A text-book of physiology for medical students and physicians . sedvolume of blood flowing through the lungs during inspiration. Theincreased capacity of the lung capillaries during the expansion ofthe lungs was shown experimentally by Heger and Spehl. Theyopened the anterior mediastinum without wounding the pleura andproved that if the lungs are tied off at the end of inspiration they con-tain more blood than when tied off at the end of expiration. The in-creased velocity of the blood-flow through the lungs during inspira-tion is explained by the fact that the greater negative pressure affect
A text-book of physiology for medical students and physicians . sedvolume of blood flowing through the lungs during inspiration. Theincreased capacity of the lung capillaries during the expansion ofthe lungs was shown experimentally by Heger and Spehl. Theyopened the anterior mediastinum without wounding the pleura andproved that if the lungs are tied off at the end of inspiration they con-tain more blood than when tied off at the end of expiration. The in-creased velocity of the blood-flow through the lungs during inspira-tion is explained by the fact that the greater negative pressure affectsthe thin-walled pulmonary veins more than the pulmonary artery;consequently the head of pressure driving the blood through thelungs,—that is, the difference in pressure between the blood in thepulmonary artery and veins—is increased. These data explainsatisfactorily the general fact regarding the respiratory waves,—?namely, that during inspiration there is a rise of aortic pressure dueto a greater output of blood from the heart, and during expiration. Fig. 272.—Diagram to represent the time relation between the respiratory waves ofblood-pressure and the respiratory movements (dog): A represents the blood-pressurerecord, showing the heart-beats and the larger respiratory waves. B represents a simul-taneous record of the respiratory movements. At the beginning of inspiration there is afall of blood-pressure, but the final and main effect is a rise. At the beginning of expi-ration there is a rise of pressure, but the final and main effect is a fall. the reverse. To account for the subsidiary fact that at the begin-ning of inspiration the pressure falls and at the beginning of expira-tion it rises for a time two explanations are offered. De Jagerrefers these temporary effects to the changes in capacity of the blood-bed in the lungs. At the end of inspiration there is a certain ca-pacity of the l)ed; when expiration comes on, the lungs shrink, thecapacity of the blood-vesse
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