The Behavior of the Arterioles and Capillaries of the Lung.

Abstract

In order to study the pulmonary circulation by direct observation and under physiological conditions, a method has been devised which permits a direct view of the vessels of the lung with the chest closed.

Under amytal anesthesia the chest wall of the cat is so prepared that only a layer of pleura remains to keep the chest wall intact. This window of the pleura is planned so that it will lie directly over the extreme edge of the right lower lobe of the lung, in the axillary line. An abdominal incision is made which allows approach to the diaphragm immediately opposite the window in the outer wall. A similar window is then prepared by dissecting the muscle fibers from the diaphram and leaving the pleural layer intact. By means of this window a beam of light is thrown through the lung at sufficient intensity to permit direct observation of the pulmonary vessels with a microscope at the outer window. By employing this method it has been possible to observe the smaller arteries and veins and the capillaries under various conditions.

In every instance the preparation was made under similar conditions, but the appearance of the lung vessels showed marked variation. In some instances 1 or 2 capillaries were open on the wall of an alveolus, while in others 6 or 8 were open and showed circulation in them.

The diameters of the capillaries also varied greatly. At times one saw a capillary of such diameter that only a single red blood cell could pass through, while on the same alveolus or on an adjoining one, a capillary of twice that diameter could be seen.

Pressure upon the abdominal aorta caused new capillaries to open up, and at times arterioles, hitherto unseen, opened.