The auditory system connects us to the outside world through sounds. Ranging from the musical tone of an orchestra performance to the annoying tapping noises your neighbor won't stop making in class, every sound is translated into the complex language neurons used to communicate.
Hopkins researchers have recently discovered another explanation for why hearing loss can lead to everyday challenges. Their new study demonstrates that hearing loss increases one's risk of falling by nearly three times. The finding exposes a major public health concern that may potentially save the US billions of dollars in health care costs if addressed properly.
In a normal ear, an external structure known as the pinna reflects sound waves in our surroundings and directs them to the auditory canal. The main function of the pinna is to help the brain determine the direction of the sound source.
Once they reach the ear, sound waves travel through the auditory canal and eventually encounter the tympanic membrane, commonly known as the eardrum. Subsequently, the waves go through three bones - malleus, incus and stapes, that serve to increase the pressure of the waves. At a higher pressure, sound waves are able to transmit through the fluid, as they pass the oval window.
At this point, the sound waves have already reached the inner ear, which consists of the cochlea and various vestibular system structures. The basilar membrane in the cochlea is arranged such that lower frequency sound waves travel further and stimulate hair cells closer to the apex of the membrane, while higher frequency sounds activate hair cells closer to the base.
Stimulated hair cells depolarize, which means that there is an increase in intracellular voltage. The hair cells then transmit the signal to neurons that make up the auditory nerve, eventually leading to the temporal lobe in the brain. The temporal lobe is the cortical area primarily responsible for receiving and processing auditory stimuli.
Deafness can occur when any point of this pathway is disrupted. In general, hearing loss can be separated into two categories: conductive hearing loss and sensorineural hearing loss.
Conductive hearing impairment occurs when the sound wave is unable to reach the inner ear, often because of damage to the eardrum or to bones in the middle ear. Sensorineural hearing impairment occurs when the inner ear isn't functioning properly. Damage to hair cells, for example, is the most common cause of sensorineural hearing impariment.
Patients subjected to hearing loss may have an increased risk of falling because they are less aware of their surroundings. Additionally, these patients can experience cognitive load, which occurs when the brain is overwhelmed by limited resources, such as reduced functioning of one of its senses.
In the study, the researchers tested the hearing ability of 2,017 subjects between the ages of 40-69. The subjects were asked questions about their age, sex and demographic background. They were also asked to report the number of falls they had experienced within the past year.
Upon analyzing the data, the researchers found that people suffering from mild hearing loss were nearly three times more likely to fall. Other factors known to cause falls, such as increased age and cardiovascular disease, were taken into account but did not affect the findings.
Hearing loss is measured using a unit called the decibel. A mild hearing loss is characterized by a measure of 25-decibel. Subjects with 25-decibel hearing loss showed a threefold increase in falls. Each subsequent 10-decibel increase raised the chances of falling by another 1.4 fold.
With such a high risk of falling, researchers are hoping to develop ways of securing the safety of patients subject to hearing loss. The study will hopefully inspire new methods of preventing falls and reducing subsequent injuries.