Reproducibility of forearm vasodilator response to intra-arterial infusion of calcitonin gene-related peptide assessed by venous occlusion plethysmography

Abstract

Aims: To assess the reproducibility of the forearm blood flow (FBF) response to intra-arterial infusion of calcitonin-gene related peptide (CGRP), measured by venous occlusion plethysmography. In addition, to compare different ways of expressing the FBF response and perform sample size calculations.

Methods: On two separate visits, CGRP (10 ng min(-1) dl(-1) forearm) was infused for 45 min into the brachial artery of six healthy subjects. Reproducibility was assessed by calculating mean difference, repeatability coefficient, within-subject coefficient of variation (WCV) and intraclass correlation coefficient.

Results: CGRP increased FBF from 2.8 +/- 0.4 and 3.2 +/- 0.7 (at baseline) to 15.4 +/- 1.4 and 15.2 +/- 1.5 ml min(-1) dl(-1) forearm (at 45 min) on visits 1 and 2, respectively (P < 0.0001 for both visits). Mean difference in FBF at 45 min between both visits was 0.3 ml min(-1) dl(-1) forearm (repeatability coefficient: 4.1 ml min(-1) dl(-1) forearm). This FBF response appeared to be more reproducible when expressed as absolute FBF in the infused arm (WCV 11%) compared with absolute FBF-ratio between both arms (WCV 37%), percentage change from baseline in FBF in the infused arm (WCV 29%) and percentage change from baseline in FBF-ratio (WCV 40%). When expressed as absolute FBF, a sample size of five (95% confidence interval: 2-12) subjects gives 90% power at a type I error probability of 0.05 to detect a 25% shift in FBF response.

Conclusions: Intra-arterial infusion of CGRP results in a forearm vasodilator response which is reproducible between days. This response is most reproducible when expressed as absolute FBF. The presented methodology provides a suitable pharmacodynamic model to assess the in vivo activity of CGRP-receptor antagonists in a small number of subjects.

Figure 1

Response of forearm blood flow (infused arm, circles; noninfused arm, squares) to intrabrachial infusion of CGRP (45 min continuous infusion, 10 ng min⁻¹ dl⁻¹ forearm) on visit 1 (closed symbols) and visit 2 (open symbols). Data (mean ± SEM) are expressed as (A) absolute FBF in the infused arm (B) FBF-ratio between the infused and noninfused arm (C) percentage change from baseline in FBF in the infused arm and (D) percentage change from baseline in FBF-ratio

Figure 2

Individual (n = 6) time-response curves (infused arm, circles; noninfused arm, squares) to intrabrachial infusion of CGRP (45 min continuous infusion, 10 ng min⁻¹ dl⁻¹ forearm) on visit 1 (closed symbols) and visit 2 (open symbols)

Figure 3

Summary responses (AUC₀₋₄₅ and ΔFBF₀₋₄₅) to intrabrachial infusion of CGRP (45 min continuous infusion, 10 ng min⁻¹ dl⁻¹ forearm) on visit 1 and visit 2. Individual responses (n = 6) are shown as thin lines with open symbols. A thick dashed line with closed circles indicates the mean response