The effect of muscular contraction upon the blood flow in the skeletal muscle, in the diaphragm and in the small intestine

Abstract

In the previous communication, p. 233, experiments were described dealing with the effect of contraction of the skeletal muscle upon its blood flow. Short and prolonged tetanic contractions were evoked in various skeletal muscles by stimulation of their cut or uncut motor nerve or by direct stimulation of the muscle. Stimulation of the motor nerve as well as that of the muscle ma involve to an unknown extent the vasomotor innervation of the respective muscles and, although strong evidence was provided that none of the effects observed were even in part due to a direct excitation of the vasomotor fibres, we thought it necessary to repeat our experiments under conditions in which direct excitation of vasomotor fibres is definitely avoided. The present communication describes experiments on the reflex contraction of the tibialis and of the quadriceps femoris (vastocrureus) muscles. So far as we are aware, there is only one reference in the literature which related to circulatory conditions in muscles during a reflex contraction. Denny-Brown (1929), by direct microsopical observations of the surface of the soleus muscle during a stretch reflex, noticed that even a modest amount of pull on the tendon opens up numerous capillaries and hastens the flow of blood in them to a remarkable extent. The tension developed was sometimes as great as 1∙5 kg. Weight. As a result of this observation, Denny-Brown believes that the capillaries are not compressed by the muscle fibres when these contract reflexly. It is, however, quite likely that the circulatory conditions in the superficial layers of the muscle differ from those in the depth of the muscle. Moreover, it is extremely difficult to remove completely all the connective tissue from the surface of the muscle, and we know from Rein's experiments (Keller, Loeser, and Rein, 1930), as well as from our own previous experiments (Anrep, Blalock, and Samaan, 1933), that during the contraction of a muscle there may be considerable dilatation in the resting tissues. In order to determine the total arterial inflow into the tibialis anticus during its reflex contraction, we performed experiments which were similar to those described in our previous communication.