Measurement of Flow & Volume of BloodIndicator Dilution with Continuous InjectionFick’s techniqueIndicator Dilution with Rapid InjectionIndicator – Dilution CurveAn ExampleDye DilutionThermodilutionMeasuring Cardiac OutputElectromagnetic FlowmetersElectromagneticFlowmeter ProbesUltrasonic FlowmetersNear / Far FieldsUT FlowmetersTransit time flowmetersTransit Time FlowmetersDoppler FlowmetersDoppler FlowmetersProblems Associated withDoppler FlowmetersDirectional DopplerDirectional DopplerPrinciples of Biomedical Systems & DevicesPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Principles of Biomedical Systems & DevicesLecture 12Measurement of Blood FlowPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Measurement of Flow & Volume of Blood A measurement of paramount importance: concentration of O2and other nutrients in cells Î Very difficult to measureª Second-class measurement: blood flow and changes in blood volume Æcorrelate well with concentrationª Third-class measurement: blood pressure Æ correlates well with blood flowª Fourth class measurement: ECG Æ correlates adequately with blood pressure How to make blood flow / volume measurements? Standard flow meters, such as turbine flow meters, obviously cannot be used ! (why?)*ª Indicator-dilution method: cont./rapid injection, dye dilution, thermodilutionª Electromagnetic flowmetersª Ultrasonic flowmeters / Doppler flowmetersª Plethysmography: Chamber / electric impedance / photoplethysmography* because, it requires cutting the blood vessel and can cause formation of blood clots*PBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Indicator Dilution with Continuous Injection Measures flow / cardiac output averaged over several heart beats Fick’s technique: the amount of a substance (O2) taken up by an organ / whole body per unit time is equal to the arterial level of O2minus the venous level of O2times the blood flow ÎvaCCdtdmCdtdmdtdVF−=∆==Blood flow, liters/min(cardiac output)Consumption of O2(mL/min)Arterial and venousconcentration of O2 (mL/L of blood)dtdVdtdmC =∆Change in [] due to continuously added indicator m to volume VVmC0=The concentration C ofan m0amount of indicatorin a volume VVmC0=∆If an additional amount m is added, then the incremental increase inconcentration isPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Fick’s technique How is dm/dt (O2consumption) measured? Where and how would we measure Caand Cv? (Exercise)ª For example, measuring Cvis tricky: We cannot measure it in one of the easily accessible main veins, b/c the [O2] of the blood returning from lower body is different then that returning from upper body (brain and kidneys consume different amount of O2.ª Measuring Ca , however, is simpler. It can be measured from any artery. Why?CardiacminL/5mL/L140L/mL190minmL/250][O][Omin)(mL/O222=−=−=vanconsumptioOutputPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Indicator Dilution with Rapid Injection In Fick’s technique the indicator is O2which is continuously injected into the CV system (through breathing). This is new replaced by the more convenient rapid-injection method:ª A known amount of a substance, such as a dye or radioactive isotope, is injected into the venous blood and the arterial concentration of the indicator is measured through a serious of measurements until the indicator has completely passed through given volume. The cardiac output (blood flow) is amount of indicator injected,divided by average concentration in arterial blood.∫=tdttCmF0)(PBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Indicator – Dilution Curve∫tdttC0)(extrapolatedAfter the bolus is injected at time A, there is a transportation delay before the concentration begins rising at time B. After the peak is passed, the curve enters an exponential decay region between C and D, which would continue decaying alone the dotted curve to t1if there were no recirculation. However, recirculation causes asecond peak at E before the indicator becomes thoroughly mixed in the blood at F. The dashed curve indicates the rapid recirculation that occurs when there is a hole between the left and right sides of the heart.PBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404An Exampleextrapolated(known amount)PBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Dye Dilution In dye-dilution, a commonly used dye is indocyanine green (cardiogreen), which satisfies the followingª Inertª Safeª Measurable though spectrometry (absorption of light by the blood)ª Economicalª Absorption peak is 805 nm, a wavelength at which absorption of blood is independent of oxygenationª 50%of the dye is excreted by the kidneys in 10 minutes, so repeat measurements is possiblePBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Thermodilution The indicator is cold – saline, injected into the right atrium using a catheter Temperature change in the blood is measured in the pulmonary artery using a thermistor The temperature change is inversely proportional to the amount of blood flowing through the pulmonary arteryPBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Measuring Cardiac OutputSeveral methods of measuring cardiac output In the Fick method, the indicator is O2; consumption is measured by a spirometer. The arterial-venous concentration difference is measure by drawing samples through catheters placed in an artery and in the pulmonary artery. In the dye-dilution method, dye is injected into the pulmonary artery and samples are taken from an artery. In the thermodilution method, cold saline is injected into the right atrium and temperature is measured in the pulmonary artery.PBS&D – Fall 2004 – Polikar http://engineering.rowan.edu/~polikar/CLASSES/ECE404Electromagnetic Flowmeters EM techniques measure instantaneous pulsatile flow, not the average flow. Based on Faraday’s law of induction that a conductor that moves through a uniform magnetic field, or a stationary conductor placed in a varying magnetic field generates emf on the conductor:When blood flows in the vessel with velocity u and passes through the magnetic field B, the induced emf e measured at the