A text-book of physiology for medical students and physicians . would at the height of systole clamp off this system and stopthe coronary circulation. That this result really happens is indi-dicated by Rebatels curves of the velocity of the flow in the coro-nary arteries. As shown in Fig. 235, the great acceleration (a) invelocity at the beginning of systole is quickly followed by a drop tozero (b) or even a negative value,—that is, a flow in the other direc-tion, toward the aorta. At the end of the first (relaxation) phaseof diastole there is again a sudden increase in velocity (c), corre-spo
A text-book of physiology for medical students and physicians . would at the height of systole clamp off this system and stopthe coronary circulation. That this result really happens is indi-dicated by Rebatels curves of the velocity of the flow in the coro-nary arteries. As shown in Fig. 235, the great acceleration (a) invelocity at the beginning of systole is quickly followed by a drop tozero (b) or even a negative value,—that is, a flow in the other direc-tion, toward the aorta. At the end of the first (relaxation) phaseof diastole there is again a sudden increase in velocity (c), corre-sponding with the injection of the arteries from the aorta, followedagain by a decrease at the end of the diastole at the time when theventricular cavity is filled with venous blood under some , moreover, has shown in an interesting series of experimentsthat when a piece of the ventricle is kept beating, by supplying itwith blood through its nutrient artery from a reservoir at con-stant pressure, each systole causes a jet of blood from the sev-. Fig. 235.—Simultaneous record of the blood-pressure (A) and the blood-velocity (B)in the coronary arteries (Chauveau and Rebatel): a, Marks the beginning of the systole(there is a rise in pressure and in velocity); 6, marks a second rise of pressure (A) due tothe closure of the coronary capillaries by the contracting ventricle (at this moment in Bthe velocity falls off rapidly); c, curve (B) shows an increase in velocity due to the open-ing of the small coronary vessels at the beginning of diastole. ered vessels at the margin of the piece. In fact, the rhythmicalsqueeze of its own vessels during systole accelerates effectively thecoronary circulation. The volume of blood flowing through theheart vessels increases with the frequency or the force of the beat,since each systole empties the coronary system more or less com-pletely toward the venous side and at each diastole the distendedaorta quickly fills the empty vessels.
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