Respiratory Volume Changes in the Pulmonary Blood Vessels in Relation to Artificial Relaxation Therapy

¹ The University of Western Ontario Faculty of Medicine, London, Ont.

The lung tissue has a synergic action on the pulmonary arteries and veins which are interwoven in it, and particularly on those of smaller size, whereby their volume is increased in inflation and decreased in deflation. This rhythmic volume change forms what has been called a "lung pulse," which is experienced passively by the capillary bed, and is most marked in vigorous exercise. Thus the lung, motivated by the musculature of the chest walls and diaphragm, has the effect of an accessory heart. This lung pump, when needed, should be kept working at full capacity. Sudden reduction of its action, as in runners or oarsmen, after a gruelling race, would have serious, even disastrous consequences. When resting in the ascent of a long stair or after other marked exertion one should breathe forcibly with the lungs well filled, for in this way blood is best moved across the "thoracic bridge" and congestion of the right heart and coronary anemia prevented. Dilatational action is by a direct pull of the lung stroma upon the arterial and venous walls during inspiration, which tends to increase the length and width of these vessels. The peripheral resistance in the pulmonary circulation is thus lowered by enlargement of the streambed due to outside assistance, and the right heart is aided. In the vascular volume decrease of expiration there is, following release of the stroma tension, a recoil of the elastic fibers of the vessel walls, leading to shortening and narrowing of the vessels. Histological, roentgenological and volumetric evidence is advanced in support of these conclusions. Advanced age, alveolar emphysema and other conditions decrease the efficiency of this lung pump.

Artificial relaxation of the lung, by abolishing stroma pull on the arteries and veins, diminishes the effective caliber of the pulmonary vasculature, so reducing the physiological blood flow while maintaining the nutritional flow in the bronchial vessels. There would probably develop in the collapsed lung region a relative tissue anoxemia and carbon dioxide increase, thus providing conditions inimical to the growth of the tubercle bacillus, while maintaining sufficient vitality in the tissues to insure regeneration and healing.