Differential Patterns of Impaired Cardiorespiratory Fitness and Cardiac Autonomic Dysfunction in Recently Diagnosed Type 1 and Type 2 Diabetes

Abstract

OBJECTIVE Both impaired cardiorespiratory fitness (CRF) and heart rate variability (HRV) are predictors of mortality, but their relative roles in recent-onset diabetes are unknown. We determined to which extent CRF and HRV are reduced and interrelated in recent-onset diabetes. RESEARCH DESIGN AND METHODS Participants from the German Diabetes Study with type 1 (n = 163) or type 2 (n = 188) diabetes with known diabetes duration <1 year and two age-matched glucose-tolerant control groups (n = 40 each) underwent spiroergometry and HRV assessment during a hyperinsulinemic-euglycemic clamp. RESULTS Compared with control subjects, patients with type 2 diabetes showed reduced VO2max (median [1st–3rd quartiles] 19.3 [16.5–22.9] vs. 25.6 [20.7–29.9] mL/kg body weight/min; P < 0.05), diminished VCO2max (23.0 [19.1–26.8] vs. 30.9 [24.5–34.4] mL/kg body weight/min; P < 0.05), blunted heart rate recovery after 2 min (−29.0 [−35.0 to −23.0] vs. −36.0 [−42.8 to −28.0] beats/min; P < 0.05), and reduced HRV in four of nine indices, whereas patients with type 1 diabetes had unaltered CRF but reduced HRV in three of nine indices (P < 0.05), indicating diminished vagal and sympathetic HRV modulation. HRV measures correlated with VO2max in patients with type 1 diabetes (r >0.34; P < 0.05) but not in those with type 2 diabetes. CONCLUSIONS CRF is reduced in recently diagnosed type 2 diabetes but preserved in type 1 diabetes, whereas cardiac autonomic function is reduced in both diabetes types but is strongly associated with CRF only in type 1 diabetes. These results support the therapeutic concept of promoting physical fitness in the early course of diabetes.