STANFORD, CA—Research by scientists at Stanford University School of Medicine has raised hopes that apparently permanent hearing loss resulting from loud explosions may be reversible in the future. If their initial findings are confirmed, soldiers exposed to improvised explosive devices (IEDs) and others who suffer damage from sources such as jet engines, car air bags, and gunfire may regain some of their hearing.
In their study, “Mechanisms of Hearing Loss After Blast Injury to the Ear,” in the July 1 issue of the online journal PLOS ONE, John Oghalai, MD, and co-authors, report finding that loud blasts cause damage to hair cells and nerve cells, rather than causing structural damage to the cochlea.
In an interview with the Stanford University School of Medicine Office of Communications, Oghalai explained that this finding, which was based on research using mice, “means we could potentially try to reduce this damage.” He said that if the cochlea had been destroyed by a large blast as earlier studies have asserted, the damage would be irreversible. However, he said, when the researchers looked inside the cochleas of the mice used in their study, they found hair cell loss and auditory nerve cell loss, but not destruction of the cochleas.
The associate professor of otolaryngology added, “With one loud blast, you lose a huge number of these cells. What’s nice is that the hair cells and nerve cells are not immediately gone… There is going to be a window where we could stop whatever the body’s inflammatory response would be right after the blast.”
He continued, “The theory now is that if the ear could be treated with certain medications right after the blast, that might limit the damage.”
WAR INJURIES ARE IMPETUS FOR RESEARCH
“The most common issue we see veterans for is hearing loss,” said Oghalai, a scientist and clinician who directs the hearing center at Lucile Packard Children’s Hospital. He noted that the increasingly common use of IEDs in war zones provided the impetus for the new study, which was primarily funded by the U.S. Department of Defense.
Among veterans with service-connected disabilities, tinnitus is the most prevalent condition and hearing loss is next. More than 60% of U.S. service members who are wounded in action have eardrum injuries, tinnitus or hearing loss, or some combination.
To determine the exact cause of permanent hearing loss in veterans, the Stanford scientists created a mouse model to study the effects of noise blasts on the ear. After exposing anesthetized mice to loud blasts, they examined the inner workings of the mouse ears over a three-month period. They used a micro-CT scanner to make an image of the workings of the ear after dissection.
“We found that the blast trauma is similar to what we see from lower noise exposure over time,” said Oghalai. “We lose the sensory hair cells that convert sound vibrations into electrical signals, and also the auditory nerve cells.”