Hypertension is a common comorbidity of type 2 diabetes mellitus (T2DM) and both are associated with increased cardiovascular risk, which is reduced by tight blood pressure (BP) and glycemic control. However the non-dipping BP status, defined as a nocturnal BP decline of less than 10% compared with daytime BP, is common in T2DM and remains an enduring cardiovascular risk factor. Cardiovascular autonomic neuropathy and endothelial dysfunction have been proposed as potential mechanisms. We hypothesized that the degree of microvascular disease rather than cardiovascular autonomic neuropathy interferes with the normal nocturnal reduction in BP.Design and Method:
Cardiovascular autonomic function and time-domain baroreflex sensitivity (xBRS) were determined in 22 diabetic patients with (DM+) and 23 diabetic patients without (DM−) manifest microvascular disease. BP dipping status was determined from 24-hour ambulatory BP measurements. Sixteen non-diabetic subjects served as controls (CTRL).Results:
None of the subjects demonstrated parasympathetic or sympathetic cardiovascular dysfunction. xBRS was lower in DM− patients compared to CTRL (7.7 ± 3.3 vs. 12.3 ± 8.3 ms·mmHg−1; P < 0.05), and further reduced in DM+ patients (4.6 ± 2.0 ms·mmHg−1; P < 0.01 vs. DM− and CTRL). The nocturnal decline in systolic and diastolic BP in DM− was blunted (12% and 14% vs. 17% and 19% in CTRL; P < 0.05) and even more so in DM+ (8% and 11%; P < 0.05 vs. DM− and P < 0.001 vs. CTRL). The percentages of non-dippers were 37%, 70% and 86% respectively in the CTRL, DM− and DM+ group. A nocturnal reduction in pulse pressure was observed in CTRL and DM− but not in DM+ patients (P < 0.05 vs. DM− and P < 0.01 vs. CTRL).Conclusions:
In T2DM patients, the degree of microvascular disease rather than CAN interferes with the normal nocturnal reduction in BP with a persistently increased pulse pressure, and coincides with reduced baroreflex sensitivity, contributing to their increased cardiovascular risk.