MUSCLE TONUS, INTRAMUSCULAR PRESSURE AND THE VENOPRESSOR MECHANISM

Abstract

A method of measuring tonus in the muscles of the human body by determining the pressure required to inject a minute amount of saline into a muscle through a hypodermic needle is described. The intratissue pressure thus shown is regarded as the principal element in the venopressor mechanism that normally induces the venous return to the heart. This view is supported by repetition of Riml''s experiment on a sympathectomized cat. In healthy young men the intramuscular pressure in the bi-ceps even when relaxed is 60-90 mm. of water column. In patients in bed it is only 20-50 mm. In the muscles of moribund animals the pressure disappears with the loss of tonus. The pressure in normal men is diminished by overbreathing; but increased by inhalation of COa and by strychnine, which thus tends to support the circulation. Failure of the circulation in illness and after severe physical injuries and surgical operations is held to be largely due to diminution of general body tonus and stagnation of the blood in the flaccid tissues.