Background Assessment of the degree of pulmonary congestion or edema (PCE) in chronic heart failure (CHF) patients requires the comparison of the instantaneously measured lung impedance (LI) with baseline LI (BLI) usually unknown due to existing PCE.
Aim: To evaluate methods to calculate BLI and appraise their validity in correlation with the clinical status of CHF patients.
Methods and Results: LI and NYHA class were assessed following admission for CHF in 222 patients (67±11 years, LVEF<35%) during 32 months of frequent outpatient clinic visits. LI measured in 120 patients when at NYHA stage I, with a normal chest X-ray who attained a 6-minute walk test> 430 meters was defined as BLI. Using measured BLI and LI values in these patients, 2 formulas for BLI were devised based on logistic regression analysis or on the disparity between BLI and LI values at different NYHA stages. Both models were equally reliable with <3% error between measured and calculated BLI (p=NS). The parameter DLIR=(LI/BLI-1)´100% that reflects the degree of PCE, or deviation from baseline, and correlates with NYHA class (r=-0.92, p<0.001) could serve for monitoring. Of study patients, 123 patients were re-hospitalized for PCE during follow up. Their DLIR 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 DLIR increasing to -29.1±12.0% (p<0.001).
Conclusion: DLIR based on calculated BLI by proposed models is related to the clinical status of CHF patients and allows the prediction of hospitalizations for PCE.
