The reproducibility of cardiac magnetic resonance imaging measures of aortic stiffness and their relationship to cardiac structure in prevalent haemodialysis patients.

BACKGROUND: Aortic stiffness is one of the earliest signs of cardiovascular disease (CVD) in patients with chronic kidney disease and an independent predictor of mortality. It is thought to drive left ventricular (LV) remodelling, an established biomarker for mortality. The relationship between direct and indirect measures of aortic stiffness and LV remodelling is not defined in dialysis patients, nor are the reproducibility of methods used to assess aortic stiffness using cardiac magnetic resonance (CMR) imaging. METHODS: Using 3T CMR, we report the results of (i) the interstudy, interobserver and intra-observer reproducibility of ascending aortic distensibility (AAD), descending aortic distensibility (DAD) and aortic pulse wave velocity (aPWV) in 10 haemodialysis (HD) patients and (ii) the relationship between AAD, DAD and aPWV and LV mass index (LVMi) and LV remodelling in 70 HD patients. RESULTS: Inter- and intra-observer variability of AAD, DAD and aPWV were excellent [intraclass correlation (ICC) > 0.9 for all]. Interstudy reproducibility of AAD was excellent {ICC 0.94 [95% confidence interval (CI) 0.78-0.99]}, but poor for DAD and aPWV [ICC 0.51 (-0.13-0.85) and 0.51 (-0.31-0.89)]. AAD, DAD and aPWV associated with LVMi on univariate analysis (ß = -0.244, P = 0.04; ß =-0.315, P < 0.001 and ß = 0.242, P = 0.04, respectively). Only systolic blood pressure, serum phosphate and a history of CVD remained independent determinants of LVMi on multivariable linear regression. CONCLUSIONS: AAD is the most reproducible CMR-derived measure of aortic stiffness in HD patients. CMR-derived measures of aortic stiffness were not independent determinants of LVMi in HD patients. Whether one should target blood pressure over aortic stiffness to mitigate cardiovascular risk still needs determination.

Relation of Aortic Stiffness to Left Ventricular Remodeling in Younger Adults With Type 2 Diabetes.

Individuals with type 2 diabetes have a three- to fivefold increased risk of developing heart failure. Diabetic cardiomyopathy is typified by left ventricular (LV) concentric remodeling, which is a recognized predictor of adverse cardiovascular events. Although the mechanisms underlying LV remodeling in type 2 diabetes are unclear, progressive aortic stiffening may be a key determinant. The aim of this study was to assess the relationship between aortic stiffness and LV geometry in younger adults with type 2 diabetes, using multiparametric cardiovascular MRI. We prospectively recruited 80 adults (aged 18-65 years) with type 2 diabetes and no cardiovascular disease and 20 age- and sex-matched healthy control subjects. All subjects underwent comprehensive bio-anthropometric assessment and cardiac MRI, including measurement of aortic stiffness by aortic distensibility (AD). Type 2 diabetes was associated with increased LV mass, concentric LV remodeling, and lower AD compared with control subjects. On multivariable linear regression, AD was independently associated with concentric LV remodeling in type 2 diabetes. Aortic stiffness may therefore be a potential therapeutic target to prevent the development of heart failure in type 2 diabetes.

CALIPSO Lidar Calibration at 532 nm: Version 4 Nighttime Algorithm.

Data products from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on board Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) were recently updated following the implementation of new (version 4) calibration algorithms for all of the level 1 attenuated backscatter measurements. In this work we present the motivation for and the implementation of the version 4 nighttime 532 nm parallel channel calibration. The nighttime 532 nm calibration is the most fundamental calibration of CALIOP data, since all of CALIOP's other radiometric calibration procedures - i.e., the 532 nm daytime calibration and the 1064 nm calibrations during both nighttime and daytime - depend either directly or indirectly on the 532 nm nighttime calibration. The accuracy of the 532 nm nighttime calibration has been significantly improved by raising the molecular normalization altitude from 30-34 km to 36-39 km to substantially reduce stratospheric aerosol contamination. Due to the greatly reduced molecular number density and consequently reduced signal-to-noise ratio (SNR) at these higher altitudes, the signal is now averaged over a larger number of samples using data from multiple adjacent granules. As well, an enhanced strategy for filtering the radiation-induced noise from high energy particles was adopted. Further, the meteorological model used in the earlier versions has been replaced by the improved MERRA-2 model. An aerosol scattering ratio of 1.01 ± 0.01 is now explicitly used for the calibration altitude. These modifications lead to globally revised calibration coefficients which are, on average, 2-3% lower than in previous data releases. Further, the new calibration procedure is shown to eliminate biases at high altitudes that were present in earlier versions and consequently leads to an improved representation of stratospheric aerosols. Validation results using airborne lidar measurements are also presented. Biases relative to collocated measurements acquired by the Langley Research Center (LaRC) airborne high spectral resolution lidar (HSRL) are reduced from 3.6% ± 2.2% in the version 3 data set to 1.6% ± 2.4 % in the version 4 release.