Comparison of cardiac magnetic resonance imaging and bio-impedance spectroscopy for the assessment of fluid displacement induced by external leg compression

Abstract

Heart failure is marked by frequent hospital admissions, often as a consequence of pulmonary congestion. Current gold standard techniques for thoracic fluid measurement require invasive heamodynamic access and therefore they are not suitable for continuous monitoring. Changes in thoracic impedance (TI) may enable non-invasive early detection of congestion and prevention of unplanned hospitalizations. However, the usefulness of TI to assess thoracic fluid status is limited by inter-subject variability and by the lack of reliable normalization methods. Indicator dilution methods allow absolute fluid volume estimation; cardiac magnetic resonance (CMR) has been recently proposed to apply indicator dilution methods in a minimally-invasive manner. In this study, we aim to compare bio-impedance spectroscopy (BIS) and CMR for the assessment of thoracic fluid status, and to determine their ability to detect fluid displacement induced by a leg compression procedure in healthy volunteers. A pressure gradient was applied across each subject's legs for 5 min (100-60 mmHg, distal to proximal). Each subject underwent a continuous TI-BIS measurement during the procedure, and repeated CMR-based indicator dilution measurements on a 1.5 T scanner at baseline, during compression, and after pressure release. The Cole-Cole and the local density random walk models were used for parameter extraction from TI-BIS and indicator dilution measurements, respectively. Intra-thoracic blood volume index (ITBI) derived from CMR, and extracellular fluid resistance (R ) from TI-BIS, were considered as thoracic fluid status measures. Eight healthy volunteers were included in this study. An increase in ITBI of 45.2 ± 47.2 ml m was observed after the leg inflation (13.1 ± 15.1% w.r.t. baseline, p < 0.05), while a decrease of -0.84 ± 0.39 Ω in R (-1.7 ± 0.9% w.r.t. baseline, p< 0.05) was observed. ITBV and R normalized by body mass index were strongly inversely correlated (r = -0.93, p< 0.05). In conclusion, an acute fluid displacement to the thoracic circulation was induced in healthy volunteers. Significant changes were observed in the considered thoracic fluid measures derived from BIS and CMR. Good correlation was observed between the two measurement techniques. Further clinical studies will be necessary to prospectively evaluate the value of a combination of the two techniques for prediction of re-hospitalizations after admission for heart failure.

Monitoring thoracic fluid content using bioelectrical impedance spectroscopy and Cole modeling

“…Our results, together with previous studies, suggest that may be an adequate parameter for monitoring early to late stages thoracic fluid accumulation due to its sensitivity to vascular, interstitial, alveolar and pleural fluids. Our early findings on the correlation between and pulmonary blood volume assessed by MRI are available in [40]. Use of additional parameters e.g.…”

Noninvasive pulmonary transit time: A new parameter for general cardiac performance

“…Previous research has shown that variations in pulmonary blood volume and PTT can be accurately evaluated using MRI . Moreover, normalized left atrial transit times are correlated with invasive left ventricular pressure measurements .…”

“…8,9 Previous research has shown that variations in pulmonary blood volume and PTT can be accurately evaluated using MRI. [10][11][12][13] Moreover, normalized left atrial transit times are correlated with invasive left ventricular pressure measurements. 14,15 CEUS-derived PTT correlates well with true volumes in an in-vitro setup, 16 with PTT measured via MRI and with levels of N-terminal pro-B-type natriuretic peptide (NT-proBNP).…”