Hemodynamics and Venous Return Lecture Notes (PDF)

PHYSIO-LEC: LE 3 | TRANS 4 Hemodynamics and Venous Return DR. JUNE CATHLEEN C. CASTILLO, DPBA | Lecture Date (11/23/24) OUTLINE ✔Compare the intrinsic and extrinsic mech...

PHYSIO-LEC: LE 3 | TRANS 4 Hemodynamics and Venous Return DR. JUNE CATHLEEN C. CASTILLO, DPBA | Lecture Date (11/23/24) OUTLINE ✔Compare the intrinsic and extrinsic mechanisms of I. Circulatory System VI. Venous Return regulating blood pressure A.Heart A.Venous System ✔Distinguish the venous system from the arterial system. B.Blood vessels B.Venous Compliance ✔Describe the mechanisms that return blood to the heart. C.Distribution of Blood C.Venous Return ✔Describe the venous return curve. Volume D.Factors that can ✔Explain the relationship between venous return, cardiac II. Hemodynamics cause transient output, and circulatory pressures. A.Blood Flow changes in Venous I. CIRCULATORY SYSTEM III. B.Hemodynamics Blood Pressure A.Blood Pressure Return E.Venous Valves F. Central Venous tissues. 📣 The circulation functions to serve the needs of the body → Transport of nutrients and hormones to tissues B.Blood Pressure Pressure → Removal of waste products Measurement G. Influence of CVP → Maintaining an appropriate environment in all the tissue IV. Regulation of Arterial and PVP on VR fluids of the body for survival and optimal function of the Blood Pressure H.CVP and Cardiac cells (internal homeostasis) A.Intrinsic and Extrinsic Output Functional parts include: Control of Vascular I. CVP Estimation by → Artery – Distribute oxygenated blood from the heart Tone PE → Arterioles and Capillaries – Primary exchange vessels B.Arterial VII. Exercise → Venules and Veins – Capacitance vessels Baroreceptors VIII. Physiology of CPR V. C.Neural Control Autonomic IX. Review Questions Nervous X. References Acts as a pump 📋 A. HEART [2025 Trans] Consists of two pumps in series 📖 System XI. Appendices → Pulmonary circulation A.Immediate Control ▪ Propels blood through the lungs for exchange of O2 B.Intermediate Term and CO2 Control → Systemic circulation C.Renal Blood Volume ▪ Propels blood to all other tissues of the body Pressure Control Intermittent, continuous blood flow occurs by distention of SUMMARY OF ABBREVIATIONS the aorta during systole and elastic recoil of large arteries ABP Arterial Blood Pressure during diastole. Ca Arterial Compliance Unidirectional flow is achieved by the arrangement of BP Blood Pressure valves CO Cardiac Output B. BLOOD VESSELS 📖 CVP Central Venous Pressure A series of distributing and collecting tubes filled with EDV End-Diastolic Volume heterogeneous fluid (blood) ESV End-Systolic Volume Arteries and veins transport blood into distinct circuits and HR Heart Rate they share a common overall structure that consists of: JV Jugular Vein → Tunica intima – Inner layer lined with a single layer of a KE Kinetic Energy specialized semipermeable epithelium called NTS Nucleus of Tractus Solitarius endothelium. PE PP Potential Energy Pulse Pressure 📋 → Tunica media – Middle layer consists of helically arranged smooth muscle cells. [2027 Trans] RVLM SBP Rostral Ventrolateral Medulla Systolic Blood Pressure 📋 → Tunica adventitia (externa) – Outer layer consists of type I collagen fibers and elastic fibers [2027 Trans] SV SVR Stroke Volume Systemic Vascular Resistance 📋 → Lumen – A hollow passageway through which blood flows [2027 Trans] VR Venous Return ❗️ Must know 📣 Lecturer 📖 Book 📋 Previous Trans LEARNING OBJECTIVES ✔Describe the component parts of the circulatory system. ✔Explain the effects of the determinants of blood pressure. ✔Demonstrate the procedures for determining blood pressure ✔Correlate the Korotkoff sounds to pressure changes in the blood vessels. LE 3 TRANS 4 TG-C10&11: *Rosales, Rosell, Roxas, Ruben, Salayo, Salazar, TE: Romero, Sabico, Sagun, AVPAA: E. Villa Page 1 of 25 Salinas, Sallan, Salongsongan, *San Andres, Sandoval, Santiago, E. Sampang, Santiago, G  Maximal resistance to blood flow. Very small artery that leads to capillaries 📖 → Lumen ranges from 30 μm or less in diameter → Slows down/resists blood flow causing a substantial drop in blood pressure Figure 2. Different types of arteries[Lecturer’s PPT} [Lecturer’s PPT} Figure 1. Diagram & Histology of arteries and veins CAPILLARIES ARTERIES Thin, short tubes that are only 1-cell thick Becomes narrow, thinner, less elastic, and more muscular Primary exchange vessels that supply blood to the tissues as it branches from the aorta to peripheral arteries. in a process called perfusion Tunica media – thickest and most visible layer Have the largest total cross-sectional and surface area Thick walls help withstand the high pressure from the → Results to slow blood flow ejected blood, especially the major vessels closest to the → Optimal condition for exchange of diffusible substance heart. between blood and tissues Lumen ranges from 5-10 μm in diameter dampened by: 📖 Pulsatile arterial blood flow caused by ejected blood is → Distensibility of the large arteries → Barely wide enough for an RBC to squeeze through → Frictional resistance in the small arteries and arterioles Have strong vascular walls since they accommodate blood flows at a high