The physics of pressure [biomedical application]

Summary form only given. The author discusses precise definitions of pressure by means of vectors and a tensor. He points out that to fully describe stress, nine separate terms are needed in general forming a tensor; under special circumstances, such as choice of certain axes, the number of elements can be substantially reduced. In the case of a fluid at rest or for a moving perfect fluid the nine general terms reduce to three. These three terms are all numerically equal so that pressure can be represented by a single entity. Conditions under which such assumptions can be made are discussed in terms of measurements of pressure in the urethra and in particular the effect of transducer orientation on the readings and their interpretation. A short discussion of the problems encountered in making pressure measurements in flowing fluids where the use of the correct pressure tappings is all important, is presented