Evaluation of alveolacapillary membrane functions in heart failure by thoracic ultrasonography

Background: The most prominent symptom of congestive heart failure (CHF) is pulmonary congestion induced dyspnea. Pulmonary congestion can be evaluated by B-line count and pleural effusion evaluation via thoracic ultrasonography along with using methods such as chest radiography. In CHF high pulmonary capillary pressure and excessive volume results in alveolar-capillary membrane remodeling. As a result of the remodelling, gas diffusion is reduced due to the tissue growth in the interstitium. There is limited data available on the relation between B-line count (which shows interstitial fluid volume, thus, indicates pulmonary congestion) and gas diffusion. This study aims to research the effect of the increased B-line count (interstitial fluid accumulation) on the diffusion capacity of the alveolar-capillary membrane through the comparison of B-line count via thoracic ultrasonography and diffusion test (DLCO) results in patients with CHF. Methods: This prospective study evaluated 80 consecutive patients admitted with pulmonary edema and decompansated heart failure to our clinic between January 2018 and December 2018. Within the first 24 hours of admissionB-line counts of the patients were calculated with echocardiography and thoracic ultrasonography. The patients were categorized into two groups based on their B-line counts being higher or lower than 15. After sufficient diuretic treatment, patients were evaluated for dyspnea using visual analogue dyspnea scale and bedside breathing difficulty test. The patients who had tolerated the tests were then subjected to respiratory function test, DLCO and 6-minute walk test (6MWT). The results of the respiratory function tests, DLCO and echocardiography were compared between two groups. Results: Total of 77 patients wereincluded in the study and 26 had lower than 15 B-line counts (18 males, mean age 48.6±3 yrs, BMI 27.9±1.09 kg/m2) and 51 had higher than 15 B-line counts (36 males, mean age 53.73±2.02, BMI 28.2±0.55 kg/m2). Patients with higher B-line counts had lower lower RVEF (p=0.003), lower RVSm (p=0.014), higher SPAP (p<0.0001), higher TRV (p=0.001), more dilated VCI radius (p<0.0001), higher LA volume (p=0.007), more mitral regurgitation (p=0.043) and more pulmonary regurgitation (p<0.0001) compared to patients with lower B-line counts. Patients with higher B-line counts had lower GFR (p=0,016), hyponatremia (p<0,0001), lower hemoglobin (p=0,004), higher AST (p=0,007) and higher NT-pro BNP (p<0,0001) compared to patients with lower B-line counts. Respiratory function test, DLCO and 6MWT results, which was performed after receieving sufficient diuretic treatment, were as followed in patients with high than 15 B-line counts compared to lower B-line counts group: lower FVC (p=0.008), lower FEV1 (p=0.036), lower corrected DLCO (p<0.0001), lower 6MWT (p<0,0001). There was no statistically significiant difference regarding FEV1/FVC between the two groups. Right heart catheterization was performed in 16 patients (6 lower than 15 B-line, 10 higher than 15 B-line) during their stay in the hospital and higher PVR (p=0.039) was found in the higher than 15 B-line group. Conclusion: B-line counts of higher than 15 may be a predictor of decrease in diffusion capacity, restrictive pattern in respiratory function, decrease in right ventricular function and increase in pulmonary vascular resistance. As for patients with higher than 15 B-line counts had worse heart failure prognostic indicators, itself may aswell indicate negative prognosis in CHF.