velocity Serve as a conduit absorbing the pressure generated by systolic contraction Contain a lot of elastin that allows stretch and recoil as well as smooth muscles that allow constriction and dilatation ELASTIC ARTERIES Conducting arteries near the heart → Usually >10mm diameter Arteries with the thickest wall that contains a high amount of elastic fibers/elastin less than those in the aorta. Examples: 📖 Frictional resistance is small and pressures are slightly Figure 3. Structure of arterioles, capillaries, and venules [Lecturer’s PPT} → Aorta VEINS → Pulmonary artery Compared to arteries, veins have large lumens, thin walls, → Brachiocephalic artery and less smooth muscles and elastic tissue → Subclavian artery → Tunica media is less pronounced, making them look → Common carotid artery collapsed under the microscope → Common iliac artery Low-pressure vessels equipped with valves promote unidirectional blood flow to the heart. MUSCULAR ARTERIES Venules and capillaries are the primary sites of Regulatory or distributing arteries further from the heart emigration or diapedesis → Ranges from 0.1-10mm in diameter → Diapedesis is the process through which WBCs adhere Decreased elastic fibers in tunica intima → Limits ability to expand Increased smooth muscle in tunica media to the endothelial lining of the vessels to squeeze through adjacent cells and enter the tissue fluid. Trans] [2027 📋 → Thick muscular layer regulates vasoconstriction and 📖 vasodilation VENULES Moderate resistance to blood flow Extremely small veins (usually 8-100 μm in diameter) Examples: Its walls consist of: → Brachial artery → Endothelium → Femoral artery → Thin middle layer with few muscle cells and elastic → Radial artery fibers → Popliteal artery → Outer layer of connective tissue fibers making up the very thin tunica externa/adventitia ARTERIOLES “Resistance vessels” Decreased wall thickness → Tunica media is restricted to 1-2 smooth muscle layers → Very thin tunica externa PHYSIOLOGY Hemodynamics and Venous Return Page 2 of 25  C. DISTRIBUTION OF BLOOD VOLUME The volume of the blood in different part of circulation: → 84% in the systemic circulation ▪ Greatest in veins and venules ▪ 64% in the venous system − 46% in small veins − 18% in large veins → 8.8% in the pulmonary circulation ▪ Equally divided among arteries, capillaries, and veins → 7.2% in the heart Figure 4. Different types of veins[Lecturer’s PPT] Figure 5. Relative proportions of elastic tissue, smooth muscle and fibrous tissue change in each type of blood vessel conferring significantly different physical and physiological properties on the vessels [Berne & Levy, 6th Ed] Summary: The aorta is predominantly elastic. Figure 6. Distribution of blood (in percentage of total blood) Peripheral arteries are less elastic and more muscular. in the different parts of the circulatory system[Lecturer’s PPT] The arterioles are predominantly muscular. The elasticity and frictional resistance of arteries Table 1. Distribution of Blood Volume*[Berne & Levy, 6th Ed] dampen pulsatile pressure Location Absolute Relative 📖 → Greatest drop of pressure at the level of small arteries and arterioles. Capillaries consist of short tubes with walls only one cell Systemic circulation Volume (mL) Volume (%) Aorta and large arteries 300 6.0 thick Small arteries 400 8.0 The conditions in capillaries are ideal for the exchange Capillaries 300 6.0 of diffusible substances between blood and tissues. Small veins 2300 46.0 On its return to the heart from the capillaries, blood Large veins 900 18.0 passes through venules and into veins of increasing Total 4200 84.0 size. The number of veins decreases near the heart. The Pulmonary circulation thickness and composition of the vein walls change. Arteries 130 2.6 Capillaries 110 2.2 Veins 200 4.0 Total 440 8.8 Heart (End-Diastole) 360 7.2 Total 5000 100 *Value refers to a 70-kg woman. II. HEMODYNAMICS A. BLOOD FLOW Quantity of blood that passes a given point in the circulation in a given period of time Overall blood flow in the total circulation of an adult person at rest is about 5000 ml/min B. HEMODYNAMICS Physics of fluid flow through vasculature Velocity – distance that a particle of fluid travels with regard to time, and it is expressed in units of distance per unit time (e.g., cm/sec) Flow – rate of displacement of a volume of fluid over time, volume per unit of time (e.g., cm³/sec) PHYSIOLOGY Hemodynamics and Venous Return Page 3 of 25  VELOCITY AND CROSS-SECTIONAL AREA BERNOULLI’S PRINCIPLE Sum of potential, kinetic, and pressure energy per unit mass of an incompressible, non-viscous fluid remains constant Flowing blood has mass and velocity → Kinetic Energy (KE) of flowing blood is proportionate to mean velocity, it is the forward force of velocity of blood → Potential Energy (PE) is the pressure exerted laterally against the walls of the vessel → Total energy (E) of the blood flowing within the vessel (assuming no gravitational effects):(conserved) E = KE + PE → Increase in velocity of blood flow or KE leads to a reciprocal decrease in the magnitude of PE, resulting to 📣 a decrease in the lateral pressure against the vessel wall Figure 7. Velocity of blood flow and