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Lectures in Cardiovascular Physiology1.Pdf Lectures in Cardiovascular Physiology By Patrick Eggena, M.D. Novateur Medmedia LLC. Lectures in Cardiovascular Physiology By Patrick Eggena, M.D. Novateur Medmedia LLC. i Copyright Copyright© Novateur Medmedia, LLC 2016 pending. All rights reserved. This book is protected by copyright. No part of it may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means - electronic, com- puter, mechanical, photocopy, recording, or otherwise - without the prior written consent of the publisher, except for brief quotations embodied in critical reviews. Note: Knowledge in the basic and clinical sciences is constantly changing. The reader is advised to carefully consult the instructions and informational material included in the package inserts of each drug or therapeutic agent before administration. Clinical cases in this publication have been used to illustrate basic principles of Physiology and are not in any way to be used as examples of how to treat patients. Care has been taken to present correct information in this book, however, the author and publisher are not responsible for errors or omissions or for any consequence from application of the information in this book and make no warranty, expressed or implied, with respect to the contents of this pub- lication. 2 Dedication This book is dedicated to Bonnie and to our children, Kendra and Brandon, and our grandchildren, Basia, Anika, and August. 3 Preface This is a thirteen hour lecture series in Cardiovascular Physiology given by the author to First Year Medical Students. Each of these lectures has been captured on video and is fol- lowed with relevant reading material from the author’s ebook, “Medical Physiology of the Heart-Lung-Kidney”. Many of the basic physiological concepts discussed in these lectures are applied to clini- cal situations, for example, the lectures on interpreting ECGs and listening to heart mur- murs, so that these programs should be helpful not only in Physiology Courses but also in Pathophysiology Courses for Medical, Osteopathic, Podiatric or Nurse Practitioner stu- dents. 4 About the Author The author was born in London, grew up on the Isle of Man and in Germany where he attended the Gymnasium Laurentianum in Warendorf, Westfalia. He emigrated to America at the age of 18, was drafted into the Army, and sent over- seas where he served as a Medic. Upon returning to the US he attended Kenyon Col- lege and Medical School at the University of Cincinnati. After serving as a house offi- cer at the Cincinnati General Hospital he started a career in Medical Research, first as an NIH post-doctoral fellow at the Brookhaven National Laboratories and the Univer- sity of Copenhagen, and then as an Established Investigator of the American Heart Association at the Mount Sinai School of Medicine. There he chaired the Physiology Course for many years, taught all aspects of Physiology, and participated in the Art and Science of Medicine courses for First and Second Year Medical Students. Students at The Mount Sinai Medical School awarded him The Excellence in Teach- ing Award on twelve occasions. Besides teaching and basic research concerning the cellular mechanism of action of vasopressin, the author has served as an Emergency Physician for the 16-hour night shift at a Veterans Administration Hospital once a week for many years before retiring last year. 5 1 Cardiac Electrophysiology Movie 1.1 Electrophysiology In this one hour video-lecture Dr. Eggena gives on overview of the cardiovascular system and considers cardiac action potentials. Basic Structure and Function of the Heart 7 1. The Chambers of the Heart The heart is made of four chambers, two atria and two ventricles (Fig.4-2). Venous blood from the peripheral organs and tis- sues enters the right atrium through the superior and inferior vena cava and then flows through the tricuspid valve into the right ventricle; from there it is pumped through the pulmonic valve into the pul- monary artery and distributed to the capil- lary beds of the right and left lungs. Here oxygen is added and carbon dioxide re- moved, that is, venous blood is arterial- Fig. 4-2. Overview of the heart and the circula- tory system. Un-oxygenated blood is returned ized. Arterialized blood collects in pulmo- via the superior and inferior vena cavae to the nary veins, flows into the left atrium, then right atrium and flows through the tricuspid enters the left ventricle through the mitral valve into the right ventricle. Blood is pumped by the right ventricle through the pulmonic valve valve and is ejected through the aortic into the pulmonary artery and through the capil- valve to be distributed to the organs and lary beds of the right and left lungs. Arterialized tissues of the body. blood drains via the