Hemodynamics PDF - Ross University

CARDIOVASCULAR PHYSIOLOGY HEMODYNAMICS PART 1 & 2...

CARDIOVASCULAR PHYSIOLOGY HEMODYNAMICS PART 1 & 2 Dr. Oleksii Hliebov, MD, PhD Associate Professor, Department of Medical Foundations [email protected] Join Dr. Hliebov's Office Hours (via Zoom): https://zoom.us/j/96858712961?pwd=UklWVU1ETmhjRUd3UlAzVXM4WkpsQT09 Meeting ID: 968 5871 2961 Passcode: 680201 Intended Learning Objectives Hemodynamics (part 1): 1. Describe the parts of the circulatory system and the functions of each within the context of the whole-system function. 2. Describe volume of distribution of blood in the body and its physiological basis. 3. Define and describe transmural blood pressure and the Law of LaPlace. Describe how in pathology its consequence can contribute to heart failure. 4. Appreciate the normal ranges of blood pressures in the circulation and cardiac chambers. 5. Define pulse pressure. Name the factors that determine it. Contrast pulse pressure in different region of circulatory system. Be able to calculate pulse pressures. 6. Define mean arterial pressure. Assuming a normal heart rate, be able to calculate mean pressures for ventricles and arteries, for both right and left circulations, in either vessels or chambers. 7. Calculate mean arterial pressure and pulse pressure. Understand how arterial compliance and stroke volume can influence pulse pressure. 8. Define and describe driving pressure. Describe how in pathology its consequence can contribute to heart failure. 9. Appreciate the difference between laminar and turbulent flow (and understand meaning of the Reynolds number). ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL | 2 OF MEDICINE Intended Learning Objectives Hemodynamics (part 2): 10. Define Darcy's law and be able to calculate mean arterial pressure (MAP), cardiac output (CO) and total peripheral resistance (PR) from the relationship MAP = CO*TPR. 11. List the parameters that affect vascular resistance. Explain which parameter is most important and why. 12. Use Poiseuille's law and Ohm's law to predict the relative changes in flow through a vessel caused by changes in vessel length, vessel radius (resistance), fluid viscosity, and pressure differences. 13. Explain the relationship between blood flow, blood velocity, and cross-sectional area. Explain how these work in arteries, capillaries, and veins. 14. Use hemodynamic parameters to calculate pulmonary vascular resistance and systemic vascular resistance. 15. Describe the difference between parallel and series vessel organization and explain the advantage. 16. Be able to calculate resistances to flow produced in series versus in parallel. Explain the advantage of parallel series. 17. Define vascular compliance, describe its influence on blood flow and pressure, and contrast the compliance of the arterial and venous portions of the circulatory system. 18. Understand what constitutes central venous pressure (CVP) and how this is affected by changes in vessel compliance. 19. Describe how the structures of arteries and veins contribute to their functions as elastic or compliant vessels. 20. Describe different forms/shapes of pulse pressure: pulsus paradoxus, pulsus parvus and tardus, hyperkinetic pulse, dicrotic pulse, pulsus alternans. 21. Describe how changes in cardiac output or peripheral resistance can be compensated to restore normal flow through the arterial system. ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL | 3 OF MEDICINE  BASIC CONCEPTS & OVERVIEW OF CIRCULATION Learning objectives for this section: 1. Describe the parts of the circulatory system and the functions of each within the context of the whole-system function. 2. Describe volume of distribution of blood in the body and its physiological basis. General Hemodynamics The heart is a dual pump It serves two circulations which are linked in series: Systemic circulation Pulmonary circulation Each circulation receives and ejects the same volume of blood per minute – ventricular matching by the Frank-Starling mechanism Cardiovascular circuity, indicating the percentage distribution of cardiac output to various organ systems in a resting individual. Image source: D.E. Mohrman, L.J. Heller. Cardiovascular Physiology. 