cross-sectional area of blood vessels [Lecturer’s PPT] (Total) Cross-sectional area significantly increases at the level of capillaries due to the number of capillaries that are in parallel with each other Blood velocity is at the lowest point at the level of adequate time for exchange of nutrients 📣 capillaries, this slow flow is important as this allows In a rigid tube, velocity (V) and flow (Q) are related to one Figure 8. Bernoulli’s principle in relation to stenosis [Lecturer’s PPT] Through stenosis: (Narrowed vessels) another by the cross sectional area (A) of the tube: → Cross sectional area decreases → α means directly proportional → Velocity increases 𝑄 𝑣= → Lateral pressure decreases 𝐴 Once past the narrowed segment, kinetic energy reverts to 𝑣α𝑄 pre-stenosis value but since turbulence occurs and leads to PE loss due to friction, the lateral pressure against the 1 𝑣α vessel walls remains low. This leads to vessel collapse and 𝐴 decrease in flow in distal segments Area of a tube: A = π r2 → Plugging this to the original equation: 1 1 Given this example below: 📣 𝑣α 𝐴 → 𝑣α 2 π𝑟 → For instance, if the r is halved, we get this relationship: 1 4 𝑣α 𝑟 2 → 𝑣α 2 π ( ) π𝑟 → Blue arrows represent KE; Green arrows represent PE 📣 2 → Given this example below: → This is an artery with stenotic areas made of plaques. At ▪ Before entering the constricted part, the velocity is the level of the stenosis, the decrease in area will lead to an increase in velocity. just 𝑣 and once it passes through it, the velocity ▪ KE increases → reciprocal decrease in the increases by four (it gets faster) magnitude of PE which will lead to the decrease in lateral pressure against the walls → After the blood had passed through the stenotic area, KE will return to its pre-stenosis value since velocity is dependent on the area, while PE will not return to its Velocity of blood is DIRECTLY proportional to the pre-stenosis value since some energy is lost in the form blood flow and is INVERSELY proportional to the cross of friction at the level of stenosis (friction leads to a decrease in total energy and PE) sectional area → As the diameter ↓, the velocity in a tube ↑ 📣 ▪ PE remains decreased as well as the pressure in Velocity decreases as blood traverses the arterial system, is at minimum at the capillaries, and increases the lateral wall Clinical example: Atherosclerotic plaques → Narrowed vessels 📣 progressively towards the venous system → Decrease in lateral pressure after the level of the constriction would lead to vessel collapse and decrease in perfusion to distal segments of the extremity → The patient would present with pain due to hypoperfusion or ischemia, secondary to the vessel collapse PHYSIOLOGY Hemodynamics and Venous Return Page 4 of 25  RELATIONSHIP BETWEEN VELOCITY AND PRESSURE Table 3. Type of flow based on Reynold’s number Total pressure = PDyn + PLat Type of Flow Reynold’s Number → PDyn = blood flow with velocity Laminar flow 3000 Unsteady Flow: Reynold’s number is between laminar Where: ▪ P - pressure flow anytime 📣 and turbulent, it can be converted to laminar or turbulent Application of Reynold’s Number: 📣 ▪ p - density of fluid ▪ v - velocity Figure 10. Application of Reynold’s Number: Anemia [Lecturer’s PPT] Given the total pressures of A, B, and C are the same, On the left is an example of laminar flow in a vessel, a both the velocity and dynamic pressures are increased type of fluid motion where fluid moves in a series of layers in the narrowed area thus, decreasing the lateral with different velocities wherein the highest velocity is the pressure center of the tube Anemia: low viscosity, high cardiac output LAMINAR VS TURBULENT FLOW → The viscosity is dependent on the hematocrit. In anemic Normal flow of blood in straight blood vessels: Laminar patients, hematocrit is low. To compensate for this low viscosity, the heart increases the cardiac output. → Hematocrit must be controlled in anemic patients because it can lead to turbulence which can cause cardiovascular complications → Plugging it into the formula, the velocity increases and the viscosity decreases. The effect is additive so the Figure 9. Laminar Flow (A) and Turbulent Flow (B) [Lecturer’s PPT] Reynold’s number in anemic patients will be very high Table 2. Laminar Flow vs Turbulent Flow Laminar Flow Turbulent Flow Type of motion wherein Fluid elements do not fluid moves as a series of remain confined in a individual layers, each specific lamina layer moving at different Rapid and radial mixing velocities Vortices (swirls) are Center tube with highest present Figure 11. Application of Reynold’s Number: Thrombus [Lecturer’s PPT] velocity, velocity Distribution of velocities decreases parabolically is chaotic 𝑁𝑅 = ρ𝐷𝑣 towards the vessel wall Greater force needed to η This layer in contact to push fluid out of the tube 𝑄 vessel wall → “motionless” → increase work of heart 𝑉= 𝐴 to pump out the fluid from 2 𝐷 2 that vessel 𝐴 = π𝑟 = π( 2 ) REYNOLD’S NUMBER 𝑄 4𝑄 Used in differentiating laminar from turbulent flow 𝑉= 2 → 𝑉= 2 π(𝐷/2) π𝐷 Predisposing factors to turbulent flow: ρ𝐷𝑣 ρ𝐷4𝑄 ρ4𝑄 → High density 𝑁𝑅 = = 2 = η ηπ𝐷 ηπ𝐷 → Large diameter of tube → High velocity flow → Where: → Low