Pulmonary effects of intravenous atropine induce ventilation perfusion mismatch

Atropine is used for a number of medical conditions, predominantly for its cardiovascular effects. Cholinergic nerves that innervate pulmonary smooth muscle, glands, and vasculature may be affected by anticholinergic medications. We hypothesized that atropine causes alterations in pulmonary gas exchange. We conducted a prospective interventional study with detailed physiologic recordings in anesthetized, spontaneously breathing rats (n = 8). Animals breathing a normoxic gas mixture titrated to a partial arterial pressure of oxygen of 110-120 were exposed to an escalating dose of intravenous atropine (0.001, 0.01, 0.1, 5.0, and 20.0 mg/kg body mass). Arterial blood gas measurements were recorded every 2 min (×5) at baseline, and following each of the 5 doses of atropine. In addition, the animals regional pulmonary blood flow was measured using neutron-activated microspheres. Oxygenation decreased immediately following intravenous administration of atropine, despite a small increase in the volume of inspired air with no change in respiratory rate. Arterial blood gas analysis showed an increase in pulmonary dysfunction, characterized by a widening of the alveolar-arteriole gradient (p < 0.003 all groups except for the lowest dose of atropine). The microsphere data demonstrates an abrupt and marked heterogeneity of pulmonary blood flow following atropine treatment. In conclusion, atropine was found to decrease pulmonary gas exchange in a dose-dependent fashion in this rat model.