Background: The objective of the present study was to characterize the spectrum of circadian blood pressure changes in type I diabetes at different stages of nephropathy by using two monitorings in each patient in order to avoid intra-individual variability.
Patients and methods: A total of 80 type I diabetic subjects and the same number of age, sex and awake mean blood pressure (BP)-matched controls were included. According to urinary albumin excretion, there were 57 normoalbuminurics, 15 persistent microalbuminurics and eight proteinurics. Two 24 h ambulatory blood pressure monitorings were performed at the same urinary albumin excretion stage in absence of antihypertensive treatment for each diabetic subject and for their respective control. Blood pressure and heart rate averages during 24 h, awake, sleep, and day : night ratio were calculated.
Results: Seven of the eight proteinuric subjects were hypertensives, whereas hypertension was absent in the normoalbuminuric and microalbuminuric groups. The intra-individual reproducibility in diabetics showed repeatability coefficients for the 24 h systolic and diastolic pressure of 33 and 42%, respectively. This reproducibility for the day : night ratio was generally worse, 57% for systolic and 59% for diastolic . A progressive increment in the mean ambulatory BP was observed across the three groups of diabetics and the differences in BP observed were most evident during the night-time period. Though no differences in the 24 h circadian pattern were present between the normoalbuminurics and their controls, nocturnal differences were observed, not only in microalbuminurics for systolic BP (P < 0.05), but also in proteinurics for both systolic BP (P < 0.01) as well as diastolic BP (P < 0.05). No differences were observed in heart rate among the diabetic groups. The non-dipping pattern in the two monitorings was observed in 80, 58, 18 and 10% of the proteinurics, microalbuminurics, normoalbuminurics and control groups , respectively.
Conclusions: Persistent abnormal circadian variability seems to be an early and frequent characteristic of type I diabetics with an increased urinary albumin excretion. Although present in some normalbuminuric subjects, the frequency of this abnormality increases as the incipient nephropathy progresses. By the time proteinuria is established, nearly all subjects present the abnormal pattern.