Comparison of whole body versus thoracic bioimpedance in relation to ultrafiltration volume and systolic blood pressure during hemodialysis

Abstract

In contrast to whole-body bioimpedance, which estimates fluid status at a single point in time, thoracic bioimpedance applied by a wearable device could enable continuous measurements. However, clinical experience with thoracic bioimpedance in patients in dialysis is still limited. In order to test the reproducibility of whole-body and thoracic bioimpedance measurements and to compare their relation with hemodynamic changes during hemodialysis, these parameters were measured pre- and end-dialysis in 54 patients during two sessions. Bioimpedance signals from both devices were moderately reproducible between two dialysis sessions (intraclass correlation of delta whole-body and thoracic resistance between session 1 and 2 was .711 [.58 - .8] and .723 [.6 - .81] respectively). There was a very high - high correlation between ultrafiltration volume and relative whole-body, respectively thoracic bioimpedance. Changes in systolic blood pressure negatively correlated to both bioimpedance techniques. Whereas the relation with ultrafiltration volume and changes in resistance was stronger for whole-body bioimpedance, the relation with changes in blood pressure was at least comparable for thoracic measurements. These results suggest that thoracic bioimpedance measurements by a wearable device may serve as an interesting alternative to whole-body measurements for continuous hemodynamic monitoring during hemodialysis.

The Feasibility of Semi-Continuous and Multi-Frequency Thoracic Bioimpedance Measurements by a Wearable Device during Fluid Changes in Hemodialysis Patients

“…These results were achieved by a consistent electrode configuration and body position of the patients between both sessions. This confirms the results of our previous work, where thoracic resistance was moderately reproducible between two dialysis sessions [ 18 ]. These results strongly suggest that patients have a subject-specific start-point of thoracic bioimpedance.…”

“…The linear relationship between the resistance signal at 8 kHz and time implies a constant rate of change. Previously, it has been shown that thoracic bioimpedance signals at low frequencies correlate very strongly w i th ultrafiltration volume [ 5 , 18 ]. The removal of the ultrafiltration volume at a constant rate may explain the linear increase in the resistance signal at 8 kHz.…”

“…In these studies, repeated single-point thoracic bioimpedance measurements (i.e., pre-dialysis, every half hour or every hour during dialysis, and post-dialysis) at a single frequency (8 kHz) already showed their potential to accurately track fluid changes during hemodialysis [ 5 , 16 ]. Moreover, changes in thoracic bioimpedance were moderately related to changes in systolic blood pressure [ 18 ]. However, an extension to semi-continuous thoracic recordings (i.e., every ten minutes), both during dialysis and during the interdialytic interval, may offer a more detailed look into the longitudinal time pattern of the bioimpedance signal.…”