Its Measurement and Role in Metabolic Regulation
Methods for measuring muscle blood flow have been evolving over the past 120 years (1,2). Studies of hormonal regulation of muscle flow and metabolism began with the classical work by Andres et al. (3). Numerous diabetes investigators interested in muscle metabolism in vivo have estimated the net balance of glucose and other metabolites across a skeletal muscle bed or limb from the product of the arterial-venous concentration difference and the blood flow. In this review, drawing upon early studies, we will emphasize some of the principles and limitations of various techniques for measuring flow to estimate net exchange or rates of production or consumption of metabolites. Table 1 summarizes pertinent strengths and limitations of the most commonly used methods for estimating either muscle blood flow or perfusion. From later studies, we will deal more directly with the issue of how flow is hormonally regulated and the relationship between skeletal muscle flow regulation and metabolic regulation. That discussion will extend beyond flow alone as an important regulated variable, emphasizing instead perfusion, which encompasses both the rate and distribution of blood flow in a tissue. We will highlight some of the new methodologies that have helped clarify further the linkage between the regulation of skeletal muscle perfusion and metabolic function.
Limb balance measurements identify sites of insulin action and resistance
It is appropriate to begin this discussion with the development of the forearm balance technique by investigators at Johns Hopkins in the early 1950s. These investigators put forward the hypothesis that through continuous infusion of a dye “tracer” (in this case Evans blue dye) that binds tightly and rapidly to serum proteins into the brachial artery and sampling from an ipsilateral antecubital vein, blood flow to the forearm could be quantified using simple spectrophotometric methods (3). They pointed out several advantages …