fluid viscosity ▪ V is the velocity ▪ Q is the flow rate A dimensionless number (no units) that represents the ratio of the inertial to viscous forces in the vessel Determine the difference between laminar flow and 📣 ▪ A is the Area ▪ D is the diameter turbulent flow using the formula: ▪ r is the radius ρ𝐷𝑣 In cases of thrombus, Reynold’s number is HIGH 𝑁𝑅 = η In thrombus, the blood clot decreases the diameter by a → Where: third, while the velocity increases. The effect of velocity ▪ ρ is the density ▪ D is the tube diameter number 📣 change is greater than diameter in terms of Reynold’s ▪ v is the velocity ▪ η is the viscosity flow would be laminar or turbulent 📣 → The function of velocity is significant in Reynold’s if the PHYSIOLOGY Hemodynamics and Venous Return Page 5 of 25  POISEUILLE’S LAW SAMPLE QUESTION FROM SYNCH Relationship between pressure and flow Q1: From 4mm in diameter, the diameter of a clogged Applies to steady or non-pulsatile laminar flow of artery was halved. The flow through the artery would Newtonian fluids through rigid cylindrical tubes decrease by how much? (given pressure gradient, → Applicable not only in blood vessels but also with viscosity, and length are constant) 📣 anything that is introduced to the body via tubes or any a. 2x 📣 body part that has tubes (e.g. trachea) b. 4x → This principle illustrates the factors affecting flow c. 8x → Poiseuille's law is only accurate or applicable under d. 16x specific conditions where its assumptions hold true ANS: D. 16x Requirements: NOTE TO ANSWER: review the poiseuille’s law formula → 1st: fluid must be newtonian (viscosity is constant) → 2nd: flow must be non-pulsatile or fully laminar → 3rd: tube must be rigid The problem with our circulatory system is that it does not following reasons: 📣 necessarily or perfectly follow this principle due to the → Blood only has apparent viscosity which changes when OHM’S LAW In physics: describes the relationship of flow or current to the total resistance the hematocrit changes (NOT newtonian) In physiology: it states that the total resistance is equal to → Flow is pulsatile since the heart is what pushes the the change in pressure over flow blood to flow through the body Using Poiseuille’s law, the following formula is derived: → Blood vessels are NOT entirely rigid ∆𝑃 8η𝑙 However, the following insights about the law still applies 𝑅= 𝑄 → 𝑅= 4 π𝑟 ❗️ to blood flow: → Flow is proportional to radius and pressure Resistance to flow depends only on the dimension of the tube and characteristics of the fluid ❗️gradient → Flow is inversely proportional to viscosity and tube length Radius –principal determinant of resistance to blood flow 4 π∆𝑃𝑟 𝑄= 8η𝑙 → Where: ▪ η is the viscosity ▪ Q is the flow rate ▪ ∆P is the pressure difference ▪ l is the length of the tube ▪ r is the radius of the tube Vessel Diameter – The biggest determinant of flow Figure 12. Resistance per unit length of individual small If the radius is doubled, the increase in flow would be 24 or blood vessels [Lecturer’s PPT] 16 times the normal flow rate Highest resistance in individual capillary, but recall Example in clinical setting: fundamental physics: → During CT Scan, a contrast dye is given. A big gauge → Resistors in parallel connection, total resistance = slower flow 📣 needle is used because the fluid is viscous, having a → A big gauge is used for a faster infusion while a small resistance divided by number of resistors → Billions of capillaries in the body are parallel to each other, therefore the total resistance significantly gauge is used for a more cautious infusion. For example, in water vs. blood infusion, compare the two different types of fluids but with a constant length, ❗️ decrease → Thus, the resistance vessels are not the capillaries but the arterioles 📣 diameter, pressure, and using the same G18 needle −3 📣 Application of Ohm’s Law: Vessel with a plaque resulted in its diameter being halved shown in the figure below ▪ At 20°C, viscosity of water is at 1𝑥10 Pa → Using the formula below, we compute for the resistance and flow: −3 ∆𝑃 8η𝑙 ▪ At 37°C, viscosity of blood is at 4𝑥10 Pa 𝑅= 𝑄 → 𝑅= 4 π𝑟 → Computing for the resistance at the point of constriction: 8η𝑙 8η𝑙 𝑅= 𝑟 4 → 𝑅= 1 4 π( ) 2 π( ) 16 ▪ Therefore, the flow rate (Q) of blood is 4x less than → Resistance will go up by 16x if the diameter is reduced the flow rate of water through a G18 needle by half. → Meanwhile for flow, it will go down by 16x. ▪ Computing for the flow: ∆𝑃 ∆𝑃 𝑅= 𝑄 → 𝑄= 𝑅 PHYSIOLOGY Hemodynamics and Venous Return Page 6 of 25  VASCULAR RESISTANCE Changes in vascular resistance can occur when there is a aneurysmal rupture? 