Isolated reduction in residual volume on body plethysmography is an early indicator of parenchymal lung disease

Abstract

Background: Isolated reduction in residual volume (RV) on body plethysmography is not less frequently observed in our population. Previous study showed that isolated reduction in RV with normal total lung capacity (TLC),diffusion lung capacity (DLCO), and normal expiratory flow rates is sometime associated with underlying lung parenchymal disease or chest wall deformity. Objective: To evaluate the clinical significance of the isolated reduction in RV with normal VC, DLCO, expiratory flow rates and the effect of BMI on it. Methods: This is a retrospective, observational study conducted at Aga Khan University Hospital Karachi, Pakistan. All adult patients who underwent body plethysmography for evaluation of dyspnea from 2012 to 2015 were enrolled. Medical records, body plethysmography and chest imaging was reviewed. Results: A total of 320 body plethysmography were reviewed. 20 (6.25%) had isolated low RV with normal TLC, DLCO and expiratory flow rates. Out of 20, eight (40%) had lung parenchymal abnormality on chest imaging. 5(25%) had diffuse parenchymal lung disease while 3 (15%) had atelectasis /mild fibrosis. No chest wall deformity was found in either case. It was observed that 17 (85%) were overweight /obese. Echocardiography was done in 12(60%) patients which was normal. Conclusion: Isolated reduction in RV may be an early indicator of lung parenchymal abnormality on body plethysmography. Population based studies on large sample size is required for further evaluation and impact of BMI on it.