Studies on diurnal blood pressure variation in kidney diseases associated with excessive salt and water retention

Salt and water retention, a cardinal feature of nephrotic syndrome, was suggested to be an important factor leading to reduced diurnal blood pressure (BP) variation in renoparenchymal disease. Twenty-four hour BP (SpaceLabs SL 90207), 24-h urine excretion of catecholamines, plasma renin activity and plasma aldosterone concentration were therefore determined in 10 nephrotic patients with normal serum creatinine levels (group A, serum creatinine 1.0+/-0.2 mg/dl), in 10 nephrotic patients with increased serum creatinine levels (group B, serum creatinine 2.4+/-0.9 mg/dl) and in 20 controls matched in respect of age and BP. To study the direct influence of fluid volume overload, diurnal BP variation was determined before and after volume depletion by ultrafiltration in 10 patients with end-stage renal failure. Diurnal BP variation was characterised by the difference of mean BP during daytime (10 pm to 8 am) and night-time (8 am to 10 pm). In group A, the systolic and diastolic day-night difference was not changed when compared with the controls (NS). In contrast, in group B the day-night difference was significantly lower than in the controls (P < 0.01). Twenty-four hour urine catecholamine excretion and plasma aldosterone were comparable between the study groups. Plasma renin activity, however, was significantly increased in group A (P < 0.05). Nocturnal BP drop was not related to plasma renin activity in the nephrotic patients. The blunted diurnal blood pressure variation in end-stage renal failure was not influenced by ultrafiltration. The study demonstrates that the blunted diurnal BP variation in kidney disease is unaffected by marked changes in total exchangeable sodium and fluid volume, but is sensitive to changes in glomerular filtration rate.