📣 Why are severe hypertension more prone to → Part of the core treatment of aneurysm is aggressive BP change in caliber of vessels Most important factor: contraction of circular smooth control, this is because if the distending pressure is too muscle cells in tunica media high, the vessel will just continue to expand. Too much Arterioles have thick coat of circularly arranged smooth expansion will increase the stress and the wall muscle fibers → can vary lumen radius thickness will thin out, and the vessel will be more prone to rupture. Thus, for patients with dilated aneurysm, the WALL TENSION goal is to control the distending pressure or BP Delicate structures of the vascular tree-like capillaries are → Cause of dilating blood vessels: the blood vessel’s not prone to rupture due to the protective effect of their spherical shape would actually lessen the tension (as small diameter as illustrated by the law of Laplace compensation). However, the increasing radius change As blood flows through a vessel, it exerts a force on the has an effect on the blood vessels and the weakening of vessel wall parallel to the wall the blood vessel wall in elderly having collagen that are Transmural pressure is the difference in pressure inside not compliant as before. These factors may lead to and outside the vessel increased stress on the vessel walls, disrupted blood flow, and higher risk of rupture → Surgical management is stenting and pharmacological management include BP control and antihypertensives to decrease the distending pressure SHEAR STRESS Tangential force of the flowing blood on the endothelial surface of the blood vessel 4η𝑄 τ= 3 π𝑟 Figure 13. Law of Laplace [Lecturer’s PPT] Shear stress → nitric oxide release → vasodilation Law of Laplace: Factors increasing shear stress: 𝑇= ∆𝑃𝑟 → High velocity flow 𝑤 → Permeability of vessel walls 𝑇 → Biochemical activity of endothelial cells 𝑃= 𝑟 → Blood coagulation Where: → Integrity of formed elements in blood → T is the tension stress on the wall Clinical Example: Hypertension → ∆P is the transmural pressure → Subendothelial and endothelial changes can predispose → r is the radius the vessels to tears and may ultimately lead to → w is wall thickness dissecting vessel aneurysm Distending pressure or transmural pressure (P) is the wall RHEOLOGIC PROPERTY OF BLOOD the center against the wall 📣 tension divided by the radius. It is directed outward from Wall tension is proportional to vessel radius for cylindrical Blood is non-newtonian since viscosity may vary at different points vessels. Approaching a spherical shape gives less tension “Apparent viscosity” than the same radius cylinder, but continued expansion → Derived value of viscosity obtained under a particular produces wall tension exceeding that of the original condition of measurement cylinder → Varies as a function of hematocrit While the vessel is dilating, the tension you need to Blood is basically a suspension of formed elements maintain the distending pressure would be higher. The (erythrocytes) in a homogeneous fluid (plasma); larger the radius, the wall stress will increase adding shear Viscosity depends on hematocrit → Resistance to blood flow is affected by viscosity or aneurysmal wall 📣 stress and more prone to rupture or dissection of the hematocrit of whole blood. Hematocrit has little effect on total peripheral resistance except when changes are Examples: 📣 necessary to balance the distending pressure 📣 The smaller the radius, the lower the tension on the wall large. In large vessels, increase in hematocrit cause increase in viscosity → Capillaries: receive a substantial amount of blood. It → Whole blood is 3-4x as viscous as water does not rupture because the radius of the capillaries is Fahraeus-Lindqvist effect very small, so to maintain the distending pressure and → In small vessels, erythrocytes move to the center of the not to rupture, the wall tension you need is also small vessel, leaving cell free plasma at the vessel wall → Dilated aorta: increase in aortic radius, thus the need leading to a less appreciable increase in viscosity for greater wall tension to maintain distending pressure Polycythemia vs. Anemia Increased wall tension puts the vessel at higher risk for → High hematocrit in polycythemia increases the total rupture or perforation resistance, increasing the work of heart and blood → Aneurysm: a portion of the vessel dilates, the radius pressure, while the opposite happens in anemia increases. To balance the distending pressure from inside the vessel, the wall stress should increase proportionally to the radius of aneurysm. The more dilated the aneurysm is, the higher wall stress and the risk of rupture PHYSIOLOGY Hemodynamics and Venous Return Page 7 of 25  III. BLOOD PRESSURE You are a 25-year old healthy medical intern on duty at the A. BLOOD PRESSURE ER today Table 4. Blood Pressure Terms 1st patient: JJ, a 65 year old male, came in for nape pain. Arterial Blood Force exerted by blood against the Nurse Marie carried the BP apparatus with an adult cuff Pressure walls of the arteries with her to the ward, so you used the pediatric cuff to take Maximal arterial pressure within the JJ’s BP. Systolic BP cardiac cycle Minimal arterial pressure within the Q2: There is a high chance that JJ’s blood pressure Diastolic BP cardiac cycle would be measured Difference between systolic and diastolic a. Erroneously low Pulse Pressure pressure b. Erroneously high 📋 MEAN ARTERIAL PRESSURE (MAP) ANS: B. Erroneously high Average force that drives blood flow into the blood 📋 Considered a better indicator of perfusion to vital vessels Retaking JJ’s BP with the correct cuff using the auscultatory method, you noted his BP at 160/90mmHg. 