The autonomic control of heart rate and insulin resistance in young adults

The pathophysiology of insulin resistance is unclear. A link between increased heart rate (HR) and insulin resistance suggests an association with sympathetic nervous system activity. To further evaluate this, we examined autonomic activity using spectral analysis of HR variability (HRV), which provides a measure of cardiac sympathovagal modulation, and related this to insulin sensitivity (Si) in 137 men and women (20 yr old). The HRV spectrum displays 2 major peaks: a high-frequency peak, reflecting vagal activity, and a low-frequency peak caused by vagal and sympathetic activity. The high to-low ratio (HLratio) reflects sympathovagal balance. Si was measured, using the iv glucose tolerance test with minimal modeling, and HR data was derived from a 15-min supine electrocardiogram. Women were more insulin resistant than men (Si, 3.94 us. 5.09 10(4) min(-1)/per pmol.L; P = 0.002), had higher HR (59 vs. 56 beats/min, P = 0.019), but had a higher HLratio (2.04 vs. 1.31, P = 0.001). In men (but not women), Si correlated with HR (r = -0.410, P = 0.001) and measures of HRV: HLratio (r = 0.291, P = 0.002) independently of body mass index. In conclusion, Si correlates with cardiac sympathovagal balance in men, but not women, suggesting gender differences in the autonomic modulation of insulin resistance.