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MIT HST 542J - The Cardiovascular System

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Harvard-MIT Division of Health Sciences and Technology HST.542J: Quantitative Physiology: Organ Transport Systems Instructor: Roger Mark ©Roger G. Mark, 2004 MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of Electrical Engineering, Department of Mechanical Engineering, Division of Biological Engineering, and the Harvard-MIT Division of Health Sciences and Technology 6.022J/2.792J/BEH.371J/HST542J: Quantitative Physiology: Organ Transport Systems INTRODUCTION: THE FUNCTIONAL ANATOMY OF THE CARDIOVASCULAR SYSTEMINTRODUCTION: THE FUNCTIONAL ANATOMY OF THE CARDIOVASCULAR SYSTEM A. FUNCTIONS OF THE CIRCULATION (i) Transport: Supplies nutrients to various cellgroups. Removes wastes; distributes heat. Most important “nutrient” is oxgen (Figure 1). Other materials: CO2, amino acids, glucose, fats, hormones, ions, urea, cells, etc. (ii) Communication: Integrative communication via hormones (iii) Heat Exchanger: Distributes heat to skin, lungs. Controls dissipation (iv) Protection: Clotting mechanisms, transport of WBCs, antibodies. B. COMPONENTS OF THE CARDIOVASCULAR SYSTEM (i) Major Components: Two pumps in series; major conduits; exchange mechanisms be-tween intravascular and extra-vascular fluid; reservoirs for fluid storage (Figure 2); fluid medium (blood). Physical characteristics of elastic arteries, collapsible veins, resistance vessels. (ii) Organization: High pressure delivery system, low-pressure capacitance system (Figure 2). Parallel organization of supply routes (Figure 3). (iii) Some Numbers: Typical Dimensions, velocities, normal values (Tables 1, 2). (iv) Perfusion and O2 Uptake of representative organs (Figure 4). C. FUNCTlONAL ANATOMY OF THE HEART (i) Anatomical Landmarks - to be discussed in Lecture. Use Textbooks for reference. (ii) The Conduction System (iii) The Cardiac Cycle (Figure 5) — Pressures, volumes, mechanical events, heart sounds. Introduction: Functional Anatomy 3Dexter 1951 Douglas 1922 Christiansen 1931 Donald 1955 Oxygen Consumption (liters/min)Cardiac Output (liters/min)Cardiac Index (liters/min/m2 ) Cardiac outputandcardiac index Oxygen consumption 4 3 2 1 0 16001400120010008006004002000 0 5 10 15 0 5 10 15 20 25 30 35 Work Output During Exercise (kilogram-metersters/min) Figure 1: Relationship between cardiac output and work output (solid curve) and between oxygen consumption and work output (dashed curve) during exercise. [Data derived from studies by Douglas and Haldance (1922); Christensen and Mitteilung (1931); Dexter, Whittenberger, Haynes, Goodale, Gorlin, and Sawyer (1951); and Donald, Bishop, Cumming, and Wade (1955).] After Figure 1-1 in Guyton, A., C. Jones, and T. Coleman. Circulatory Physiology: Cardiac Output and its Regulation. 2nd ed. Philadelphia: W.B.Saunders, 1973. 6.022j—2004 4After B. Folkow and E. Neil, Circulation. Oxford University Press, 1971, pp. 6-7.Introduction: Functional Anatomy 5Systemic CirculationL eft PumpWindkessel Windkessel Precap. Precap. Postcap. Capillary Capillary Postcap. Capacitance Capacitance Sphincter Section Venous CompartmentVenous Compartment“High Pressure” SystemControl of Systemic Pressure and Flow DistributionPulmonary CirculationR ight 100 mm Hg25 mm Hg“L ow Pressure” SystemControl of Blood Volume and Venous R eturnApprox. Volumes (cc.)VesselsR esistance VesselsE xchange VesselsR esistance VesselsVesselsPumpVesselsR esistance VesselsR esistance VesselsE xchange VesselsVesselsmm Hg120100 80 60 40 20 0180 300 400 300 180 130 110 2003,2004,380 620Figure by MIT OCW.Figure 2Figure by MIT OCW. After Green, H.D. "Circulation: Physical Principles." in Glasser, O.[ed.], Medical Physics. Vol. 1. Chicago: The Year Book Publishers, 1949. Figure 3: Arrangement of the parallel routes by which the circulation passes from the aorta to the vena cava. Representatives of the different categories of route discussed in the text are indicated. The Xs indicate the location of control points where arterioles may control the flow. RA, right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle; PV, portal vein. (from Green, H.D.: Circulation: Physical Principles, in Glasser, O. [ed.]: Medical Physics, Vol. 1 [Chicago: The Year Book Publishers, Inc., 1949], p. 210. Original illustration kindly furnished by H.D. Green.) 6.022j—2004 6 ( ) ( ) PH ead and Neck A rms L ungs B ronchial L eft A trium C oronary L eft Ventricle T runk Hepatic Splenic M esenteric K idney afferentK idney efferentPelvic Organs L egs R ight A trium R ight Ventricle H epatic ortal25 % 10 % 10 % 10 % 15 % 40 % 10 % 5 % 15% 10%15% 10% 15% 10% (a) 5,000 ml/min. (b) 250 ml/min. Kidney Skin Brain Heart Coronary Liver Muscle Other Viscera Figure by MIT OCW. Figure 4: Estimated distributions of cardiac output (A) and oxygen consumption (B) to different organs of the body in a man at rest. The estimates are very rough, from data taken from many sources and not very consistent. The kidney is greatly overperfused; the muscles, underperfused. In exercise the proportion of blood flow to muscle increases enormously, as it does for skin in hot environments. Table 1: Geometry of Mesenteric Vascular Bed of the Dog* Total Total Kind of Diameter Cross- Length Volume Vessel (mm) Number sectional (cm) (cm3)Area (cm2) Aorta 10 1 0.8 40 30 Large arteries 3 40 3.0 20 60 Main artery branches 1 600 5.0 10 50 Terminal branches 0.6 1,800 5.0 1 25 Arterioles 0.02 40,000,000 125 0.2 25 ⎫ Capillaries 0.008 1,200,000,000 600 0.1 60 ⎪ ⎪ ⎪ Venules 0.03 80,000,000 570 0.2 110 ⎪ ⎪ ⎬ Terminal veins 1 1,800 30 1 30 740 Main venous branches 2 600 27 10 270 ⎪ ⎪ ⎪ ⎪ Large veins 6 40 11 20 220 ⎪ ⎭ Vena cava 12 1 1..2 40 50 930 * Data of F. Mall. Introduction: Functional Anatomy 7Figure by MIT OCW. After Fig. 4-14 in Berne and Levy, Cardiovascular Physiology. 3rd ed. St. Louis, MO: The C.V. Mosby Co., 1977. Figure 5: Left atrial, aortic, and left ventricular pressure pulses correlated in time with aortic flow, ventricular volume, heart sounds, venous pulse, and electrocardiogram for complete cardiac cycle in the dog. [from R. M. Berne and M. N. Levy, Cardiovascular Physiology (4th edition). The C. V. Mosby Company, 1998.] 6.022j—2004 8Table 2: Representative Values for Human Circulation Cardiac Output: 5 liters/min. (resting) 15-25 liters/min. (exercise) Heart Rate: 60–80 beats/min. (resting) 120–160 beats/min.

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