VOLUME SENSITIVITY OF BLOOD-PRESSURE IN END-STAGE RENAL-DISEASE

Background. The influence of interdialysis (ID) volume expansion on th e blood pressure (BP) change and on the BP level at the end of the ID time period was studied in 167 chronic haemodialysis patients. Our ana lysis focused on 120 patients not receiving antihypertensive drugs (un treated group). The remaining 47 patients were receiving antihypertens ive medication (treated group). Methods. The ID weight gain was consid ered equivalent to the volume gain. In each patient the mean ID BP cha nge (as percent change of initial BP) and the mean ID volume expansion related to the lean body mass (ml.kg(-1)) were determined from 25 con secutive ID time periods. The individual volume sensitivity of BP was expressed as the BP change divided by the volume expansion. Basal over hydration was estimated as mean ID initial weight minus dry weight. Re sults. All patients gained volume during ID time periods and the BP wa s increased in 91%. The change of mean BP (MBP) was directly correlate d with volume expansion (r = 0.45, P <0.00001) only in the untreated g roup. These patients showed a volume sensitivity unrelated with age, s erum urea and calcium concentrations and haematocrit. Sensitivity of d iastolic BP (DBP), an indicator of the capacity to respond to volume e xpansion by vasoconstriction (autoregulatory process), exhibited a neg ative correlation with the initial DBP level (r = -0.36, P <0.0001) an d with the serum potassium (in women, r=-0.35, p<0.02). These factors appeared to counteract the volume-induced DBP response. The MBP levels at the end of ID time periods were independent of volume expansion an d basal overhydration. Hypertensive patients showed a higher sensitivi ty than normotensive patients (0.35 +/- 0.2 versus 0.20 +/- 0.19% per ml.kg(-1) P < 0.005). Final MBP showed a positive correlation with ini tial MBP and, to a smaller extent, with serum urea concentration. Conc lusions. In our study the ID change of BP is partially dependent on vo lume gain. Volume sensitivity is a measure of the BP responsiveness an d is higher in hypertensive patients. Final BP depends on the height o f initial BP and other factors accounting for volume sensitivity, whos e precise nature remain to be clarified.