Progression of diabetic nephropathy-is diurnal blood pressure rhythm as important as absolute blood pressure level?

BACKGROUND: Hypertensive non-diabetic patients who lack the normal nocturnal decline in blood pressure ('non-dippers') have an increased incidence of cardiovascular complications. Poor blood pressure control is known to exacerbate the decline in glomerular filtration rate in patients with diabetic nephropathy. METHODS: The aim of this study was to assess the contribution of abnormal blood pressure diurnal rhythm to the progression of diabetic nephropathy. We retrospectively studied 26 diabetic patients with hypertension, proteinuria and relentless progressive impairment of renal function due to diabetic nephropathy between 1990 and 1996. Patients underwent ambulatory blood pressure monitoring and were classified as either 'dippers' or 'non-dippers' according to their blood pressure diurnal rhythm. Dippers were patients whose mean sleeping blood pressure (both systolic and diastolic) was 10% less than blood pressure whilst awake. Weight, glycated haemoglobin, serum creatinine (micromol/l) and blood pressure (mmHg) were recorded on a 3-monthly basis. Twenty four hour urine protein excretion and creatinine clearance were recorded annually. The rate of decline of creatinine clearance was derived from serum creatinine estimation. RESULTS: In the 'dipper' group, the rate of decline of creatinine clearance was -2.9 ml/min/year and in those with abnormal blood pressure diurnal rhythm it was -7.9 ml/min/year (P<0.05). There was no significant difference in day-time mean blood pressures, glycated haemoglobin, age and numbers with insulin-dependent diabetes mellitus. CONCLUSION: We found that there was a profound effect of non-dipping upon the rate of decline of renal function in patients with diabetic nephropathy.