Finapres tracking of systolic pressure and baroreflex sensitivity improved by waveform filtering

OBJECTIVE: Arterial pressure waveforms distort between brachial and finger arteries, causing differences mainly in systolic pressure. Distortion, reportedly, can be removed by applying a waveform filter to the finger pressure. DESIGN: We analysed the data from two studies that detected discrepancies in systolic tracking between Finapres and brachial pressures. The first set comprised waveforms of seven volunteers during incremental bicycle exercise to exhaustion and the second set comprised waveforms of eight volunteers during increasing phenylephrine infusion. METHODS: We applied the filter and compared 1 min averaged unfiltered and waveform-filtered finger and brachial pressures. RESULTS: During exercise, finger systolic pressure overestimated brachial increasingly, from 7(SD 10) mmHg at rest to 27(17) mmHg at maximal exertion. Differences were reduced by waveform filtering from 3 (SD 9)mmHg at rest to 1 (SD 15)mmHg at maximal exertion. During phenylephrine infusion finger systolic pressure overestimated brachial pressure, but the magnitude of the overestimate decreased from 14 (SD 15)mmHg at baseline to -1(SD 16)mmHg at maximal rate. After waveform filtering overestimation was an almost constant 6(SD 11)mmHg. Median baroreflex sensitivities from brachial, unfiltered and waveform-filtered finger pressure were 5.8, 7.5 and 5.3 ms/mmHg and correlation increased after filtering. The results indicate improved systolic pressure tracking after waveform filtering. CONCLUSIONS: Finger pressure distortion follows a general pattern correctable by waveform filtering. Waveform filtering allows a 'brachial' view to be obtained from Finapres data.