Measuring forearm blood flow and interpreting the responses to drugs and mediators.

Venous occlusion plethysmography has been widely used to study forearm blood flow. The principle of the technique is straightforward: the rate of swelling of the forearm during occlusion of venous return is used to assess the rate of arterial inflow. Provided that perfusion pressure (arterial blood pressure) remains constant, changes in flow reflect changes in smooth muscle tone in small arteries and arterioles. Local infusion into the brachial artery allows assessment of the direct effect of drugs on vascular tone and has been used to probe the roles of endogenous mediators. The technique is at its most powerful when dose-response relationships to different drugs or mediators within a single study are being compared but can also be used for comparison of responses to drugs between healthy control subjects and patient populations. However, when responses between groups are being compared, it is important to take into account the starting conditions of baseline blood flow and pressure. This article describes venous occlusion plethysmography, discusses the presentation and analysis of data (dose of drug or concentration? forearm blood flow or resistance?), and highlights certain potential problems and limitations of the technique as a means of studying disease states.