Bioelectrical impedance spectroscopy as a fluid management system in heart failure

Abstract

Episodes of hospitalization for heart failure patients are frequent and are often accompanied by fluid accumulations. The change of the body impedance, measured by bioimpendace spectroscopy, is an indicator of the water content. The hypothesis was that it is possible to detect edema from the impedance data. First, a finite integration technique was applied to test the feasibility and allowed a theoretical analysis of current flows through the body. Based on the results of the simulations, a clinical study was designed and conducted. The segmental impedances of 25 patients suffering from heart failure were monitored over their recompensation process. The mean age of the patients was 73.8 and their mean body mass index was 28.6. From these raw data the model parameters from the Cole model were deduced by an automatic fitting algorithm. These model data were used to classify the edema status of the patient. The baseline values of the regression lines of the extra- and intracellular resistance from the transthoracic measurement and the baseline value of the regression line of the extracellular resistance from the foot-to-foot measurement were identified as important parameters for the detection of peripheral edema. The rate of change of the imaginary impedance at the characteristic frequency and the mean intracellular resistance from the foot-to-foot measurement were identified as important parameters for the detection of pulmonary edema. To classify the data, two decision trees were considered: One should detect pulmonary edema (n(pulmonary) = 13, n(none) = 12) and the other peripheral edema (n(peripheral) = 12, n(none) = 13). Peripheral edema could be detected with a sensitivity of 100% and a specificity of 90%. The detection of pulmonary edema showed a sensitivity of 92.31% and a specificity of 100%. The leave-one-out cross-validation-error for the peripheral edema detection was 12% and 8% for the detection of pulmonary edema. This enables the application of BIS as an early warning system for cardiac decompensation with the potential to optimize patient care.

Monitoring thoracic fluid content using bioelectrical impedance spectroscopy and Cole modeling

“…The expected effect of an extracellular fluid shift into the intracellular space while the total fluid volume remains constant, is an increase in , a decrease in , and an increase in K. Furthermore, K may also increase as a result of increased due to drainage of extracellular fluid from tissue. In HF patients, K increased from 0.57 to 0.63 and in pleural effusion patients from 0.57 to 0.62 [24,26]. The pleural effusion study included a separate control group of healthy subjects with K = 0.94, which is comparable to our results.…”

“…Previous studies have used Cole modeling for BIS measurements obtained with a transthoracic electrode configuration in the context of thoracic fluid accumulation [24,26]. Only a limited number of parameters were available for comparison with our results ( and ).…”

“…During this process, fluid may also shift between the extracellular and intracellular space, through cellular membranes, due to changes in trans-membrane ion concentration. HF patients were studied while undergoing inpatient treatment with intravenous diuretics after hospital admission with pulmonary edema [26]. Because direct, non-invasive measures of thoracic fluid or excess fluid volume are typically not available in standard clinical practice, changes in body weight were used as a surrogate.…”

“…Based on the results reported by the two studies in HF and pleural drainage patients [26,24], we derived the ratio = / , which may be used as a measure of fluid distribution because the resistivity of intracellular and extracellular fluids is stable [39]. The expected effect of an extracellular fluid shift into the intracellular space while the total fluid volume remains constant, is an increase in , a decrease in , and an increase in K. Furthermore, K may also increase as a result of increased due to drainage of extracellular fluid from tissue.…”

“…Studies in HF patients with pulmonary edema, i.e. excess fluid distributed within the lungs, in the interstitium and alveoli, have shown that thoracic bioimpedance is also sensitive to fluid drained by intravenous administration of diuretics [26][27][28]. These studies have revealed that thoracic bioimpedance decreases once a large amount of fluid is drained from the thorax.…”