Airway dysfunction in obesity: Response to voluntary restoration of end expiratory lung volume

Abstract

Introduction: Abnormality in distal lung function may occur in obesity due to reduction in resting lung volume; however, airway inflammation, vascular congestion and/or concomitant intrinsic airway disease may also be present. The goal of this study is to 1) describe the phenotype of lung function in obese subjects utilizing spirometry, plethysmography and oscillometry; and 2) evaluate residual abnormality when the effect of mass loading is removed by voluntary elevation of end expiratory lung volume (EELV) to predicted FRC. Methods: 100 non-smoking obese subjects without cardio-pulmonary disease and with normal airflow on spirometry underwent impulse oscillometry (IOS) at baseline and at the elevated EELV. Results: FRC and ERV were reduced (44±22, 62±14% predicted) with normal RV/TLC (29±9%). IOS demonstrated elevated resistance at 20 Hz (R20, 4.65±1.07 cmH 2O/L/s); however, specific conductance was normal (0.14±0.04). Resistance at 5-20 Hz (R5-20, 1.86±1.11 cmH2O/L/s) and reactance at 5 Hz (X5, -2.70±1.44 cmH2O/L/s) were abnormal. During elevation of EELV, IOS abnormalities reversed to or towards normal. Residual abnormality in R5-20 was observed in some subjects despite elevation of EELV (1.16±0.8 cmH2O/L/s). R5-20 responded to bronchodilator at baseline but not during elevation of EELV. Conclusions: This study describes the phenotype of lung dysfunction in obesity as reduction in FRC with airway narrowing, distal respiratory dysfunction and bronchodilator responsiveness. When R5-20 normalized during voluntary inflation, mass loading was considered the predominant mechanism. In contrast, when residual abnormality in R 5-20 was demonstrable despite return of EELV to predicted FRC, mechanisms for airway dysfunction in addition to mass loading could be invoked.