Cardiac Output and Blood Pressure PDF

U N I T IV CVS Textbook of Medical Physiology, 11th Edition Cardiac Output Dr. Makkawi.A.A. Osman Ph.D Department of physi...

U N I T IV CVS Textbook of Medical Physiology, 11th Edition Cardiac Output Dr. Makkawi.A.A. Osman Ph.D Department of physiology School of Medicine Session No (2) GUYTON & HALL Copyright © 2006 by Elsevier, Inc.  The cardiac output Is the volume of blood ejected by each ventricle each minute. It equal 5 L/min in an average adult male at rest , less in females.  Control of the COP COP = HR X SV Its controlled by controlling: heart rate & stroke volume. Control of the heart rate:- Normal heart rate ranges between 60-100 beates/min. Less than 60= bradycardia. More than 100 = tachycardia.  Factors affecting the HR Neural factors :-  HR is increased by sympathetic & decreased parasympathetic. Hormonal factors:-  HR is increased by catecholamines & thyroid hormones. Physiological factors:-  HR is increased by exercise and decreased by sleep. Physical factors:-  HR is increased by high temperature & decreased by cold. Drugs:-  HR is increased by atropine  HR is decreased by propranolol.  Control of stroke volume (SV) Volume of blood ejected by each ventricle each beat. Equal 70 ml in an average adult male at rest. Factors affecting the SV are:- SV is ↑ by sympathetic stimulation. Parasympathetic has no direct effect on the stroke volume because it doesn't supply the ventricle.  Stroke Volume  Volume (ml) of blood ejected per beat Figure 20–19  Control of stroke volume (SV)  Hormonal factors :-  SV ↑ by catecholamines & thyroid hormones.  Physiological factors:-  SV is ↑ by exercise.  Physical factors:-  SV is ↑ by high temperature and ↓ by cold.  Drugs :-  SV ↑ is by digitalis & ↓ by beta blockers (Atenolol).  Ions :-  SV is ↑ by calcium ions  Hypercalcemia can stops the heart in systolic phase  The blood pressure Definition :- The systolic pressure is the maximum pressure in arteries during systole of the heart. Ranges between 110 – 140 mmHg in normal adults. The diastolic pressure is the minimum pressure in arteries during diastole of the heart. Ranges between 70 – 90 mmHg in normal adults. The pulse pressure: is the difference between the systolic & diastolic pressure. The mean arterial pressure: is the mean pressure during the cardiac cycle. It equals the diastolic + 1/3 of the pulse pressure. Example: If the blood pressure of a subject = 120/80. The systolic pressure = 120mmHg. The diastolic = 80 mmHg. The pulse pressure = 120-80 = 40 mmHg. The mean arterial pressure = 80+(1/3 x 40) =93 mmHg.  Control of blood pressure BP = cardiac output x peripheral resistance. The blood pressure is controlled by controlling the cardiac output & the peripheral resistance through the following mechanisms: Control of Blood Pressure Controlling cardiac output and peripheral resistance regulates blood pressure  Very rapid mechanism Neural mechanism that act in second. Include : The baroreceptors: which stimulated by hypotension. The chemoreceptors:stimulated by chemical changes in the blood due to hypotension. Regulation of Cardiac Cycle Autonomic nerve impulses alter the activities of the S-A and A-V nodes  Less rapid mechanisms Hormonal mechanisms that act in minutes. Include hormones that cause vasoconstriction like ADH, angiotensin II and catecholamines. Secretion of these hormones is stimulated by hypotension.  Long term mechanisms  Take days to act.  Include factors that increase blood volume by:  Reabsorption of water in the kidney by ADH.  Reabsorption of sodium, followed by water, in the kidney by aldosterone hormone.  Excretion of sodium followed by water, by atrial natriuretic peptide hormone.  Drinking of water due to stimulation of the thirst center. Measuring Arterial Blood Pressure Figure 11.18 ‫)ﻻ إﻟﻪ إﻻ‬ ‫أﻧﺖ‬ ‫ﺳﺒﺤﺎﻧﻚ‬ ‫إﻧﻲ ﻛﻨﺖ‬ ‫ﻣﻦ‬ ‫اﻟﻈﺎﻟﻤﻴﻦ(‬