The requirements of different parts of the body with respect to their oxygen supply, on the one hand, and the removal of metabolic débris, on the other, varies greatly from time to time. As the satisfaction of these needs depends primarily on the circulation, it is evident that excellent facilities for adjustment of the blood flow to them must be available. A recent writer1 has indicated specifically what this may mean when a healthy person passes from a condition of bodily rest into heavy muscular activity. The delivery of blood by the left ventricle is augmented enormously, an increase of from 5 to 25 liters a minute being an ordinary result. He reminds us that a balance of blood vessel constrictions and dilatations accompanies this enhancement in output, shunting blood toward the working muscles. As Krogh and others have shown, the capillary bed in such contractile parts expands in
THE BLOOD IN THE LUNGS. JAMA. 1926;87(12):942–943. doi:10.1001/jama.1926.02680120052017
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