of blood flow highest in the center of the vessel and lowest toward the vessel walls. The parabolic profile develops because the layer of blood next to the vessel wall adheres to the wall and, essentially, does not move. The next layer of blood (toward the center) slips past the motionless layer and moves a bit faster. Each successive layer of blood toward the center moves faster yet, with less adherence to adjacent layers. The length of the arrows shows the approximate velocity of blood flow. Laminar blood flow has a parabolic profile, with velocity lowest at the vessel wall and highest in the center of the stream. Turbulent blood flow exhibits axial and radial flow. When an irregularity occurs in a blood vessel (e.g., at the valves or at the site of a blood clot), the laminar stream is disrupted, and blood flow may become turbulent. In turbulent flow, the fluid streams do not remain in the parabolic profile but, instead, the streams mix radially and axially. Because energy is wasted in propelling blood radially and axially, more energy (pressure) is required to drive turbulent blood flow than laminar blood flow. Turbulent flow is often accompanied by audible vibrations called murmurs. Page 6 of 11 BATCH 2014 HEMODYNAMICS Reynold’s Number (NR) a dimensionless number that is used to predict whether blood flow will be laminar or turbulent. NR = Reynold's number Has no unit ρ = Density of blood ('rho') d = Diameter of blood vessel v = Velocity of blood flow η = Viscosity of blood ('eta') If (NR) is less than 2000, blood flow will be laminar. If it is greater than 2000, there is increasing likelihood that blood flow will be turbulent. Values greater than 3000 always predict turbulent flow. The major influences on Reynold's number in the cardiovascular system are changes in blood viscosity and changes in the velocity of blood flow. Decreases in viscosity (e.g., decreased hematocrit) cause an increase in Reynold's number. Narrowing of a blood vessel, which produces an increase in velocity of blood flow, causes an increase in Reynold's number. The effect of narrowing a blood vessel (i.e., decreased diameter and radius) on Reynold's number is initially puzzling because, according to the equation, decreases in vessel diameter should decrease Reynold's number (diameter is in the numerator). however, the velocity of blood flow also depends on diameter (radius), according to the earlier equation, v = Q/A or v = Q/πr2. Thus, velocity (also in the numerator of the equation for Reynold's number) increases as radius decreases, raised to the second power. Hence, the dependence of Reynold's number on velocity is more powerful than the dependence on diameter. To illustrate the application of Reynold's number in predicting turbulence: Anemia is associated with a decreased hematocrit (decreased mass of red blood cells) and, because of turbulent blood flow, causes functional murmurs. Reynold's number, the predictor of turbulence, is increased in anemia due to decreased blood viscosity. A second cause of increased Reynold's number in patients with anemia is a high cardiac output, which causes an increase in the velocity of blood flow (v = Q/A). To illustrate the application of Reynold's number in predicting turbulence. Thrombi are blood clots in the lumen of a vessel. Thrombi narrow the diameter of the blood vessel, which causes an increase in blood velocity at the site of the thrombus, thereby increasing Reynold's number and producing turbulence. F. Compliance of Blood Vessels The compliance or capacitance of a blood vessel describes the volume of blood the vessel can hold at a given pressure. Compliance is related to distensibility and is given by the following equation: C=V/P C = Compliance (mL/mm Hg) V = Volume (mL) P = Pressure (mm Hg) the higher the compliance of a vessel, the more volume it can hold at a given pressure. veins are most compliant and contain the unstressed volume (large volume under low pressure). Veins are the capacitance vessels of the body. Veins have higher compliance than the arteries. arteries are much less compliant and contain the stressed volume (low volume under high pressure). Laminar Flow and Reynold’s Number: Group 2 Araño, Escobillo, Peña, Ronquillo, Yu Page 7 of 11 BATCH 2014 HEMODYNAMICS flows from the arteries, to the arterioles, to the capillaries, to the veins, and back to the heart. This decrease in pressure occurs as blood flows through the vasculature because energy is consumed in overcoming the frictional resistances. Mean pressure in the aorta is very high, averaging 100 mm Hg. Arterial walls have low compliance due to thicker walls. The slope of each curve is the compliance. Compliance of the veins is high; in other words, the veins hold large volumes of blood at low pressure. Compliance of the arteries is much lower than that of the veins; the arteries hold much less blood than the veins, and they do so at high pressure. The characteristics of the arterial walls change with increasing age: The walls become stiffer, less distensible, and less compliant. At a given arterial pressure, the arteries can hold less blood. Another way to think of the decrease in compliance associated with aging is that in order for an "old artery" to hold the same volume as a "young artery," the pressure