Antecedent Hypoglycemia Impairs Autonomic Cardiovascular Function

Antecedent Hypoglycemia Impairs Autonomic Cardiovascular Function Implications for Rigorous Glycemic Control Gail K. Adler 1 2 , Istvan Bonyhay 2 3 , Hannah Failing 1 2 , Elizabeth Waring 2 3 , Sarah Dotson 1 2 and Roy Freeman 2 3 1 Division of Endocrinology, Diabetes, and Hypertension, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts 2 Harvard Medical School, Boston, Massachusetts 3 Department of Neurology, Beth Israel Deaconess Medical Center, Boston, Massachusetts Corresponding author: Roy Freeman, rfreeman{at}bidmc.harvard.edu Abstract OBJECTIVE— Glycemic control decreases the incidence and progression of diabetic complications but increases the incidence of hypoglycemia. Hypoglycemia can impair hormonal and autonomic responses to subsequent hypoglycemia. Intensive glycemic control may increase mortality in individuals with type 2 diabetes at high risk for cardiovascular complications. We tested the hypothesis that prior exposure to hypoglycemia leads to impaired cardiovascular autonomic function. RESEARCH DESIGN AND METHODS— Twenty healthy subjects (age 28 ± 2 years; 10 men) participated in two 3-day inpatient visits, separated by 1–3 months. Autonomic testing was performed on days 1 and 3 to measure sympathetic, parasympathetic, and baroreflex function. A 2-h hyperinsulinemic [hypoglycemic (2.8 mmol/l) or euglycemic (5.0 mmol/l)] clamp was performed in the morning and in the afternoon of day 2. RESULTS— Comparison of the day 3 autonomic measurements demonstrated that antecedent hypoglycemia leads to 1 ) reduced baroreflex sensitivity (16.7 ± 1.8 vs. 13.8 ± 1.4 ms/mmHg, P = 0.03); 2 ) decreased muscle sympathetic nerve activity response to transient nitroprusside-induced hypotension (53.3 ± 3.7 vs. 40.1 ± 2.7 bursts/min, P < 0.01); and 3 ) reduced ( P < 0.001) plasma norepinephrine response to lower body negative pressure (3.0 ± 0.3 vs. 2.0 ± 0.2 nmol/l at −40 mmHg). CONCLUSIONS— Baroreflex sensitivity and the sympathetic response to hypotensive stress are attenuated after antecedent hypoglycemia. Because impaired autonomic function, including decreased cardiac vagal baroreflex sensitivity, may contribute directly to mortality in diabetes and cardiovascular disease, our findings raise new concerns regarding the consequences of hypoglycemia. Footnotes Published ahead of print at http://diabetes.diabetesjournals.org on 3 December 2008. Readers may use this article as long as the work is properly cited, the use is educational a