ON THE VASODILATATION IN HUMAN SKELETAL MUSCLE DURING POST-HAEMORRHAGIC FAINTING

Journal/Book: J. Physiol. (1945) 161-175. 1945;

Abstract: From the Department of Physiology The Queens University Belfast (Received 20 January 1945) SUMMARY 1. Post-haemorrhagic fainting was induced by venous tourniquets on the thighs combined with venesection. This procedure induced fainting in twenty-eight out of thirty-two subjects. 2. Blood flow was studied in the normal forearm and hand in the sympathectomized and in the nerve-block forearm. During fainting: 1. Blood flow in the normal forearm increases the arterial pressure falls. Therefore there is vasodilatation in this region. 2. Blood flow through the hand which is mostly skin and bone decreases. Therefore the vasodilatation in the forearm is in the skeletal muscles. 3. Sympathectomy abolishes the forearm vasodilatation. Therefore it is brought about by the vasomotor centre and sympathetic nervous system. 4. Blood flow is greater in the normal than in the nerve-block i.e. acutely sympathectomized forearm during fainting. Therefore the vasodilatation is actively excited; and there must be sympathetic vasodilator fibres in the forearm muscles. 5. The vasomotor centre probably excites vasodilatation in the arterioles of all skeletal muscles. This may explain the sudden fall in the arterial blood pressure in fainting. ___MH

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