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Variable day/night bias in 24-h non-invasive finger pressure against intrabrachial artery pressure is removed by waveform filtering and level correction

Westerhof, Berend E.a; Guelen, Iljaa; Parati, Gianfrancob; Groppelli, Antonellab; van Montfrans, Gert A.c; Wieling, Wouterc; Wesseling, Karel H.a; Bos, Willem Jan W.d

Origianl Papers: Blood pressure measurement: Original article

Background  Twenty-four-hour finger arterial pressure (FAP) recordings show a negative bias against intrabrachial artery pressure (BAP) and the bias is greater during the night, thereby overestimating the nocturnal blood pressure dip. We have available a methodology with which to reconstruct BAP from FAP by waveform filtering (transfer function) and generalized level (bias) correction that reduces the bias for short-term blood pressure records.

Objective  To investigate if this methodology also decreases the extra bias during the night, thereby yielding a better estimate of the nocturnal dip.

Methods  Twenty-four-hour FAP and BAP blood pressure recordings were simultaneously obtained in eight healthy normotensive volunteers and 14 patients with hypertension (ages 19–60 years), during standardized scheduled activities. The data were analysed off-line, applying the brachial reconstruction technique (reBAP) consisting of a waveform filter and level correction. Simultaneous beats yielded systolic, diastolic and mean pressures that were averaged per 30 min, per day, per night, per activity, over the 24-h period, and for volunteers and patients separately.

Results  Over the full 24 h, FAP systolic, diastolic and mean values for the total group differed from BAP by +1 ± 10, −8 ± 7 and −10 ± 8 mmHg (mean ± SD), respectively. Similarly, reBAPs differed by +1 ± 11, −2 ± 7 and −2 ± 7 mmHg. BAPs dipped by 20 ± 8, 13 ± 6 and 15 ± 6 mmHg, respectively, during the night. These dips were overestimated by +8, +4 and +4 mmHg by FAP, but not by reBAP: −1, +1 and +1 mmHg. The volunteer and the patient groups showed slight differences in results, but these were not statistically significant.

Conclusions  The generalized reconstruction technique to obtain near-brachial pressure from non-invasive FAP almost completely removed bias over the full 24-h day–night period and improved tracking of diurnal changes for all three blood pressure values.

aTNO TPD Biomedical Instrumentation and bthe Ospedale SanLuca, Milano, Italy, cAcademic Medical Centre, Amsterdam and dSt Antonius Hospital, Nieuwegein, The Netherlands.

Correspondence and requests for reprints to B.E. Westerhof, TNO–TPD–BMI Academic Medical Centre, Suite K2-228, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Tel: +31 (0)20 5662927; fax: +31 (0)20 6976424; email:

Received 27April 2001

Revised 10 April 2002

Accepted 7 June 2002

© 2002 Lippincott Williams & Wilkins, Inc.