The Gomez' equations and renal hemodynamic function in kidney disease research

Abstract

Diabetic kidney disease (DKD) remains the leading cause of end-stage renal disease. A major challenge in preventing DKD is the difficulty in identifying high-risk patients at an early, pre-clinical stage. Albuminuria and eGFR as measures of renal function in DKD research and clinical practice are limited by regression of one-third of patients with microalbuminuria to normoalbuminuria and eGFR is biased and imprecise in the normal-elevated range. Moreover, existing methods that are used to assess renal function do not give detailed insight into the location of the renal hemodynamic effects of pharmacological agents at the segmental level. To gain additional information about the intrarenal circulation in-vivo in humans, mathematical equations were developed by Gomez et al in the 1950s. These equations used measurements of GFR, renal blood flow (RBF), effective renal plasma flow (ERPF), renal vascular resistance (RVR), hematocrit and serum protein to calculate afferent and efferent arteriolar resistances, glomerular hydrostatic pressure and filtration pressure. Although indirect and based on physiological assumptions, these techniques have the potential to improve researchers' ability to identify early pre-clinical changes in renal hemodynamic function in patients with a variety of conditions including DKD, thereby offering tremendous potential in mechanistic human research studies. In this review, we focus on the application of Gomez' equations and summarize the potential and limitations of this technique in DKD research. We also summarize illustrative data derived from Gomez' equations in patients with type 1 (T1D) and type 2 diabetes (T2D) and hypertension.

Keywords: Gomez' equations; diabetic kidney disease; glomerular filtration rate; renal blood flow; renal hemodynamics.

Fig. 1.

Renal hemodynamic profile vs. estimated glomerular filtration rate (GFR). While endogenous filtration markers (serum creatinine and cystatin C) can estimate GFR (eGFR), the application of Gomez' equations to measurements of insulin and para-aminohippurate (PAH) clearances can generate a complete intrarenal hemodynamic profile. RPF, renal plasma flow; R_A, afferent arteriolar resistance; R_E, efferent arteriolar resistance; π_G, glomerular oncotic pressure; FF, filtration fraction; P_GLO, intraglomerular pressure; ΔP_F, filtration pressure across glomerular capillaries.