in the "old artery" must be higher than the pressure in the "young artery." Arterial pressures are increased in the elderly due to decreased arterial compliance. This high mean arterial pressure is a result of two factors: the large volume of blood pumped from the left ventricle into the aorta (cardiac output) and the low compliance of the arterial wall. The pressure remains high in the large arteries, which branch off the aorta, because of the high elastic recoil of the arterial walls. Thus, little energy is lost as blood flows from the aorta through the arterial tree. Beginning in the small arteries, arterial pressure decreases, with the most significant decrease occurring in the arterioles. At the end of the arterioles, mean pressure is approximately 30 mm Hg. This dramatic decrease in pressure occurs because the arterioles constitute a high resistance to flow. Arterioles have high resistance Since total blood flow is constant at all levels of the cardiovascular system, as resistance increases, downstream pressure must necessarily decrease (Q = ΔP/R, or ΔP = Q × R). In the capillaries, pressure decreases further for two reasons: frictional resistance to flow and filtration of fluid out of the capillaries. When blood reaches the venules and veins, pressure has decreased even further. Pressure in the vena cava is only 4 mm Hg and in the right atrium is even lower at 0 to 2 mm Hg. G. Pressures in the Cardiovascular System Blood pressures are not equal throughout the cardiovascular system. If they were equal, blood would not flow, since flow requires a driving force (i.e., a pressure difference). ***See Slides 78 and 79*** Pressure Profile in the Vasculature Group 2 The mean pressure is highest in the aorta and large arteries and decreases progressively as blood Araño, Escobillo, Peña, Ronquillo, Yu Page 8 of 11 BATCH 2014 HEMODYNAMICS Systemic arterial pressure during the cardiac cycle. Systolic pressure is the highest pressure measured during systole. Diastolic pressure is the lowest pressure measured during diastole. Pulse pressure is the difference between systolic pressure and diastolic pressure. H. Arterial Pressure in the Systemic Circulation although mean pressure in the arteries is high and constant, there are oscillations or pulsations of arterial pressure. These pulsations reflect the pulsatile activity of the heart: ejecting blood during systole, resting during diastole, ejecting blood, resting, and so forth. Each cycle of pulsation in the arteries coincides with one cardiac cycle. Diastolic pressure is the lowest arterial pressure measured during a cardiac cycle and is the pressure in the artery during ventricular relaxation when no blood is being ejected from the left ventricle. Systolic pressure is the highest arterial pressure measured during a cardiac cycle. It is the pressure in the artery after blood has been ejected from the left ventricle during systole. The "blip" in the arterial pressure curve, called the dicrotic notch (or incisura), is produced when the aortic valve closes. Aortic valve closure produces a brief period of retrograde flow from the aorta back toward the valve, briefly decreasing the aortic pressure below the systolic value. Pulse pressure is the difference between systolic pressure and diastolic pressure. If all other factors are equal, the magnitude of the pulse pressure reflects the volume of blood ejected from the left ventricle on a single beat, or the stroke volume. Pulse pressure can be used as an indicator of stroke volume because of the relationships between pressure, volume, and compliance. Assuming that arterial compliance is constant, arterial pressure depends on the volume of blood the artery contains at any moment in time. Mean arterial pressure is the average pressure in a complete cardiac cycle and is calculated as follows: Mean Arterial Pressure = diastolic pressure + 1/3 pulse pressure Group 2 Araño, Escobillo, Peña, Ronquillo, Yu MAP = Diastolic pressure + 1/3 (Systolic pressure – Diastolic pressure) MAP = 3/3 Diastolic pressure + 1/3 Systolic pressure – 1/3 Diastolic pressure MAP = 2/3 Diastolic pressure + 1/3 Systolic pressure Notice that mean arterial pressure is not the simple mathematical average of diastolic and systolic pressures. This is because a greater fraction of each cardiac cycle is spent in diastole than in systole. Thus, the calculation of mean arterial pressure gives more weight to diastolic pressure than systolic pressure. The pulsations in large arteries are even greater than the pulsations in the aorta. In other words, systolic pressure and pulse pressure are higher in the large arteries than in the aorta. It is not immediately obvious why pulse pressure should increase in the "downstream" arteries. The explanation resides in the fact that, following ejection of blood from the left ventricle, the pressure wave travels at a higher velocity than the blood itself travels (due to the inertia of the blood), augmenting the downstream pressure. Furthermore, at branch points of arteries, pressure waves are reflected backward, which also tends to augment pressure at those sites. Given that blood flows from the aorta to the large arteries, it may seem odd that systolic pressure and pulse pressure are higher in the downstream arteries. The