pulmonary veins into the left atrium and enters the left ventricle via the mitral valve. The left ventricle then pumps the The left ventricle is a powerful muscle arterialized blood through the aortic valve into shaped into a chamber that functions as a the aorta, which supplies blood to the various pump when it contracts. Because the left peripheral organs and muscles. ventricle must generate great pressure to move blood to the head, arms, legs, and to all the visceral organs (i.e., the kidneys, ner because much less pressure is needed gut, liver, pancreas, and spleen), the wall to force blood through the vessels in the of the left ventricle bulges with muscle. lungs. Compared to the ventricles, the The wall of the right ventricle is much thin- walls of the atria are flabby because there 8 is normally little resistance as blood flows unimpeded across the tricuspid or mitral valves into the ventricles. Of course, the atrial walls do contain muscle that con- tracts to fill the ventricles with about one- third more blood than they would other- wise contain. But contraction of the atria is usually not essential, because when they fail to contract in a coordinated and effec- tive way - as seen commonly in patients with atrial fibrillation - the heart still deliv- Fig. 4-3. The electrical conducting system of ers sufficient blood to adequately perfuse the heart. The impulse is initiated at the SA node and travels over three path- ways in the tissues, at least at rest. As we shall dis- the atria to the AV node. The impulse is de- cuss shortly, the electrical potentials - layed by slow conduction in the AV node which are generated by the heart and can and then spreads rapidly via the His- Purk- be measured with electrodes at the sur- inje system to the right and left ventricles. face of the body (i.e., by electrocardio- gram) - are proportional to the amount of muscle in the walls of the various heart pulses through the AV node. Parasympa- chambers, so that the electrical signals thetic fibers have little, if any, effect on con- generated by the atria (the P waves) are tractility of ventricular muscle. By contrast, weak compared to the signals coming sympathetic fibers (and circulating epineph- from the ventricles (the QRS waves). rine) have important effects on increasing contractility of the ventricles and altering 2. Innervation of the Heart coronary blood flow. Sympathetic stimuli also increase the firing rate of SA nodal The heart is innervated by the autonomic pacemaker cells and increase the velocity nervous system. Activation of parasympa- of impulse conduction through the AV thetic fibers in the vagi decreases contrac- node. These effects of sympathetic stimula- tility of atrial muscle. Impulses received tion become apparent during exercise but from the right vagus slow impulse forma- at rest are overshadowed by the parasym- tion by the SA node; impulses received pathetic restraint imposed on the heart. from the left vagus inhibit conduction of im- 9 This is seen in patients with heart trans- Impulses spread over both the right and plants where the denervated heart beats left atria to reach the atrio-ventricular (AV) about 100 beats per minute - well above node, which lies at the septum between the usual resting heart rate of about 70 the atria near the tricuspid valve. The fi- beats per minute. This indicates that under brous tissue around the tricuspid and mi- normal (resting) conditions the parasympa- tral valves that separates the atrial cham- thetic system tonically restrains the heart bers from the ventricles forms an electri- from beating faster. cally tight seal, so that the only pathway over which impulses can reach the ventri- 3. The Specialized Conduct- cles from the atria is via the AV node. ing System of the Heart Thus, the AV node serves as a gate that A heart that is disconnected from its nerve regulates the impulse traffic from atria to input continues to beat in a regular rhythm, ventricles. Impulses are conducted slowly albeit somewhat faster than normal. This through the AV node, which gives the atria intrinsic rhythm of the heart is generated sufficient time to contract and to fill the by pacemaker cells located in the sino- ventricles with blood before they, in turn, contract. An impulse spreads from the SA atrial (SA) node where the superior vena node through the AV node in about 0.16 cava joins the right atrium (Fig.4-3). Im- seconds. pulses spread from here over the atria. Al- though the regular muscle fibers of the On leaving the AV node, electrical im- atrial wall can conduct impulses from one pulses travel via the bundle of His, which fiber to the next through gap junctions, then divides into a right and a left branch there are three specialized pathways over at the top of the interventricular septum.
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