Total power and high frequency components of heart rate variability and risk factors for atherosclerosis.

Introduction: Low heart rate variability, HRV, is associated with diabetic neuropathy and with ischemic heart disease, IHD. The time context points to diabetes preceding changes in HRV, while changes in HRV precede the development of atherosclerosis and IHD. The purpose of the study was to analyse the association between the physiological risk factors of IHD and HRV in a prospective design.

Methods: In 1998 and 2002, data was gathered in a study concerning the risk factors for atherosclerosis. From among the participants it was possible to include 50 women and 24 men in a sub-study concerning HRV. Heart rate variability was measured partly during a clinical examination with exposure to a simple stress test, and partly during the first 4 h of sleep. The clinical examination, which lasted 45 min, resulted in 9, 5-minute HRV measurements, while the sleep period was divided into 2 periods of 2 h each, for which average HRV measurements were calculated. The associations between HRV and risk factors for IHD were analysed using the GLM, repeated measures method. As the dependent variables in the GLM analyses 11 levels (9 while awake and 2 while sleeping) of total power and high frequency variability, respectively, were used. The included risk factors were; body mass index, waist-hip ratio, systolic blood pressure, fibrinogen, cholesterol, HDL-cholesterol, HbA1c, testosterone, DHEAs, cortisol and catecholamines. Catecholamines were measured in urine and only in 1998. Cortisol was measured in both urine and saliva in 1998, but only in saliva in 2002. The results were adjusted according to the starting time of the measurements.

Results: Among the women, waist-hip ratio and HbA1c were significantly and negatively associated with both TP and HF. Stress hormones were not associated with HRV. Among the men, waist-hip ratio, HbA1c, and fibrinogen in 2002, and cortisol and noradrenaline in 1998 were significantly and negatively associated with TP and HF.

Conclusion: The study showed gender differences in the observed associations. In both gender, waist ratio and HbA1c were negatively associated with TP and HF. Furthermore, in the men, but not in the women, stress hormones in 1998, i.e. cortisol and noradrenaline, was negatively associated with TP and HF. The presented data give rise to discussion of the pathophysiology behind heart rate variability and ischemic heart disease, which may be different between women and men.