answer is that the driving force for blood flow in the arteries is the mean arterial pressure, which is influenced more by diastolic pressure than by systolic pressure. Note in that while systolic pressure is higher in the large arteries than in the aorta, diastolic pressure is lower; thus, mean arterial pressure is lower downstream. Although systolic pressure and pulse pressure are augmented in the large arteries (compared with the aorta), from that point on, there is damping of the oscillations. The pulse pressure is still evident, but decreased, in the smaller arteries; it is virtually absent in the arterioles; and it is completely absent in the capillaries, venules, and veins. This damping and loss of pulse pressure occurs for two reasons: Page 9 of 11 BATCH 2014 HEMODYNAMICS o (1) The resistance of the blood vessels, particularly the arterioles, makes it difficult to transmit the pulse pressure. o (2) The compliance of the blood vessels, particularly of the veins, damps the pulse pressure-the more compliant the blood vessel, the more volume that can be added to it without causing an increase in pressure. Several pathologic conditions alter the arterial pressure curve in a predictable way pulse pressure will change if stroke volume changes, or if the compliance of the arteries changes. pressure, pulse pressure, and mean pressure all will be decreased. Aortic regurgitation When the aortic valve is incompetent (e.g., due to a congenital abnormality), the normal one-way flow of blood from the left ventricle into the aorta is disrupted. Instead, blood that was ejected into the aorta flows backward into the ventricle. Such retrograde flow can occur because the ventricle is relaxed (is at low pressure) and because the incompetent aortic valve cannot prevent it, as it normally does. I. Venous Pressure in the Systemic Circulation By the time blood reaches the venules and veins, pressure is less than 10 mm Hg; pressure will decrease even further in the vena cava and the right atrium. The reason for the continuing decrease in pressure is now familiar: The resistance provided by the blood vessels at each level of the systemic vasculature causes a fall in pressure. Pressure and Velocity in the Systemic Circulation Effect of arteriosclerosis and aortic stenosis on arterial pressures. Arteriosclerosis In arteriosclerosis, plaque deposits in the arterial walls decrease the diameter of the arteries and make them stiffer and less compliant. In order to preserve flow, you need higher pressure. Because arterial compliance is decreased, ejection of a stroke volume from the left ventricle causes a much greater change in arterial pressure than it does in normal arteries (C = ΔV/ΔP or ΔP = ΔV/C). Thus, in arteriosclerosis, systolic pressure, pulse pressure, and mean pressure all will be increased TA: total cross-sectional area of the vessels, which increases from 4.5 cm2 in the aorta to 4500 cm2 in the capillaries RR: relative resistance which is highest in the arterioles Arteriosclerosis is different from atherosclerosis, athero is for the whole body, arterio is in the arteries. Aortic stenosis If the aortic valve is stenosed (narrowed), the size of the opening through which blood can be ejected from the left ventricle into the aorta is reduced. Thus, stroke volume is decreased, and less blood enters the aorta on each beat. Systolic Group 2 Araño, Escobillo, Peña, Ronquillo, Yu Page 10 of 11 BATCH 2014 HEMODYNAMICS K. The Law of Laplace Wall tension (T) is equal to the product of the transmural pressure (P) and the radius (r) divided by the thickness of the wall (w): T=Pr/w J. Venous Pressures Circulation in the Pulmonary The entire pulmonary vasculature is at much lower pressure than the systemic vasculature. The pattern of pressures within the pulmonary circulation is similar, however. Blood is ejected from the right ventricle into the pulmonary artery, where pressure is highest. Thereafter, the pressure decreases as blood flows through the pulmonary arteries, arterioles, capillaries, venules, and veins and back to the left atrium. An important implication of these lower pressures on the pulmonary side is that pulmonary vascular resistance is much lower than systemic vascular resistance. This conclusion can be reached by recalling that the total flow through the systemic and pulmonary circulations must be equal (i.e., cardiac output of the left and right hearts is equal). Though the left ventricle is thicker than the right ventricle (due to higher pressure exerted), both produce the same Cardiac Output. Because pressures on the pulmonary side are much lower than pressures on the systemic side, to achieve the same flow, pulmonary resistance must be lower than systemic resistance (Q = ΔP/R). Group 2 Araño, Escobillo, Peña, Ronquillo, Yu In chronic hypertension (1) heart walls will thicken (2) radius decreases (3) chest pain is present, which is caused by lack of oxygen in the heart. (as the heart muscle hypertrophies, coronary arteries don’t hypertrophize) (4) Eventually, the heart will become thinner and dilated due to low oxygen received. (5) When the heart fails, given low wall thickness, high pressure, high radius, there is high tension. “When in doubt, arterioles is the key.“ -Jude Eric L. Cinco, MD, 2009 Page 11 of 11