... the reliability of the system to record stationary events
Has 2 qualities: stability and uniqueness.
System will respond uniquely to any statically applied signal regardless of the way the signal is applied.
Hysteresis is an example of lack of uniqueness.
... the ability of the system to faithfully record rapidly changing events.
Affected by noise and dynamic response of the system
... describes the rapidly time varying signal that arises from various sources that are not directly related to the physiologic event being measured.
Confounding noise - noise that have a fundamental frequency equal to that of the physiological event being measured.
e.g. Swan Ganz catheter in RV
Dynamic response of a second order system (e.g. catheter transducer system) can be characterised by:
* elasticity
* mass
* friction
which are reflected in:
... the inherent frequency of any oscillating system at which the system would tend to oscillate if disturbed.
... is calculated from the ratio of the amplitude of 2 successive peaks (of oscillation)
Optimal damping: D=0.64
Overshoot is 6-7% of the original deflection
Critical damping: D=1
--> damping is such that overshoot is just avoided.
Should record accurately up to 10th harmonics
Thus, required Fn
= 15 x fundamental frequency
= (Pulse rate/4) Hz
--> Maximal frequency response and minimal amplitude distortion for up to the 10th harmonics.
Should have D=0.64
3 types:
... the (usually undesirable) effects of the recording system have on the physiologic event.
e.g. presence of cathether causing vessel reaction, or disturbance of the blood flow.
In catheter-transducer systems...
About | |
Created | 20050601 |
Reviewed | 20050602 |