Describe the effects of resonance and damping on an invasive arterial blood pressure tracing.
Many candidates seemed to get some of the basic concepts but few were able to expand on
It was expected that candidates could describe 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. 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.
Some damping is inherent in any system and acts to slow down the rate of change of signal
between the patient and pressure transducer. It may be caused by air bubbles or blood clots
or occlusion. This reduces the deflection of the transducer diaphragm and hence the size of
the waveform. The effect of damping on temporal response was rarely mentioned.
Accurate graphical representations of invasive pressure traces are important. Many
candidates provided poor drawings without axis, labels, reference to normal or discussion in