Describe the potential causes, and effects, of resonance and damping on an invasive arterial blood pressure trace.
For a good answer candidates were expected to mention that the arterial pressure
waveform is made up of many different sine waves (as determined by Fourier Analysis) with
each sine wave having a specific frequency. Every system has its own natural oscillatory
frequency, or resonant frequency. The pressure measuring system has a resonant frequency
at which oscillations occur, and if this is less than 40 Hz, it falls within the range of
frequencies present in the blood pressure waveform and oscillations may produce a sine
wave which is superimposed on the blood pressure wave form. The resonant frequency can
be increased by using a short, wide, stiff catheter. In respect to damping, some damping is
inherent in any system and acts to slow down the rate of change of signal between the
patient and pressure transducer. Mention of causes of damping and the optimal damping
coefficient (0.677) were expected. An under-damped system is one whereby resonance
occurs causing the signal to oscillate and overshoot (damping factor <0.7) and an overdamped is one whereby the signal takes a long time to reach equilibrium but will not
overshoot. It may not reach equilibrium in time for a true reading to be given (damping factor >1.0). Both resonance and damping can alter the measured systolic and diastolic values but the mean pressure is not affected
Moxham, I. M. "Physics of invasive blood pressure monitoring." Southern African Journal of Anaesthesia and Analgesia 9.1 (2003): 33-38.
Stoker, Mark R. "Principles of pressure transducers, resonance, damping and frequency response." Anaesthesia & intensive care medicine 5.11 (2004): 371-375.
Gilbert, Michael. "Principles of pressure transducers, resonance, damping and frequency response." Anaesthesia & Intensive Care Medicine 13.1 (2012): 1-6.
Schwid, Howard A. "Frequency response evaluation of radial artery catheter-manometer systems: sinusoidal frequency analysis versus flush method." Journal of clinical monitoring4.3 (1988): 181-185.
Gardner, Reed M. "Direct blood pressure measurement—dynamic response requirements." Anesthesiology: The Journal of the American Society of Anesthesiologists 54.3 (1981): 227-236.