The sequence of lobar emptying in man 1

Abstract

In this study N 2 concentrations throughout expiration are measured in upper and lower lobe bronchi and the main stem bronchus. Flow from each lobe has been calculated from these values in normal man, and in patients with diffuse airway obstruction or pulmonary fibrosis. Following a breath of oxygen, lower lobe has a higher apparent ventilation to volume ratio than upper lobe in normal supine man. In patients with obstructive airway disease or diffuse lower lobe fibrosis the upper lobe is apparently better ventilated than lower lobe and shows greater differences in ventilation within the upper lobe. Well ventilated intralobar and intrasegmental units empty early and poorly ventilated units empty late in expiration. However the poorly ventilated lobe empties first and the better ventilated lobe later in the breath. This sequence of interlobar emptying minimizes the slope of the alveolar nitrogen plateau as seen at mouth level. The intralobar sequence of emptying can be altered by varying expiratory flow rates and by cardiac action.