Analysis of endothelium-dependent vasodilation by use of the radial artery pulse wave obtained by applanation tonometry

Objectives: To evaluate applanation tonometry as a method to obtain arterial pulse waves suitable for pulse wave analysis of the height of the diastolic inflection point (IP), and to use this technique to study endothelium-mediated vasodilation by evaluation of the contribution of nitric oxide (NO) to the reduction in the height of the IP induced by beta2-adrenergic stimulation. Methods: The radial artery pulse waveform was recorded by applanation tonometry in young healthy subjects before and after interventions both locally in the forearm and systemically by different vasodilators and vasoconstrictors, and vasodilatation was analysed as a change in the height of the IP. The mechanism behind the reduction in the height of the IP induced by terbutaline was investigated by systemic interventions with both N(G)-monomethyl-L-arginine (L-NMMA) and noradrenaline (NA). Results: Applanation tonometry was a convenient method to obtain radial artery pulse waves of good quality. The reduction in IP was substantially more pronounced when vasodilators were given systemically than when given locally in the forearm, indicating that the effect was obtained through an effect on peripheral pulse wave reflection. Systemically given L-NMMA, but not NA, increased the IP (P<0(.)05). Systemically given L-NMMA also caused a more pronounced attenuation than NA of the reduction in IP following terbutaline injection (P<0(.)05). Conclusion: Changes in IP following beta2-adrenergic stimulation appears to be a measurement of pulse wave reflection mainly governed by NO. Applanation tonometry and pulse wave analysis is a minimally invasive method suitable to assess endothelium-dependent vasodilation in large-scale studies.