📖 The average arterial pressure during a single cardiac organs than SBP Nurse Marie asked you if you can recheck JJ’s BP since by palpatory method, she noted his systolic BP at 210. [Guyton & Hall] cycle, ~80 mmHg Pressure generated as blood is pumped out of the left Q3: Palpatory method should be done prior to ventricle into the aorta and distributing arteries auscultatory method to avoid detecting an MAP = (CO x SVR) + CVP a. Erroneously low systolic blood pressure → CVP is usually 0 at the level of the heart → MAP ≈ CO x b. Erroneously high systolic blood pressure SVR MAP) 📋 → MAP is directly proportional to CO and SVR (↑ SVR = ↑ [2025 Trans] ANS: A. Erroneously low systolic blood pressure 📣 → CO = HR x SV Q4: After an hour, you checked JJ’s BP and it was Normal MAP: 70-100 mmHg 180/120. What is the patient’s MAP? At normal resting heart rates, MAP can be approximated or Given: SYS → 180 mmHg; DIA → 120 mmHg computed clinically using this formula a. 100 mmHg b. 140 mmHg c. 150 mmHg ANS: B. 140 mmHg Formula: MAP = (1 systolic + 2 diastolic)/3 [180 + 2(120)]/3 = 140 mmHg DETERMINANTS OF ARTERIAL BP Table 5. Determinants of ABP Physical Factors Physiological Factors Fluid Volume Cardiac output → ↑ means more fluid → HR x SV presses against the wall of Total Peripheral walls 📋 artery, ↑ pressure in arterial Resistance [2025 Trans] → Also called Systemic Arterial Compliance → Vascular Resistance 📋 Figure 14. Mean Arterial Pressure with Cardiac Output and static elastic characteristic [2027 Trans] Systemic Vascular Resistance [Lecturer’s PPT] of system CASE SCENARIO ARTERIAL ELASTICITY Your second patient, Michael, a 70 year-old male, came in Table 6. Normal Artery vs Rigid Artery at the ER with severe headache and nape pain. The ER consultant asked you to take the patient’s mean arterial Normal Aorta and Rigid Artery pressure. The first Korotkoff sound came in at 180 mmHg. Pulmonary Arteries The last audible Korotkoff sound disappeared at 120 Systole: aorta distends Systole: no distension mmHg. Diastole: recoils and Diastole: cannot recoil propels blood forward Q1: What is the patient’s Mean Arterial pressure? High elastin, Highly With age, ↓ elastin & ↓ arterial e. 140 mmHg distensible compliance (Ca) → increased f. 150 mmHg pulse pressure (PP) Converts pulsatile output Increased pressure for ANS: A. 140 mmHg into steady flow → ↓ work ventricles to pump blood vs a NOTE TO ANSWER: of the heart large “afterload” → ↑ work of 1. Identify which is the given values heart 2. Recall the formula for Mean Arterial Pressure: MAP = (1 systolic + 2 diastolic) / 3 PHYSIOLOGY Hemodynamics and Venous Return Page 8 of 25  Figure 16.For a given volume increment (V2 − V1), reduced Ca results in increased PP, whereby (P4 − P1) > (P3 − P2). [Berne & Levy, 7th Ed] STROKE VOLUME AND PULSE PRESSURE Table 7. Stroke Volume & Pulse Pressure STROKE VOLUME (SV) PULSE PRESSURE (PP) Volume of blood pumped out Difference between systolic of the left ventricle during and diastolic pressure each systolic cardiac contraction SV = EDV - ESV PP = SV / Ca Normal: 80 ml Normal: 40 mmHg A large SV produces larger PP at any given compliance Figure 15. Compliant arteries (A and B). Rigid arteries (C As the SV increases → greater mean BP → PP increases and D). Blood flows through the capillaries during systole (C), Clinical Pearl: but ceases during diastole (D). [Berne & Levy, 6th Ed] →Hemorrhage: decreased SV → decreased PP →Advanced Age: decreased elastin in aorta → In a normal compliant aorta decreased Ca → increased PP → During systole, the heart contracts and pumps out a Widened PP: ↑ systolic pressure and ↓ Ca (arterial certain SV (volume of blood). compliance) (e.g. rigid arteries) → Since the Ca is normal, the aorta can stretch its walls Narrow PP: occur with ↓ SV (e.g. ↓ in blood volume, ↓ ▪ It can save a substantial fraction of SV along its effectivity of pump (cardiac failure)) arterial walls. ▪ There is an amount of blood not pumped out during systole → During diastole (heart relaxation), the aorta recoils. ▪ The volume of blood stored in the walls would be displaced during the recoil. ▪ This ensures that though the heart is relaxed, the capillary flow would still be continuous along the tissues. In a rigid artery → During systole, no blood (SV) is stored or saved in the walls since they are not elastic or distensible → During diastole, no SV will be pushed forward by the aorta to the capillaries ▪ Flow to the capillaries would cease or decrease ARTERIAL COMPLIANCE (Ca) Figure 17. Effect of a change in SV on PP, in which Ca is constant [Berne & Levy, 6th Ed] Change in volume over a given change in pressure Normal Ca = 2 ml/mmHg CASE SCENARIO Compliance decreases with age because arteries become You took the BP again and it increased to 200/120. After stiffer taking the Xray, the result indicated that Michael has a 📖 If CO and TPR are constant, decrease in Ca → increased rigid, atherosclerotic aorta. [Berne & Levy, 7th Ed] PP Q5: What is the patient’s PP? ↓ Ca also imposes a greater workload on the left ventricle a. 80 mmHg 📖 (i.e., increased afterload), even if SV, TPR, and arterial b. 120 mmHg [Berne & Levy, 7th Ed] pressure are equal in the two ventricles ANS: A. 80 mmHg (Know the Definition of