Portable Heart Monitor (IMAGE) Washington University School of Medicine Caption Portable heart monitors were worn by study volunteers who practiced calorie restriction and others of about the same age who ate standard diets so that scientists could measure their heart rate variability. Credit Washington University School of Medicine Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.