Investigation of endothelial function by pulse contour analysis: a protocol for drug administration and timing of pulse contour assessment.

AIMS: Pulse contour analysis (PCA) obtained by finger photoplethysmography produces a digital volume pulse (DVP) including an inflection point in its down-slope. The reflection index (RI: ratio of the inflection point height over the maximal DVP) is responsive to vasodilatation. We aimed to optimize the drug dose and time interval for assessing endothelial function using PCA in healthy volunteers and patients with severe coronary artery disease.
METHODS: Time and dose to RI response relationships were constructed in 16 volunteers and nine patients to inhaled salbutamol (100-400 microg) or sublingual nitroglycerin (NTG; 25-400 microg).
RESULTS: For the volunteers, the time to maximum RI response to inhaled salbutamol and sublingual NTG was 10.73 +/- 0.41 and 3.66 +/- 0.21 min, respectively. A plateau in the RI response to salbutamol occurred between 5 and 15 min after inhalation and results were averaged over this period. A dose-dependent response was observed to inhaled salbutamol and sublingual NTG (P= 0.05 and P < 0.001 by repeated-measures anova, respectively) in healthy volunteers. By contrast, in patients with severe coronary artery disease inhaled salbutamol (100-400 microg) did not cause a significant change in RI.
CONCLUSIONS: In healthy volunteers the RI response to inhaled salbutamol (100-200 microg) averaged over 5-15 min after administration may be used to investigate endothelial function by PCA. The response to sublingual NTG (50 microg) should be determined at 4 min. This technique may not be suitable for the assessment of endothelial function in subjects with extensive coronary artery disease owing to the small responses observed and potential confounding effect of vasoactive medication.