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© 2002 The American Society for Nutritional Sciences J. Nutr. 132:1757S-1759S, June 2002

Supplement: Waltham International Symposium

Evaluation of Multifrequency Bioelectrical Impedance Analysis for the Assessment of Extracellular and Total Body Water in Healthy Cats

Denise A. Elliott2, Robert C. Backus, Marta D. Van Loan* and Quinton R. Rogers

Department of Molecular Biosciences, School of Veterinary Medicine, University of California–Davis, Davis, CA and * U.S. Department of Agriculture Western Human Nutrition Research Center, Davis, CA

2To whom correspondence should be addressed. E-mail: denise.elliott{at}effem.com.

KEY WORDS: • multifrequency bioelectrical impedance analysis • body composition • total body water • extracellular water • bioimpedance

EXPANDED ABSTRACT

Multifrequency bioelectrical impedance analysis (MF-BIA) is a promising, noninvasive, rapid, safe, portable, reproducible, electrical method of assessing body composition that has the potential to quantify total body water (TBW), extracellular water (ECW) and intracellular water (ICW), and thereby enable prediction of the fat-free mass (FFM), fat mass (FM) and body cell mass (BCM) (1). To our knowledge, there have not been any reports evaluating the use of MF-BIA in cats. The purpose of this study was to develop the scaling constants and assess the effects of animal position, animal length measurement and electrode configuration on the volume prediction accuracy of the Hydra ECF/ICF Bioimpedance Analyzer (Model 4200; Xitron Technologies, San Diego, CA) compared to TBW estimated by deuterium water (D2O) space and ECW estimated by bromide (Br) space in healthy cats.


   MATERIALS AND METHODS
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 MATERIALS AND METHODS
RESULTS
 LITERATURE CITED
 
The experimental protocols adhered to the NIH guidelines and were approved by the Animal Use and Care Administration Advisory Committee of the University of California at Davis. Twenty adult domestic shorthair cats (5 M, 5 F, 5 MC, 5 FS) were evaluated. All cats were considered to be healthy on the basis of physical examination. The cats were weighed to the nearest 0.01 kg and body condition was scored using a five-category subjective body condition scoring system, where 1 = thin, 2 = lean, 3 = ideal body condition, 4 = heavy, 5 = obese. Morphometric measurements were obtained on the right side of the cat with the cat in a normal standing position using a flexible tape graduated in millimeters (Fig. 1). The height was recorded from the ground to the dorsal border of the scapula (a, scapula height) and the ground to the dorsal border of the pelvis (b, pelvic height). The length was determined from the external occipital protuberance to the base of the tail (c, head to tail), from the lateral canthus of the eye to the base of the tail (d, eye to tail), and from the tip of the nose to the base of the tail (e, nose to tail).



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  		FIGURE 1 Position of morphometric measurements obtained on the right side of the cat with the cat in a normal standing position, and position of intradermal electrodes sets: (a) Scapula height; (b) pelvic height; (c) head to tail; (d) eye to tail; (e) nose to tail; (f) base of the skull (external occipital protuberance) and the tail base on and perpendicular to the dorsal midline (body); (g) lateral condyle of the right humerus and the lateral aspect of the right proximal tibia at the level of the femorotibial joint (ipsilateral); (h) lateral condyle of the left humerus and the lateral aspect of the right proximal tibia at the level of the femorotibial joint (contralateral).

 
Blood samples were collected for background concentrations of deuterium and bromide. Tracer doses of D2O (0.4 g/kg BW, deuterium oxide 99.8 APE; Cambridge Isotope Laboratories, Andover, MA) and NaBr (30 mg/kg BW, NaBr, ACS reagent assay > 99%; Sigma Chemical, St. Louis, MO) were administered intravenously after food and water were withheld for 24 h. An additional venous blood sample was obtained after a 90-min equilibration period to determine the concentration of the dilutional indicators. Concentrations of D2O in condensed water were determined in duplicate using Fourier transform infrared spectroscopy (2). Bromide concentrations were assessed by high-pressure liquid chromatography (3).

