The measure is called leg bioimpedance. Body composition machines use bioimpedance to calculate body fat by measuring how easily weak electrical currents can pass through tissue.
Researchers at the Stanford University School of Medicine in California proposed the measure as a new risk factor for heart failure after analyzing data on over half a million United Kingdom residents aged 49–69.
In a paper published in the Journal of the American Heart Association, they report how they found that lower leg bioimpedance was tied to a higher risk of heart failure.
Heart failure is a condition in which the heart continues beating but fails to pump enough oxygen-rich blood to meet the needs of organs in the body.
In the United States, the condition affects around 5.7 million adults and has an estimated annual cost of $30.7 billion.
Predicting heart failure
Should the new finding be confirmed by analyzing data from a different population, it could lead to earlier diagnosis and potentially even prevention of heart failure.
The Stanford team also developed a formula that accurately predicts a person’s risk of developing heart failure in the next 8 years. It brings together leg bioimpedance, age, sex, and whether or not the individual has a history of heart attack.
Senior study author Erik Ingelsson, a professor of medicine at Stanford University, says that he would like to see manufacturers of body composition analyzers add the formula to their calculations.
“The ideal scenario,” he explains, “would really be that you stand on the scale, and in addition to getting your body fat percentage, you also get your risk for heart failure within the next 8 years.”
‘Easily measurable’ risk factor
For the new study, he and his colleagues sifted through more than 3,500 factors relating to health, lifestyle, and disease that have been collected on each person enrolled in the UK Biobank project.
They used an approach called “machine learning” to search for risk factors tied to heart failure. This revealed some expected results, such as having or having had diabetes, having had a heart attack, or having chronic heart disease.
Leg impedance was high on the list of unexpected results. Prof. Ingelsson says that one of the reasons they “homed in” on it is that it “is easily measurable.”
Measures of leg impedance were taken as part of body composition measurement. People were invited to stand on equipment that resembles “a standard scale but with handlebars.”
The machine sends a weak electrical current through electrodes under the feet and measures the extent to which tissue in the legs resists or impedes the current. The more water and fluid in the tissue, the more easily the electricity passes through it and the lower the impedance.
An early indicator of fluid buildup
Prof. Ingelsson suggests that people with low leg impedance in their study may have been starting to build up fluid in the legs. Fluid buildup in the legs happens often in heart failure.
He and his colleagues wondered if they may have come across a way of identifying water retention that is present but not high enough to be spotted before shortness of breath, fatigue, and other more obvious signs of heart failure.
This point was taken up by Barry Borlaug, a cardiologist and medical professor at the Mayo Clinic in Rochester, MN, who was not involved with the study.
He explains that, subject to further research, he can see how leg impedance might be used as a predictor of heart failure — especially in those who are less physically active.
“A number of people might have the abnormalities in their hearts and lungs that cause symptomatic heart failure, but they don’t experience these symptoms because they are so sedentary.”
Prof. Barry Borlaug
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