AUTONOMIC FUNCTION IN TYPE-I DIABETES-MELLITUS COMPLICATED BY NEPHROPATHY - A CROSS-SECTIONAL ANALYSIS IN THE PRESYMPTOMATIC PHASE

The purpose of this study was to determine the prevalence of parasympa thetic and sympathetic autonomic dysfunction in long-standing type I d iabetics with established nephropathy and to correlate autonomic funct ion with cardiac risk factors. We used prospective analysis of heart r ate variations to standardized testing and 24-hour blood pressure cont rol prior to enrollment in a study utilizing various methods of intens e diabetic control to prevent deterioration of kidney function. The se ttings were outpatient clinical research units. The patients were 42 t ype I diabetics with proteinuria (total urinary protein greater than o r equal to 300 mg/day or urinary albumin greater than or equal to 100 mg/day) and creatinine clearance greater than or equal to 30 mL/min. H eart rate variation during respiratory cycles with change in posture f rom supine to upright, and during the Valsalva maneuver was recorded b y a computerized method. Mean arterial blood pressure was recorded for 24 h by a computerized method. Heart rate variations in this group we re abnormal during timed respiratory cycles in 26 of 40 patients (56%) , during changes in posture in 15 of 40 patients (38%), and during Val salva maneuver in 13 of 34 patients (38%) whose retinal disease permit ted Valsalva testing. Blunted day/night mean arterial pressure ratios occurred in 18 of 41 (44%) patients and were more severe in men than i n women (1.00 v 1.06, P less than or equal to .05). Absence of deep te ndon reflexes was associated with an increased incidence of both paras ympathetic (respiratory rate variation) and sympathetic (postural rate variation) abnormalities (both P less than or equal to .05). Loss of vibration sensation was not associated with autonomic functional abnor malities. Patients in whom heart rate variations during respiratory cy cles were decreased had significantly lower mean serum albumin and hig her incidence of the need for laser treatment for retinal microvascula r disease. Individuals with an HDL cholesterol less than or equal to 4 0 mg/dL had a significantly higher incidence of blunted day/night mean arterial pressure ratios. Gender differences occurred in mean levels of HDL cholesterol (women, 54 v men, 45 mg/dL, P < .05). The results o f autonomic nerve testing were not predictable from history, physical examination, or blood testing. The levels of blood pressure, serum, to tal cholesterol, triglyceride, creatinine, urinary protein excretion, and creatinine clearance did not correlate with either prevalence or s everity of autonomic nerve testing. Follow-up to determine the relevan ce of autonomic nerve testing as an independent cardiac risk factor in this high-risk population is ongoing.