Effects of atropine on natural deflation flows and P-V curves of the isolated lung lobe.

Abstract

Static pressure-volume (P-V) curves and natural deflation flows (NDF) in isolated dog's lung lobes were obtained before and after atropine. Since elastic pressure was the driving force for the expiratory flow this preparation was devoid of the influence of compressive forces. A significant shift to the left of the P-V curve was observed after atropine. Mean increase in volume in the range from 30 to 2 cmH2O transpulmonary pressure (Ptp) was 0.6 ml/g (about 4% increase in percent of maximal lung volume MLV). NDF at the same Ptp (referred to as airway conductance) were significantly higher after atropine (mean increase 3 ml/s per g, about 0.15 l/s). Increase in lung volume after atropine was interpreted as evidence of relaxation of residual bronchomotor tone which in turn, by increasing airway diameters, may produce higher flows. When NDF were plotted against volume, differences between control and atropine were reduced. This was attributed to the observed leftward displacement of the P-V curve. The linear relationship found between NDF and volume in the range 2-8 cmH2O of Ptp (about 35-75% MLV) suggests a proportionate change in airway conductance with lung size. This could indicate that the lobes behaved homogeneously during passive deflation. This pattern was not modified by atropine.