Pulse Pressure) PULSE PRESSURE Pulse Pressure = Systolic BP - Diastolic BP Main determinants: SV and Ca (Physical determinants of arterial BP); → PP = SV / Ca PHYSIOLOGY Hemodynamics and Venous Return Page 9 of 25  Q6: If his aorta is RIGID, which of the following is TRUE? PALPATORY METHOD 📋 [2025 Trans] a. The rigid aortic wall will not allow it to distend during systole b. The rigid aortic wall will not allow it to distend during diastole ANS: A. Understand arterial compliance and how the aorta responds to the pumping action of the heart B. BLOOD PRESSURE MEASUREMENT BLOOD PRESSURE MEASUREMENT Figure 19. Palpatory Method Done before the auscultatory method to avoid auscultatory gap Performed by palpating the radial pulse at the wrist Estimates only the SBP → Pressure at which the first pulse appears Procedure: 📣 Real-time BP can’t be measured 1. Attach the cuff to the patient’s arm snugly, with the edge of the cuff around 2 cm above the antecubital fossa 2. Connect the manometer to the cuff, making sure that the patient does not see the meter 3. Palpate the patient’s radial pulse by placing your index and middle fingers over the radial artery. Figure 18. Schematic diagram of different non-invasive blood a. Do not use your thumb – has its own pulsation pressure measuring methods [Lecturer’s PPT] 4. Inflate the cuff up to 20-30 mmHg above the point when continuous 📋 Non-invasive BP measurement that can be intermittent or [2027 Trans] → Intermittent BP measurement: use an inflatable cuff pulse can no longer be felt. Slowly deflate at 2-4 mmHg per pulse. 5. Note the manometer reading at which the pulse the ▪ Can be done manually (through auscultatory or pulse reappears = PALPATORY SYSTOLIC BP palpatory method) or by automated method (e.g., 6. After pulse felt, you can completely deflate cuff oscillometry) → Continuous BP measurement: use volume clamp method and arterial applanation tonometry systolic blood pressure 📣 Note: You can only get one value which is the palpatory ▪ Arterial applanation tonometry can be automated AUSCULTATORY BP MEASUREMENT (automated systems) and can be done manually (hand-held sensors) Table 8. Factors leading to inaccurate BP readings ↓ Variance Cause 📋↑ Variance [2025 Trans] (mmHg) (mmHg) Cuff is too small 10 - 40 10-40 Cuff over clothing 10 - 40 Arm unsupported 10 Back/feet unsupported 5 - 15 Legs crossed 5-8 Figure 20. Auscultatory Method Not resting 3-5 minutes 10 - 20 Patient talking Labored breathing 10 - 15 5-8 method 📋 More sensitive and precise compared to the palpatory [2025 Trans] Use a sphygmomanometer, which cuffs an artery, and a Full bladder 10 - 15 stethoscope to listen for the Korotkoff sounds. Pain 10 - 30 Steps: Arm below heart level 1.8/inch 1. Ask the patient to loosen any tight clothing or to 1.8/inch Arm above heart level remove long sleeve garments to access their upper arm (do not use the arm that may have a medical PROPER BLOOD PRESSURE MEASUREMENT problem). Use an accurate and properly maintained device 2. Place the cuff around the upper arm and secure it. Recognize subject factors, such as anxiety and recent 3. Connect the cuff tubing to the sphygmomanometer nicotine use tubing and secure it. Position the subject appropriately 4. Rest the patient’s arm on a surface that is leveled with Select the correct cuff and position it correctly their heart. Perform the measurement using the auscultatory or 5. Place the bell or the diaphragm of the stethoscope on automated oscillometric method and accurately record the the cubital fossa approximately above the brachial values obtained. artery. 6. Inflate the bag with the rubber bulb at a pressure 20mmHg higher than the palpatory reading. PHYSIOLOGY Hemodynamics and Venous Return Page 10 of 25  7. Deflate the bag 2-4 mmHg per pulse Sound is louder in between systolic and diastolic. 8. Manometric reading at appearance of first sound → Sound will be softer until it disappears, at the level of the note as SYSTOLIC BP 9. Continue releasing the pressure 10. Manometric reading just before the disappearance of diastolic pressure (B) → Last sound detected is diastolic pressure 📋[2025 Trans] sound → note as DIASTOLIC BP 11. Completely release the pressure 12. Tell the patient their BP monitoring. Figure 24. Korotkoff Sound Volume Phases [Lecturer’s PPT] 📋 OSCILLOMETRIC MEASUREMENT Figure 21. Position for Auscultatory BP Measurement [Lecturer’s Used for self monitoring of blood pressure PPT] Use of maximum volume change as an indication of the average of systolic and diastolic blood pressure within the artery Uses reliable solid-state transducers and microprocessors that allow pressure changes in the cuff to be detected Pulse detection by oscillometric machines depends on the amount of change in the volume of the arm with each pulse and on the regularity and rate of those pulses → With regular pulses and relatively smooth changing arm volume, it is much easier for the microprocessor to estimate the systolic and diastolic blood pressure. → However, if pulses are irregular and there are arm movements under the cuff, pressure changes in the cuff will not rise and fall smoothly, leading to difficulty in making precise calculations. Figure 22. Brachial