Higher levels of cystatin C are associated with worse cognitive function in older adults with chronic kidney disease: the chronic renal insufficiency cohort cognitive study.

OBJECTIVES: To determine the association between cognition and levels of cystatin C in persons with chronic kidney disease (CKD). DESIGN: Prospective observational study. SETTING: Chronic Renal Insufficiency Cohort Cognitive Study. PARTICIPANTS: Individuals with a baseline cognitive assessment completed at the same visit as serum cystatin C measurement (N = 821; mean age 64.9, 50.6% male, 48.6% white). MEASUREMENTS: Levels of serum cystatin C were categorized into tertiles; cognitive function was assessed using six neuropsychological tests. Scores on these tests were compared across tertiles of cystatin C using linear regression and logistic regression to examine the association between cystatin C level and cognitive performance (1 standard deviation difference from the mean). RESULTS: After multivariable adjustment for age, race, education, and medical comorbidities in linear models, higher levels of cystatin C were associated with worse cognition on the modified Mini-Mental State Examination, Buschke Delayed Recall, Trail-Making Test Part (Trails) A and Part B, and Boston Naming (P < .05 for all). This association remained statistically significant for Buschke Delayed Recall (P = .01) and Trails A (P = .03) after additional adjustment for estimated glomerular filtration rate (eGFR). The highest tertile of cystatin C was associated with greater likelihood of poor performance on Trails A (odds ratio (OR) = 2.17, 95% confidence interval (CI) = 1.16-4.06), Trails B (OR = 1.89, 95% CI = 1.09-3.27), and Boston Naming (OR = 1.85, 95% CI = 1.07-3.19) than the lowest tertile after multivariate adjustment in logistic models. CONCLUSION: In individuals with CKD, higher serum cystatin C levels were associated with worse cognition and greater likelihood of poor cognitive performance on attention, executive function, and naming. Cystatin C is a marker of cognitive impairment and may be associated with cognition independent of eGFR.

Central pulse pressure in chronic kidney disease: a chronic renal insufficiency cohort ancillary study.

Central pulse pressure (PP) can be noninvasively derived using the radial artery tonometric methods. Knowledge of central pressure profiles has predicted cardiovascular morbidity and mortality in several populations of patients, particularly those with known coronary artery disease and those receiving dialysis. Few data exist characterizing central pressure profiles in patients with mild-moderate chronic kidney disease who are not on dialysis. We measured central PP cross-sectionally in 2531 participants in the Chronic Renal Insufficiency Cohort Study to determine correlates of the magnitude of central PP in the setting of chronic kidney disease. Tertiles of central PP were <36 mm Hg, 36 to 51 mm Hg, and >51 mm Hg with an overall mean (+/-SD) of 46+/-19 mm Hg. Multivariable regression identified the following independent correlates of central PP: age, sex, diabetes mellitus, heart rate (negatively correlated), glycosylated hemoglobin, hemoglobin, glucose, and parathyroid hormone parathyroid hormone concentrations. Additional adjustment for brachial mean arterial pressure and brachial PP showed associations for age, sex, diabetes mellitus, weight, and heart rate. Discrete intervals of brachial PP stratification showed substantial overlap within the associated central PP values. The large size of this unique chronic kidney disease cohort provides an ideal situation to study the role of brachial and central pressure measurements in kidney disease progression and cardiovascular disease incidence.

Detection of skin erythema in darkly pigmented skin using multispectral images.

OBJECTIVE: To develop a technique using a fixed, discrete set of wavelengths that can detect erythema in persons with darkly pigmented skin. The resulting erythema detection approach will then be incorporated into a handheld, point-of-care device that is clinically viable and affordable. DESIGN: A multispectral imaging system was used to acquire spectral images of induced erythema. Individual images were combined into a single image using different fusion algorithms. Image fusion algorithms based on published literature and using linear and nonlinear color space transformation were tested to optimize the contrast between erythematic and uninvolved skin. SETTING: A research laboratory at Georgia Institute of Technology, Atlanta, Georgia. PARTICIPANTS: Fifty-six subjects, of whom 28 had darkly pigmented skin, were recruited from a pool of students, faculty, and staff. MAIN OUTCOME MEASURES: The ability of detection algorithms to detect erythema was measured using Weber contrast. A simple threshold classifier determined accuracy, sensitivity, and specificity for each algorithm. MAIN RESULTS: Four algorithms enhanced contrast of erythema by an order of magnitude over that of a digital photograph. The accuracy of the detection algorithms ranged from 66% to 95%. Sensitivity and specificity ranged from 0% to 100%. One fusion algorithm exhibited an accuracy of more than 90% and sensitivity and specificity of more than 90%. CONCLUSION: The results indicate that erythema in different skin tones can be identified using 2 to 3 filters. Increasing accuracy and discrimination will be targeted via use of filters with narrower half-wave bandwidths, more consistent camera lighting, and improved machine vision techniques.

Assessment of an ultrasonic dermal scanner for skin thickness measurements.

The measurement precision of a 20 MHz ultrasound dermal scanning system, Episcan, manufactured by Longport Inc. was investigated for its use in the measurement of skin thickness. Results from measurements of relatively ideal homogeneous, uniformly thick plastic plates indicate that the scanner can accurately measure to depths of 8-34 mm from the surface of the transducer or approximately 18 mm from the surface of the latex probe-cover with a high level of precision, less than 1% of the mean thickness. The precision was determined to be dependent on the depth of the scan. Using the measured optimal gain of 45%, a sample rate of 0.013 micros, and an A-scan record length of 1024 points, we determined the thickness resolution of the device is on the order of 0.003 mm for 2 mm thick layers and 0.01 mm for 5 mm thick layers. We conclude that variations greater than this value for clinical dermal thickness measurements are not due to instrument precision, but must result from the limitations of analyzing the data from real tissue.