Why are resonance and damping important when measuring invasive blood pressure?

Invasive blood pressure measurement uses a cannula connected to a saline column and pressure transducers to convert an arterial pressure waveform into an electrical signal.

The resonant frequency of the measuring system needs to be outside the range of frequencies present in the blood pressure waveform to avoid resonance, which distorts the displayed pressure waveform. The fundamental frequency is the heart rate and the first 10 harmonics contribute to the pressure waveform. Therefore, the resonant frequency of the measuring system needs to be at least 10 times the fundamental frequency. Using short non-compliant tubing, the fundamental frequency of the system can be raised, and this reduces resonance.

The loss of energy to the surroundings, as a result of damping, will affect the speed at which an invasive pressure measuring system is able to respond to the changes in arterial pressure.

An over-damped system results in a blood pressure waveform that is excessively blunt and slow to return to baseline. An under-damped system shows excessive oscillations following each pressure wave. Both make interpretation of systolic and diastolic pressure inaccurate.

A critically damped arterial pressure waveform shows no oscillations before returning to baseline, but the response time will be relatively slow. For this reason, optimal damping is preferred for measuring systems. It has a damping coefficient of 0.64 and demonstrates the most rapid attainment of baseline with an acceptable level of oscillations.