BME 501 Advanced Topics in Biomedical Systems Spring 2014 Dr. Kay 1BME 501 Lecture Notes – Apr 21 Measuring Cardiac Output • Fick’s Principle • Indicator Dilution Cardiac Pathophysiology • Shunts • Cardiomyopathy • Cardiac Failure Exercise-Induced Cardiac Remodeling • Type of Exercise Affects Nature of Changes 2Stroke Volume • Increased afterload decreases velocity and extent of myocardial contraction • Decreased stroke volume (SV) • Increased end diastolic volume (EDV) • Increased preload 3Stroke Volume • Increased preload • Increased strength of contraction • Increased SV • New, shifted P-V loop • Overall, SV is less than before and ejection fraction has decreased 4• Rate at which pulmonary capillaries take up O2 in lungs must equal increase in O2 concentration in blood multiplied by pulmonary blood flow • Pulmonary blood flow is output of right ventricle (RV) • Can be used to measure cardiac output (CO) Measuring Cardiac Output: Fick’s Principle 5• : Pulmonary blood flow (output of RV) • : mixed venous oxygen concentration • : arterial oxygen concentration Measuring Cardiac Output: Fick’s Principle QCVCA6• : O2 in deoxygenated “mixed venous” blood entering lungs per minute • : O2 in oxygenated “arterial” blood leaving lungs per minute Measuring Cardiac Output: Fick’s Principle Q ×CV Q ×CA7• : O2 uptake by pulmonary blood per minute • : O2 removal from alveolar gas per minute • : Fick Equation • Measuring Cardiac Output: Fick’s Principle Q×CA-Q ×CV VO2 VO2= Q×(CA-CV) Q =VO2CA- CV8Example: • Resting human absorbs ~250 ml O2 per minute from alveolar gas ( ) • Arterial blood contains 195 ml O2 per liter (CA) • Mixed venous blood entering lungs contains 145 ml O2 per liter (CV) • Cardiac output from RV: Measuring Cardiac Output: Fick’s Principle VO2 VO2CA- CV=250 ml O2/min50 ml O2/L = 5 L/min9Limitations: • Requires cardiac catheterization to obtain mixed venous blood from RV/pulmonary trunk • Must measure O2 uptake for 5-10 minutes; beat-to-beat changes in stroke volume cannot be resolved • Only valid at steady state (RV output = LV output) • Cannot be used during exercise because RV catheter can cause arrhythmias Measuring Cardiac Output: Fick’s Principle 10• Known mass of foreign substance (dye) injected rapidly into a central vein or into right heart • Indicator becomes diluted in venous blood stream, carried through lungs and heart, and ejected into systemic arteries • Systemic arterial blood sampled from radial or femoral artery • Indicator concentration plotted against time Measuring Cardiac Output: Indicator Dilution Method 11• m: mass of dye injected • C(t): measured plasma concentration of dye at time ‘t’ • : plasma volume flow rate • V: volume of distribution (plasma volume) • : mean plasma concentration of dye Measuring Cardiac Output: Indicator Dilution Method C =mV12• Can use area under concentration curve to solve for plasma volume flow rate Measuring Cardiac Output: Indicator Dilution Method 13• Dye recirculates, creating hump on concentration-time curve • Can extrapolate on a log-scale plot to correct for recirculation • Thermal dilution: – Rapidly inject known mass of cold saline into RA or RV – Thermistor in pulmonary artery measures temperature – CO calculated as the injected amount of cold divided by area “under” temperature-time plot Measuring Cardiac Output: Indicator Dilution Method 14Pros and Cons: • Better time resolution than Fick method (~30 seconds vs. 5-10 minutes) • Can be used during exercise • Error involved in extrapolating decay of concentration-time curve can be problematic, especially in diseased hearts • Thermal dilution technique avoids recirculation hump Measuring Cardiac Output: Indicator Dilution Method 15Cardiac Pathophysiology: Shunts • Atrial-septal defect (ASD): enables blood to flow between left and right atria • Can lead to lower-than-normal O2 levels in arterial blood supplying brain, organs, tissues • Generally, left heart has higher pressure than right heart • Shunt usually left-to-right • Increase RV preload causes overload of pulmonary circuit, pulmonary hypertension 16Cardiac Pathophysiology: Shunts • Pulmonary hypertension creates increased RV afterload • May cause RV failure: dilation, decreased systolic function • If RA pressure rises above pressure in LA, blood shunted right-to-left • Oxygen-poor blood ejected into systemic vascular system • Produces cyanosis, shortness of breath, dizziness due to greater quantity of deoxygenated hemoglobin in systemic circulation 17Cardiac Pathophysiology: Shunts • Ventricular-septal defect (VSD): enables blood to flow between left and right ventricles • Membranous region near AV node most commonly affected • Muscular VSDs less common • During ventricular contraction, pressure in LV greater than in RV • Pushes blood from LV into RV 18Cardiac Pathophysiology: Shunts • 2 net effects of LV-to-RV shunt: – Circuitous refluxing of blood causes volume overload on LV – Added pressure and volume in RV causes pulmonary hypertension • Pressure in pulmonary artery can exceed systemic pressure • Reverses direction of shunt, oxygen-poor blood enters systemic circulation • Results in cyanosis, shortness of breath, dizziness 19Cardiac Pathophysiology: Cardiomyopathy • Measurable deterioration of function of myocardium (heart muscle) • Four main types: – Dilated cardiomyopathy – Hypertrophic cardiomyopathy – Restrictive cardiomyopathy – Arrhythmogenic RV dysplasia • Can be inherited or acquired • Many times, cause is not known • Often leads to heart failure 20Cardiac Pathophysiology: Dilated Cardiomyopathy • Most common type of cardiomyopathy • Can affect atria and/or ventricles • Often starts in LV • Heart muscle begins to stretch and become thinner • Inside of chamber enlarges • Often spreads to RV, then atria • Heart muscle of dilated chambers does not contract normally, cannot pump blood effectively • Heart weakens, heart failure can occur 21Cardiac Pathophysiology: Hypertrophic Cardiomyopathy • Quite common (incidence rate ~1 out of 500) • Occurs when heart muscle cells enlarge and cause wall of ventricles to thicken • Usually affects LV • Makes inside of ventricle smaller,