Conductive hearing loss

Conductive hearing loss Hearing loss that is caused by blockage or other interference in the path by which sound energy is transferred to the inner ear. 

An 8-year-old girl presented with bilateral moderate conductive hearing loss, bilateral microtia, left external auditory canal stenosis, and right external auditory canal atresia, after prenatal isotretinoin exposure. Co-morbidities included developmental delay, ventricular septal defects, hypotonia, and retinal maldevelopment. The left EAC was sharply upsloping with a 2-mm-diameter meatus. A CT scan showed normal middle and inner ears bilaterally. Serial CT scans over 6 years showed progressive development of a left canal cholesteatoma. 

Audiologists are concerned with three kinds of hearing loss conductive hearing loss, in which sound waves are not properly transmitted to the inner ear sensorineural hearing loss, in which the cochlea or the auditory nerve is damaged and mixed hearing loss, which is a combination of these. 

Conductive Hearing Loss. Otosclerosis, inefficient movement of the three bones in the middle ear, results in hearing loss from poor conduction. This disease is treatable with surgery to replace the malformed, misaligned bones with prosthetic pieces to restore conductance of sound waves to the cochlea. 

CT has a high clarification rate in suspected malformations of the external and middle ear, including the detection of other causes for conductive hearing loss. Only in a few cases can no cause be found. The rate where imaging finds a morphological correlate in suspected inner ear malformation is clearly lower (about one fifth). CT is somewhat inferior in the detection of inner ear malformations compared to MRI. 

Mixed hearing loss is a blend of sensorineural and conductive hearing loss and generally results in increases in all ABR frequency thresholds. 

Conductive hearing loss is a form that usually involves an outer or middle ear obstruction that reduces transmission of sound vibrations through air space, bone, or tissue into the middle ear. The treatment for this problem is with medicine or surgery. Hearing aids may also be used. 

In a study where both peripheral and central nervous system effects were measured in rats co-exposed to u-hexane and toluene (Pryor and Rebert 1992), toluene exposure at 1,400 ppm for 14 hours a day for 9 weeks prevented the peripheral neurotoxicity (decreased grip strength and nerve conduction velocities) caused by exposure to 4,000 ppm 77-hcxanc alone. There was no reciprocal action of 77-hexane on the motor syndrome (shortened and widened gait and widened landing foot splay) and hearing loss caused by toluene. Brainstem auditory response amplitudes were decreased by 77-hcxanc, co-exposure to toluene did not block this effect. 

Some patients may experience hearing loss, which may accompany diabetes. Usually, type 2 diabetes is described in individuals with MELAS, although type 1 or insulin-dependent diabetes also may be observed. Palpitations and shortness of breath may be present in some patients with MELAS secondary to cardiac conduction abnormalities such as Wolff-Parkinson-White syndrome. Acute onset of gastrointestinal manifestations (e.g., acute onset of abdominal pain) may reflect pancreatitis, ischemic colitis, and intestinal obstruction. Numbness, tingling sensation, and pain in the extremities can be manifestations of peripheral neuropathy. Some patients may have the presentation of Leigh syndrome (i.e., subacute necrotizing encephalopathy). 

Noise is unwanted sound. It is a form of vibration conducted through solids, liquids, or gases. Noise can startle, annoy, and disrupt concentration, sleep, or relaxation. It can interrupt communication and interfere with job performance and safety, and it can lead to hearing loss and circulatory problems. Noise levels greater than 90 dBA should be avoided. Workers must wear hearing protection if workplace noise levels are greater than 90 dBA. 

Acoustic Trauma Loud noise from explosions, artillery guns or cannons or from similar sources of pressure waves may mpture the eardmm or damage the stmcture of the middle or inner ear. Such conductive damage has the name acoustic trauma. In some cases there is temporary damage. The injured tissue may heal, restoring hearing to full or nearfull sensitivity. In other cases, the physical injury will produce permanent hearing loss. 

The relative loudness of a sound compared with the threshold of human hearing is measured in decibels (dB). Conversation is usually conducted at 40 to 60 dB, while a car passing at 10 meters may be 80 to 90 dB, a jet engine 100 meters away may be 110 to 140 dB, and a rifle fired 1 meter away is 150 dB. Long-term (not necessarily continuous) exposure to sounds greater than 85 dB may cause hearing loss. 

---