Obesity-Associated Alterations in Lung Function in Mice Measured with Head-Out Plethysmography

Declines in lung function worsen quality of life and increase the risk of mortality. Obesity and non-alcoholic fatty liver disease are associated with worsened lung function. To investigate this association, we assessed lung function in lean and diet-induced obese conscious mice using our newly developed leak-free head-out plethysmography system. Obesity was associated with increased volume (P<0.0001), minute ventilation (volume per minute; P<0.0001), mid-expiratory flow (flow rate at 50% expiratory volume; P<0.0001), end-inspiratory pause (pause at end of inspiration; P<0.0001) and decreased expiratory time (P<0.0001). We next compared the response to methacholine (0, 25, 50, 100 mg/ml in PBS flow 0.2ml/30sec) measured using our head-out plethysmography system with forced oscillation technique (using the standard flexiVent system) measures taken in the same mice. Many of the measures gathered using head-out plethysmography were associated with measures collected using the forced oscillation technique. Minute ventilation was most significantly associated with maximal airway resistance, maximal airway elastance, tissue damping, and tissue elastance (r=-0.59 P<0.0001; r=-0.54 P<0.005; r=-0.48 P<0.005; r=-0.40 P<0.005 respectively). Volume, corrected for energy expenditure, was most significantly associated with maximal resistance of the conducting airways (r=-0.57 P<0.0001). Although fatty liver is associated with changes in lung function, we found neither hepatic vagotomy nor knocking down obesity-induced hepatic GABA production improved lung function in obese mice. Still, our head-out plethysmography system is ideal for assessing the response to interventions aimed at improving obesity-associated declines in lung function.