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The study of the pulmonary vessels presents numerous difficulties, even in open chest experiments, because these vessels are placed between the right and the left heart. Therefore, changes of flow and pressure due to changes of right or left cardiac function are reflected by passive changes in caliber of the pulmonary vessels. The effect of drugs or nerve stimuli on the vessels of the lungs themselves is further complicated by the weakness of their musculature and by the fact that the pulmonary capillaries may be distended through either dilatation of the arterioles or contraction of the venules.In order to study changes of filling of the lung vessels, the following technique was employed:1. Right heart catheterization through a jugular vein and penetration of the catheter into the main pulmonary artery.2. Left heart catheterization through a femoral artery and penetration into the left atrium.3. Placement of a third catheter into the other femoral artery for recording peripheral pressure. 4. Opening of the chest following tracheotomy and artificial respiration. Placement of a pulmonary lobe between a photocell and a source of light. 5. Permanent distention of the lungs with a continuous jet of oxygen (or air) reaching the bifurcation of the trachea through a catheter. In later experiments, artificial respiration with air was continued throughout the experiment and the lobe under study was kept distended with a jet of nitrogen. 6. Use of one strain-gage and two electromanometers for recording pressures, and use of a chopper-amplifier connected to the photocell. 7. Use of a Sanborn Polyviso with direct-writing tracings recorded at a speed of 1 mm/sec. 8. Injection of drugs through cannulation of the right jugular vein. ACTION OF DRUGS ON THE PULMONARY VESSELSWith the above described method, the effects of 42 injections of drugs have been studied in 9 successful animal experiments. The drugs were:(a) Epinephrine in doses from 0.1 to 1 mg. (b) Nor-1-epinephrine in doses from 0.2 to 3 mg. (c) Histamin in doses from 1 to 5 mg. (d) Acetylcholine in doses from 2 to 5 mg. (e) Serotonin in doses from 2 to 15 mg.Isolated experiments have been made also with pitressin, peptone, and choledyl.

A large pulmonary artery is found in a number of different diseases and is usually revealed by roentgenology or angiocardiogram. Most of the cases presenting a large pulmonary artery have abnormal dynamics of the lesser circulation. It is important to ascertain the underlying causes of this finding in order to establish proper treatment.

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