Assessment by bioimpedance of forearm cell mass: a new approach to calibration.
OBJECTIVE
Changes in skeletal muscle mass are involved in several important clinical disorders including sarcopenia and obesity. Unlike body fat, skeletal muscle is difficult to quantify in vivo, particularly without highly specialized equipment. The present study had a two-fold aim: to develop a regional (40)K counter for non-invasively estimating cell mass in the arm, mainly skeletal muscle cell mass, without radiation exposure; and to test the hypothesis that cell mass in the arm is highly correlated with electrical impedance after adjusting for the arm's length.


METHODS
Forearm cell mass was estimated using a rectangular lead-shielded (40)K counter with 4-NaI crystals; impedance of the arm was measured at multiple frequencies using a segmental bioimpedance analysis (BIA) system. The system's within- and between-day coefficient of variation (CV) for (40)K-derived elemental potassium averaged 1.8+/-1.3 and 5.8+/-1.2%, respectively. The corresponding BIA system's CVs were 1.0+/-0.4 and 2.1+/-1.0%, respectively.


RESULTS
Participants in the study were 15 healthy adults (eight females, seven males; age 39+/-2.8 y, BMI 22.9+/-4.5 kg/m(2)). The right arm's K (5.2+/-1.7 g) was highly correlated with length-adjusted impedance (r(2)=0.81, 0.82, and 0.83 for 5, 50 and 300 kHz, respectively; all P<0.001); multiple regression analysis showed no additional improvement by adding age or sex to the prediction models.


CONCLUSIONS
These results demonstrate the feasibility of calibrating BIA-measured electrical properties of the arm against estimates of arm cell mass, mainly of skeletal muscle, obtained by regional (40)K counting. This simple and practical approach should facilitate the development of BIA-based regional cell mass prediction formulas
Pietrobelli
A
A
Obesity Research Center, St. Luke's/Roosevelt Hospital, Columbia University, College of Physicians and Surgeons, New York 10025, USA.
Nuñez
C
C
Zingaretti
G
G
Battistini
N
N
Morini
P
P
Wang
Z M
ZM
Yasumura
S
S
Heymsfield
S B
SB
D000328:Adult; D001823:Body Composition; D001834:Body Water; D002138:Calibration; D017097:Electric Impedance; D005260:Female; D005542:Forearm / Q000033:anatomy & histology*; D006801:Humans; D007201:Indicator Dilution Techniques; D008297:Male; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000166:cytology*; D011197:Potassium Radioisotopes; D012044:Regression Analysis; D012680:Sensitivity and Specificity; D012727:Sex Characteristics
D011197:Potassium Radioisotopes