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Cardiovascular physiology. Dr James Ker 2 scenario`s in cardiology: • Systemic diseases affecting the cardiovascular system. • Primary cardiovascular diseases. How can these diseases affect the cadiovascular system ? Components of the cardiovascular system: • Myocardium: myocarditis, cardiac failure etc • Valves: Stenosis, incompetence etc • Electrical system: Dysrhythmias. • Vessels: Arteries, veins, lymphatic vessels. Physiological disturbances: • Disturbances in the following may occur: • Blood pressure • Cardiac rhythm • Valvular function • Cardiac systole and diastole • Blood flow Blood pressure: • BP = Cardiac output (CO) x peripheral vascular resistance (PVR) • 3 components of blood pressure: • Systolic component • Diastolic component • Mean arterial pressure • BP = 120/80 mmHg • Mean arterial pressure = (S + 2D)/3 or • D + 1/3 PP • Pulse pressure=S – D (120-80=40 mmHg) Cardiac output: • CO = Stroke volume x heart rate • Thus: 2 ways to increase CO: SV vs CO Determines systolic BP Systolic vs diastolic HT Normal CO: 5L/min Cardiac index=CO corrected for body surface area Causes of increased CO: • Fever • Anaemia • Hyperthyroidism • Pregnancy • Exercise • Etc.. Presents as: • Systolic HT with: • ↑ pulse pressure • Stroke volume: Volume of blood pumped by ventricle during systole (70 ml at rest) Physiological control of CO: • Preload: Venous filling • Afterload: BP against which LV must expel stroke volume • Inotropy: Strength of myocardial contraction. Starling`s law, catecholamines Physiological control of heart rate: • Intrinsic: SA node • Extrinsic: Hormonal: thyroid, catecholamines Neurological: Autonomic nervous system Fever, electrolytes Peripheral vascular resistance: • Determined by diameter of peripheral arteries. • Determines diastolic blood pressure Control of PVR: • Hormonal: AT II, endothelins, NO, bradykinin, catecholamine etc • Neurological: Autonomic nervous system • Myogenic/Local. The ECG: • Einthoven`s trangle • Einthoven`s law Einthoven`s triangle: I + - - III II + + Einthoven`s law: • Lead II = Lead I + Lead III • Standard limb leads: I, II, III • Lead I: connects 2 arms • Lead II: connects right arm with left leg • Lead III: connects left arm with left leg aV leads: • Limb leads are bipolar • Unipolar limb leads=aV leads: aVR, aVL and aVF Precordial (V) leads: • V1: Just to the right of the sternum in the 4`th intercostal space. • V2: Just to the left of the sternum in the 4`th intercostal space. • V3: Halfway between V2 and V4 • V4: Left midclavicular line in the 5`th intercostal space • V5, 6: 5`th intercostal space in anterior and midaxillary line respectively Physiological use of the ECG: • Rhythm: Sinus vs other • Chamber thickening: Atrial and ventricular hypertrophy • Damage: Endocardial, myocardial, pericardial • Info on systemic conditions: Hypothermia, electrolyte disturbances, pH disturbances Rate, complexes, intervals: • P-wave: Atrial depolarization • QRS-complex: Ventricular depolarization • T-wave: Ventricular repolariation