Most common tinnitus cause III. - Dangerous decibels

source: freeimages.com

Noise is actually the sound pressure measured in decibels (dB) - who is interested in detailed information can read, for example, more on Wikipedia . The main thing that interests us is that decibels are measured logarithmically. In case of sound pressure it means that for every 3 decibels more it has double the energy. For example, the sound with intensity of 13 decibels two times more "noisier" than the sound with intensity of 10 decibels. Sound intensity 16 dB is 2x louder than the sound intensity 13 dB and up to 4 times louder than the sound of an intensity of 10 dB - etc.

Healthy human ear can usually register sounds for intensity of 0 dB - this is the threshold point. Some extremely sensitive individuals can hear sounds even weaker and theoretically should have gone in the measurement of auditory sensitivity to minus values. Simply, the human ear is extremely sensitive organ and is not designed for prolonged toleration of loud noise.

It's good to remember :

Danger to human hearing begins at around 85 dB. Normal human ear can withstand continuous noise of this intensity without damage for about 8 hours a day. Every 3 dB more, shortens time by half. So e. g. 91 dB is a safe value for only two hours a day, then we should take a rest for the day. Of course it also depends on the sensitivity of a particular individual, someone can endure more, someone less. Noise with an intensity of 130 dB and higher causes hearing damage almost immediately.

Anatomy of human ear I. – An overview

I do not want to bother reader with wide explanation and therefore I provide only quick overview. Human ear, like ear of all mammals, consists of three main parts: outer ear, middle ear and inner ear.

Anatomy of human ear

Outer ear

Outer ear serves to gather sound waves and to lead them into external auditory canal, which is capped with drum called tympanic membrane. This membrane transfers vibrations further into middle ear.

Middle ear

Tympanic membrane carries sound forward to three bones named: hammer (malleus), anvil (incus), and stirrup (stapes). They amplify the sound (nearly thirty times) and bring it to the snail-shaped organ called cochlea, which is already element of inner ear.

Inner ear

Inner ear is neurosensory part of ear, which is literally “electronics” of ear as a whole – and it is highly sensitive to damage. Cochlea or cochlear apparatus or Organ of Corti is placed directly in cranial bone and it contains around 16000 neurosensory hearing cells called hair cells. These are of two types: inner hair cells (IHC) and outer hair cells (OHC). Function of IHC is to change sound waves to electric signal, which goes through auditory nerve or Cochlear nerve into brain. OHC serve as additional amplifier of those signal.
Damaged hair cells (most often by acoustic trauma) can't accomplish their purpose and outcome of such state is hearing loss. IHC are in general more resistant to damage than OHC, which are dying sooner and thus amplifying of sound is not sufficient – it results in lower hearing sensitivity.

Here is very illustrative video on this issue:



On the following image we can see the difference between intact and damaged hair cells:

source: pnas.org

Most common tinnitus cause II. - Prevention, first aid and treatment of acoustic trauma

source: freeimages.com

If anyone has been the victim of acoustic trauma, he or she should act within 48 hours, but ideally within 24 hours! Did you woke up after a noisy concert hard of hearing? Have you been watching live fireworks? Someone threw a firecracker under your legs and whistles blow in your ears? Go straight to your ear doctor, preferably directly to the hospital. Keep in mind that there is time in play.

If your audiologist is a professional, he will send you to the hospital. Ideally, after necessary examinations (audiometry and tympanometry) to determine the degree of hearing damage, you receive cocktail of glucocorticoids, vitamins and vasodilating agents intravenously. Glucocorticoids have anti-inflammatory effects, improving the nourishment of cells and increase the chances, that traumatized auditory cells recover. However, they also have lot of side-effects, but only with prolonged use. Usually overall it is ten drips, one drip per day.

Big doses of NAC and Magnesium as soon as possible after acoustic trauma are very effective too. See study on this issue: http://www.ncbi.nlm.nih.gov/pubmed/24396768.

If you are not hospitalized and taken intravenous therapy only outpatient, try to use hyperbaric chamber for additional treatment. At a pressure of 2.5 atmospheres blood plasma gets several times more oxygen than the normobaric pressure. Oxygen`s diffusion into tissues helps prevent damaged hearing cells and avoid apoptosis (neuro-sensory cells in the inner ear breathe only by diffusion). Reportedly, at 3 atmospheres, the level of oxygen in the plasma is so big that organism could survive without blood cells.

If you do all of this on due time, you have a great chance that your hearing gets almost to its original state and prospective tinnitus can disappear.

NOTE: Above procedure applies even in case of Idiopathic sudden hearing loss (hearing loss that is due to unknown causes). When you lie down to sleep in the evening and in the morning you wake up deaf - usually affects only one ear.

Most common tinnitus cause I. - What is acoustic trauma

The most common cause for tinnitus is so called acoustic trauma, or the hearing damage by exposition to loud noise. Shooting without hearing protection, fireworks on Fourth July, New Year and other celebrations, petards, motorcycle exhaust strokes without noise reduction, loud music at concerts, discoteques or pubs, workplace with constant high level of noise - all that can be marked as source of acoustic trauma. Cases are known, and not at all rare, that individual caused himself tinnitus by listening to the loud music in car or using MP3 player.

Acoustic trauma generally arises in all situations where ears are exposed to very loud noises for long enough to ensure that the sensory cells are metabolically exhausted. Noise intensity of 140 db or more causes such exhaustion immediately (e.g. shot, explosion etc.). We can say that the cell is literally drowning in their own secretions (various forms of aggressive oxygen free radicals etc.), which it cannot degrade fast enough. After a short time apoptosis (programmed cell death) begins. Unlike birds and reptiles, by mammals dead neuro cells are not replaced by new ones, so the loss is permanent. However, cell death does not occurs instantly, and here is a chance to repair the damage.

Too loud!

Early sign of acoustic trauma is temporary deafness. Overloaded hair cells temporarily cease to function, those most damaged forever. Hearing gradually begins to return to its original value, but never to such state as before acoustic trauma (also depends on the actual severity of acoustic trauma). I myself have realized few days after acoustic trauma, that I hear a little bit worse.
Unfortunately, it still does not stop here. Some research has shown that stabilization of hearing after acoustic trauma can last up to five years from the moment of acoustic trauma, and may get even worse during that time. It is probably related to the gradual death of damaged hair cells, which have survived the acoustic trauma itself, but perish after a few months or years. It also means favorable forecast to gradually improve potential tinnitus, which often accompanies acoustic trauma.

Acoustic trauma results in loss of perception of higher frequencies, shift in the perception of sound (depending on the degree of severity) and distinctive hole in the zone near 4000 Hz. If you stop hearing in 15 kHz band, you do not need to worry much, these are not frequencies that commonly occur in life. But 4 kHz occurs commonly and hearing loss manifests as follows: the sound is blunted, like when you mute heights in equalizer. Everything sounds somewhat differently and you have decline in quality of perception.