Estimating pulmonary congestion in elderly patients using bio-impedance technique: Correlation with clinical examination and X-ray results

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Abstract

The bio-impedance technique provides a safe, low-cost and non-invasive alternative for lung fluid level monitoring. Here we have investigated the feasibility of a novel bio-impedance system in measuring pulmonary congestion in elderly patients suffering from congestive heart failure (CHF). The system employed a parametric reconstruction algorithm to assess mean lung resistivity. Fourteen patients were studied before and following treatment to reduce lung congestion. Significant correlation was found between the changes of radiographic scores and resistivity values following treatment (R = 0.57, p < 0.04). A significant difference in resistivity values between patients having low and high congestion degrees was also demonstrated (p < 0.01). Moreover, the bio-impedance technique successfully diagnosed an improvement of congestion level in 10 out of 14 patients, while the radiographic score indicated such an improvement in only 5 out of the 14 patients. These results, along with our previous validation studies, suggest that the bio-impedance technique is a feasible bedside system for monitoring of pulmonary congested patients, thus facilitating effective treatment strategies.

Introduction

Congestive heart failure is caused by various cardiac diseases, but may also be caused, or precipitated, by other pathologies such as pneumonia, sepsis, viral infection, acute mountain sickness, over hydration, and anaphylaxis. In congestive heart failure (CHF) patients, an inadequacy of the heart to maintain blood circulation in accordance with the tissue's metabolic needs, results in congestion and edema of the lungs, as well as in other body tissues [1].

Current pulmonary congestion monitoring methods have limited applicability. The thermal dye double-indicator dilution is an invasive technique for monitoring lung fluids with an accuracy of ∼20%, which is difficult to employ as a standard monitoring routine since it incorporates the insertion of two catheters. Moreover, it underestimates congestion level in patients with intravascular pulmonary shunts, and may be inappropriate in some cases such as asymmetrical lung fluid content (unilateral pulmonary congestion) or poorly perfused lung regions [2], [3]. Non-invasive techniques include mainly imaging modalities such as X-ray chest radiography. Although widely practiced, the clinical diagnostic value of X-ray chest radiographs has been found to be inconsistent [4], [5], [6], [7], and the technique suffers from limitations due to interpretation difficulties caused by coexisting lung diseases [8]. Other imaging modalities, e.g. CT, NMR or MRI, demonstrate high accuracy of as much as ∼3%, however involve large expenses that preclude them from frequent utilization [9], [10].

In the present study, we have estimated pulmonary congestion in elderly patients using a novel bio-impedance system (CardioInspect, Israel). The system consists of an eight-electrode belt, and uses multiple current injection combinations and voltage measurements for reconstruction. Unlike tomographic bio-impedance modalities (e.g. electrical impedance tomography, EIT), which are sensitive to electrical and geometrical noise, the system utilizes a parametric inverse problem algorithm, to reconstruct only two parameters—the specific left and the right lung resistivity values. This results in a robust, stable reconstruction, and noise sensitivity is much reduced. In previous publications, we have demonstrated the system's reproducibility and capability to discriminate between healthy and congested patients [11], [12]. We have also shown that the system follows lung resistivity changes during administration of diuretics [13]. In this study we further validate the applicability of the system in diagnosing pulmonary congestion by correlating its measurements to clinical examinations and X-ray chest radiographs.

Section snippets

Study group

The study comprised of 14 patients (mean age 79 ± 10 years, n = 9 females/5 males) with clinical signs of pulmonary congestion of varying degrees, that were hospitalized in the departments of internal or geriatric medicine in Sheba Medical Center. The study was approved by a local ethics committee. Patients’ condition was diagnosed by medical history, physical findings, chest radiography, electrocardiogram and echocardiography. None of the patients had history or clinical signs of chronic pulmonary

Results

The mean lung bio-impedance measurements at the reference and post-treatment phases are summarized in Table 2. Significant differences in the mean left and right lung resistivity values (a total of 28 measurements, two per patient, that include pre- and post-treatment values), were found between patients who were clinically diagnosed by the physician as suffering from high level pulmonary congestion and those diagnosed with a low level: 838 ± 133 Ω cm (n = 10 measurements) vs. 1002 ± 164 Ω cm (n = 18

Discussion

Pulmonary congestion in congestive heart failure arises from the accumulation of excessive amount of fluids, transferred from the pulmonary capillaries to the pulmonary interstitium, or into the alveoli, due to the increased hydrostatic pressure in the capillaries. As a consequence, the lungs become less compliant, a condition that results in dyspnea, hypoxemia and tachypnea. The lack of appropriate treatment of this condition, usually by diuretic agents, will cause deterioration and severe

Conflict of interest

None.

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