Smallest Effective Dose Research Articles

In isolated lung preparations of the dog under negative pressure ventilation and perfused with defibrinated blood1. Acetylcholine in the smallest effective doses causes a slight fall in pulmonary arterial pressure (or an increase in inflow), and in large doses a rise in pulmonary arterial pressure (or decrease in inflow). With small doses the venous outflow may show a slight decrease which is converted to an increase on raising the dose of acetylcholine.2. The effects described above are in part, if not solely, independent of bronchomotor mechanisms.3. The pulmonary arterial pressure rise or fall due to acetylcholine injections occur in nicotinised preparations, are enhanced by eserine and suppressed by atropine.4. The apparent relationship between the type of vascular response to acetylcholine and the height of the perfusion pressure which is described, is determined by factors which are peculiar to the perfusion apparatus and which govern the concentration of the ester in the blood reaching the lungs. No evidence has been obtained that the degree of distension of the pulmonary blood‐vessels determines their response to acetylcholine.5. Adrenaline in small doses may have no effect upon the pulmonary arterial pressure yet cause an increase in venous outflow.6. A method is described for measuring the blood inflow and outflow from lungs under negative pressure ventilation.The expenses of the research have been defrayed by a grant to one of us (I. de B. D.) from the Government Grant Committee of the Royal Society, to whom we express our thanks.