Factors determining the 24-h blood pressure profile in normotensive patients with type 1 and type 2 diabetes

Abstract

Some controversy still exists about factors involved in the abnormal circadian pattern of blood pressure (BP) in diabetes, while prognostic value of non-dipping condition is being increasingly recognised. This study was aimed at evaluating the relative influence of autonomic neuropathy (AN) and albumin excretion on 24-h BP profile in type 1 and type 2 diabetes. We measured AN cardiovascular tests, 24-h ambulatory BP, and urinary albumin excretion rate (UAE) in 47 type 1 and 34 type 2 normotensive non-proteinuric diabetic patients. In type 1 diabetic patients day–night differences (Δ) in systolic and diastolic BP were lower in those with AN than in those without (3 ± 9 vs 10 ± 6%, P < 0.01, and 8 ± 9 vs 16 ± 6%, P < 0.001), and in univariate regression analysis they were inversely related to both autonomic score, index of degree of AN (r = −0.61, P < 0.001 and r = −0.65, P < 0.001), and to 24-h UAE (r = −0.39, P < 0.01 and r = −0.46, P < 0.001). In type 1 diabetic patients AN was also associated with lower nocturnal decrease in UAE (patients with AN vs without AN: −37 ± 214 vs 49 ± 37%, P < 0.05), and with a stronger relationship between simultaneous 24-h UAE and 24-h BP (for systolic BP patients with AN vs without AN: r = 0.62, P < 0.01 vs r = 0.28, NS). In type 2 diabetic patients Δ systolic BP was reduced in patients with AN compared to those without (4 ± 7 vs10 ± 4%, P < 0.01), and it was related only to autonomic score (r = −0.42, P < 0.01). Using a stepwise regression analysis, in type 1 diabetic patients autonomic score was the variable of primary importance for Δ BP, while in type 2 diabetic patients it was the unique determinant not only of Δ systolic BP but also of 24-h systolic BP. In conclusion, AN is the pivotal factor of blunted nocturnal fall in BP in both type 1 and type 2 diabetic patients. In type 1 diabetic patients AN is associated with attenuated circadian pattern of albuminuria and with a steeper relationship between albuminuria and BP, in type 2 diabetic patients AN is the only factor related to elevated 24-h BP levels. Longitudinal studies are needed to establish the potential role of autonomic dysfunction as a progression promoter for nephropathy and hypertension in type 1 and type 2 diabetes respectively.