THE DEVELOPMENT OF CONCEPTS OF VOLUME CONTROL

The history of hemodialysis includes some aspects concerning specifica lly the extracellular volume and blood pressure control issue. The goa l of this historical paper is to review what appears today as the main steps in the analysis of blood pressure normalization using the extra cellular volume (and sodium content of the body) control. Clinical obs ervations have more often preceded the formal expression of concepts. The 'dry weight' concept was formulated seven years after the first ma intenance dialysis patient's malignant hypertension was cured by a com bination of low salt diet and strong ultrafiltration leading to a decr eased extracellular volume. Fifteen years later, the development of sh ortened hemodialysis sessions-with restricted possibilities of volume control-has led to a resurgence of hypertension in dialysis patients. This late increasing prevalence of hypertension was reported in the li terature only several years after shortened dialysis had become almost universal. Some concepts not yet formalized, such as the 'lag time' b etween volume and blood pressure variation in dialysis may be needed t o analyze and understand what may presently appear as a failure of vol ume control of blood pressure in hemodialysis patients.