New approaches for the evaluation of renal vascular function in diabetes

Abstract

In this issue of Diabetologia, two new approaches are described for the assessment of intra-renal blood flow in people with diabetes. The first approach used the technique of dynamic assessment of the resistance index (RI) in the renal interlobar arteries before and after administration of sublingual glyceryl trinitrate, and the second used MRI to assess total renal blood flow in relation to mean arterial pressure, thereby enabling direct measurement of overall renal RI. The results of the first study raise the possibility that dynamic evaluation of the intra-renal RI could be used as an early detector of vascular alterations in type 2 diabetes, before the onset of microalbuminuria. The results of the second study suggest that decreases in renal blood flow in people with longstanding type 1 diabetes reflect intra-renal vascular stiffening and raise the possibility that in microalbuminuric patients it may also reflect increased intraglomerular pressure. Non-invasive assessment of intra-renal blood flow has traditionally been performed using renal duplex Doppler ultrasound of the interlobar cortical arteries. The ratio of the difference between peak systolic and end diastolic velocity divided by peak systolic velocity, termed the intra-renal resistance index (RI), has provided an index of intra-renal arterial stiffness. In type 2 diabetes, intra-renal RI increases with age, blood pressure, BMI, the severity of markers of systemic atherosclerosis and left ventricular diastolic dysfunction, and decreased glomerular filtration rate (GFR) [1][2][3]. This association between increased intrarenal RI with decreased GFR remains after allowance for age, blood pressure and the degree of albuminuria [1]. Furthermore, higher baseline intra-renal RI measurements are associated with a greater subsequent decline in GFR [4]. There is also some evidence to suggest that the intra-renal RI differs depending on the underlying renal disease and is increased to a greater extent in people with diabetic renal diseases compared with non-diabetic renal diseases even after adjustment for multiple clinical variables, including creatinine clearance [5].Two new approaches have recently been described for the assessment of intra-renal blood flow in people with diabetes. The first approach used the concept of dynamic assessment of RI in the renal interlobar arteries. This method has previously been used to assess intra-renal blood changes induced by the administration of renin-angiotensin system blocking agents [6]. However, in this instance, intrarenal RI was assessed by Bruno et al. [7] before and after administration of sublingual glyceryl trinitrate. In the second