Evaluation of filtering methods for acquiring radial intra-artery blood pressure waveforms

The methods for evaluating noninvasive blood pressure (NIBP) monitors using an intra-arterial reference are detailed in the ANSI/AAMI/ISO 81060-2:2009 standard. In a recent study, GE Healthcare obtained invasive radial arterial blood pressure waveforms. The work presented here describes the development of filtering strategies for obtaining high fidelity intra-arterial pressure waveforms for NIBP accuracy testing using the 81060-2 standard. The natural frequency and damping factor of each subject-catheter-transducer system was computed from fast-flush transients. These parameters were used to construct filters for removing or reducing resonance artifacts. Additionally, new optimal damping factors were evaluated for designing compensation filters. Theoretical measurement systems using actual damping factors (< 0.4) and natural frequencies were found capable of generating significant systolic resonance artifacts (≥ 8 mmHg). Typical filters that may be standardly available in monitoring equipment were observed to be potentially inadequate in removing resonance artifact. Filters with particular optimal damping factors (0.6-0.7) were effective in removing resonance artifact. Clinicians need to understand that resonance artifacts potentially exist in intra-arterial waveforms and that the adjustments of monitoring systems may not be adequate. Optimal filters for obtaining intra-arterial waveforms should take into account the damping factor and natural frequency of the measuring system. In research and device evaluation studies it is necessary that optimal filtering be done to minimize the effects of under-damping.