EFFECTS OF VAGAL BLOCKADE ON LUNG-MECHANICS IN NORMAL MAN

We compared the effects of inhalation of large doses (240μg) of a nonabsorbable atropine congener (Sch 1000) to those of intravenous injection of 1.25 mg atropine on airway resistance (Raw), N2 closing volume, maximal expiratory flow-volume (MEFV), pressure-volume, and maximum flow-static recoil (MFSR) curves. In addition, we determined the influence of these procedures upon esophageal elastance and on the time dependence of maximum expiratory flow (MEF) rates. Despite a decrease in esophageal elastance, intravenous (iv) atropine produced a marked decrease in lung recoil pressures, and a slight increase in lung compliance, whereas inhalation did not modify the static mechanical properties of the lung. Both procedures caused a decrease in Raw by about 50%, and a similar increase in MEF at high lung volumes, but only iv atropine increased MEF at lower lung volumes; consequently, upstream resistance was more lowered after the intravenous procedure than after inhalation, more markedly so at lower lung volumes. The intercept of MFSR plot with lung recoil axis increased after inhalation, whereas it decreased after iv atropine. Finally, iv atropine suppressed the time dependence of MEF rates, but inhalation did not. We conclude that there is resting vagal tone throughout the tracheobronchial tree, including terminal lung units, in normal man; the dilating action of aerosolized particles is confined to the large, central airways; no information, even of qualitative nature, on the compressibility of the flow-limiting airways may be deduced from analysis of MFSR plot, at least in living man; and the time dependence of MEF seems to be independent of the bronchomotor tone normally present in the central airways.