Determinants and functional significance of renal parenchymal volume in adults.

BACKGROUND AND OBJECTIVES: The significance of renal parenchymal volume and the factors that influence it are poorly understood. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Renal parenchymal volume (RPV) was measured on contrast-enhanced CT scans after exclusion of sinus fat and vessels in 224 healthy subjects evaluated as kidney donors and in a separate cohort of 22 severely obese individuals before and after 6 months of weight loss. GFR was measured by iohexol clearance in 76 of the transplant donors. RPV was correlated with age, GFR, and various anthropometric parameters. RESULTS: In potential transplant donors, RPV correlated with body surface area (BSA; r = 0.68) and was 7% larger in men but did not vary with age or race. Gender and body size were independent determinants of RPV. RPV correlated well with GFR (r = 0.62) and accounted for almost all of the variability in a model of GFR that included age, race, gender, and body surface area. GFR correlated more strongly with RPV than with creatinine-based equations. The same relationship between RPV and BSA was observed in obesity, and RPV decreased with weight loss. CONCLUSIONS: In healthy adults younger than 65 years, renal parenchymal volume is governed by body size and gender but not age or race and is strongly correlated with GFR. This indicates that renal parenchymal volume varies to meet metabolic demand and is closely linked to renal function.

Home blood pressure monitoring in CKD.

BACKGROUND: Blood pressure (BP) control is the mainstay of stalling the progression of cardiorenal disease, yet the performance characteristics of BPs obtained in the clinic (CBPs) by routine or standardized methods or at home (HBP) in diagnosing hypertension or assessing its control are unknown. METHODS: Two hundred thirty-two patients (20% black; 4% women; mean age, 67 years; 35% with diabetes) with chronic kidney disease (CKD) underwent a single 24-hour ambulatory BP (ABP) monitoring (ABPM) and concomitant recording of CBP and HBP for 1 week. Hypertension is defined as systolic BP of 130 mm Hg or greater or diastolic BP of 80 mm Hg or greater on average awake 24-hour ABPM. RESULTS: Average ABP was 135.2 +/- 15.9/75.6 +/- 11.0 mm Hg. Thirty-five percent of patients had isolated systolic hypertension; 3%, isolated diastolic hypertension; 27%, combined systolic and diastolic hypertension; and 35%, normotension or well-controlled BP. The prevalence of "white-coat effect" was estimated as 28% to 30% by means of CBPs and 24% by means of HBPs. Well-controlled BP in the clinic, but poorly controlled BP by means of ABPM, masked hypertension, was seen in 26% to 29% by means of CBPs, but only 13% with HBP monitoring. CONCLUSION: In patients with CKD, HBP is superior in reducing the misclassification of hypertension caused by the white-coat effect and masked hypertension commonly seen with CBPs. An average HBP of approximately 140/80 mm Hg appears to be the best correlate of hypertension defined by means of ABPM.

Reduced plasma pyrophosphate levels in hemodialysis patients.

Pyrophosphate (PPi) is a known inhibitor of hydroxyapatite formation and has been shown to inhibit medial vascular calcification in vitamin D-toxic rats. It was demonstrated recently that endogenous production of PPi prevents calcification of rat aorta that are cultured in high concentrations of calcium and phosphate. For determining whether PPi metabolism is altered in hemodialysis patients, plasma levels and dialytic clearance of PPi were measured in stable hemodialysis patients. Predialysis plasma [PPi] was 2.26 +/- 0.19 microM in 38 clinically stable hemodialysis patients compared with 3.26 +/- 0.17 in 36 normal subjects (P < 0.01). Approximately 30% of plasma PPi was protein bound, and this was not altered in dialysis patients. There was a weak inverse correlation with age in normal individuals but not in dialysis patients. Plasma [PPi] in dialysis patients was correlated with plasma [PO4(3-)] (r = 0.56) but not with [Ca2+], parathyroid hormone, or the dose of dialysis, and levels did not vary between interdialytic periods of 2 and 3 d. Plasma [PPi] decreased 32 +/- 5% after standard hemodialysis in 17 patients. In vitro clearance of PPi by a 2.1-m2 cellulose acetate dialyzer was 36%, and the mean PPi removal in five patients was 43 +/- 5 micromol, consistent with a similar in vivo clearance. Cleared PPi was greater than the plasma pool but less than the estimated extracellular fluid pool. Erythrocyte PPi content decreased 24 +/- 4%, indicating that intracellular PPi is removed as well. It is concluded that plasma [PPi] is reduced in hemodialysis patients and that PPi is cleared by dialysis. Plasma levels in some patients were below those that have previously been shown to prevent calcification of vessels in culture, suggesting that altered PPi metabolism could contribute to vascular calcification in hemodialysis patients.