Principles of Biomedical Systems & Devices Lecture 8: Cardiovascular Dynamics Dr. Maria Tahamont
Review of Cardiac Anatomy Four chambers Two atria-receive blood from the vena cave and pulmonary veins Two ventricles-pump blood out of the heart in the aorta and pulmonary arteries Four valves-tricuspid and mitral (bicuspid) and aortic and pulmonary semi lunar
Internal Structure of heart
Importance of Valves The cusps of the valves point in the direction of flow from atria to ventricles and ventricles to arteries. Valves guarantee that the blood flows in one direction Valves prevent back flow Chordae tendineae prevent the cusps of the atrioventricular valves from opening into the atria during ventricular contraction
Chordae Tendineae
Path of Blood Through Heart Vena Cava Right Atrium Body Tricuspid V. Aorta Right Ventricle Aortic Semi lunar V. Pulmonary Semi lunar V. Left Ventricle Pulmonary Artery Mitral (bicuspid) V. Lungs Left Atrium Pulmonary veins
Circulatory Routes There are two circulatory routes The Systemic Circulation delivers oxygenated blood to the body systems The Pulmonary Circulation delivers deoxgenated to the lungs This design allows the delivery of adequate oxygen to the body while an equal amount of blood is being re-oxygenated in the lungs
Review of Cardiac Conduction Sinoatrial Node (natural pace maker) Atrioventricular node Atrioventricular Bundle (Bundle of His) Right and Left Branch Bundles Purkinji Fibers Remember that cardiac cells are self excitatory, they spontaneously depolarize
Pacemaker Potentials and Cardiac Action Potentials
Timing and Route of Cardiac Action Potential
Systole and Diastole The electrical events in the heart lead to mechanical event Systole-contraction Diastole-relaxation The point of contraction is to generate pressure Pressure gradients across the valves control blood flow from one area to another
Pressure Flow Relationships When pressure in the atria exceeds pressure in the ventricles the atrioventricular valves open and blood flows from atria to ventricles When ventricular pressure exceeds atrial pressure the atrioventricular valves close to prevent back flow When ventricular pressure exceed arterial pressure blood flows from ventricles to arteries When arterial pressure exceed ventricular pressure the semi lunar valves close preventing back flow
Cardiac Cycle
Cardiac Output Cardiac Output (CO) is the volume of blood ejected by the left ventricle into the aorta each minute Cardiac Output = Stroke Volume x Heart Rate Stoke Volume (SV) is the amount of blood ejected per beat Heart rate (HR) is the number of beats/min
Cardiac Output CO (ml/min) = SV (ml/beat) x HR (beats/min) = 70 (ml/beat) x 75 (beats/min) = 5250 ml/min Heart rate depends on the demands of the body, HR is elevated or depressed depending on needs Stroke Volume depends primarily on how much blood has returned to the heart Cardiac Output is regulated the factors that effect both HR and SV
Regulation of Stroke Volume There are 3 factors that effect Stroke Volume: Preload the degree of stretch on the heart before it contracts Contractility the forcefulness of contraction of individual ventricular muscle fibers Afterload the pressure that must be exceeded before blood can be ejected from the ventricles
Preload The greater the preload (stretch) the greater the force of contraction The more the heart fills during diastole, the greater the force of contraction during systole (Frank-Starling Law of the Heart) The preload is proportional to the volume of blood in the ventricle at the end of diastole (end diastolic volume)
End Diastolic Volume Two factors effect end diastolic volume (EDV) The length of ventricular diastole- how long it takes to fill the ventriclethis depends on heart rate Venous return the volume of blood that returns to the right atrium The same volume of blood flows to both the systemic and pulmonary circulations
Contractility Myocardial contractility is the strength of contraction at any given preload, that is the amount of stretch Within limits, the greater the preload the more force of contraction This is related to the number of cross bridge connections that can be made in the individual myocardial cells
Afterload Afterload is the pressure that must be overcome so the semilunar valves open Pulmonary circulation-about 20 mmhg Systemic circulation-about 80 mmhg At any given preload, increases in afterload decrease stroke volume because more blood remains in the ventricle after systole
Regulation of Heart Rate The sinoatrial node is the natural pace maker of the heart but initiates contractions at about 100 beats/min The rate of the sinoatrial node is regulated by the autonomic nervous system Parasympathetic fibers in the Vagus nerve slow the rate Sympathetic fibers in the Cardiac Accelerator nerves increase the rate
Nervous Regulation of Heart Rate The cardiovascular center is located in the medulla oblongata The medulla receives input from Higher brain centers-cerebral cortex, limbic system, hypothalamus Proprioceptors-monitor movement Chemoreceptors-monitor blood chemistry Baroreceptors-monitor blood pressure
The ECG