1. Measurement of Blood Pressure
Direct Measurement:
extravascular transducer: connected to vasculature via saline-filled catheter
intravascular transducer: placed directly inside vasculature, use semiconductor strain gauge
Indirect Measurement:
Pressure Cuff Methods
Tonometry 1

2. Extravascular Pressure Measurement
port can be used to flush system, remove air bubbles
flexible diaphragm
heparin-filled catheter
blood vessel 2

3. Catheter Model
sensor
diaphragm
distributed model 3

4. Catheter Model (cont.)
fluid flowing in a catheter experiences hydraulic inertance, resistance, and compliance.
hydraulic resistance: due to friction between sheering fluid molecules. or
: pressure difference across segment, DL (Pa = N/m2)
F: flow rate (m3/s)
average fluid velocity (m/s)
A: cross-sectional area (m2) 4

5. hydraulic resistance can be expressed in terms of catheter length:
L: total catheter length (m)
r: radius (m)
hydraulic viscosity (Pa-s)
valid for laminar flow 5

6. Hydraulic inertance is due to the mass of the liquid:
a = acceleration (m/s2)
m = mass (kg)
r = density of liquid (kg/m3) 6

7. Catheter, Sensor Compliance
compliance has to do with the elasticity of the catheter: 7