Derivation of baseline lung impedance in chronic heart failure patients: use for monitoring pulmonary congestion and predicting admissions for decompensation

Abstract

The instantaneous lung impedance (ILI) is one of the methods to assess pulmonary congestion or edema (PCE) in chronic heart failure (CHF) patients. Due to usually existing PCE in CHF patients when evaluated, baseline lung impedance (BLI) is unknown. Therefore, the relation of ILI to BLI is unknown. Our aim was to evaluate methods to calculate and appraise BLI or its derivative as reflecting the clinical status of CHF patients. ILI and New York Heart Association (NYHA) class were assessed in 222 patients (67 ± 11 years, LVEF <35 %) during 32 months of frequent outpatient clinic visits. ILI, measured in 120 asymptomatic patients at NYHA class I, with no congestion on the chest X-ray and a low-normal 6-min walk, was defined as BLI. Using measured BLI and ILI values in these patients, formulas for BLI calculation were derived based on logistic regression analysis or on the disparity between BLI and ILI values at different NYHA stages. Both models were equally reliable with <3 % difference between measured and calculated BLI (p = NS). ΔLIR = (ILI/BLI - 1) × 100 % reflected the degree of PCE, or deviation from baseline, correlated with NYHA class (r = -0.9, p < 0.001) and could serve for monitoring. Of study patients, 123 were re-hospitalized for PCE during follow up. Their ΔLIR decreased gradually from -21.7 ± 8.2 % 4 weeks pre-admission to -37.8 ± 9.3 % on admission (p < 0.001). Patients improved during hospital stay (NYHA 3.7 ± 0.5 to 2.9 ± 0.8, p < 0.0001) with ΔLIR increasing to -29.1 ± 12.0 % (p < 0.001). ΔLIR based on calculated BLI correlated with the clinical status of CHF patients and allowed the prediction of hospitalizations for PCE.

Prediction of readmissions and mortality in patients with heart failure: lessons from the IMPEDANCE‐HF extended trial

“…In the present study, we obtained a ΔLIR mean value of −30% at discharge in the ΔPC ≤ median subgroup, representing significant residual congestion, and mean ΔLIR = −20% in the ΔPC > median subgroup when ΔLIR = 0 corresponds to the normal baseline condition. Previously, we have shown that a ΔLIR value of −30% is compatible with mild to moderate alveolar oedema, while a value of −20% corresponds to mild–moderate interstitial congestion . This explains the absence of rales on lung auscultation at discharge in 52% of patients in the present study, at a time when lung impedance and the chest radiograph demonstrate interstitial congestion .…”

“…Unlike the existing impedance devices, the present device has the ability to differentiate a true signal from the lungs (positive signal) from the noise signal of surrounding chest wall, which is at least an order of magnitude larger. The sensitivity of this device to measure small accumulation of lung fluid has allowed the initiation of pre‐emptive LI‐guided treatment long before the appearance of the initial clinical signs of lung oedema and attendant deterioration . A method to determine individual normal or ‘dry’ baseline LI for each HF patient has been previously reported .…”

“…The sensitivity of this device to measure small accumulation of lung fluid has allowed the initiation of preemptive LI-guided treatment long before the appearance of the initial clinical signs of lung oedema and attendant deterioration. [10][11][12][13][14] A method to determine individual normal or 'dry' baseline LI for each HF patient has been previously reported. 14 Baseline LI for each patient was calculated upon entry to the study and was used to calculate a new parameter, the ΔLIR = [(current LI/BLI) À 1] × 100%.…”

“…While the change in the level of blood N‐terminal pro‐brain natriuretic peptide (NT‐proBNP) during hospitalization for HF was found to be a useful predictor of readmissions, using of NT‐proBNP to guide therapy is controversial . Finally, a promising method to monitor and assess lung fluid content is the lung impedance (LI) technique . The recently published randomized IMPEDANCE‐HF trial demonstrated the efficacy of LI‐guided monitoring in the treatment of HF patients and has shown that LI‐guided therapy decreased hospitalizations for HF as well as HF‐associated and all‐cause mortality.…”

“…8,9 Finally, a promising method to monitor and assess lung fluid content is the lung impedance (LI) technique. [10][11][12][13][14] The recently published randomized IMPEDANCE-HF trial demonstrated the efficacy of LI-guided monitoring in the treatment of HF patients 15 and has shown that LI-guided therapy decreased hospitalizations for HF as well as HF-associated and all-cause mortality. The trial has also confirmed that a significant proportion of HF patients were discharged with residual excess pulmonary fluid.…”