Agreement between finger plethysmography- and brachial oscillometry-derived blood pressure measurements

Blood pressure (BP) is commonly assessed by brachial oscillometry in clinical practice, whereas in physiological studies, finger plethysmography is often employed. This study assessed the limits of agreement between BP metrics obtained from each device.

In 96 participants, we simultaneously recorded BP by brachial oscillometry (BP+; Uscom, Sydney, NSW, Australia) and finger plethysmography (Finometer MIDI, MLE1054-V; Finapres Medical Systems B.V., Amsterdam, the Netherlands). Agreement between the two devices was assessed by correlation and Bland-Altman analysis. We assessed average BP differences between the two devices using the criteria of the Association for the Advancement of Medical Instruments (AAMI), which require systolic and diastolic BP differences to be within ≤5 ± 8 (mean ± SD).

Bland-Altman analysis showed wide limits of agreement (±~17 mmHg or greater) between finger-derived brachial and oscillometric BP. Both systolic and mean BP exhibited positive proportional biases (both P<0·05). Systolic BP differed significantly between devices (7·4 ± 17·7 mmHg, P<0·001), which did not meet the AAMI criteria. No mean bias was observed for diastolic BP (-1·5 ± 8·6 mmHg, P = 0·097), and the SD of ±8·6 mmHg is potentially acceptable given the finger signal may be expected to capture biological variability in BP. Mean BP showed poor concordance (3·7 ± 10·5 mmHg, P<0·001).

These findings indicate that systolic and mean BP measurements made by brachial oscillometry do not agree with those from finger plethysmography. In contrast, diastolic BP values show acceptable agreement.