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Detection and Volume Estimation of Cerebral Embolism using Transcranial Doppler

Detection and Volume Estimation of Cerebral Embolism using Transcranial Doppler Leonid Bunegin, Claudia Miller, and Bob Chin. Principle of Detection. Large acoustic impedance difference between emboli and blood. MCA Velocity Profiles resulting from Air and Particulate Emboli.

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Detection and Volume Estimation of Cerebral Embolism using Transcranial Doppler

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  1. Detection and Volume Estimation of Cerebral Embolism using Transcranial Doppler Leonid Bunegin, Claudia Miller, and Bob Chin

  2. Principle of Detection • Large acoustic impedance difference between emboli and blood.

  3. MCA Velocity Profiles resulting from Air and Particulate Emboli

  4. Detection Limits for Air and Particulate Emboli • 0.5 uL Air Emboli - 60% detection • 0.75 uL Air Emboli – 80% detection • >1.0 uL Air Emboli – 100% detection • 5 X 107 one micron diameter microsheres • 5 X 104 twenty five micron diameter microsheres

  5. Principle of Volume Estimation • Specular reflection at the embolus blood interface. • Emboli produce Doppler shifts which, when translated into audio frequencies, have distinctive distributions of frequencies that are unique to the emboli • Emboli pass through the Doppler field once.

  6. Raw Audio Output for Background, Air, Sensor Movement and Electrocautery

  7. Background Artifact and Air Embolus Audio Spectra

  8. Sensor Movement Artifact and Air Embolus Audio Spectra

  9. Cautery Artifact and Air Embolus Audio Spectra

  10. Filtered Audio Output of Air Filtered Audio Spectrum of Air Bandpass filter 225-450 Hz

  11. Calibration Curve In Vivo • Injection of 1.0, 5.0, 10.0, 20,0, 40.0, 65.0 uL of air into internal carotid artery • Record TCD audio output • Bandpass filtration (225-450Hz) of raw audio output • FFT on filtered audio output • Integrate FFT over bandpass range

  12. Calibration Curve In Vivo

  13. Monitoring setup in Patients undergoing CPB

  14. TCD Video and Audio Output of Cautery and Background Artifact, Air and Particulate Emboli

  15. Detecting Particulate Emboli FFT of Filtered Audio Output; Bandpass 500-1000 Hz FFT of Raw Audio Output

  16. Expected Benefits of Cerebral Embolism Detection Technology to EVA • Monitor embolism occurrence under reduced pressure EVA conditions • Monitor CBFV during in flight activities • Relate CBFV and cognitive function • As a function of embolic frequency and volume • Following exposure to VOCs and environmental toxins

  17. Potential Clinical Benefits to Cerebral Embolism Detection Technology • Prognostic of potential for embolic stroke • Monitoring open-heart and carotid endarterectomy surgery • Resolution of the controversy regarding transient ischemic attacks and the role of emboli • Monitor embolism formation during diving ascents

  18. COGNITIVE and NEUROPHYSOLOGIC RESPONSES TO LOW LEVEL ORGANIC SOLVENT EXPOSURE

  19. HYPOTHESIS Neurobehavioral symptoms reflect cognitive deficits secondary to altered delivery of essential metabolic substrates following exposure to organic solvents. Cerebral blood flow in sGWVs is altered following organic solvent exposure

  20. Protocol Clean Air Exposure Acetone Exposure Acclimation Sham Exposure Pulmonary Function Baseline Cognitive Challenge Baseline Baseline Cognitive Challenge Baseline Pulmonary Function Baseline Cognitive Challenge Baseline Subjective Self-Assessment

  21. Subject Demographics Asymptomatic Symptomatic • Sex male male • Age 30.1"6.7 36.8"9.6 • Education 13.5"1.7 14.1"3.1 • Hand 1.25"0.5 1.25"0.5

  22. Correlation between fTCD and SPECT Dahl A, et al. Stroke 23(1);15-19,1992

  23. Correlation between fTCD and fMRI Deppe M, et al. J Cereb Blood Flow Metab 20(2);263-269, 2000

  24. Correlation between fTCD and PET Sabri O, et al. J Nuclear Medicine 44(5);671-681, 2003

  25. CONCLUSIONS The higher resting MCABFV in sGWVs suggests decreased cerebro-vascular tone. Failure of MCABFV to increase during cognitive challenge under acetone exposure may indicate impaired auto-regulatory mechanism.

