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**Blood Pressure and Sound (2)**

Dept. of Biomedical Engineering YOUNHO HONG

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**IBP ( Invasive BP ) measurement**

catheter Blood vessel Pi pill up with some liquid (ex.saline) diaphragm strain gages cable Po t Pi If we choose sticky and dense liquid, We can’t get the signal of Pi just like the graph. To get the signal, We should concern with distance, diameter of a catheter and liquid, air- bubble inside a catheter. t Po

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**IBP ( Invasive BP ) measurement**

# Equivalent Circuit Model Of Catheter-Sensor System (1) Resistance L A resistivity P1 P2 R viscosity

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**IBP ( Invasive BP ) measurement**

(2) Capacitance or Compliance (3) Inductance or Inertance

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**IBP ( Invasive BP ) measurement**

multi physics Electric Circuit Fluid Mechanics voltage current charge pressure flow volume

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**Equivalent Circuit Model of IBP**

Vi Compliance of diaphragm + Vo - i catheter Pi liquid diaphragm strain gages cable Po damping ratio natural frequency

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**Equivalent Circuit Model of IBP**

(1) Frequency Transfer Function

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**Equivalent Circuit Model of IBP**

w |H| Wn w -π -π/2 ∠H

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**Equivalent Circuit Model of IBP**

Methods to solve 2nd order ODE

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**Steady State Freq. Response**

-4/π -1.8π ∠H |H| f f1 f2 K 0.5

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Unit Step Response In reality, We need a unit step function for a starting point. For example, should be input signal underdamping critical damping overdamping

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**Transient Step Response**

bulb balloon saline underdamping critical damping overdamping

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Example (7.1) A 5mm-long air bubble has formed in the rigid-walled catheter to a Statham P23Dd sensor. The catheter is 1m long, 6 French diameter, and filled with water at 20 ℃. Plot the frequency-response curve of the system with and without the bubble. log f 1.34 1.95

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Example (7.2) By changing only the radius of the catheter, redesign the (no-bubble) catheter of Figure 7.9 to achieve the damping ratio ζ=1. Calculate the resulting natiral frequency fn. 1.46 log f

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Thank you.

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MEDICAL INSTRUMENTATION

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