Each cat was anesthetized with ketamine (1 mg/kg IV, to effect; Ketalar; Parke-Davis, Morris Plains, NJ), and diazepam (0.5 mg/kg IV, to effect; Valium; Roche Laboratories, Nutley, NJ) and positioned on a nonconductive table. Intradermal tetrapolar platinum electrodes (Grass platinum subdermal 27-gauge needle electrodes; Astro-Med, West Warwick, RI) were positioned at the external occipital protuberance on and perpendicular to the dorsal midline and the tail base on and perpendicular to the dorsal midline (body); the lateral condyle of the right humerus and the lateral aspect of the proximal tibia at the level of the femorotibial joint (ipsilateral); and the lateral condyle of the left humerus and the lateral aspect of the proximal tibia at the level of the femorotibial joint (contralateral) (Fig. 1). MF-BIA measurements were performed with a Hydra ECF/ICF Bioimpedance Analyzer connected to the corresponding intradermal electrodes while the cat was positioned in sternal recumbence. Ten measurements of resistance (R) and reactance (Xc) were obtained, and the corresponding impedance and phase angle were computed from R and Xc at 50 frequencies ranging from 5 to 1000 kHz. MF-BIA measurements were repeated with the cat positioned in left lateral recumbence, using all electrode arrays. The path lengths between each of the tetrapolar electrode configurations were recorded using a flexible tape graduated in millimeters. Six MF-BIA configurations were evaluated: sternal ipsilateral (SI), sternal contralateral (SC), sternal body (SB), left lateral ipsilateral (LLRI), left lateral contralateral (LLRC) and left lateral body (LLRB).

The generated Z- and two-spectral data for each electrode array and body position were fitted to an enhanced version of the Cole–Cole model of current conduction through heterogeneous biological tissues using iterative nonlinear curve-fitting algorithms derived for use with the Hydra Bioimpedance Spectrometer (1). The enhanced modeling program extends the original Cole–Cole model to allow for the frequency-invariant time delays caused by the speed at which electrical information is transferred through a conductor to yield the resistance of extracellular fluid (RE) and intracellular fluid (RI), respectively (1). The apparent resistivity constants of the ECW and ICW were determined by the iterative prediction of VICW/VECW for each configuration. The values for ECW and ICW were predicted from the modeled RE and RI using equations formulated from Hanai’s mixture theory, which describe the effects of nonconductive material on the apparent resistivity of the surrounding conductive fluid (1).

In addition to descriptive statistics, relationships among variables were determined by analysis of variance, general linear models procedure and least-squares linear regression techniques using standard statistical software (Statistical Analysis System; SAS Institute Inc., Cary, NC). Bland–Altman plots were constructed to display differences between the MF-BIA predicted and the D2O determined TBW, and the MF-BIA predicted and the Br determined ECW. All data were expressed as means ± SE unless otherwise noted. Any value of P < 0.05 was considered significant.


   RESULTS
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 MATERIALS AND METHODS
 RESULTS
LITERATURE CITED
 
The mean age of the 20 healthy cats was 5.51 ± 0.69 y, mean body weight was 5.28 ± 0.24 kg, and mean body condition score was 4.0 ± 0.2. The mean deuterium determined TBW of the 20 cats was 2.62 ± 0.09 L (median 2.67 L, range 1.70–3.27 L), and the mean volume of the bromide determined ECW was 1.01 ± 0.04 L (median 1.09 L, range 0.63–1.34 L). There were no significant differences between the dilution determined and the MF-BIA determined TBW or ECW.

The MF-BIA configuration that had the smallest standard error of the estimate (SEE) compared with that of the D2O determined TBW was the sternal contralateral path-length (SCP) configuration (r = 0.84, SEE = 0.26 L). The difference between the D2O determined and the MF-BIA (SCP) determined TBW was -0.0001 ± 0.06 L, and the limits of agreement were -0.50 to 0.50 L (Fig. 2). Conversely, the MF-BIA configuration that had the largest SEE compared with that of the D2O determined TBW was the left lateral body scapula height (LLRBSH) configuration (r = 0.41, SEE = 0.62 L). The difference between the D2O determined and the MF-BIA (LLRBSH) determined TBW was 0.0001 ± 0.14 L, and the limits of agreement were -1.22 to 1.22 L (Fig. 2).



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  		FIGURE 2 Representative Bland–Altman plots illustrating the narrowest and widest difference between total body water (TBW) estimated by multifrequency bioelectrical impedance analysis (BIA) and deuterium oxide (D2O) dilution plotted against the mean of the two methods. (A) Sternal contralateral path length (see Fig. 1 for diagram). (B) Left lateral body scapula height. Solid line is the mean difference (bias); dashed lines are the limits of agreement (mean difference ± 1.96 SD).

