Exercise and Coronary Blood Flow PDF MD3001 9/7/2022

9/7/2022 Learning outcomes To explain the limits of cardiac perfusion and the difficulties in matching the body’s demand for cardiac output versus cardiac tissue demand. 9. Exercise and coronary blood flow MD3001 To predict and explain the changes in cardiovascular parameters in response to dynam...

9/7/2022 Learning outcomes To explain the limits of cardiac perfusion and the difficulties in matching the body’s demand for cardiac output versus cardiac tissue demand. 9. Exercise and coronary blood flow MD3001 To predict and explain the changes in cardiovascular parameters in response to dynamic and static exercise. To relate the major systems and effectors of blood pressure together and explain their dependencies. Dr Alun Hughes 1 2 2 Lecture overview Cardiovascular physiology 1) 2) 3) 4) 5) 6) 7) 8) 9) Coronary blood supply Dynamic exercise Static exercise Circulation of blood Physiological properties of the heart Cardiac contractility and the cardiac cycle Control of cardiac output Vasculature Microcirculation Control of blood pressure Control of blood volume Exercise and blood flow through special regions 3 3 4 4 Coronary blood flow through left ventricle Coronary blood supply Right coronary artery – Walls of RA and RV – SA and AV node – Posterior part of interventricular septum (proximal portion of AV bundle of His) – Small areas of LA and LV (in some people) Left coronary artery – Walls of LA and LV – Most of the interventricular septum including AV bundle Great and small cardiac veins – Via coronary sinus into right atrium Guyton p246 5 Rang and Dale’s Pharmacology (figure 22.5) 6 1 9/7/2022 Issues with coronary blood flow Control of coronary blood flow • Myocardium cannot function anaerobically Primary controller is local metabolism – Anaerobic glycolysis ↑↑ lac6c acid produc6on – In proportion to need of cardiac musculature for O2 – Stimulates release of vasodilators (e.g. adenosine) • Arterioles close mechanically during systole • ↓ diastolic filling period during exercise • ↑ oxygen demand and ↑ metabolic demand during exercise Sympathetic stimulation – Indirectly • Work output of heart ↑ 6-9x during strenuous exercise – Uses 70-80% of coronary blood flow O2 at rest • • • ↑ demand must be met by ↑ flow 7 Via ↑ heart rate and ↑ contrac6lity which ↑ metabolism – Directly High degree of sympathetic innervation Role unclear, but may contribute to pathophysiologies 8 Sympathetic stimulation of skeletal muscle arteries Noradrenaline causes vasoconstriction of skeletal muscle arterioles vs α1 receptors Adrenaline causes vasodilation of skeletal muscle arterioles via β2 receptors β2 would dominate! 9 2