The spectrum of circadian blood pressure changes in type I diabetic patients

Background The objective of the present study was to characterize the spect rum of circadian blood pressure changes in type I diabetes at different sta ges of nephropathy by using two monitorings in each patient in order to avo id intra-individual variability. Patients and methods A total of 80 type I diabetic subjects and the same nu mber of age, sex and awake mean blood pressure (BP)-matched controls were i ncluded. According to urinary albumin excretion, there were 57 normoalbumin urics, 15 persistent microalbuminurics and eight proteinurics. Two 24 h amb ulatory blood pressure monitorings were performed at the same urinary album in excretion stage in absence of antihypertensive treatment for each diabet ic 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 group s. The intraindividual reproducibility in diabetics showed repeatability co efficients for the 24 h systolic and diastolic pressure of 33 and 42%, resp ectively. This reproducibility for the day: night ratio was generally worse , 57% for systolic and 59% for diastolic. A progressive increment in the me an 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 th e normoalbuminurics and their controls, nocturnal differences were observed , not only in microalbuminurics for systolic BP (P < 0.05), but also in pro teinurics 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. Th e non-dipping pattern in the two monitorings was observed in 80, 58,18 and 10% of the proteinurics, microalbuminurics, normoalbuminurics and control g roups, respectively. Conclusions Persistent abnormal circadian variability seems to be an early and frequent characteristic of type I diabetics with an increased urinary a lbumin excretion. Although present in some normalbuminuric subjects, the fr equency of this abnormality increases as the incipient nephropathy progress es. By the time proteinuria is established, nearly all subjects present the abnormal pattern.