Vector length as a proxy for the adequacy of ultrafiltration in hemodialysis.

BACKGROUND: Evaluation of dialysis adequacy has focused on parameters of solute (principally urea) clearance. Relatively little attention has been paid to the adequacy of ultrafiltration. At a given phase angle, the bioimpedance vector length reflects the degree of tissue hydration, as the vector lengthens with ultrafiltration. METHODS: We determined the relative risk of death associated with different bioimpedance vector lengths in a 3009 patient hemodialysis cohort using proportional hazards regression. RESULTS: The mean phase angle was 4.8 degrees, and the mean vector length 300 +/- 70 ohm/m (range 140 to 630 ohm/m). Vector length was much longer in women than men (mean 340 vs. 270 ohm/m) and significantly longer in African Americans and patients without diabetes. Adjusted for the effects of age, gender, race, diabetes, vintage, weight, albumin, prealbumin, creatinine, hemoglobin, ferritin, and dialysis dose, the relative risk (RR) of death was 0.75 (95% CI 0.57 to 0.88) per 100 ohm/m decrease in vector length. The effect of vector length on RR was somewhat more pronounced among men (vector length x gender interaction, P= 0.07). Considering vector length of 300 to 350 ohm/m as the referent category, the RRs of death were 1.54 (95% CI 1.08 to 2.21) and 2.83 (95% CI 1.55 to 5.14) for patients with vector length 200 to 250 and <200 ohm/m, respectively. CONCLUSION: Shorter predialysis bioimpedance vectors, indicating greater soft tissue hydration, were associated with diminished survival in hemodialysis patients. These findings validate clinical observations linking longevity to maintenance of dry body weight.

Inflammation and nutrition in renal insufficiency.

Protein-energy malnutrition (PEM) and inflammation are common in patients with chronic kidney disease (CKD) and worsen as the CKD progresses toward the end-stage renal disease (ESRD). These conditions are major predictors of poor clinical outcome in kidney failure, as reflected by a strong association between hypoalbuminemia and cardiovascular disease (CVD). It has been suggested that inflammation is the cause of both PEM and CVD and, hence, the main link among these conditions, but these hypotheses are not well established. Increased release or activation of inflammatory cytokines, such as interleukin-6 or tumor necrosis factor alpha, may suppress appetite, cause muscle proteolysis and hypoalbuminemia, and may be involved in atherogenesis. Increasing serum levels of proinflammatory cytokines caused by reduced renal function, volume overload, oxidative or carbonyl stress, decreased levels of antioxidants, increased susceptibility to infection in uremia, and the presence of comorbid conditions may lead to inflammation in CKD patients. In hemodialysis patients, the exposure to dialysis tubing and dialysis membranes, poor quality of dialysis water, back-filtration or back-diffusion of contaminants, and foreign bodies in dialysis access maybe additional causes of inflammation. Similarly, episodes of overt or latent peritonitis, peritoneal dialysis (PD) catheter and its related infections, and constant exposure to PD solution may contribute to inflammation in these patients. The degree to which PEM in dialysis patients is caused by inflammation is not clear. Because both PEM and inflammation are strongly associated with each other and can change many nutritional measures and outcome concurrently in the same direction, the terms malnutrition-inflammation complex syndrome (MICS) and/or malnutrition-inflammation-atherosclerosis (MIA) have been suggested to denote the important contribution of both of these conditions to poor clinical outcome. Maintenance dialysis patients who are underweight or who have low serum levels of cholesterol, creatinine, or homocysteine may be suffering from the MICS/MIA and its subsequent poor outcome. Consequently, obesity and hypercholesterolemia may appear protective, which is known as reverse epidemiology. Although MICS/MIA may have a significant contribution in reversing the traditional CVD risk factors in dialysis patients, it is not clear whether PEM or inflammation and their complications can be effectively managed in CKD and ESRD or whether their management improves clinical outcome.

Impedance vector distribution by sex, race, body mass index, and age in the United States: standard reference intervals as bivariate Z scores.

Bioelectrical impedance measurements were collected in the Third National Health and Nutrition Examination Survey (NHANES III), but their results have not been published. In the NHANES III population, resistance (R) and reactance (Xc) values at 50-kHz frequency were obtained with a Valhalla Scientific meter (model 1990B; San Diego, CA, USA). The RXc graph method was used to identify bivariate pattern distributions of mean vectors (95% confidence ellipses by sex, race, age, and body mass index [BMI]), and individual impedance vectors (50%, 75%, and 95% tolerance ellipses). Data from 10 222 adults (5261 men and 4961 women) formed 90 four-way classification groups, with two sexes, three races or ethnicities (non-Hispanic white, non-Hispanic black, Mexican American), five age classes (20-29, 30-39, 40-49, 50-59, and 60-69 y), and three BMI classes (19-24.9, 25-29.9, and 30-34.9 kg/m(2)). Sex, race or ethnicity, BMI and age, in decreasing order, influenced the vector distribution pattern. Mean vectors in women were significantly longer than those in men. Within each sex, the mean vector of non-Hispanic white subjects was shorter and with a smaller phase angle than that of corresponding BMIs from the two other race/ethnic populations. Tolerance ellipses were calculated from sex- and race-specific reference populations 20 to 69 y old and 19 < or = BMI < 30 kg/m(2) (8022 subjects, 4226 men and 3796 women). After transformation of impedance vector components into bivariate Z scores (standardized deviates, as differences from the mean divided by the standard deviation of the reference population), we constructed one standard, reference, RXc-score graph (50%, 75%, and 95% tolerance ellipses) that can be used with any analyzer in any population. The pattern of impedance vector distribution and reference bivariate intervals for the individual impedance vector are presented for comparative studies (free software at E-mail: apiccoli@unipd.it).

Prediction of the Third and Fourth Heart Sounds by Doppler Echocardiography.

Doppler echocardiographic variables were sought for predicting the third and fourth heart sounds, as documented by phonocardiography. Phonocardiographic recordings of gallop sounds and Doppler echocardiographic investigations of mitral inflow and pulmonary venous flow were evaluated in 85 subjects by discriminant and multiple regression analysis. Of 85 subjects 47% had a third sound and 72% a fourth sound, evaluated by phonocardiography. A correct identification of 85% subjects with, and 82% without, the third sound was possible by discriminant analysis using the ratio of peak early diastolic to peak atrial mitral flow velocity (FV), the interval from peak ECG R wave to peak early diastolic mitral FV, and the early diastolic mitral FV deceleration time. At the observed prevalence of the third heart sound (47%), the predictive positive value was 81% and the predictive negative value was 86%. A correct identification of 72% of the subjects with, and 83% without, a fourth sound was possible by discriminant analysis using the ratio of peak early diastolic to peak atrial mitral FV, the interval between the end of atrial mitral FV and the peak ECG R wave, and the duration of pulmonary venous reverse FV at atrial systole. At the observed prevalence of the fourth heart sound (72%) the predictive positive value was 92% and the predictive negative value was 54%. By multiple regression analysis, up to 50% of the amplitude of both gallop sounds was predictable by a combination of Doppler echocardiographic variables.