EE 5340/7340 Introduction to Biomedical Engineering Catheterization & Cardiac Output

1. EE 5340/7340 Introduction to Biomedical EngineeringCatheterization & Cardiac Output Carlos E. Davila, Electrical Engineering Dept. Southern Methodist University slides can be viewed at: http:// www.seas.smu.edu/~cd/ee5340.html EE 5340/7340, SMU Electrical Engineering Department, © 2004

2. Example of Catheters EE 5340/7340, SMU Electrical Engineering Department, © 2004

3. Measurement of Heart Valve Surface Area Bernoulli’s Equation: pressure due to kinetic energy pressure due to potential energy Pt : total fluid pressure P : local static fluid pressure (this is the term we want to measure) r : fluid density g : acceleration of gravity h : height of fluid w.r.t. a given reference u: fluid velocity EE 5340/7340, SMU Electrical Engineering Department, © 2004

4. Measurement of Heart Valve Surface Area (cont.) heart valve orifice c.s. area = A P1 P2 pressure sensors EE 5340/7340, SMU Electrical Engineering Department, © 2004

5. Measurement of Heart Valve Surface Area (cont.) Assumptions: • frictionless flow • difference in heights at 2 sensor locations is zero (h1 = h2) • velocity at location 1 is small compared to location 2 • velocity (u1 << u2) Bernoulli’s equation at location 1: (1) EE 5340/7340, SMU Electrical Engineering Department, © 2004

6. Measurement of Heart Valve Surface Area (cont.) Bernoulli’s equation at location 2: (2) subtract (2) from (1): or: EE 5340/7340, SMU Electrical Engineering Department, © 2004

7. Measurement of Heart Valve Surface Area (cont.) flow at orifice: assumes velocity through orifice = velocity at location 2 orifice c.s. area: EE 5340/7340, SMU Electrical Engineering Department, © 2004

8. Measurement of Heart Valve Surface Area (cont.) If friction is taken into account: cd : discharge coefficient semilunar valve: cd = 0.85 mitral valve: cd = 0.6 EE 5340/7340, SMU Electrical Engineering Department, © 2004

9. Phonocardiography: Measurement of Heart Sounds 100 aortic pressure dicrotic notch aortic valve opens mm Hg mitral valve closes mitral valve opens left ventricular pressure R 0 T P ECG S Q heart sounds (phonocardiogram) 3rd 4th 4th 2nd 1st EE 5340/7340, SMU Electrical Engineering Department, © 2004

10. Heart Sound Generation heart sounds are due to vibrations produced by acceleration or deceleration of blood, some theories: • first: movement of blood during V. systole, closure of AV valves, turbulence at aortic and pulmonary valves. • second: deceleration and flow reversal of blood in aorta and pulmonary artery; closure of semilunar valves. • third: termination of rapid filling of ventricles from atria. • fourth: due to propulsion of blood into ventricles during atrial contraction. • heart murmurs: due to turbulence resulting from heart valve stenosis (impeded flow through valve) or regurgitation (backflow through valve after valve closure). EE 5340/7340, SMU Electrical Engineering Department, © 2004

11. Heart Sound Measurement • Stethoscope: Transmit sounds from the chest wall to ears. • frequency response: many resonances: 10 1 0.1 log f 40 1000 • firmly applied chest piece attenuates low frequencies; • skin serves as diaphragm, becomes taught. EE 5340/7340, SMU Electrical Engineering Department, © 2004

12. Heart Sound Measurement (cont.) • Dynamic microphone: + Vo _ diaphragm frequency response: 20-2000 Hz EE 5340/7340, SMU Electrical Engineering Department, © 2004

13. + _ Heart Sound Measurement (cont.) • crystal microphone piezoelectric crystal chest frequency response: 0.1 - 1000 Hz EE 5340/7340, SMU Electrical Engineering Department, © 2004

14. Measurement of Blood Flow • Indicator Dilution Methods: cardiac output • Fick Method • Rapid Injection Methods • Dye Dilution • Thermodilution • Electromagnetic Flowprobes • Ultrasound Flowprobes EE 5340/7340, SMU Electrical Engineering Department, © 2004

