Pulmonary Circulation 



4S3 



238 (2198) 



A study of the pulmonary circulation by the transillumination 



method. 



By HARRY L. HALL (by invitation). 



[From the Department of Physiology, Western Reserve University 

 Medical School, Cleveland, Ohio.] 



Method: The lungs of a pithed cat are aerated by Meltzer's 

 method of intra-tracheal insufflation, temporarily interrupted 

 once per minute. A constantly inflated lobe is carefully elevated 

 from the open thorax and its margin fixed by two serrated clips. 

 If an area near the margin is transilluminated by a suitable optical 

 system the alveoli with their related blood vessels can be directly 

 observed and studied by means of a horizontally arranged micro- 

 scope magnifying 50 to 100 diameters. 



Owing to the wall-thickness of the intra-lobular arteries and 

 veins and their immediate branches, the circulating blood is only 

 visible in the smaller vessels, i. e., (a) in the pre-arterioles and 

 arterioles passing between the alveoli, (b) in the capillary net- 

 work formed on the surface of the alveoli and embracing the 

 air cells and (c) in the smaller venules before they merge into 

 the efferent intra-lobular veins. 



Circulation in Vessels of Different Size: In the pre-arterioles 

 the blood stream is often clearly visible. The cellular elements 

 are in densely packed mass formation, the flow is pulsating with 

 a rapid systolic forward movement and a diastolic decrease in 

 velocity, amounting occasionally to a total stoppage of the flow 

 in diastole. Expansion and relaxation of the walls is not ob- 

 served. In the arterioles the stream is no longer pulsating, the 

 individual blood cells are distinguishable and travel in ranks 

 of two to six. In the capillaries, the blood corpuscles travel in 

 single file, and in a continuous stream, but the rate of flow varies 

 in different capillaries even in the network surrounding the 

 same alveolus. In the smaller venules the stream is constant and 

 a little more rapid than in the capillaries. Individual cells are 

 distinguishable and eddies often occur at the junctions. In still 

 larger venules and the smallest veins the stream is no longer 

 constant, but a definite pulsation occurs, the onward flow tend- 

 ing to be reduced during systole and increased during diastole. 