9ed. ROSS UNIVERSITY SCHOOL OF MEDICINE | 5 ROSS UNIVERSITY SCHOOL OF MEDICINE Basic Theory of Circulation The blood flow to each tissue of the body is precisely controlled This requires both (1) control of cardiac output to pressurize and add volume to the circulation, and (2) control of peripheral resistance so that tissues that need flow at any moment get it Cardiovascular circuity, indicating the percentage distribution of cardiac output to various organ systems in a resting individual. Image source: D.E. Mohrman, L.J. Heller. Cardiovascular Physiology. 9ed. ROSS UNIVERSITY SCHOOL OF MEDICINE | 6 ROSS UNIVERSITY SCHOOL OF MEDICINE Parallel Arrangement of Vessels Blood supply within each circulation has a parallel arrangement of vessels Enables independently regulated blood flow to each organ or region Cardiovascular circuity, indicating the percentage distribution of cardiac output to various organ systems in a resting individual. Image source: D.E. Mohrman, L.J. Heller. Cardiovascular Physiology. 9ed. ROSS UNIVERSITY SCHOOL OF MEDICINE | 7 ROSS UNIVERSITY SCHOOL OF MEDICINE Arterial Circulation The primary purpose is: To receive blood from a single source Hold it under pressure Release it through many, many super-small exits into capillaries Entry of blood into the arterial tree and exit into capillaries is well controlled (maintain adequate flow into and out of tissues) Inadequate entry (e.g., heart failure) and inadequate resistance (e.g., anaphylaxis) can result in too low blood pressure to drive flow into those tissues where it is needed Distribution of blood (in percentage of total blood) in the different parts of the circulatory system. Image source: Guyton and Hall. Textbook of Medical Physiology. 13ed. ROSS UNIVERSITY SCHOOL OF MEDICINE | 8 ROSS UNIVERSITY SCHOOL OF MEDICINE Venous Circulation The primary purpose is: To return blood to the heart To hold most of the volume of the blood, against that time (e.g., in exercise), when reserve blood might be needed to supply much more tissue per unit of time than is normal This is a lower-pressure circulation with gravity effects, so some of the anatomy is different in order to enhance the one-way flow pattern from capillaries to the atrium There are sometimes other “pumps” that assist e.g., skeletal muscle pump, or respiratory pump The action of the one-way venous valves. Contraction of skeletal muscles helps to pump blood toward the heart, but the flow of blood away from the heart is prevented by closure of the venous valves. Image source: Human physiology. Stuart I. Fox. Pierce College.14 ed. ROSS UNIVERSITY SCHOOL OF MEDICINE | 9 ROSS UNIVERSITY SCHOOL OF MEDICINE Parameters Affecting Hemodynamics 1. Individual blood vessel diameter Decreases from arteries to capillaries (vascular branching) Increases from capillaries to veins (vessel merging) 2. Mean blood flow velocity Lowest in capillaries 3. Total cross-sectional area Increases from arteries to capillaries (vessel branching) Flow, velocities, blood volumes, blood pressure, and vascular resistances in the peripheral vasculature from aorta to right atrium. Image source: D.E. Mohrman, L.J. Heller. Cardiovascular Physiology. 9ed. ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 10 Parameters Affecting Hemodynamics (cont.) 4. Blood volume distribution 84% of blood is in the systemic circulation: 64 % in veins 13 % arteries 7 % arterioles and capillaries 7 % of blood is in the heart 9% of blood is in the pulmonary circulation 5. Total peripheral resistance Arterioles and small muscular arteries are sites of the greatest resistance 6. Mean blood pressure Flow, velocities, blood volumes, blood pressure, and vascular resistances in the peripheral vasculature from aorta to right atrium. Image source: D.E. Mohrman, L.J. Heller. Cardiovascular Physiology. 9ed. ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 11  TRANSMURAL BLOOD PRESSURE THE LAW OF LAPLACE Learning objectives for this section: 3. Define and describe transmural blood pressure and the Law of LaPlace. Describe how in pathology its consequence can contribute to heart failure. Transmural Blood Pressure !! = !" − !# !! - transmural pressure !" - pressure inside (pressure distending or stretching the vessel) !# - external pressure (pressure compressing the vessel) This is the blood pressure measured with a blood pressure (BP) cuff Influences vessel diameter Image source: The Big Picture. Medical Physiology. McGraw-Hill Education. J.D. Kibble, C.R.Halsey. ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 13 The Law of LaPlace As !" increases, this stretches the vessel wall and increases the circumferential wall tension (T) At any given vessel radius (r), the wall tension (T) exactly counteracts the transmural pressure differential ( !" − !