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Finometer, finger pressure measurements with the possibility to reconstruct brachial pressure
Ilja Guelen1, Berend E Westerhof, Gertrude L Van Der Sar
1TNO Biomedical Instrumentation, Academic Medical Centre, Suite K2-228; Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Guelen@tpd.tno.nl
Objective:
To evaluate three methods aimed at the reconstruction of brachial pressure from non-invasive finger arterial pressure measurements as implemented in the Finometer trade mark, (FMS, Finapres Measurement Systems, Arnhem, Netherlands), the successor to the Finapres trade mark (TNO Biomedical Instrumentation, Amsterdam, Netherlands).
Methods:
Finger arterial pressure (FinAP) may differ from intra-brachial pressure (BAP). Pulse shape differences are removed by applying a generalized waveform filter. Pressure level differences are corrected by a generalized level correction equation using filtered systolic and diastolic levels and by level calibration, which uses an additional return-to-flow (RTF) systolic pressure measurement on the ipsilateral upper arm for an individual calibration of the reconstructed brachial pressure.
Validation:
These methods were validated in 37 subjects, aged 41 to 83 years after a cardiac catheterization procedure. Intra-brachial and Finometer pressures were recorded simultaneously. Finometer pressures were compared after application of waveform filtering and level correction (flcAP), and after an additional RTF calibration (reBAP).
Results:
Finger arterial systolic, diastolic and mean pressures for the group differed from BAP by -9.7 +/- 13.0, -11.6 +/- 8.0 and -16.3 +/- 7.9 mmHg (mean +/- SD) respectively. Similarly flcAP differed by -1.1 +/- 10.7, -0.2 +/- 6.8 and -1.5 +/- 6.6 mmHg and reBAP differed by 3.1 +/- 7.6, 4.0 +/- 5.6 and 2.7 +/- 4.7 mmHg.
Conclusion:
Reconstruction of BAP from FinAP as implemented in the Finometer reduces the pressure differences, with an individual RTF calibration to well within AAMI requirements.