By the year 2030, an estimated 70 million people in the U.S.—about 20 percent of the total population—will be older than 65. Going forward, this number is only expected to rise due to a combination of declining birth rates and increased life expectancy.
A well-known witticism is “Age is an issue of mind over matter. If you don’t mind, it doesn’t matter.” But as we get older, we face an increase in a variety of life-threatening diseases and illnesses, so we should mind the matter of aging.
One of the leading causes of death in older adults is pneumonia, an infection of the lungs. A major risk factor for pneumonia in older people is not being able to effectively clear their airways due to muscle weakness. Common causes of weakened respiratory muscles are age, spinal cord injury, muscular dystrophies and Lou Gehrig’s disease (ALS).
The diaphragm is a thin muscle that separates your chest cavity from your abdomen. It is the primary muscle for breathing and is very important in airway clearance (i.e., coughing and sneezing). Specialized nerve cells called phrenic motor neurons control the diaphragm muscle. There are different types of phrenic motor neurons. Smaller ones activate smaller muscle fibers and are responsible for low-force, repetitive tasks such as breathing. Larger motor neurons activate larger muscle fibers and control higher force jobs such as clearing the airway. Our lab has found that just like other muscles, the diaphragm gets weaker and smaller with age (sarcopenia). We have also shown that we lose some phrenic motor neurons, especially the large ones, as we get older. This loss of nerve cells causes the diaphragm muscle to have trouble generating the force needed to clear the airways.
For the most part, older people can breathe fine, but they may have trouble coughing and sneezing effectively. Not being able to clear mucus and bacteria from their airways may increase their risk for respiratory infections. Understanding the causes of age-related degeneration of the diaphragm muscle will lay the groundwork for effective therapies and improve the healthy lifespan of our aging population.
Obaid Khurram, PhD, recently graduated from the Mayo Clinic Graduate School of Biomedical Sciences. Obaid studied motor control of the diaphragm muscle, particularly in cases of motor neuron loss. He will continue studying motor control of skeletal muscles during his postdoctoral training at Northwestern University.