# ) generating the following relationship: T = (!" −!# ) ∗ ( This is called LaPlace’s law. So, the bigger the vessel radius, the bigger the wall tension required to counter any given transmural pressure The LaPlace law associates the tension (T) in the walls with its radius (r) and the pressure (P) of its contents Image source: The Big Picture. Medical Physiology. McGraw-Hill Education. J.D. Kibble, C.R.Halsey. ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 14 The Law of LaPlace and Failing Heart Normal Heart Failing Heart Extremely increased ventricular Ventricular preload preload Muscle contraction Decreased actin-myosin interactions The bigger the radius, the harder it is to generate pressure Increased tension (Frank-Starling) Decreased tension Blood ejection Reduced blood ejection ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 15 The Law of LaPlace and Aortic Aneurism T = (!" −!# ) ∗ ( Increased in radius Increased tension Increased radius Increased tension Aneurism rupture Image source: https://www.whitesquarevascularsurgery.com/our-blog/abdominal-aortic-aneurysm--the-triple-a-to-avoid/ ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 16  PULSE PRESSURE MEAN ARTERIAL BLOOD PRESSURE DRIVING PRESSURE Learning objectives for this section: 4. Appreciate the normal ranges of blood pressures in the circulation and cardiac chambers. 5. Define pulse pressure. Name the factors that determine it. Contrast pulse pressure in different region of circulatory system. Be able to calculate pulse pressures. 6. Define mean arterial pressure. Assuming a normal heart rate, be able to calculate mean pressures for ventricles and arteries, for both right and left circulations, in either vessels or chambers. 7. Calculate mean arterial pressure and pulse pressure. Understand how arterial compliance and stroke volume can influence pulse pressure. 8. Define and describe driving pressure. Describe how in pathology its consequence can contribute to heart failure. Pulse Pressure Systolic pressure (SP) it is the maximum pressure that can be reached in the left ventricle and aorta Diastolic pressure (DP) it is the lowest aortic pressure, reached at the end of diastole Pulse pressure (PP) - is the difference between the highest (systolic) and the lowest (diastolic) pressure !)*+, !(,++)(, !! =.! − /! Image source: https://www.cvphysiology.com/Blood%20Pressure/BP003 ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 18 Pulse Pressure is Determined by The rise in aortic pressure from its diastolic to systolic value is determined by: The compliance of the aorta (discussed later) The left ventricular stroke volume Image source: https://www.cvphysiology.com/Blood%20Pressure/BP003 ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 19 Pulse Pressure Heart Chamber Pressure (mm Hg) Right atrium 0-4 Right ventricle 25 systolic / 4 diastolic Pulmonary artery 25 systolic / 10 diastolic Left atrium 8 -10 Left ventricle 120 systolic / 10 diastolic Aorta 120 systolic / 80 diastolic Pulmonary capillary wedge pressure =?1 !'%$$"'% = 15 // 01 − 10 // 01 ≈ 5 // 01 Image source: Human physiology. Stuart I. Fox. Pierce College.14 ed. ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 25  TYPES OF BLOOD FLOW REYNOLDS NUMBER Learning objectives for this section: 9. Appreciate the difference between laminar and turbulent flow (and understand meaning of the Reynolds number). Types of Blood Flow Turbulent Flow: Laminar Flow: Greatly impedes flow Slowest flow occurs near the edge of the Requires an increased pressure to maintain vessel due to friction. flow Fastest flow occurs in the center of the vessel Produces sound (cardiac auscultation) Image source: D.E. Mohrman, L.J. Heller. Cardiovascular Physiology. 9ed. ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 27 Reynolds Number /,@( 4 >/,@( ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 41 Practice Problem A 58-year-old male smoker presents to the emergency department complaining of fatigue and dyspnea on exertion. His hemodynamic parameters are below: Cardiac output: 5 L/min Mean pulmonary artery pressure: 10 mm Hg Right atrial pressure: 0 mm Hg Pulmonary wedge pressure: 10 mm Hg Left ventricular pressure: 120/10 mm Hg Arterial pressure: 120/80 mm Hg Heart rate is 80 bpm What is the best estimate of systemic vascular resistance in mm Hg/mL/min? !"#$% !'%$$"'% !! = )! − +! 4%E? 5G'D=T !'%$$"'% − S5 U'%$$"'% 456! !"#$% !'%$$"'% !! = 120 // 01 − 80 // 01 = 40 // 01 R!S = ⇒ @V @V 1 456! = +! + !! 