Changes induced by central obesity during spontaneous ventilation in upright position. Differences in classical lung volumes between the lean and the obese patient. Expiratory reserve volume (ERV) is greatly reduced in the obese, leading to a reduction of functional residual capacity (FRC) and total lung capacity (TLC). Residual volume (RV) is unchanged. Tidal volume (TV) and inspiratory capacity (IC) are only slightly reduced. The main mechanism for this pattern is the cephalic displacement of the diaphragm by the abdominal content (thick red arrow on the “obese” side), which leads to an increase in pleural pressure (high-density red spots, as compared to scarce red spots on the “lean/gynoid obesity” side). *Intended as a pattern where adipose tissue distributes mainly around the hips and the proximal extremities, whereas abdominal fat is relatively lower. EELV, end-expiratory lung volume; IRV, inspiratory reserve volume; VC, vital capacity; WOB, work of breathing.