Noise Induced Hearing Loss - NIHL

Our ears are sensitive to loud noise. We may acquire a hearing loss from acoustic trauma, such as explosions, gun shots, and similar sudden loud noises, or we can get hearing loss from repeated sound stimulation, as working in a factory with machines that produce loud noises. In the past hearing losses were related to some old professions, like blacksmiths and makers of metal pans and pots.


During the II World War acoustic trauma and noise induced hearing loss became a serious problem. Soldiers were affected by loud sounds from artillery (guns, cannons, granades), explosions of shells and bombs. Pilots were constantly exposed to the noise of their airplanes.


The Department of Otolaryngology at Washington University in Saint Louis was commissioned by the United States Army Air Force to make an experimental study on acoustic trauma, hoping that understanding the involved mechanisms would help to establish adequate mechanisms of prevention. These studies led to interesting neurophysiological experiments so that, when I arrived in Saint Louis in 1958 acoustic trauma experiments in guinea pigs were still being carried on.


But even after the end of the war noise induced hearing loss continued to be an increasingly prevalent disorder. The airplanes became less noisy. Industrial noise was controlled. But we got discos and iPods and we found that musicians are subject to this problem. Not only the pop musicians who use electronic amplification for their instruments, but also symphony orchestra musicians, particularly those who play string instruments, who happen to sit right in front of the trumpets, trombones, tubas and woodwinds.


There is no cure for noise induced hearing loss, but it can be prevented. This is common knowledge, but few people take it seriously. Since the hearing loss is insidious and  progresses very slowly, you do not notice it until it gets serious.


I want to show you what happens in the inner ear subjected to noise exposure. These are acoustic trauma illustrations, but the end result is the same. The only difference is time. Incidentally, the ear damage depends on these two dimensions: noise intensity and length of time of exposure.


Fig. 1 shows the basal turn of a normal cochlea.

Fig. 1

Fig. 2 shows the result of a brief exposure to loud sound. The organ of Corti looks normal, except for a red blood cell inside the tunnel of Corti, showing that some hemorrhage waws caused by the intense sound stimulation.

Fig. 2

Fig. 3 shows more changes. Reissner’s membrane collapsed and the nuclei of the external hair cells are picnotic (reduced in size).

Fig. 3

Fig. 4 shows a ruptured Reissner’s membrane. The tip of the rupture shows an attempt of regeneration, that proves that the rupture was not a histological artifact. We no longer see the external hair cells, but the internal hair cell is present.

Fig. 4

Fig. 5 shows a totally destroyed organ of Corti.

Fig. 5

If you use your iPod at loud volumes more than 12 hours per week, this is what will gradually happen to your inner ears. And do not forget that we usually take our ears for granted. Only people with hearing losses know what it really means to them. Do not let a preventable hearing loss happen to you.