The Regulation of the Blood Pressure with Special Reference to Muscular Work

Summary. The effect of various gas mixtures and of muscular work has been studied on the blood pressure of cats and dogs in chloralose anaesthesia and in rabbits under urethane. A gradual increase of the carbon dioxide content of inspired oxygen caused relatively slight changes in the blood pressure of the cat. After elimination of the sinus and aortic mechanisms a primary fall and a secondary rise of considerable magnitude ensued, the former due to peripheral vasodilatation and the latter due to central stimulation. Similar though less pronounced changes were sometimes observed also before the denervation. The rise in blood pressure by chemoreflex action of oxygen want was increased after elimination of the baroreceptor mechanism by means of ergotamine. Denervation of the reflexogenic areas reversed the effect of oxygen lack in the cat. Moderate muscular work, induced by electrical stimulation of the hind legs, caused little change in the blood pressure apart from an initial transitory fall. The same result was obtained after section of the spinal cord. In animals deprived of their sinus and aortic reflexes the blood pressure was greatly lowered during muscular work. A rise above the resting level was sometimes observed after the termination of work. This rise was accentuated or could be provoked by inhalation of gas mixtures rich in carbon dioxide and pcor in oxygen. It was eften considerable, when the sinus and depressor mechanisms had been eliminated. It is concluded that the blood pressure during muscular work is maintained at an adequate level chiefly by the mediation of the baroreceptor reflex mechanism. In addition the blood pressure may be influenced by central actions secondary to carbon dioxide accumulation or deficient oxygen supply or both.