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Wk 3 notes 1 - CARDIOVASCULAR PHYSIOLOGY Basic Principles...

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CARDIOVASCULAR PHYSIOLOGY Basic Principles of Cardiovascular Physiology Here are some general concepts of cardiovascular physiology that may help in understanding the pharmacodynamics of the cardiovascular drugs and how they are used to treat the pathophysiologic alterations which characterize hypertension, CHF, angina, and other cardiovascular conditions. BLOOD PRESSURE The basic formula for the determination of blood pressure is: Blood Pressure = Cardiac Output x Total Peripheral Resistance o Since Blood pressure is determined by the product of cardiac output (C.O.) and total peripheral resistance (T.P.R.), it stands to reason that alterations in either or both of these will affect blood pressure. In other words, an increase in either one or both of these will increase blood pressure and, conversely, a decrease in either will produce a decrease in blood pressure. o Of the two factors, T.P.R. is far more responsible for blood pressure than is cardiac output. In other words, alterations in T.P.R. produce much more dramatic changes in blood pressure than will alterations in cardiac output. CARDIAC OUTPUT The basic formula for the determination of cardiac output is: Cardiac Output = Heart Rate x (Ventricular)Stroke Volume o Since cardiac output (C.O.) is determined by the product of heart rate (H.R.) and Stroke Volume (S.V.), it stands to reason that any alteration of one or both of these factors will affect cardiac output and, consequently, blood pressure. In other words, an increase in heart rate (up to a point) and/or an increase in ventricular stroke volume will result in an increase of cardiac output and blood pressure. [Note: Excessively fast heart rate will actually result in a decrease in cardiac output because the heart rate is too fast to allow the ventricle to fill with blood.] [Note: Stroke Volume refers to the number of cc's of blood ejected by the ventricle with each systole.] By combining these two definitions, a new formula for blood pressure is recognized. It is: Blood Pressure = Heart Rate x Stroke Volume x Total Peripheral Resistance Or B.P. = H.R. x S.V. x T.P.R. 1
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CARDIOVASCULAR PHYSIOLOGY What are the physiologic determinants of each of these factors? 1. HEART RATE o Circulating Catecholamines (especially norepinephrine, epinephrine, and dopamine) o Serum Calcium Ion Concentration o The Neurotransmitters of the Autonomic Nervous System (especially norepinephrine and epinephrine) 2. STROKE VOLUME o Myocardial Contractility (the muscular force with which the ventricle contracts) o Ventricular Preload (the force exerted on the ventricular wall by the contained
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