 
The MF-BIA configuration that had the smallest SEE compared with that of the bromide determined ECW was the sternal body head to tail (SBHT) configuration (r = 0.91, SEE = 0.07 L). The difference between the bromide determined and the MF-BIA (SBHT) determined ECW was 0.0001 ± 0.02 L, and the limits of agreement were -0.16 to 0.16 L (Fig. 3). Conversely, the MF-BIA configuration that had the largest SEE compared with that of the bromide determined ECW was the left lateral contralateral head to tail (LLRCHT) configuration (r = 0.74, SEE = 0.15 L). The difference between the bromide determined and the MF-BIA (LLRCHT) determined ECW was 0.0001 ± 0.03 L, and the limits of agreement were -0.30 to 0.30 L (Fig. 3).



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  		FIGURE 3 Representative Bland–Altman plots illustrating the narrowest and widest difference between extracellular water (ECW) estimated by multifrequency bioelectrical impedance analysis (BIA) and sodium bromide (Br) dilution plotted against the mean of the two methods. (A) Sternal body from head to tail. (B) Left lateral contralateral from head to tail. Solid line is the mean difference (bias); dashed lines are the limits of agreement (mean difference ± 1.96 SD).

 
This study has demonstrated that MF-BIA can be used to estimate TBW and ECW in healthy cats. The technique is safe, noninvasive, portable, simple and provides instantaneous results. It remains to be demonstrated that the predictive equations for TBW and ECW developed in these healthy adult cats will provide reliable and accurate estimates of TBW and ECW in additional populations of healthy cats. In addition, further research is needed with the MF-BIA method to determine its accuracy in healthy geriatric cats, kittens, cats during pregnancy and lactation, and in hospitalized cats.


   FOOTNOTES
 
1 Presented as part of the Waltham International Symposium: Pet Nutrition Coming of Age held in Vancouver, Canada, August 6–7, 2001. This symposium and the publication of symposium proceedings were sponsored by the Waltham Centre for Pet Nutrition. Guest editors for this supplement were James G. Morris, University of California, Davis, Ivan H. Burger, consultant to Mars UK Limited, Carl L. Keen, University of California, Davis, and D’Ann Finley, University of California, Davis. Back

3 Current address: Waltham USA, 3250 East 44th St., Vernon, CA 90058. Back

4 Abbreviations used: BCM, body cell mass; Br, bromide; D2O, deuterium oxide; ECW, extracellular water; FFM, fat-free mass; FM, fat mass; F, female; FS, female spayed; ICW, intracellular water; LLRB, left lateral body; LLRC, left lateral contralateral; LLRI, left lateral ipsilateral; M, male; MC, male castrated; MF-BIA, multifrequency bioelectrical impedance analysis; R, resistance; RE, resistance of the extracellular water; RI, resistance of the intracellular water; SB, sternal body; SC, sternal contralateral; SI, sternal ipsilateral TBW, total body water; Xc, reactance. Back


   LITERATURE CITED
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 RESULTS
 LITERATURE CITED
 

1. De Lorenzo, A., Andreoli, A., Matthie, J. R. & Withers, P. O. (1997) Predicting body cell mass with bioimpedance by using theoretical methods: a technological review. J. Appl. Physiol. 82:1542-1558.[Abstract/Free Full Text]

2. Backus, R. C., Havel, P. J., Gingerich, R. L. & Rogers, Q. R. (2000) Relationship between serum leptin immunoreactivity and body fat mass as estimated by use of a novel gas-phase Fourier transform infrared spectroscopy deuterium dilution method in cats. Am. J. Vet. Res. 61:796-801.[Medline]

3. Miller, M. E., Cosgriff, J. M. & Forbes, G. B. (1989) Bromide space determination using anion-exchange chromatography for measurement of bromide. Am. J. Clin. Nutr. 50:168-171.[Abstract/Free Full Text]




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D. A. Elliott, R. C. Backus, M. D. Van Loan, and Q. R. Rogers
Extracellular Water and Total Body Water Estimated by Multifrequency Bioelectrical Impedance Analysis in Healthy Cats: A Cross-Validation Study
J. Nutr., June 1, 2002; 132(6): 1760S - 1762.
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