The First Rise in the Muscle Record
The brief first elevation in the muscle record when registered simultaneously with arterial blood pressure is observed to occur at the same time with the sharp initial rise in the blood-pressure curve (see [Fig. 12]). The first sharp rise in blood pressure is due to contraction of the vessels in the area of distribution of the splanchnic nerves, for it does not appear if the alimentary canal is removed, or if the celiac axis and the superior and inferior mesenteric arteries are ligated. The betterment of the muscular contraction is probably due directly to the better blood supply resulting from the increased pressure, for if the adrenal veins are clipped and the splanchnic nerves are stimulated, the blood pressure rises as before and at the same time there may be registered a higher contraction of the muscle.
Figure 12.—Top record, arterial blood pressure with membrane manometer. Middle record, contractions of tibialis anticus loaded with 125 grams and stimulated 80 times a minute. Bottom record, splanchnic stimulation (two minutes). Time, half minutes.