93 // 01 3 R!S = = 18.6 // 01. /=?/X 1 5 X//=? 456! = 80 // 01 + ∗ 40 // 01 = 80 // 01 + 13 // 01 = 93 // 01 3 ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 42  RESISTANCES TO BLOOD FLOW Learning objectives for this section: 15. Describe the difference between parallel and series vessel organization and explain the advantage. 16. Be able to calculate resistances to flow produced in series versus in parallel. Explain the advantage of parallel series. Resistance in Series Not typical in the body: involves fluid passing through multiple resistance points in the same vessel/along the same fluid path Example: Renal circulation goes through two capillary beds, at glomerulus and then along tubules, with two sets of arterioles providing resistance R1 R2 R3 R4 Resistances at each constriction site are directly added together to determine total resistance: For resistances (R1, R2, and R3) arranged in series, total resistance, Rt, equals the sum of the individual resistances. P, pressure; Q, flow. $!"!#$ = $% + $& + $' + $( + ⋯ + $) If we will add one more resistance into the system, the total resistance will rise ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 44 Resistance in Parallel Typical kind found in body Involves common artery, and vein, with multiple side by side capillary beds. Flow through these vessels, (e.g., within the triceps brachii) will be R1 in parallel R2 To determine the total resistance, one sums the inverse of each individual resistance: R3 R4 1 1 1 1 1 1 = + + + + ⋯+ $!"!#$ $% $& $' $( $) For resistances (R1, R2, and R3) arranged in parallel, the reciprocal of the total resistance, Rt, equals the sum of the reciprocals of the individual resistances. P, pressure; Q, flow. The total resistance of a parallel system is less than the lowest individual resistance ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 45 Resistance in Parallel If we will add one more resistance into the system, the total resistance will be reduced. Compare: R1 = 2 R1 = 2 R2 = 2 R2 = 2 2 2 > 3 4 R3 = 2 R3 = 2 R4 = 2 1 1 1 2 1 1 1 2 :()(*+ = + + 2 2 2 = 1 1 1 3V 2 = 3 > :()(*+ = 1 1 1 1 + + + 2 2 2 2 = 4V 2 = 4 ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 46 Arteriovenous Fistula An arteriovenous fistula (AVF) is an abnormal connection between an artery and a vein Causes decreasing in resistance to blood flow, increased preload, and increasing in cardiac output R1 R2 R3 R4 Artery Fistula Vein ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 47 Practice Problem The diagram below represents a capillary bed. Each vessel has a resistance (R1-R5) as indicated. R1 and R5 are in series, and R2-R4 are in parallel. What is the total resistance? What is the flow through this capillary bed? R2 = 1/18 P1 = 90 mm Hg R1 = 1 R3 = 1/18 R5 = 2 P2 = 0 mm Hg A R4 = 1/18 D B C Resistance from point A to point B = 1 Δ! !1 − !2 \ F#GH = = 1 1 1 1 S%$=$DE?T% S Resistance from point B to point C = = 1 1 1 = 3[ = 1[ =6 S#"#!+ + + 18 18 18 18 6 90 // 01 − 0 // 01 >G#"/%$ \ F#GH = = 10 Resistance from point C to point D = 2 9 "?=D D=/% Total resistance = 1 + 6 + 2 = 9 ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 48  VASCULAR COMPLIANCE Learning objectives for this section: 18. Define vascular compliance, describe its influence on blood flow and pressure, and contrast the compliance of the arterial and venous portions of the circulatory system. 19. Understand what constitutes central venous pressure (CVP) and how this is affected by changes in vessel compliance. 20. Describe how the structures of arteries and veins contribute to their functions as elastic or compliant vessels. Compliance Vascular compliance (or vascular capacitance) (C) is the ability to be stretched (the ability of a vessel to distend and increase volume). Measures the change in volume (Δ*) produced by a given change in pressure (ΔP). 7ℎG=>, ;= , ;= ?