Cardiac Output Cardiac Output (CO) = Stroke Volume (SV) x Heart Rate (HR) Oxygen delivery = CO x arterial oxygen content (CaO2) Cardiac output must be the same in both sides of the heart except patients with regurgitant murmurs patients with structural heart abnormalities Fick principle VO2 = (Ca-Cv) x CO volume of oxygen consumed = tissue extraction of oxygen times CO applies "conservation of mass" concept to oxygen consumption in body CO = O2 consumption / [ (O2 in pulmonary vein) - (O2 in pulmonary artery) ] Key the equation above refers to difference of oxygen content between the pulmonary vein (oxygenated blood) and pulmonary artery (deoxygenated blood) when dealing with systemic circulation, one has to substract O2 in systemic veins (deoxygenated blood) from O2 in systemic arteries (oxygenated blood) to avoid negative values Changes in CO ↓ SV in ventricular tachycardia if HR is too high, diastolic filling is incomplete and CO decreases exercise CO maintained by SV in early stages of exercise CO maintained by HR in late stages of exercise Stroke Volume Stroke Volume (SV) SV = CO/HR = End-Diastolic Volume (EDV) - End-Systolic Volume (ESV) volume of blood ejected per heart beat SV ~ 70 mL Variables (assessed by echocardiogram) EDV volume of blood in ventricle before ejection ESV volume of blood in ventricle after ejection Changes in SV ↑ SV in anxiety, exercise, pregnancy ↓ SV in failing heart "SV CAP" Stroke Volume affected by Contractility, Afterload, Preload ↑ SV via (1) ↑ contractility, (2) ↓ afterload, (3) ↑ preload ↑ Contractility, ↑ SV via catecholamines ↑ activity of Ca2+ pump in SR ↑ intracellular Ca2+ ↓ extracellular Na+ ↓ activity of Na+/Ca2+ exchanger digitalis ↑ intracellular Na+ → ↑ intracellular Ca2+ ↓ Contractility, ↓ SVvia β1 blockade ↓ cAMP heart failure systolic dysfunction acidosis hypoxia/hypercapnea ↓ PO2/↑ PCO2 non-dihydropyridine Ca2+ channel blockers ↑ Myocardial O2 demand via ↑ afterload (∝ arterial pressure) ↑ contractility ↑ HR ↑ heart size aka ↑ wall tension Ejection Fraction Ejection Fraction (EF) = SV/EDV fraction of EDV ejected per SV an index of ventricular effectiveness ↓ EF via systolic heart failure an index of cardiac contractility ↑ EF, ↑ contractility EF ~ 0.55 or 55% Pulse Pressure Pulse Pressure (PP) = Systolic Pressure - Diastolic Pressure PP reflects volume of blood ejected from left ventricle on a single beat PP ∝ SV Mean Arterial Pressure Mean Arterial Pressure (MAP) average pressure in a complete cardiac cycle Equations MAP = CO x Total Peripheral Resistance (TPR) MAP = 2/3 Diastolic Pressure + 1/3 Systolic Pressure MAP = 1/3 PP + Diastolic Pressure as HR increases, diastole decreases and systole increases in the percentage of time spent, thus influencing the MAP Preload and Afterload Preload aka ventricular EDV preload "pumps up the heart" ↑ preload by exercise (slightly) ↑ blood volume e.g., over-transfusion excitement sympathetics Pathology right wall myocardial infarction (inferior wall) ST elevation seen in leads II, III, and avF preload dependent for cardiac function, thus do not diurese Afterload aka MAP ∝ TPR Pharmacology venodilators (e.g., nitroglycerin) ↓ preload vasodilators (e.g., hydrAlAzine) ↓ Afterload (Arterial)
QUESTIONS 1 of 8 1 2 3 4 5 6 7 8 Previous Next Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (M1.CV.13.126) An 83-year-old male presents with dyspnea, orthopnea, and a chest radiograph demonstrating pulmonary edema. A diagnosis of congestive heart failure is considered. The following clinical measurements are obtained: 100 bpm heart rate, 0.2 mL O2/mL systemic blood arterial oxygen content, 0.1 mL O2/mL pulmonary arterial oxygen content, and 400 mL O2/min oxygen consumption. Using the above information, which of the following values represents this patient's cardiac stroke volume? QID: 100642 Type & Select Correct Answer 1 30 mL/beat 3% (3/104) 2 40 mL/beat 82% (85/104) 3 50 mL/beat 7% (7/104) 4 60 mL/beat 4% (4/104) 5 70 mL/beat 1% (1/104) M 1 Question Complexity E Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic (M1.CV.13.146) A 27-year-old man is running on the treadmill at his gym. His blood pressure prior to beginning his workout was 110/72. Which of the following changes in his cardiovascular system may be seen in this man now that he is exercising? QID: 100662 Type & Select Correct Answer 1 Increased systemic vascular resistance 26% (26/99) 2 Decreased heart rate 1% (1/99) 3 Decreased stroke volume 2% (2/99) 4 Decreased systemic vascular resistance 67% (66/99) 5 Decreased blood pressure 3% (3/99) M 1 Question Complexity E Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 4 Review Tested Concept Review Full Topic Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (M1.CV.12.94) A 40-year-old Caucasian male presents to the emergency room after being shot in the arm in a hunting accident. His shirt is soaked through with blood. He has a blood pressure of 65/40, a heart rate of 122, and his skin is pale, cool to the touch, and moist. This patient is most likely experiencing all of the following EXCEPT: QID: 100610 Type & Select Correct Answer 1 Confusion and irritability 4% (4/99) 2 Decreased preload 3% (3/99) 3 Increased stroke volume 75% (74/99) 4 Decreased sarcomere length in the myocardium 6% (6/99) 5 Increased thromboxane A2 10% (10/99) M 1 Question Complexity E Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic
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