Non-invasive radiofrequency sensing for monitoring cardiac function and fluid shift: a proof-of-concept during hemodialysis
M Wosten, M Z H Kolk, E L Hogervorst, H Bakker, C A T Van Den Berg, K G F Gerritsen, L W Van Laake, B R SteensmaAbstract
Introduction
Non-invasive home-monitoring of patients with heart failure (HF) has strong potential to improve outcomes in HF patients. The novel radiofrequency sensing (RFS) technology uses a small, on-body radio antenna to detect cardiac motion and thorax impedance. RFS was developed for monitoring hemodynamic changes in HF patients to enable early detection of decompensation. To assess feasibility of detecting hemodynamic changes such as fluid shifts and changes in stroke volume (SV) using RFS, the current proof-of-concept study was conducted. For this assessment, the fluid shift during hemodialysis was used as a reverse model for HF decompensation where fluid is being removed instead of accumulating.
Methods
Synchronized RFS and ECG measurements were performed in patients during hemodialysis with ultrafiltration for fluid removal. Figure 1 shows a schematic overview of the set-up and acquired signals. Additionally, extracted ultrafiltration volume (UF), decreased intravascular blood volume (dBV), heart rate and non-invasive blood pressure were measured during the full session at a 15-minute interval. We evaluated changes in RFS-derived SV and thorax impedance during hemodialysis. SV is expected to fall with intravascular fluid removal, and thorax impedance, an indicator of pulmonary fluid status, is also expected to decrease. Additionally, intrapatient correlation was determined between the RFS-derived SV change and dBV and between impedance and UF, as both were hypothesized to decrease concurrently.
Results
In total 15 RFS measurements were performed in 5 patients. Patient characteristics included a mean age of 54 years, 20% female and a mean hemodialysis duration of 4 hours. At the end of the measurement median UF was 2.2L and median dBV was 10%. Figure 2 shows the change in SV and impedance between the start and the end of the measurement. The RFS-derived SV and the RFS thorax impedance both decreased in a large majority of the measurements (respectively 93% and 87%). Averaged over all measurements, the median of the absolute intrapatient Spearman correlation coefficient for change in SV against dBV and for impedance against UF was respectively 0.62 [IQR 0.20-0.80] and 0.74 [IQR 0.37-0.89].
Conclusion
This proof-of-concept study demonstrates that RFS was able to non-invasively detect hemodynamic changes. The moderate to strong intrapatient correlations between RFS-based parameters and UF and dBV additionally support the hypothesis for accurate assessment of hemodynamic changes.For image description, please refer to the figure legend and surrounding text.For image description, please refer to the figure legend and surrounding text.