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      Methods and Reproducibility of Measurement of Resistivity in the Calf Using Regional Bioimpedance Analysis

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          The usefulness of regional bioimpedance analysis (RBIA) in determining the dry weight in dialysis patients is currently being investigated. The aim of this study was to evaluate the reproducibility of measurement of resistivity in the calf. Methods: Twenty-five normal subjects and 10 patients undergoing regular hemodialysis were studied. Four electrodes inserted into a blood pressure cuff were placed on the calf. Bioimpedance was continuously measured over 3- to 5-min periods (Xitron Hydra). After a resting period of 1 min, cuff pressure was increased to above the systolic blood pressure (SBP) for a few seconds to expel excess ECF fluid and then deflated. The effect on recordings of moving the electrodes 2 cm higher and then 2 cm lower than the normal position was studied in 8 normal subjects. In a second study of reproducibility, post-dialysis measurements were made twice in 10 patients who maintained the same post-dialysis target weight throughout the study period. Results: The mean resting resistivity (ρ₀) in normal subjects was 532.6 ± 95 Ω·cm rising to 583.9 ± 99.7 Ω·cm when cuff pressure was applied (ρ<sub>p</sub>). The average values of ρ₀ and ρ<sub>p</sub> in patients post-dialysis were 489 ± 74 and 537 ± 77 respectively showing that there were no significant differences in ρ₀ and ρ<sub>p</sub> between normal subjects and patients post-dialysis. The mean values of change in resistivity when the electrodes were shifted between the lowest and highest positions on the calf were –3.66 ± 4.45 and –1.44 ± 3.82%, respectively. Repeat measurement of resistivity in patients post-dialysis varied by 2.04 ± 2.29% while post-dialysis body weight varied by 0.17 ± 0.47%. Conclusion: In this study, resistivity measurement by RBIA at the calf showed similar levels of fluid loading in patients post-dialysis as in normal subjects. This study also showed that change in electrode position resulted in a mean change in resistivity of <5% and repeated measurements showed a change in resistivity <3% while body weight changes were <0.2%. This technique appears to have an acceptable level of reproducibility for its application to the assessment of patient hydration.

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          Adjusting Dry Weight by Extracellular Volume and Body Composition in Hemodialysis Patients

          Background: At present, the determination of dry weight in patients on hemodialysis is largely made empirically by trial and error. Extracellular volume (ECV) assessment by bioimpedance analysis (BIA) is a preferable technique for determining dry weight, and it also provides useful data on body composition. Methods: We measured the ECV of 74 normal subjects and 121 stable chronic hemodialysis patients postdialysis. In addition, for the dialysis patients, we measured intracellular volume (ICV) and lean body mass (LBM) by BIA, and analyzed the ECV, blood pressure and complications of dialysis. We adjusted dry weight according to the ECV and repeated a BIA exam 4 months later to evaluate changes in body composition, blood pressure and dialysis status of these patients. Results: The ECV as a percentage of weight (ECV%) of hypertensive patients was significantly higher than that of normotensive patients (24.29 ± 3.56% vs. 21.50 ± 2.38%, p < 0.001). All patients with excessive ECV% had hypertension, but not all hypertensive patients had excessive ECV%. None of the normotensive patients had ECV excess. Some hypertensive patients with symptoms of dialysis complications still had excessive ECV%. Eight hypertensive patients with excessive ECV had decreased dry weight. ECV% (29.80 ± 2.03% vs. 27.10 ± 2.99%, p < 0.001) and blood pressure (159 ± 7 / 97 ± 4 vs. 137 ± 10 / 86 ± 8 mm Hg, p = 0.006 for systolic and p = 0.004 for diastolic) decreased. ECV was the only portion of body composition that decreased (p < 0.001) after decreasing dry weight, the other parameters remaining unchanged. Twenty symptomatic normotensive patients improved with elevation of the dry weight. The ECV (p = 0.007), ICV (p = 0.009) and LBM (p < 0.001) were significantly increased after increasing dry weight, while the ECV% (p = 0.39) and fat (p = 0.46) remained unchanged. Conclusions: (1) For hypertensive patients, ECV must be evaluated in order to adjust dry weight and correct hypertension. (2) For normotensive patients, if dialysis complications occur, dry weight should be increased until symptoms disappear or the blood pressure begins to rise.
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            Interdialytic Weight Gain and Dry Weight

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              Bioimpedance spectrometry in the determination of body water compartments: Accuracy and clinical significance


                Author and article information

                Blood Purif
                Blood Purification
                S. Karger AG
                22 January 2003
                : 21
                : 1
                : 131-136
                aRenal Research Institute and Division of Nephrology and Hypertension, Beth Israel Medical Center, New York, N.Y. and bDepartment of Nephrology, San Bortolo Hospital, Vicenza, Italy
                67855 Blood Purif 2003;21:131–136
                © 2003 S. Karger AG, Basel

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                Page count
                Figures: 4, Tables: 4, References: 26, Pages: 6
                Self URI (application/pdf):

                Cardiovascular Medicine, Nephrology

                Dialysis, Bioimpedance analysis, Resistivity, Dry weight, Body fluid


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