  26. High Fidelity Cerebral Circulation Model

  27. Model Schematic

  28. High Fidelity Cerebral Circulation Model ModelHuman Brain Volume 1400 mL 1400±118 mL1 Brain Tissue Elasticity G0 40 mmHg/mm 36±6 mmHg/mm10 CBF*** 508 mL/min 510±105 mL/min2,3 r-ICA BF 203 mL/min 204 mL/min3 l-ICA BF 203 mL/min 204 mL/min3 BA BF 101 mL/min 102 mL/min3 MCABFV 49 cm/sec 41±7 cm/sec4 MCA diameter 3 mm 2.9±0.3 mm5 HR 70 b/min 70 b/min Serum density 1.0373 g/mL 1.0333 g/mL6 kinematic viscosity 1.429 cp-mL/g 1.339 cp-mL/g6

  29. Assumption for Calculation of Minimum Oxygen Requirement of the LMCA Territory MCA territory is 34.7±16.4% of hemisphere.9 Hemisphere mass is 591±48 g.1 Average brain oxygen requirement is 3.3 mL O2/100 g/min or 0.033 mL O2/g/min.8 a. Mass of MCA territory; hemisphere mass X 35% of hemisphere 591 g X 0.35 = 207 g b. O2 requirement for MCA territory MCA territory mass X average brain oxygen requirement 207 g X 0.033 mL O2/g/min = 6.8 mL O2/min

  30. Assumptions for Calculation of Predicted Blood Flow and Oxygen Delivery to LMCA Territory 1. MCA diameter is 3 mm or 0.3 cm (cross-sectional area is 0.071 cm3) 5 2. O2 content of blood is 21 mL O2/100 g (98% saturation, Hbg at 15 g)7,8 a. MCA blood flow MCA flow velocity X MCA cross-sectional area b. O2 delivery MCA blood flow X O2 content of blood

  31. References 1. Witelson SF, Kigar DL, Harvey T. The exceptional brain of Albert Einstein, Lancet, 353:2149-53, 1999. 2. Buijs PC, Krabbe‑Hartkamp MJ, Bakker CJ, de Lange EE. Ramos LM, Breteler MM, Mali WP. Effect of age on cerebral blood flow: measurement with ungated two‑dimensional phase‑contrast MR angiography in 250 adults. Radiology. 209(3):667‑74, 1998. 3. Scheel P, Ruge C, Petruch UR, Schoning M. Color duplex measurement of cerebral blood flow volume in healthy adults. Stroke. 31(1):147‑50, 2000. 4. Ringelstein EB, Kahlscheuer B, Niggemeyer E, Otis SM. Transcranial Doppler sonography: anatomical landmarks and normal velocity values. Ultrasound in Medicine & Biology. 16(8):745‑61, 1990. 4. Serrador JM, Picot PA, Rutt BK, Shoemaker JK, Bondar RL. MRI measures of middle cerebral artery diameter in conscious humans during simulated orthostasis. Stroke. 31(7):1672‑8, 2000. 6. Bunegin L, Wahl D, Albin MS. Detection and volume estimation of embolic air in the middle cerebral artery using transcranial Doppler sonography. Stroke. 25(3):593‑600, 1994. 7. West JB. Respiratory Physiology. Williams and Wilkins, Baltimore 1975, 75. 8. Gangong WF. Review of medical physiology. Lange, Los Altos, California 1977, 494, 453. 9. Zhang Z, Zhang RL, Jiang Q, Raman SB, Cantwell L, Chopp M. A new rat model of thrombotic focal cerebral ischemia. Journal of Cerebral Blood Flow & Metabolism. 17(2):123‑35, 1997. 10. Walsh EK, Schettini A, Calculation of brain elastic parameters in-vivo. Am J Physiol. 247,1984

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