As the population of the United States continues to gain excess weight, the risk for cardiovascular disease will substantially increase in response. Not only does weight contribute to this increased risk, but high sodium diets and low physical activity amplify the risk. To study the effects of risk factor modification on vascular health, the NHLBI-funded clinical trial SAVE (Slow Adverse Vascular Effects of excess weight) was developed. This trial is studying three hundred moderately overweight (BMI of 24.9-39.9) young adults (aged 20-45) who will receive a nutritional and activity intervention. Participants will be randomly assigned to either a low sodium or a usual sodium control group. The primary outcome is pulse wave velocity, a reproducible measure of vascular stiffening. This application is proposing to evaluate the effects of weight loss, increased physical activity and sodium restriction on the autonomic nervous system (ANS) by adding a measure of autonomic balance to the parent SAVE study. It has been well documented that obesity and high sodium intake are associated with an imbalanced ANS, and that this imbalance has detrimental effects on the vasculature. Autonomic balance is measured via heart rate variability and respiratory frequency. A commercially available monitor (ANSAR) can provide a quantitative measurement of both branches of the ANS: the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS). This reproducible technique is a fifteen minute noninvasive test that captures a participant's blood pressure, respiratory rate and electrocardiogram.
The aims of this proposal are to 1) Measure the effect of weight loss and increased physical activity on the ANS, 2) Measure the additional effect of sodium reduction on ANS above weight loss and physical activity, 3) Determine the association between the ANS and vasculature health as measured by pulse wave velocity (PWV), intima-media thickness (IMT) and adventitial diameter (AD). We hypothesize that following weight loss and increased physical activity, participants will have a decrease in SNS activity and an increase in PNS activity restoring the optimum balance of the ANS. There will be a larger decrease in SNS activity and a larger increase in PNS activity in the low sodium arm compared to the normal sodium arm. Also, there will be a positive association between autonomic balance and vascular measures; those with higher sympathetic and lower parasympathetic activity will have higher PWV, thicker IMT and larger AD. At 6 months, those with the largest restoration in autonomic balance will have lower PWV, thinner IMT and smaller AD. ? ? ?
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