Segment-specific resistivity improves body fluid volume estimates from bioimpedance spectroscopy in hemodialysis patients

• Published in: Journal of applied physiology (1985) Vol. 100; no. 2; pp. 717 - 724
• Main Authors: Zhu, F, Kuhlmann, M. K, Kaysen, G. A, Sarkar, S, Kaitwatcharachai, C, Khilnani, R, Stevens, L, Leonard, E. F, Wang, J, Heymsfield, S, Levin, N. W
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01-02-2006; American Physiological Society
• Subjects: Algorithms; Biological and medical sciences; Body Composition; Body Fluid Compartments; Body Water; Electric Impedance; Extracellular Fluid; Female; Fluids; Fundamental and applied biological sciences. Psychology; Hemodialysis; Humans; Intracellular Fluid; Magnetic Resonance Imaging; Male; Middle Aged; Radioisotope Dilution Technique; Renal Dialysis; Reproducibility of Results; Spectrum analysis; Spectrum Analysis - methods; Human; Vertebrata; Body fluid; magnetic resonance imaging; Mammalia; whole body; bioimpedance; Body segment; Nuclear magnetic resonance imaging; Body composition; segments
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00669.2005

1 Renal Research Institute and Beth Israel Medical Center, New York; 2 Division of Nephrology, University of California, Davis, California; 3 Department of Chemical Engineering, Columbia University, and 4 Body Composition Unit, St. Lukes Hospital, New York, New York
Submitted 6 June 2005
; accepted in final form 20 October 2005
Discrepancies in body fluid estimates between segmental bioimpedance spectroscopy (SBIS) and gold-standard methods may be due to the use of a uniform value of tissue resistivity to compute extracellular fluid volume (ECV) and intracellular fluid volume (ICV). Discrepancies may also arise from the exclusion of fluid volumes of hands, feet, neck, and head from measurements due to electrode positions. The aim of this study was to define the specific resistivity of various body segments and to use those values for computation of ECV and ICV along with a correction for unmeasured fluid volumes. Twenty-nine maintenance hemodialysis patients (16 men) underwent body composition analysis including whole body MRI, whole body potassium ( 40 K) content, deuterium, and sodium bromide dilution, and segmental and wrist-to-ankle bioimpedance spectroscopy, all performed on the same day before a hemodialysis. Segment-specific resistivity was determined from segmental fat-free mass (FFM; by MRI), hydration status of FFM (by deuterium and sodium bromide), tissue resistance (by SBIS), and segment length. Segmental FFM was higher and extracellular hydration of FFM was lower in men compared with women. Segment-specific resistivity values for arm, trunk, and leg all differed from the uniform resistivity used in traditional SBIS algorithms. Estimates for whole body ECV, ICV, and total body water from SBIS using segmental instead of uniform resistivity values and after adjustment for unmeasured fluid volumes of the body did not differ significantly from gold-standard measures. The uniform tissue resistivity values used in traditional SBIS algorithms result in underestimation of ECV, ICV, and total body water. Use of segmental resistivity values combined with adjustment for body volumes that are neglected by traditional SBIS technique significantly improves estimations of body fluid volume in hemodialysis patients.
body composition; bioimpedance; whole body; segments; body fluid; magnetic resonance imaging
Address for reprint requests and other correspondence: F. Zhu, Renal Research Institute, Yorkville Dialysis Center, 1555 3rd Ave. #218, New York, NY 10128 (e-mail: fzhu{at}rriny.com )