Brachial artery tonometry and the Popeye phenomenon: explanation of anomalies in generating central from upper limb pressure waveforms.

BACKGROUND: Noninvasive applanation tonometry studies of the brachial and radial artery pressure waves show that the arterial pulse is substantially amplified between the brachial and radial sites. Brachial tonometry waveforms have also been used to calibrate carotid tonometry waves as a measure of central pressure in major clinical trials. These trials assume identity of mean and of DBP in calculation of central (carotid) SBP. None of these trials showed superiority of central over brachial pressure in predicting outcome, but all showed equivalence of SBP and pulse pressure at brachial and carotid sites!
METHOD: We tested this method by measuring pressure waves at brachial, radial and carotid sites by applanation tonometry in 100 patients, with attention to any subtle difference between brachial and radial waveforms, and with both calibrated to cuff SBP and DBP.
RESULTS: The results confirmed no proximal and strong distal amplification in the arm. However, this was accompanied by blunting of the brachial compared with radial waveform with brachial pressure 2.7 mmHg higher during most of the cardiac cycle. Form factor of the ensemble-averaged brachial wave [39.1 standard deviation (SD) 4.9%] was similar to the carotid (40.2 SD 4.1%) but different to the radial wave (34.8 SD 3.7%; P < 0.01).
CONCLUSIONS: All findings were explained by inability to applanate the brachial artery, and resulting systematic error in generating brachial waveforms. In estimation of central pressure with applanation tonometry, the radial pressure wave, which can be accurately applanated, should be used, and calibrated to the brachial cuff.