| Outcome Measures: |
Primary: Renal Oxygenation, Measured by blood oxygen level dependent (BOLD MRI), before and after Lasix injection;Regions of interest (ROI) analysis for BOLD MRI will be performed on a Leonardo Workstation (Siemens Medical Systems, Germany). Typically, 1 to 3 regions in each, cortex and medulla, per kidney per slice will be defined leading to a total of about 10 ROIs per region (cortex and medulla) per subject. The mean and standard deviation of these 10 measurements will be used a R2\* measurement for the region, for the subject and for that time point. Additionally, two (delta) R2\*s will be calculated as defined below: (delta) R2\*(medulla, furosemide) = R2\* (medulla, pre-furosemide) - R2\* (medulla, post-furosemide); (delta) R2\*(cortex, medulla) = Baseline R2\* (medulla) - Baseline R2\* (cortex)., 1 hour|Renal Perfusion, Measured by pseudocontinuous arterial spin labeling (pCASL) MRI; ROI analysis will be used to estimate (delta) M (difference in signal intensity between non-selective and selective inversion images). Using the same ROI, M0 will be estimated from the proton density image. T1 measurements from the same ROI will be obtained by fitting the signal intensity vs. inversion time data as described previously (104) using XLFit (ID Business Solutions Ltd., UK) or T1 maps created using MRI Mapper (Beth Israel Deaconess Medical Center, Boston). Partition coefficient will be assumed to be 0.8 ml/gm (105, 106). These values will then be used to estimate regional blood flow., 1 hour | Secondary: Glomerular Filtration Rate, Measured by Iohexol clearance; An intravenous (IV) line was placed, and participants were asked to empty their bladders. Spot plasma and urine samples were collected prior to iohexol infusion. Iohexol was administered through bolus IV injection (5 mL of 300 mg/mL; Omnipaque 300, GE Healthcare). An equilibration period of 120 min was used and blood collections for iohexol plasma disappearance were drawn at +120, +150, +180, +210, +240 min (11). Because the Brøchner-Mortensen equation underestimates high values of GFR, the Jødal-Brøchner-Mortensen equation was used to calculate the GFR (12). We report absolute GFR (mL/min) and RPF (mL/min) in the main analyses because the practice of indexing GFR and RPF for body surface underestimates hyperfiltration and hyperperfusion (14), and body surface area (BSA) calculations introduce noise into the clearance measurements., 4 hours|Effective Renal Plasma Flow, Measured by para-aminohippurate (PAH) clearance; An intravenous (IV) line was placed, and participants were asked to empty their bladders. Spot plasma and urine samples were collected prior PAH infusion. PAH (2 g/10 mL, prepared at the University of Minnesota, with a dose of \[weight in kg\]/75 × 4.2 mL; IND #140129) was given slowly over 5 min followed by a continuous infusion of 8 mL of PAH and 42 mL of normal saline at a rate of 24 mL/h for 2 h. After an equilibration period, blood was drawn at 90 and 120 min, and RPF was calculated as PAH clearance divided by the estimated extraction ratio of PAH, which varies by the level of GFR (13). We report absolute GFR (mL/min) and RPF (mL/min) in the main analyses because the practice of indexing GFR and RPF for body surface underestimates hyperfiltration and hyperperfusion (14), and body surface area (BSA) calculations introduce noise into the clearance measurements., 4 hours|Tubular Injury Markers, Measured by markers of kidney injury in plasma; Cystatin C (mg/L) was measured by immunoturbidimetric method (Kamiya Biomedical) by our Clinical Translational Research Center Core Laboratory., 4 hours
|
