Phase angle in localized bioimpedance measurements to assess and monitor muscle injury

Abstract

Localized bioimpedance (L-BIA) measurements are an innovative method to non-invasively identify structural derangement of soft tissues, principally muscles, and fluid accumulation in response to traumatic injury. This review provides unique L-BIA data demonstrating significant relative differences between injured and contralateral non-injured regions of interest (ROI) associated with soft tissue injury. One key finding is the specific and sensitive role of reactance (Xc), measured at 50 kHz with a phase-sensitive BI instrument, to identify objective degrees of muscle injury, localized structural damage and fluid accretion, determined using magnetic resonance imaging. The predominant effect of Xc as an indicator of severity of muscle injury is highlighted in phase angle (PhA) measurements. Novel experimental models utilizing cooking-induced cell disruption, saline injection into meat specimens, and measurements of changing amounts of cells in a constant volume provide empirical evidence of the physiological correlates of series Xc as cells in water. Findings of strong associations of capacitance, computed from parallel Xc (XCP), with whole body counting of 40-potassium and resting metabolic rate support the hypothesis that parallel Xc is a biomarker of body cell mass. These observations provide a theoretical and practical basis for a significant role of Xc, and hence PhA, to identify objectively graded muscle injury and to reliably monitor progress of treatment and return of muscle function.

Prediction of body water compartments by raw bioelectrical impedance parameters in athletes: Comparison between series and parallel measurements

“…Ultimately, based on this finding, we can assume that Xc/Hs is indirectly related to the cell content in a water solution, which supports its translational value as a biomarker of cell integrity or quality. 10 On the other hand, Xc/Hp enables a differential description of cells and ICW and, perhaps, a quantification of body cell mass. 13,16,18 As mentioned before, the standard commercial BIA devices provide R and Xc assuming a series resistor and capacitor array and thus the mixture of resistors and capacitors at 50 kHz.…”

“…However, in the human body, water and cells exist in parallel, thus the equation to transform from series to parallel equivalence partially accounts for this physiological model of cells and water because of the real RC electrical circuit in the human body. 10,15 Thus, the parallel transformation of series BI measurements is a plausible hypothesis for the complex expression of cells (membranes) and fluid distributions. Congruently, at least two studies 16,19 reported the direct correlation between total body potassium from wholebody 40K counting and CAP and Xc parallel.…”

“…Alternatively, bioelectrical impedance analysis (BIA) is a safe, practical, noninvasive, and valid method to assess and monitor TBW, ICW, and ECW, 7,8 further enabling the interpretation of soft tissue hydration and membrane integrity. 9,10 Impedance (Z) is determined by BIA as an impediment to the passage of an applied alternating electrical current that is related to water and electrolytes in body fluids and tissues. 8 In practical terms, Z has two components: resistance (R) and reactance (Xc).…”

“…8,12 Raw BIA parameters obtained with an alternating current at 50 kHz measured using a tetrapolar phase-sensitive device can be physiologically analyzed as a series or parallel circuit (Figure 1) and the interpretation depends on the biophysical model employed. 10,13,14 The standard commercial BIA devices provide R and Xc assuming a series resistor and capacitor array and thus the mixture of resistors and capacitors at 50 kHz. As described by Rutkove and colleagues, 15 the parallel transformation of series measurements takes into account the real anatomical relationships between muscles.…”

Phase angle in applications of bioimpedance in health and disease

“…Traumatic muscle injury is endemic in sport. Nescolarde et al [14] describe the innovative method of localized BIA (L-BIA) and its application to identify the severity of injury and track healing until the injury has healed adequately to return to play. They carefully elucidate the technical criteria for valid L-BIA measurements including placement of electrodes on injured and contralateral non-injured region of interest to reliably determine pathology-induced perturbations in L-BIA measurements.…”