BIOMEDICAL ENGINEERING BIOMEDICAL TRANSDUCERS (BMF)
PRESSURE MEASUREMENT Rossana E. Madrid LAMEIN DBI FACET/UNT INSIBIO/CONICET Latest update 03/04/14 Table of contents Pressure units and ranges
Pressure measurement in the cardiovascular system Direct Measurement Indirect Measurement Catheter-Transducer System Oscilometric Method Dopplet Ultrasound Methods Intraocular pressure measurement Brief history 1628 1727 1929 1956 PRESSURE UNITS Physiological Pressure Units [mmHg] or [cmH2O]
1 mmHg = 133,32 Pa = kPa 1 cmH2O = 98,0665 Pa Expressed relative to ATMOSPHERIC PRESSURE [atm] 1 atm = 101,325 kPa mbar = 0.1 kPa PHYSIOLOGICAL PRESSURE RANGES
NORMAL ANOMALOUS PRESSURE IN THE CARDIOVASCULAR SYSTEM Characteristics
PARAMETER PRIMARY SIGNAL CHARACTERISTICS PRESSURE RANGES Blood Pressure (arterial, direct) Range of f: DC to 200 Hz 20 a 300 mmHg Blood Pressure (arterial, indirect) Range of f: DC to 5 Hz Blood Pressure (venous, direct) Range of f: DC to 40 Hz -5 a 20 mmHg PRESSURE MEASUREMENT IN THE CARDIOVASCULAR SYSTEM
INTRAVASCULAR SENSOR DIRECT MEASUREMENT EXTRAVASCULAR SENSOR AUSCULTATORY METHOD OSCILOMETRIC METHOD INDIRECT MEASUREMENT Detection ofarterial wall motion DOPPLER ULTRASOUND METHOD Detection of Doppler blood flow velocity in artery DIRECT PRESSURE MEASUREMENT
Catether Pressure Transducer(Intravascular) Diaphragm Pressure Transducer (Extravascular) PRESSURE CATETHERS Needle (different diameter and shapes) Flexible plastic catethers X Rays to place the catether must be radiopaque Blood coagulation must be avoid Special material Heparine With a catheter you can... Blood pressure waves Cardiac Minute Volume
Indicator Dilution Principle Mtodo de Fick CTS Angiography Angiografa. Inyeccin de lquidos opacos CATHETER TIP PRESSURE TRANSDUCER
INTRAVASCULAR SENSOR CATHETER TIP PRESSURE TRANSDUCER Transduction Principles Semiconductor Strain gauges Capacitive Sensors Optical Methods Ej: Mikro-Tip Catheter Pressure Transducer P = -50 a 300 mmHg fresonance= 35 a 50 kHz CATHETER TIP PRESSURE TRANSDUCER
INTRAVASCULARSENSOR CATHETER TIP PRESSURE TRANSDUCER ADVANTAGES No delays Flat response up to several kHz No need of saline solution to avoid coagulation Less affected by mechanical movement of the catheter DISADVANTAGES Fragile Expensive EXTRAVASCULAR SENSOR DIAPHRAGM DISPLACEMENT TRANSDUCER
ELASTIC DIAPHRAGM Strain gauge Variable Capacitor Optical Sensor Inductive Sensor EXTRAVASCULAR SENSORES
ExternalTransducers Blood Pressure Elastic deflextion Electrical Signal Statham Transducer Standard for Blood Pressure Measurement Hg manometer DYNAMIC PROPERTIES OF DIRECT PRESSURE MEASURMENT CATHETER TRANSDUCER SYSTEM
Hydraulic Model of a pressure transducer P(t) = Applied Pressure M = Fluid Mass K = Stiffness Electrical Model Dynamic system of a 2nd order system Stiffness=Rigidez ELASTICITY MASS FRICTION CTS Distributed parameters System
But Clinical sets Second order system Rt