Intra-Parenchymal Renal Resistive Index Variation (IRRIV) Describes Renal Functional Reserve (RFR): Pilot Study in Healthy Volunteers.

Sara Samoni,Mario Meola,Alessandra Brendolan,Mitchell H Rosner,Claudio Ronco,Massimo De Cal,Silvia De Rosa,Ilaria Petrucci,Gianluca Villa,Federico Nalesso

doi:10.3389/fphys.2016.00286

Abstract

An increase of glomerular filtration rate after protein load represents renal functional reserve (RFR) and is due to afferent arteriolar vasodilation. Lack of RFR may be a risk factor for acute kidney injury (AKI), but is cumbersome to measure. We sought to develop a non-invasive, bedside method that would indirectly measure RFR. Mechanical abdominal pressure, through compression of renal vessels, decreases blood flow and activates the auto-regulatory mechanism which can be measured by a fall in renal resistive index (RRI). The study aims at elucidating the relationship between intra-parenchymal renal resistive index variation (IRRIV) during abdominal pressure and RFR. In healthy volunteers, pressure was applied by a weight on the abdomen (fluid-bag 10% of subject's body weight) while RFR was measured through a protein loading test. We recorded RRI in an interlobular artery after application of pressure using ultrasound. The maximum percentage reduction of RRI from baseline was compared in the same subject to RFR. We enrolled 14 male and 16 female subjects (mean age 38 ± 14 years). Mean creatinine clearance was 106.2 ± 16.4 ml/min/1.73 m2. RFR ranged between −1.9 and 59.7 with a mean value of 28.9 ± 13.1 ml/min/1.73 m2. Mean baseline RRI was 0.61 ± 0.05, compared to 0.49 ± 0.06 during abdominal pressure; IRRIV was 19.6 ± 6.7%, ranging between 3.1% and 29.2%. Pearson's coefficient between RFR and IRRIV was 74.16% (p < 0.001). Our data show the correlation between IRRIV and RFR. Our results can lead to the development of a “stress test” for a rapid screen of RFR to establish renal susceptibility to different exposures and the consequent risk for AKI.

Highlights

The assessment of the risk for renal injury in a given patient is a key determinant in developing strategies for renal protection
BMI, body mass index; BSA, body surface area; sCr, serum creatinine; CrCl, creatinine clearance; RRI, renal resistive index; RFR, renal functional reserve; stress RRI, the lowest RRI reached during IRRIV test; IRRIV, intra-parenchymal renal resistive index variation
On the basis of the linear regression model performed, we found that an increase of IRRIV was correlated to an increase of RFR

Summary

Introduction

The assessment of the risk for renal injury in a given patient is a key determinant in developing strategies for renal protection. Glomerular filtration rate (GFR) is the parameter most used to assess renal function, it is not able to express the capacity of the kidney to increase filtration in response to specific stimuli. Renal Functional Reserve and Haemodynamic provocative stimuli were first demonstrated in 1923 (Addis and Drury, 1923) and since these changes in kidney function in response to various stimuli have proven useful in assessing renal reserve which may be a key determinant in the risk for kidney injury after a stress exposure (either hemodynamic or nephrotoxic) (Sharma et al, 2014; Husain-Syed et al, 2015). It is generally accepted that animal protein ingestion, which represents a kidney stress test, can induce a large rise in GFR likely through modifications in renal hemodynamics (Sharma et al, 2014, 2016). GFR may be maximized in certain hyperfiltration states such as diabetic nephropathy and cannot increase further in response to a protein load (Zeier et al, 1992)

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