Blood Pressure and Sound 2 Dept of Biomedical

Blood Pressure and Sound (2) Dept. of Biomedical Engineering 2003200449 YOUNHO HONG

IBP ( Invasive BP ) measurement diaphragm Blood vessel Pi catheter cable Po pill up with some liquid (ex. saline) strain gages Pi Po t t 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, airbubble inside a catheter.

IBP ( Invasive BP ) measurement # Equivalent Circuit Model Of Catheter-Sensor System A L (1) Resistance resistivity P 1 R P 2 viscosity

IBP ( Invasive BP ) measurement (2) Capacitance or Compliance (3) Inductance or Inertance

IBP ( Invasive BP ) measurement multi physics Electric Circuit voltage current charge Fluid Mechanics pressure flow volume

Equivalent Circuit Model of IBP catheter Pi liquid Po diaphragm cable Vi i strain gages + Vo Compliance of diaphragm damping ratio natural frequency

Equivalent Circuit Model of IBP (1) Frequency Transfer Function

Equivalent Circuit Model of IBP |H| Wn ∠H -π/2 -π w w

Equivalent Circuit Model of IBP Methods to solve 2 nd order ODE

Steady State Freq. Response |H| ∠H K -4/π 0. 5 -1. 8π f 1 f 2 f f 1 f 2

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

Transient Step Response Po balloon P bulb saline overdamping critical damping underdamping

Example (7. 1) A 5 mm-long air bubble has formed in the rigid-walled catheter to a Statham P 23 Dd sensor. The catheter is 1 m long, 6 French diameter, and filled with water at 20 ℃. Plot the frequency-response curve of the system with and without the bubble. 1. 34 1. 95 log f

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

Thank you.