THE REGULATION OF ARTERIAL BLOOD PRESSURE

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Abstract
In the barbitalized dog arterial pressure, cardiac output, heart rate, plasma vol., "average circulation time," "appearance time," and the hematocrit were detd. and the total peripheral resistance (T.P.R.), blood vol., total red cell vol., stroke vol., and the vol. of blood in the heart, lungs and large arteries were calculated in the control state, after opening a large arterio-venous shunt, during stimulation of the carotid sinus nerve and the central end of the vagus nerve, after spinal cord section and following the injn. of epinephrine and paredrine. As a result of opening the arterio-venous shunt the arterial pressure decreased -4%, cardiac output increased +40%, and T.P.R. decreased -28% on the average. As a result of stimulation of the carotid sinus nerve the arterial pressure decreased -47%, cardiac output decreased -7%, and T.P.R. decreased -38% on the avg. As a result of spinal cord section the arterial pressure decreased -47%, cardiac output decreased -19%, and T.P.R. decreased -33% on the avg. As a result of stimulation of the central end of the vagus nerve the arterial pressure increased =65%, cardiac output increased +13%, and T.P.R. increased +56% on the average. The plasma vol., total red blood cell vol. and blood vol. were increased in every case following spinal cord section. A method for determining the avg. circulation time is descr. It appears that the change in arterial pressure brought about by stimulation of the carotid sinus nerve or spinal cord section is caused to a large extent by a decrease in cardiac output and to a small extent by a decrease in T.P.R. It is concluded that changes in arterial pressure brought about by these vasomotor influences are largely the result of changes in the tone of the smooth muscles of the veins (post arteriolar vessels) which increases or decreases the cardiac output.