Prediction of limb lean tissue mass from bioimpedance spectroscopy in persons with chronic spinal cord injury

Background: Bioimpedance spectroscopy (BIS) is a non-invasive, simple, and inexpensive modality that uses 256 frequencies to determine the extracellular volume impedance (ECVRe) and intracellular volume impedance (ICVRi) in the total body and regional compartments. As such, it may have utility as a surrogate measure to assess lean tissue mass (LTM). Objective: To compare the relationship between LTM from dual-energy X-ray absorptiometry (DXA) and BIS impedance values in spinal cord injury (SCI) and able-bodied (AB) control subjects using a cross-sectional research design. Methods: In 60 subjects (30 AB and 30 SCI), a total body DXA scan was used to obtain total body and leg LTM. BIS was performed to measure the impedance quotient of the ECVRe and ICVRi in the total body and limbs. Results: BIS-derived ECVRe yielded a model for LTM in paraplegia, tetraplegia, and control for the right leg (RL) (R-2 = 0.75, standard errors of estimation (SEE) = 1.02 kg, P < 0.0001; R-2 = 0.65, SEE = 0.91 kg, P = 0.0006; and R-2 = 0.54, SEE = 1.31 kg, P < 0.0001, respectively) and left leg (LL) (R-2 = 0.76, SEE = 1.06 kg, P < 0.0001; R-2 = 0.64, SEE = 0.83 kg, P = 0.0006; and R-2 = 0.54, SEE = 1.34 kg, P < 0.0001, respectively). The ICVRi was similarly predictive of LTM in paraplegia, tetraplegia, and AB controls for the RL (R-2 = 0.85, SEE = 1.31 kg, P < 0.0001; R-2 = 0.52, SEE = 0.95 kg, P = 0.003; and R-2 = 0.398, SEE = 1.46 kg, P = 0.0003, respectively) and LL (R-2 = 0.62, SEE = 1.32 kg, P = 0.0003; R-2 = 0.57, SEE = 0.91 kg, P = 0.002; and R-2 = 0.42, SEE = 1.31 kg, P = 0.0001, respectively). Conclusion: Findings demonstrate that the BIS-derived impedance quotients for ECVRe and ICVRi may be used as surrogate markers to track changes in leg LTM in persons with SCI.