Abstract

Body Positional Effects on Bioimpedance Spectroscopy Measurements for Lymphedema Assessment of the Arm

Louise A. Koelmeyer, BAppSc (OT),1 Leigh C. Ward, BSc (Hons), FNSA, PhD,2 Catherine Dean, BAppSc (PT), MA, PhD,3 and John Boyages, MBBS, FRANZCR, PhD1. Lymphatic Research Biology, 2020.

Background: Bioimpedance spectroscopy (BIS) measurements have conventionally been performed using a device that uses gel-backed electrodes with the patient in a supine position. More recently, impedance devices that use stainless steel electrodes with the patient in a standing position have become available. The aim of this study was to assess and compare BIS measurements made in three different body positions using two different impedance devices (lead device and stand-on device) in women with and without arm lymphedema.

Methods: A cross-sectional study design was used to recruit two cohorts of women, healthy controls (n=47) and those who had been diagnosed with breast cancer (n=53) and were either at risk of (n=14) or with unilateral arm lymphedema (n=39). BIS measurements were taken three times in each position for each device.

Results: Impedance measurements were reliably made using either a lead or stand-on device with a coefficient of variation being 0.6% or lower. Absolute impedance measurements for the stand-on device were larger than the comparable lead device values due to the difference in electrode position, but were highly correlated (r=0.92, p<0.0001). Interarm impedance ratios and L-Dex scores were slightly (3.1% equivalence), but significantly different.

Conclusion: The findings support impedance measurements being made reliably using either the lead or standon device, representing supine and upright measurement positions, respectively. Data between devices were, however, not directly interchangeable.

Main findings

• The aim of this study was to assess and compare BIS measurements made in three different body positions using two different impedance devices (lead device and stand-on device) in healthy women and those at risk of or living with arm lymphedema consequent to breast cancer treatment. Specifically, we plan to evaluate the following:
  • Intrareliability measurement (technical) error across positions and between devices.
  • Repeatability of BIS measurements over time using stand-on device.
  • Differences in impedance measurements for control and lymphedema groups across three body positions and two devices.
  • Impedance ratio differences between devices.
  • Ratio and L-Dex scores comparing current clinical protocol (lying, lead device) with proposed new protocol (standing, stand-on device).
• One hundred participants were enrolled into the study and were divided into one of two groups. The healthy control group included 47 women who had no history of breast cancer or lymphedema, and the lymphedema group included 53 women who were at risk of (n=14) or had been diagnosed with unilateral arm lymphedema (n=39) following breast cancer treatment.
• Both devices were found to have excellent reliability with the CVs being 0.6% or lower. Irrespective of body position and whether in the lymphedema group or control group, both devices measured impedance with the similar precision as indicated by the similar low (<1%) coefficient of variations (CVs).
• Absolute impedance values were significantly greater (p<0.001) when measured by the stand-on device compared to the lead device irrespective of whether the participant was measured in sitting or standing. This reflects the longer interelectrode distance between the palm and the sole of the foot in the stand-on device compared to the wrist to ankle distance for the lead device.
• As expected, impedance measurements for the stand-on device were higher than the comparable lead device values due to the difference in position of electrodes, providing a longer interelectrode length (wrist to palm). These differences were consistently observed for measurements obtained in lying, sitting, or standing positions.
• Significant differences between the devices in absolute measures resistance were observed, which means, in the clinic or research setting, the devices should not be used interchangeably.
• The significant differences between the devices in absolute measures were not surprising for several reasons. First, there are differences in the anatomical position of the sense electrodes, located at the wrist and ankle for the lead device and on the palm of the hand and the sole of the foot for the standon device. This effectively increases the interelectrode length and the electrical volume being measured using the stand-on device, leading to an increase in the measured resistance. The magnitude of this effect is also likely to be increased further since the additional tissue volume of hands and feet is of relatively small cross-sectional area compared to the rest of the limb or trunk and impedance is inversely related to crosssectional area. Second, when moving from upright to supine, fluid that tends to pool in the extremities due to gravity redistributes to the trunk. Since, the trunk is of larger crosssectional area than the limbs, this has the effect of decreasing the measured resistance.
• For any individual being measured, the limits of agreement analysis show a 2SD limit, which is potentially a clinical difference of –0.1 ratio units or approximately –10L-Dex units. Since 10L-Dex units is the conventionally accepted threshold presumptive of lymphedema,25 this raises the possibility of misclassification of patients who are at risk for lymphedema. In this study population, the difference between the standard clinical measuring protocol of the two devices (lead device in lying and stand-on device in standing) could potentially lead to a misclassification of patients with clinically ascribed lymphedema in only 2% (two individuals in this cohort of 100).