. A text-book of human physiology . ent upon tbese and uponthe variations in the pulmonary circulation. The mechanism by which theseinfluences are brought to bear are rather complicated, and we have to takeinto account the following conditions. The following circumstances tend during inspiration to increase the Woodpressure in the aorta: (1) The aspiration of the blood to the right heart increases; 230 CIRCULATION OF THE BLOOD (2) The diastole of the heart is favored; (3) The flow of the blood in the pulmonary vessels is facilitated because oftheir dilatation; (4) The pressure in the abdominal
. A text-book of human physiology . ent upon tbese and uponthe variations in the pulmonary circulation. The mechanism by which theseinfluences are brought to bear are rather complicated, and we have to takeinto account the following conditions. The following circumstances tend during inspiration to increase the Woodpressure in the aorta: (1) The aspiration of the blood to the right heart increases; 230 CIRCULATION OF THE BLOOD (2) The diastole of the heart is favored; (3) The flow of the blood in the pulmonary vessels is facilitated because oftheir dilatation; (4) The pressure in the abdominal cavity increases because of the descentof the diaphragm; and the blood is forced in greater quantity to the right heart. The following circumstances tend to lower the aortic pressure: (1) The heart systole is rendered more difficult because of the increased suc-tion in the thorax; (2) At the beginning of inspiration, while the pulmonary vessels are stilldilating, a part of the blood expelled from the right ventricle must remain in. Fig. 96.—Respiratory variations of blood pressure in the rabbit. To be read from right toleft. The upper line represents the blood pressure, the middle line the respiratory move-ments (downward stroke, inspiration), the lower line the time record in seconds. them, and by this means the mass of blood flowing from the left heart decreasesuntil the pulmonary vessels have been filled, after which the flow is expiration naturally these mechanisms work in the reverse direction. Among these factors the alterations of hlood flow to the right heart is ofthe first importance. The respiratory variations of the aortic pressure wit-nessed in a dog breathing quieth^ (Fig. 95) could be explained therefore in thefollowing manner. In expiration the right heart has less blood at its disposal,the left heart receives less blood, and the aortic pressure falls. When inspira-tion sets in, and the flow to the right heart becomes greater, it can drive agreate
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