Volume sensitivity of blood pressure in end-stage renal disease

BACKGROUND: The influence of interdialysis (ID) volume expansion on theblood pressure (BP) change and on the BP level at the end of the ID timeperiod was studied in 167 chronic haemodialysis patients. Our analysisfocused on 120 patients not receiving antihypertensive drugs (untreatedgroup). The remaining 47 patients were receiving antihypertensivemedication (treated group). METHODS: The ID weight gain was consideredequivalent to the volume gain. In each patient the mean ID BP change (aspercent change of initial BP) and the mean ID volume expansion related tothe lean body mass (ml.kg-1) were determined from 25 consecutive ID timeperiods. The individual volume sensitivity of BP was expressed as the BPchange divided by the volume expansion. Basal overhydration was estimatedas mean ID initial weight minus dry weight. RESULTS: All patients gainedvolume during ID time periods and the BP was increased in 91%. The changeof mean BP (MBP) was directly correlated with volume expansion (r = 0.45, P< 0.00001) only in the untreated group. These patients showed a volumesensitivity unrelated with age, serum urea and calcium concentrations andhaematocrit. Sensitivity of diastolic BP (DBP), an indicator of thecapacity to respond to volume expansion by vasoconstriction (autoregulatoryprocess), exhibited a negative correlation with the initial DBP level (r =-0.36, P < 0.0001) and with the serum potassium (in women, r = -0.35, p< 0.02). These factors appeared to counteract the volume-induced DBPresponse. The MBP levels at the end of ID time periods were independent ofvolume expansion and basal overhydration. Hypertensive patients showed ahigher sensitivity than normotensive patients (0.35 +/- 0.2 versus 0.20 +/-0.19% per ml.kg-1, P < 0.005). Final MBP showed a positive correlationwith initial MBP and, to a smaller extent, with serum urea concentration.CONCLUSIONS: In our study the ID change of BP is partially dependent onvolume gain. Volume sensitivity is a measure of the BP responsiveness andis higher in hypertensive patients. Final BP depends on the height ofinitial BP and other factors accounting for volume sensitivity, whoseprecise nature remain to be clarified.