[Autonomic imbalance and renal dysfunction cause loss of nocturnal decrease in blood pressure in diabetic nephropathy].

Many diabetic patients with nephropathy show loss of the nocturnal decrease in blood pressure. However, the mechanism is not yet fully understood. Twenty-four-hour blood pressure in type II diabetic patients was evaluated by ambulatory blood pressure monitoring(with TM2425 A and D Co. Tokyo). The power spectrum of blood pressure was also analyzed as an index of autonomic cardiovascular modulation using the same device. The ratio of lower frequency(LF) to higher frequency(HF) of heart rate rhythmic oscillations was determined as an index of sympathovagal balance. Patients were divided into two subgroups (Diabetes mellitus group, serum creatinine level < 1.5 mg/dl, n = 25; Renal failure group, serum creatinine level > or = 1.5 mg/dl, n = 20) on the basis of renal function. Mean 24-hour, awake and asleep systolic blood pressure were 151.8 +/- 18.3(SD), 155.7 +/- 17.4 and 140.5 +/- 23.3 mmHg (Diabetes mellitus group) and 152.2 +/- 22.7, 152.6 +/- 22.1 and 150.0 +/- 26.5 mmHg (Renal failure group), respectively, which were higher(p < 0.01) than those(122.7 +/- 9.1, 126.0 +/- 10.2 and 112.9 +/- 10.7 mmHg) in age- and sex-matched control subjects(n = 20). The ratio between asleep and awake systolic blood pressure was 0.90 +/- 0.10 (Control group) and 0.90 +/- 0.11(Diabetes mellitus group), which were lower(p < 0.01) than that(0.98 +/- 0.09) in the Renal failure group. The Control and Diabetes mellitus groups showed a high awake mean LF/HF power ratio(1.91 +/- 0.55 and 1.95 +/- 0.48). On the other hand, the Renal failure group showed a low ratio (1.50 +/- 0.46) (p < 0.01), but each group showed no significant difference in the asleep mean LF/HF power ratio. These findings suggest that sympathovagal imbalance is worse in the waking hours in diabetic nephropathy patients with renal dysfunction, and this causes loss of the nocturnal decrease in blood pressure.