Objective: Measurement of finger artery pressure with Finapres offers noninvasive continuous blood pressure, which, however, differs from brachial artery pressure. Generalized waveform filtering and level correction may convert the finger artery pressure waveform to a brachial waveform. An upper-arm cuff return-to-flow measurement may be used to calibrate the blood pressure on an individual basis. We tested these corrective methods as implemented in the Finometer device.
Methods: Intrabrachial artery pressure (BAP) and finger artery pressures were recorded simultaneously in 37 cardiac patients, aged 41-83 years, who underwent a cardiac catheterization procedure. Finger artery pressures were compared after waveform filtering and level correction and after an additional return-to-flow calibration. Measurements were performed in supine and sitting positions. Accuracy and precision were considered clinically acceptable if the mean and standard deviation of the return-to-flow intrabrachial artery pressure (reBAP)-BAP differences were smaller than 5 +/- 8 mmHg (Association for the Advancement of Medical Instrumentation requirements).
Results: Finger artery systolic, diastolic and mean pressures for the group differed from that of intrabrachial artery pressure by -10 +/- 13, -12 +/- 8 and -16 +/- 8 mmHg, respectively. After waveform filtering and level correction the filtered level corrected arterial pressure differed by -1 +/- 11, -0 +/- 7 and -2 +/- 7 mmHg. After individual calibration, reBAP differed by 3 +/- 8, 4 +/- 6 and 3 +/- 5 mmHg. Comparable results were found in the sitting position but only when the supine return-to-flow calibration was used.
Conclusion: Reconstruction of intrabrachial artery pressure from finger artery pressure with waveform filtering and level correction reduces the pressure differences substantially, with diastolic and mean within Association for the Advancement of Medical Instrumentation requirements. After one supine return-to-flow calibration, all pressure differences meet the requirements. Return-to-flow calibration should not be repeated in sitting position.