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Non-Invasive Blood Pressure Monitoring in Mice: A Cost-Effective Approach

This project aims to develop a non-invasive method for continuous blood pressure waveform monitoring in mice. Current methods involve surgical implants or expensive systems. The proposed approach utilizes a tail cuff with photosensor and an analog circuit to obtain the blood pressure waveform economically.

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Non-Invasive Blood Pressure Monitoring in Mice: A Cost-Effective Approach

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  1. Non-Invasive Blood Pressure Waveform Monitoring in Mice By Andrew McClellan Laura Miller

  2. The Need for Blood Pressure Measurements • Baseline levels • Effects of pharmacological drug administration • Exercise or Food Studies • Behavioral Response Studies • Effects of genetic alterations

  3. Need for Continuous Waveform Measurements vs. Single Measurements • Single measurements only give max and min (systolic / diastolic) • Continuous waveforms needed for frequency analysis • autonomic nervous system responses • blood pressure variability • baroreceptor function • Examining blood pressure changes over time, like during behavioral tests

  4. What Currently Exists

  5. Beat to beat BP measurements: Korotkoff Method Human: inflatable arm cuff Mouse: inflatable tail cuff http://www.geocities.com/lorijean_2002/academia/sphygmomanometer.jpg www.TSE-systems.com

  6. What Currently Exists

  7. What Currently Exists for Mice: Implantable transmitters • Catheter pressure transducers (Data Sciences International) • Continuous waveform • Require surgical implantation into carotid artery • Mice need at least 3 weeks post-surgery recovery time for stabilization of BP/HR • Transmitters are expensive and require corresponding receiver hardware and analysis software ($600/transmitter + $100/each battery exchange + $1000s in receivers and software) Mills PA, et alA new method for measurement of blood pressure, heart rate, and activity in the mouse by radiotelemetry. J Appl Physiol. 2000 May;88(5):1537-44 Mills P, et al.The design and performance of an implantable device for monitoring blood pressure, heart rate, and movement activity from conscious freely moving laboratory mice.2nd International Conference on Methods and Techniques in Behavioral Research, 1998.

  8. What Currently Exists

  9. What Currently Exists: finger cuff measurements Finapres • Non-invasive • Continuous waveform • Finger cuff Bogert LW, et al. Non-invasive pulsatile arterial pressure and stroke volume changes from the human finger. Exp. Physiol 90.4 pp 437-446. 2005

  10. What Currently Exists Problem: There are no blood pressure devices that non-invasively measure a continuous waveform in mice

  11. Our project goal Non-invasive, continuous blood pressure waveform measurement in mice

  12. Challenges From Adapting a Human Device • Size – mice are much smaller • Physiological Parameters – HR = 500-700bpm, BP = 100-250mmHg • Cuff – must work for above pressures • System response – high frequency

  13. Peňáz Method • Dynamic pulsatile unloading of the arterial walls • Volume clamp method • Pressure needed to maintain mean arterial volume equals the blood pressure waveform

  14. Plethysmographic Signal • Obtained through measuring optical impedance through blood vessel in tail • Optical impedance corresponds to volume of blood in artery

  15. How it Works • Blood volume αblood pressure • Blood volume α optical impedance (plethysmographic signal) • Use optical impedance to determine necessary pressure to maintain mean arterial volume

  16. Transduction Blood Volume = Blood Pressure (photosensor) P-signal (voltage) invert & offset (speaker) (tail cuff) Pressure Wave

  17. Tail Cuff with Photosensor www.TSE-systems.com

  18. ramp-up ramp-up Peňáz Method • Obtain plethysmographic signal • Ramp up cuff-pressure until Vp-p of plethymographic signal is max (offset) • Invert plethysmographic signal • Convert electrical signal to a pressure waveform in the tail cuff • Increase gain until p-signal fluctuations in plethysmographic signal are minimal increase gain max

  19. ramp-up ramp-up increase gain max Peňáz Method

  20. Circuit offset audio amp buffer gain

  21. Schematic plethysmographic signal Harvard plethysmogram / pressure monitor computer pressure signal analog circuit amplify offset tail cuff speaker pump

  22. Lab Setup

  23. Economic Analysis Device: • Tail Cuff with Photosensor $400 • Circuit components $10 • Speaker $5 • Power Source $100 • Air pump $50 • Pressure Sensor $100 $665 Acquisition software/hardware • Windaq $2000

  24. Plan of Attack • Use existing tail cuff • Obtain a plethysmographic signal • Build an analog circuit to amplify and offset the signal • Use speaker to transduce voltage to pressure • Obtain blood pressure waveform • Check waveform against catheter transducer

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