Effect of Regular Exercise on Vascular Function and Cardiovascular Risk in a Sedentary Work Force

Overview

This study will evaluate the effects of NHLBI's employee exercise program, Keep the Beat, on blood vessel function. Damage to blood vessels can cause narrowing of the vessels, resulting in reduced blood flow to parts of the body such as the heart. Stem cells called endothelial progenitor cells, or EPCs, may be able to heal blood vessel damage. Exercise, such as walking on a treadmill, can help move EPCs from the bone marrow where they originate into the blood stream to help heal the damaged blood vessels. The Keep the Beat program encourages NHLBI employees to exercise 15 minutes during the workday and provides exercise facilities to accomplish this. NHLBI employees who have access to NIH exercise facilities may be eligible for this study. Candidates must have no history of heart disease, must not currently be exercising more than 1.5 hours per week and must not have participated in the Keep the Beat program for 3 months prior to entering the study. They are screened with blood tests and blood pressure measurements. Participants undergo the following tests and procedures before beginning the study and 3 months after participating in Keep the Beat: * Blood tests to identify EPCs and their function, measure the level of nitric oxide (a gas produced by healthy blood vessels), and measure C-reactive protein (an inflammatory marker that may be a risk factor for cardiovascular disease). * Brachial artery reactivity study to measure how well the arteries widen. An ultrasound device is placed over the subject's artery just above the elbow. The device measures the size of the artery and the flow of blood through it before and after a pressure cuff is inflated around the forearm. * Treadmill exercise testing to evaluate physical fitness. Subjects exercise on a treadmill for as long as they can. An exercise specialist is present throughout the test. Heart rhythm and oxygen saturation are monitored continuously and blood pressure is measured every 3 minutes.

Evidence suggests that Americans are becoming increasingly sedentary at work and at home due to technological advances. Physical inactivity coupled with excess caloric intake, especially of calorie-rich fast foods, are responsible for the epidemic of obesity in this country. Physical inactivity in obese and non-obese individuals increases the risk of cardiovascular disease and all-cause mortality. Premature cardiovascular disease leads to lost productivity in the work place, impaired quality of life, and escalating health care costs. In response to these concerns, the American Heart Association advocates 30 minutes of aerobic exercise most days; however, busy schedules coupled with a lack of convenient access to exercise equipment (or motivation to use it) limit adoption of regular exercise by many. One year ago, the National Heart, Lung, and Blood Institute (NHLBI) initiated the Keep the Beat program which encourages Institute employees to engage in fifteen minutes of exercise during the work day, and provides exercise equipment at specific work sites to accomplish this goal. Yet, fewer than 10% of NHLBI employees regularly participate in Keep the Beat and many who initially enrolled have failed to continue participation. The purpose of our prospective cohort study is to determine whether participation in the Keep the Beat program can improve an important measure of cardiovascular risk-arterial endothelial function-by stimulating bone marrow-derived endothelial progenitor cells to repair endothelium. We propose to characterize important components of vascular health by measuring endothelial nitric oxide bioactivity, as determined by brachial artery reactivity to shear stress and nitric oxide metabolites in blood, and vascular repair potential, as determined by endothelial progenitor cell number and function, at baseline and at 3 months in National Institutes of Health employees who agree to participate in Keep the Beat. Secondary analyses will include other biomarkers of risk, such as C-reactive protein, blood pressure, body mass index, lipid profile, fasting glucose/insulin, and homeostasis model assessment index, to be measured in our study and subgroup analyses of participants at particularly high cardiovascular risk (greater than 20% over 10 years), minorities, and women. Demonstration of improved vascular function, with implications of reduced cardiovascular risk, may serve as an incentive for greater employee participation in established employer-initiated programs, and for adoption of similar programs by other employers. If objective benefit cannot be demonstrated in vascular function and other biomarkers of risk, modification of the program may be required to reduce cardiovascular risk.