Power spectral analysis of heart rate variability during the 100-g oral glucose tolerance test in pregnant women

OBJECTIVE - The aims of the present study were to 1) evaluate autonomic function during the oral glucose tolerance test (OGTT) in pregnant women and 2) investigate whether gestational diabetes mellitus (GDM) modifies autonomic control of heart rate variability. RESEARCH DESIGN AND METHODS - We prospectively studied 27 pregnant women (15 without GDM, 12 with GDM) during a 100-g OGTT. The maternal electrocardiogram was recorded before and 60 min after glucose ingestion, when peak glucose levels are expected. The time and frequency domains of maternal cardiac intervals were analyzed. RESULTS - There was a significant decrease in the high-frequency (HF) band in both groups after the ingestion of glucose. The normalized low-frequency (LF) band significantly increased and the normalized HF band significantly decreased after glucose ingestion. The LF-to-HF ratio was significantly higher in the group with GDM at baseline and significantly increased in both groups after glucose ingestion. A regression analysis revealed a significant decrease in the HF band with increasing blood glucose levels. CONCLUSIONS - Acute elevation of blood glucose levels during the OGTT caused substantial autonomic alterations, including sympathetic activation and parasympathetic withdrawal. Both arms of the autonomic system were affected during the test, thus lending support to the concept that these changes are centrally integrated. The autonomic changes were less pronounced in women with GDM compared with in normal control subjects, suggesting that chronic hyperglycemia and hyperinsulinemia may alter modulation of the autonomic nervous system.