THE PHYSIOLOGICAL EFFECTS OF PRESSURE

Summary Our knowledge of physiological effects of pressure is as yet too incomplete to permit of generalizations, and we are still very much in the dark regarding the mechanism of pressure action. Any influence of hydrostatic pressure must be secondary to a decrease in volume. In non‐living systems this results in important changes in physical and chemical properties and gives a basis for the explanation of the changes produced in living material. Such factors as the velocity of chemical reaction and the viscosity of fluids are, in general, increased quite out of proportion to the volume change. High pressures bring about an irreversible polymerization of many substances, including proteins. The same order of pressure inactivates most enzyme solutions, bacterial toxins, antibodies, viruses, and other biological agents. The simpler forms of life, such as bacteria and yeast cells, are only slightly less resistant, but all are killed by sufficiently high pressure. On higher forms relatively low pressures cause death, especially when long continued. There are many known instances where small pressures cause a stimulation of physiological processes, and this may prove to be a general phenomenon occurring at pressures below those resulting in depression. In the case of muscle contracting under pressure there is a marked augmentation in the response, and the application of pressure may, independently of any other form of stimulus, result in the prolonged liberation of energy. Provided that the pressure increase is not too extreme, all the changes observed are reversed with decompression. The action of pressure on physiological mechanisms has a special interest because it is a fundamental one on molecular relationships extending throughout the cell structure. Furthermore, it is an agent which can be supplied and removed with great rapidity and as such provides a unique tool for the study of physiological problems.