CC2: Equipment Flashcards
System components of pressure management systems
-X ray (single or biplane)
-Physiological recording system
=> ECG
=> Transducer
=> Pressure line
=> Catheter
=> Blood gas and O2 saturation analyser
=> CO analyser
-Contrast power injector
-Crash trolley: defibrillator, temporary pacing, intra-aortic balloon pump
Definitions of stability, sensitivity and frequency response
Stability - faithfully transmitting each of the necessary components of the wave form without distortion
Sensitivity - ratio of the amplitude of the recording signal to the amplitude of the input signal
Frequency response - the range of frequencies that something can record at enabling accurate reproduction of wave form
Describe the flushing system
-Ensures a fluid to blood connection to the transducer, preventing air entering system
-Most common system is a bag of heparinised-saline enclosed in a pressure bag
-Pump up to 300mmHg (higher than pressure of patient)
What is a transducer?
-Electronic device that that converts energy from one form (physiological) into another form (electrical)
Are transducers 100% efficient?
-No transducer is 100% efficient
-Some power is always lost in conversion (heat)
What type of transducer is used in cath lab?
-Strain Gauge
-measures small displacement and the forces that cause them
What are the 2 types of transducer?
Disposable
-Use a special arrangement of resistors (Wheatstone bridge) to detect movement of diaphragm
Non-disposable
-Use a capacitor to detect movement of diaphragm (not used in cath lab anymore)
How does pressure transducer work?
-Transducer is connected to patient with fluid filled manometer line
-Column of fluid inside manometer line moves in response to changes in blood pressure
-Fluid movement displaces tranducer’s diaphragm
-This displacement is amplified and converted to an electrical signal to display the pressure
What is the resonant frequency (natural frequency) of the system?
-The rate at which the fluid column will oscillate
What 3 properties determine the resonant frequency?
-Transducer diaphragm (how much movement is required for stated pressure - pressure volume coefficient)
-Manometer line (length, diameter, rigidity)
-Air bubbles/leaks
What position is the transducer in?
-Levelled against the mid-point of the chest (V5/V6)
Why is transducer position more important for right side?
-Systolic pressure on right side is <30mmHg
-Variation in position will have more of an impact
List 5 sources of error in pressure transducer
-Zero setting
-Calibration
-Transducer height
-Under damping
-Over damping
Explain zero setting in pressure transducer
-Even when no pressure is applied, a transducer will display a certain offset voltage
-Transducer must be exposed to atmospheric pressure and balanced
-Monitor then applies an equal and opposite voltage to the transducer, so the display reads zero
Why should Transducer be balanced every few hours?
-Zero level may drift with changes in room temp
Explain transducer height in pressure transducer
-If transducer is above heart, lower pressure recorded
-If transducer is below heart, higher pressure recorded
Explain calibration in pressure transducer
-Some transducers require adjustment of the output voltage or gauge factor
-A known pressure is applied to the transducer using a mercury manometer
-Gauge factor is adjusted until the measured pressure is equal to applied external pressure
-Gauge factor may also change with room temp so check regularly
Explain overdamping in pressure tranducer
-Results from friction as fluid moves inside tube
-Transducer oscillations are removed and decrease in frequency response
-Excess damping causes loss of detail in waveform and underestimation of pressures
Explain underdamping in pressure transducer
-If diaphragm and fluid oscillate at a frequency > the resonant frequency, sine wave oscillation can be super-imposed on to the trace and lead to distortion of up to 40% overshoot
List 6 causes of overdamping
-Blood clot/air in the line
-Contract media
-Small lumen
-Loose catheter connection
-Kink in catheter
-Soft/compliant tubing
List 3 causes of underdamping
-Tubing too stiff
-Tubing too long
-Catheter positioned in turbulent jet
What is a manometer line?
-Length of plastic tubing used to connect the sheath or catheter to the transducer
What is a catheter?
-Long hollow tube that supplies avenue for contrast media, embolising materials or therapeutic medications/instruments
What are the 2 types of catheter?
-Diagnostic
-Guide