15. Indicator Dilution Methods indicators: • oxygen • dye • heat • consider a given volume of water: V, • add to it a given mass of indicator: m • resulting change in indicator concentration: or: EE 5340/7340, SMU Electrical Engineering Department, © 2004

16. Indicator Dilution Methods (cont.) • Now suppose the volume of water is time-varying: V(t) • In order to maintain the same DC, must make m time varying as well: • or: • take time derivative: or F = Flow = dV/dt EE 5340/7340, SMU Electrical Engineering Department, © 2004

17. Fick Method Indicator is O2 gas F = blood flow (l/min) dm/dt = O2 consumption (l/min) Ca = arterial O2 concentration (lO2/lblood) Cv = venous O2 concentration (lO2/lblood) EE 5340/7340, SMU Electrical Engineering Department, © 2004

18. O2 gas flowmeter soda-lime canister Fick Method (cont.) nose plug O2 is supplied continuously sample venous blood: Cv (Cv in peripheral veins varies widely) PA (absorbs excess CO2) sample arterial blood: Ca EE 5340/7340, SMU Electrical Engineering Department, © 2004

19. Indicator Dilution via Rapid Injection • In indicator dilution, one continuously adds indicator to an expanding volume of water in order to maintain a constant DC: • If the ratio is not constant, we get: (1) EE 5340/7340, SMU Electrical Engineering Department, © 2004

20. Rapid Injection • This is the case in the rapid injection method, a quantity of indicator is added over a short period of time. Equation (1) becomes: • take derivative: (2) EE 5340/7340, SMU Electrical Engineering Department, © 2004

21. Rapid Injection (cont.) Assume that: (2) becomes: or: (3) EE 5340/7340, SMU Electrical Engineering Department, © 2004

22. Rapid Injection (cont.) Now integrate both sides of (3): where we assumed F is constant. Solving for flow: EE 5340/7340, SMU Electrical Engineering Department, © 2004

23. Typical DC(t) Curve due to recirculation t t1 0 t1 typically around 30 s EE 5340/7340, SMU Electrical Engineering Department, © 2004

24. Indicators • Non-Toxic Dye: • indocyanine green: injected in pulmonary artery, DC(t) measured from blood drawn from catheter placed in femoral or brachial artery (leg). • Heat: used in thermodilution EE 5340/7340, SMU Electrical Engineering Department, © 2004

25. Thermodilution inject 4 ml of cold saline F = flow (m3/sec) Q = heat in injectate in Joules rb = density of blood (kg/m3) (can be determined from hematocrit) cb = specific heat of blood (J/kgoK) (can be determined from hematocrit) DTb(t) = Tb - Tbaseline (oK) ri = density of injectate (kg/m3) (known) ci= specific heat of injectate (J/kgoK) (known) EE 5340/7340, SMU Electrical Engineering Department, © 2004

26. Swan Ganz Catheter pulmonary artery cold saline injected from syringe R. Atrium thermistor Tb thermistor Ti balloon due to recirculation exponential fit t Tbaseline t1 0 t1 typically around 30 s EE 5340/7340, SMU Electrical Engineering Department, © 2004

27. Density and Specific Heat of Blood EE 5340/7340, SMU Electrical Engineering Department, © 2004

28. Example of Swan Ganz Catheter EE 5340/7340, SMU Electrical Engineering Department, © 2004

29. Example of Swan Ganz Catheter (cont.) A. Rounded, Tapered Tip B. Deflated Profile Flush with Catheter C. Polyurethane or Latex Balloon Option D. Polyurethane Catheter Material E. Large High-Flow Port Holes F. Vivid Depth Insertion Marks G. Triple Seal Extension Divided Junction (DJ) H. Transparent Extensions I. Color coded, Labelled Extensions J. Three Thread Winged, Connector Hub K. Easy Handling Stopcock L. Balloon Inflation/Deflation Indicator (I) M. Mushroom Shaped Lumens for Strength and Flow N. Rugged Computer Connector O. Thermoset, Industry Standard Thermistor P. Pressure Release Valve (PRV) (Available Upon Request) Q. Contamination Sheath (CMS) EE 5340/7340, SMU Electrical Engineering Department, © 2004

30. Examples of Cardiac Output Computers World Medical Columbus EE 5340/7340, SMU Electrical Engineering Department, © 2004