Haemodynamic effects of hypothalamic stimulation on skin and muscle venous beds

Twenty three points mainly located in the posterior hypothalamus were stimulated to study its effect on the pressures, flows and calculated segmental resistances of the skin and muscle venous beds of hind limbs in the dog. Stimulation of these points produced a uniform pattern of rise in pressures of the muscle veins consisting consisting of a steep rise during stimulation followed by a rapid decline to basal level on its cessation. Skin veins, on the other hand registered a gradual increase in pressure during stimulation followed by a secondary rise during post stimulatory period. Large veins of both muscle and skin exhibited comparatively smaller pressure increases than small vein. These pressure changes were accompanied by a similar marked rise in systemic arterial pressure. Out of 23 points, 21 points produced similar increases in the calculated resistances of skin and muscle veins. Two points produced greater increase of the skin vein resistance. Total venous resistance of the limb was therefore, raised by all the points stimulated. None of these points elicited any fall in the pressures or calculated resistances of either the muscle or skin venous bed. Muscle venous outflow always registered an increase while the skin venous outflow recorded either a small increase or decrease or at times no change during the hypothalamic stimulation. These findings demonstrate that hypothalamic stimulation can profoundly alter the haemodynamics of the hind limb venous beds and actively mobilize the post capillary venous sections of both skin and muscle venous beds.