Background: It has been postulated that in contrast to the radial artery (RA), brachial artery (BA) tonometry is not capable of accurately acquiring the peaked profile of intra-arterial pressure. We investigated this statement in an invasive study through comparison of the measured form factors (FF).

Materials and methods: In 16 subjects (aged 39–82y, 7 males) undergoing an elective coronary angiography, left arm BA and RA pressure waves were recorded invasively (using two high-fidelity tipcatheter pressure wires) and noninvasively (using hand-held applanation tonometry). An average curve per location/technique was constructed. FF was calculated as (mean − min)/(max − min) × 100. Invasive vs. non-invasive and BA vs. RA data were compared.

Results: Form factors and their ratios are shown in the Table as mean±SD.

In the studied cohort, applanation tonometry tended to overestimate BA FF (i.e. measuring a flattened curve) by 2.1%, yet it also tended to underestimate RA FF (i.e. measuring a more peaked profile) by 2.5%. Combined, these inaccuracies may amplify the BA/RA ratio.

Conclusions: Both RA and BA hand-held applanation tonometries introduce inaccuracies of similar magnitude but in opposite direction. These inaccuracies may lead to errors in the assessment of central pressure and brachial-to-radial amplification. Whether these inaccuracies may be improved by investigator-independent automated applanation tonometry should be investigated.