artery vs sounds heard during the manual auscultatory measurement [Berne & Levy, 6th Ed] KOROTKOFF SOUNDS Pulsatile sounds you can hear when taking blood pressure. Due to the turbulence caused by brachial artery compression. Figure 25. How to Read an Oscillometric Reading [Lecturer’s PPT] OTHER NON-INVASIVE BP MONITORING Volume Clamp Method → Continuous non-invasive BP monitoring → Obtained by applying pressure via the finger cuffs such that the blood volume flowing through the finger arteries Figure 23. Korotkoff Sound Volume in Between Systolic (Left) is held constant and Diastolic (Right) [Lecturer’s PPT] → CNAP – the machine When the BP apparatus is pumped way above the systolic ▪ Detects blood volume changes in the finger, BP, the Korotkoff sound disappears. transforming plethysmograph signals into continuous As you deflate the cuff, the Korotkoff sounds will reappear blood pressure information once it reaches the systolic BP (A) → First sound detected is systolic pressure 📋[2025 Trans] PHYSIOLOGY Hemodynamics and Venous Return Page 11 of 25  2. Miscuffing Ideal cuff: Bladder length 80% of arm circumference and Figure 26. BP-monitoring Device and Reading width of at least 40% of arm circumference (length-to-width [Lecturer’s PPT] ratio of 2:1) INVASIVE BLOOD PRESSURE MONITORING → Available cuffs per range (i.e. pediatric cuffs, small Continuous BP Monitoring adult cuffs, obese cuffs) 📋 Done through the cannulation of a peripheral artery → Cuff too small: erroneously high BP (usually radial artery [2025 Trans] ) → Cuff too big: erroneously low BP Commonly utilized in the management of critically ill and Edge of cuff 2-3 cm above the antecubital fossa 📋 perioperative patients Ask for patient’s permission to lift their sleeve before cuffing [2025 Trans] More accurate because it provides real-time BP 3. Auscultatory Gap (Cook & Taussig in 1917) BP before you take your auscultatory BP 📣 This is the reason why you always take your palpatory Refers to the absolute or relative silence occasionally found on listening over an artery during deflation of the blood pressure cuff Usually begins at a variable point below the systolic pressure and continues for 10 to 50 mmHg Said to occur in up to 20% of elderly hypertensive cases Figure 27. Arterial Cannulation Technique [Lecturer’s PPT] Figure 29. Auscultatory Gap [Lecturer’s PPT] Errors that may be noted if palpatory BP is not taken before auscultatory BP: → Underestimation of systolic BP ▪ Example in Figure 29: True systolic BP is at 180, true diastolic BP is at 80 ▪ For instance, you did not take the palpatory BP and Figure 28. How BP is Measured Using Arterial Cannulation you stopped inflating the cuff at 160. The next count that you hear will be at 140, so you’ll be reporting 📣 [Lecturer’s PPT] the BP of the patient at 140/80 instead of 180/80 COMMON CAUSES OF ERROR IN MEASUREMENT → Overestimation of diastolic BP 1. Patient Factors ▪ If you miss the auscultatory gap, the systolic Alcohol and nicotine consumption, bladder distention, pressure that you’ll detect would be the true systolic exercise, and body temperature. pressure (180 mmHg) but the diastolic pressure that minutes before getting the BP 📣 → Caffeine and smoking should be avoided at least 30 Ask the patient to remove clothing at cuff location 📣 you'll pick up would be the start of the auscultatory gap (160 mmHg) 4. Observer Error Patient should be positioned properly “Terminal digit preference” → Some practitioners round off → Middle of cuff below level of the right atrium → to nearest tens erroneously HIGH BP Should read to the nearest 2 mmHg and slowly deflate cuff → Above the right atrium→ erroneously LOW BP at 2-4 mmHg → Crossed legs → Increase in BP by 2-8mmHg Measure on both arms during initial visit → >10mmHg 5. Device/Equipment Error difference can be pathologic Miscalibrations At least 3 measurements should be made, 1-2 mins in Get multiple readings from both manual and automated BP between readings Among adult Filipinos, what device is recommended for accurate blood pressure determination and monitoring? From Philippine Society of Hypertension (2020): → A properly validated automated oscillometric sphygmomanometer (digital device) is recommended for in-office or out-of-office use PHYSIOLOGY Hemodynamics and Venous Return Page 12 of 25  → The aneroid sphygmomanometer (manual device) SUMMARY OF FACTORS AFFECTING THE CALIBER OF may be used provided that the examiner is efficient ARTERIES and well trained and that the device is periodically Table 10: Summary of factors affecting the caliber of the arteries checked according to standard maintenance procedures Vasoconstriction Vasodilation → The aneroid sphygmomanometer is recommended Local Factors for special cases like presence of arrhythmias or Decreased local temperature Increased CO2 and extremes in BP levels decreased O2 📣 6. White Coat Hypertension (WCH) Autoregulation Increased K+, adenosine, “Kinabahan lang ako” as said by patients lactate Elevated clinic BP with normal ambulatory or home BP Decreased local pH ESH (European Society of Hypertension) definition: office Increased local temperature reading of at least 140/90 and a mean 24 hour BP of Endothelial Products