(,++)(, Δ! If _` rises – compliance rises as well If _a rises – compliance goes down Image source: https://www.istockphoto.com/photo/hand-holding-a-plastic-bag-full-of-water-gm1219923711-357006541 ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 50 Static vs Dynamic Compliance Static compliance – is a physical property of a vessel, determined by connective/elastic tissue present (elastin/collagen). Altered by age and disease Dynamic compliance – is a change in vascular tone due to smooth muscle contraction. Altered by SNS activity Image source: https://www.istockphoto.com/photo/hand-holding-a-plastic-bag-full-of-water-gm1219923711-357006541 ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 51 Elasticity vs Compliance Elasticity (aka elastic recoil) - is the ability of something to resume its former shape when it is no longer being stretched Arteries are elastic vessels: They resist expansion and have lower compliance They readily “bounce back” with recoil force that raises the pressure within the vessel (greater elasticity) Veins are highly compliant vessels: They expand in size easily and have higher compliance They “bounce back” less than arteries for the same volume within, as they have lower elasticity Image source: https://www.istockphoto.com/photo/hand-holding-a-plastic-bag-full-of-water-gm1219923711-357006541 ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 52 Compliance for Arteries and Veins Compliance is indicated by the slope of the curve: Increased slope – increased compliance Veins exhibit high compliance when at low pressure Compliance decreases at high pressure The compliance of a vein is about 20-times greater than an artery Arteries exhibit low compliance at both low and high pressures The volume-pressure relationship (i.e., compliance) for an artery and vein are depicted in the top figure. Bottom figure represents changes in vascular compliance after increased vessel tone (increased SNS tone). Image source: https://www.cvphysiology.com/Blood%20Pressure/BP004 ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 53 Changes in Compliance A reduction in compliance decreases the change in volume for any given change in pliance Low com blood pressure. Can result from: pliance nce Low complia Constriction (dynamic compliance) High com Age (static compliance) Arterial disease (static compliance) Age increases vessel stiffness – decreased compliance Vasoconstriction – decreased compliance Stiffness (or elastance) is the reciprocal of compliance The volume-pressure relationship (i.e., compliance) for an artery and vein are depicted in the top figure. Bottom figure represents changes in vascular compliance after increased vessel tone (increased SNS tone). Image source: https://www.cvphysiology.com/Blood%20Pressure/BP004 ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 54 Capacitance Vessels (Veins) Increased sympathetic activity to venous smooth muscle cells Smooth muscles contract and increase venous tone Veins act as a reservoir for blood because of their high compliance (around 20 times more compliant than arteries). Increased tone causes a decrease in This reservoir is used to increase venous return and cardiac output. venous compliance Venous blood reservoir is displaced towards the heart Increased venous return and cardiac output ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 55 Central Venous Pressure Venous pressure represents the average blood pressure within the venous compartment Central venous pressure (CVP) - pressure in the thoracic vena cava near the right atrium Changes in CVP (∆7^!) can result from change in blood volume (∆^) within the thoracic veins and by changes in compliance of these veins (70) ∆^ ∆7^! = 7, Weight of blood in the vessels cause venous pressures to be as high as 90 mm Hg The venous valves and pump maintain a relatively low venous pressure in the legs Effect of gravitational pressure on the venous pressures throughout the body in the standing person. Image source: Guyton and Hall. Textbook of Medical Physiology. 13ed. ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 56 Factors Affecting Central Venous Pressure A decrease in CO (e.g., LV failure) will lead to blood backing up in the venous circulation, increasing CVP An increase in blood volume increases CVP Venous constriction increases CVP Changing position from standing to supine increases CVP Arteriolar dilation causes increased flow of blood from the arterial to the venous side. This increases proportion of blood in the venous system and increases CVP Muscle contraction of limbs and abdomen compresses veins and due to one-way venous. Valves moves blood back to the heart, increasing CVP Arteriolar constriction will reduce the volume of blood in the venous system, decreasing CVP ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 57 Static Compliance of the Aorta Keeps blood moving during ventricular diastole. The aorta is distended during systole The aorta recoils during diastole Blood moves forward When the arteries are normally compliant, a During ventricular diastole the previously Helps maintain through the systemic substantial fraction of the stroke volume is stretched arteries recoil. The volume of blood coronary perfusion stored in the arteries during ventricular that is displaced by the recoil furnishes circulation systole. The arterial walls are stretched. continuous capillary flow throughout diastole. Image source: Berne & Levy physiology (6th ed). Editors: Bruce M. Koeppen, Bruce A. Stanton. ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 58 ABNORMALITIES OF THE ARTERIAL PULSE AND PRESSURE WAVES Learning objectives for this section: 21. Describe different forms/shapes of pulse pressure: pulsus paradoxus, pulsus parvus and tardus, hyperkinetic pulse, dicrotic pulse, pulsus alternans.  Paradoxical Pulse (Pulsus Paradoxus) Paradoxical Pulse Pulsus Paradoxus A paradoxical pulse may be detected by a palpable decrease in the pulse’s amplitude on quiet inspiration. If the sign is less pronounced, a blood pressure cuff is needed. Systolic pressure decreases by more than 10 mm Hg during inspiration. A paradoxical pulse is found in pericardial tamponade and frequently in exacerbations of asthma and COPD. It is sometimes noted in constrictive pericarditis. Small, Weak Pulse Pulsus Parvus et Tardus The pulse pressure is diminished, and the pulse feels weak and small. The upstroke may feel slowed, the peak prolonged. Causes include (1) decreased stroke volume, as in heart failure, hypovolemia, and severe aortic stenosis; and (2) increased peripheral resistance, as in exposure to cold and severe heart failure. Hyperkinetic Pulse The pulse pressure is increased, and the pulse feels strong and bounding. The rise and fall may feel rapid, the peak brief. Causes include (1) increased stroke volume, decreased peripheral resistance, or both, as in fever, anemia, hyperthyroidism, aortic regurgitation, arteriovenous fistulas, and patent ductus arteriosus; (2) increased stroke volume because of slow heart rates, as in bradycardia and complete heart block; and (3) decreased compliance (increased stiffness) of the aortic walls, as in aging or atherosclerosis. ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 60 Paradoxical Pulse (Pulsus Paradoxus) Pulsus Alternans The pulse alternates in amplitude from beat to beat even though the rhythm is basically regular (and must be for you to make this judgment). When the difference between stronger and weaker beats is slight, it can be detected only by sphygmomanometry. Pulsus alternans indicates left ventricular failure and is usually accompanied by a left sided S3. Dicrotic Pulse Pulsus Bisferiense A bisferiens pulse is an increased arterial pulse with a double systolic peak. Causes include pure aortic regurgitation, combined aortic stenosis and regurgitation, and, though less commonly palpable, hypertrophic cardiomyopathy. Bigeminal Pulse This disorder of rhythm may mimic pulsus alternans. A bigeminal pulse is caused by a normal beat alternating with a premature contraction. The stroke volume of the premature beat is diminished in relation to that of the normal beats, and the pulse varies in amplitude accordingly. ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 61  HEMODYNAMIC EFFECTS OF INCREASED CARDIAC OUTPUT AND PERIPHERAL RESISTANCE Learning objectives for this section: 22. Describe how changes in cardiac output or peripheral resistance can be compensated to restore normal flow through the arterial system. Effect of Increased Cardiac Output Top: Instantaneous increase in cardiac output. MABP rises quickly as arterial filling (Qh) exceeds arterial emptying (Qr) Bottom: Steady-state increase in cardiac output. Increased MABP forces increased flow (Qr) until arterial emptying equals arterial filling Image source: Berne & Levy physiology (6th ed). Editors: Bruce M. Koeppen, Bruce A. Stanton. ROSS UNIVERSITY SCHOOL OF MEDICINE ROSS UNIVERSITY SCHOOL OF |MEDICINE 63 Effect of Increased Peripheral Resistance Top: Instantaneous increase in peripheral resistance. MABP rises quickly as arterial emptying (Qr) is reduced to below arterial filling (Qh) Bottom: Steady-state increase. Increased pressure forces increased exit flow (Qr) until arterial emptying equals arterial filling ROSS UNIVERSITY SCHOOL OF ROSS UNIVERSITY MEDICINE SCHOOL OF |MEDICINE 64  Questions? Dr. Oleksii Hliebov, MD, PhD Associate Professor, Department of Medical Foundations [email protected] Join Dr. Hliebov's Office Hours (via Zoom): https://zoom.us/j/96858712961?pwd=UklWVU1ETmhjRUd3UlAzVXM4WkpsQT09 Meeting ID: 968 5871 2961 Passcode: 680201