Physiology of communication

 

Consider the parts in and around the outer and middle ear (e.g., an ear canal, tympanic membrane, malleus, incus, stapes, and oval window). These are elements of the conductive portion of hearing function.

Analyze physiology of communication (ILO3, PLO3)

Apply knowledge of anatomy and physiology of communication to diagnose and treat patients with communication disorders (ILO3, PLO3)

Directions
Identify pathologies and conditions that arise which would result in conductive hearing loss (e.g., how would blast injury in a military veteran affect conductive hearing loss?).
Explain the effect of arthritis on the ossicular chain.
Explain the effect of infections within the middle ear chambers.

Sample Solution

Conductive Hearing Loss Pathologies and Conditions:

Several pathologies and conditions can disrupt the normal transmission of sound waves through the outer and middle ear, leading to conductive hearing loss. Here are some examples, including how a blast injury might affect it:

  • Blast Injury (Military Veteran): A blast injury can cause conductive hearing loss through several mechanisms:
    • Tympanic Membrane Perforation: The sudden overpressure from a blast wave can rupture the eardrum (tympanic membrane), disrupting its ability to vibrate in response to sound waves.
    • Ossicular Chain Disruption: The force of the blast can dislocate or fracture the delicate bones of the ossicular chain (malleus, incus, stapes), interrupting the mechanical transfer of vibrations to the inner ear.
    • Middle Ear Hemorrhage or Fluid: Bleeding or fluid accumulation in the middle ear space due to the trauma can impede the movement of the ossicles and the tympanic membrane.
    • Foreign Body Impaction: Blast debris can be forced into the ear canal, causing a blockage.
  • Other Pathologies and Conditions:
    • Ear Canal Obstruction: Cerumen (earwax) impaction, foreign bodies, or tumors in the ear canal can physically block sound waves from reaching the tympanic membrane.
    • Tympanic Membrane Issues: Perforations (due to infection, trauma, or surgery), scarring (tympanosclerosis), or retraction of the eardrum can impair its vibration.
    • Middle Ear Effusion: Fluid buildup in the middle ear due to allergies, colds, or Eustachian tube dysfunction can dampen the movement of the ossicles.
    • Otosclerosis: Abnormal bone growth around the stapes can fixate it, preventing it from vibrating properly and transmitting sound to the oval window.
    • Congenital Abnormalities: Malformations of the outer ear, ear canal (atresia), or middle ear structures can cause conductive hearing loss.
    • Cholesteatoma: A skin growth in the middle ear can damage the ossicles and other structures, leading to conductive hearing loss.

Effect of Arthritis on the Ossicular Chain:

Arthritis, particularly rheumatoid arthritis (RA), is a chronic inflammatory disease that primarily affects synovial joints. The ossicles in the middle ear (malleus, incus, and stapes) are connected by synovial joints. Therefore, arthritis can indeed affect the ossicular chain in the following ways:

  • Inflammation of the Ossicular Joints: RA can cause inflammation (synovitis) of the incudomalleolar (between malleus and incus) and incudostapedial (between incus and stapes) joints. This inflammation can lead to swelling, pain, and stiffness within these tiny joints, hindering their normal movement.
  • Erosion of Cartilage and Bone: Chronic inflammation can lead to the erosion of the cartilage and even the bone tissue of the ossicles themselves. This structural damage can disrupt the precise mechanical linkage required for efficient sound transmission.
  • Joint Fixation (Ankylosis): In severe cases, the inflammatory process can lead to the fusion or fixation (ankylosis) of the ossicular joints. This immobility of the ossicles prevents them from vibrating in response to the tympanic membrane’s movement, significantly impairing sound conduction.
  • Increased Porosity and Demineralization: Studies have shown that rheumatoid arthritis can cause increased porosity and demineralization of the ossicular bones, potentially weakening their structural integrity and affecting their ability to vibrate effectively.
  • Hearing Loss: The resulting impairment of ossicular chain function due to arthritis leads to conductive hearing loss. The severity of hearing loss can vary depending on the extent of the joint involvement and damage.

Effect of Infections Within the Middle Ear Chambers:

Infections within the middle ear chambers, commonly known as otitis media, can significantly affect conductive hearing function through several mechanisms:

  • Fluid Buildup (Effusion): The inflammatory response to infection causes the lining of the middle ear to produce fluid (effusion), which can be serous (thin and watery), mucoid (thick and mucus-like), or purulent (containing pus). This fluid occupies the air-filled space of the middle ear, dampening the vibration of the tympanic membrane and the ossicles. Sound waves lose energy as they try to travel through the fluid, resulting in muffled hearing.
  • Tympanic Membrane Changes: The pressure from the fluid buildup can cause the tympanic membrane to bulge outward, altering its normal vibratory characteristics and reducing its sensitivity to sound waves. In severe cases, the pressure can lead to a perforation (rupture) of the tympanic membrane, creating a direct pathway for sound to be lost and potentially causing further conductive hearing loss.
  • Ossicular Immobility: The fluid in the middle ear can physically impede the free movement of the ossicular chain. The increased density and viscosity of the fluid can create resistance to their vibrations, hindering the efficient transfer of sound energy to the oval window.
  • Adhesions and Scarring: Chronic or recurrent middle ear infections can lead to the formation of adhesions (scar tissue) within the middle ear space. These adhesions can tether the tympanic membrane to the ossicles or restrict the movement of the ossicular chain itself, causing persistent conductive hearing loss.
  • Ossicular Damage: In severe or untreated cases, middle ear infections, particularly those involving cholesteatoma formation, can directly damage or erode the ossicles, leading to discontinuity or dysfunction of the ossicular chain and significant conductive hearing loss.
  • Eustachian Tube Dysfunction: Middle ear infections are often linked to Eustachian tube dysfunction. If the Eustachian tube remains blocked, it prevents proper ventilation and drainage of the middle ear, perpetuating the fluid buildup and hindering the resolution of the conductive hearing loss.

In summary, pathologies and conditions affecting the outer and middle ear structures, including blast injuries, arthritis, and middle ear infections, can all disrupt the efficient conduction of sound waves to the inner ear, resulting in conductive hearing loss. Understanding the specific mechanisms by which these issues interfere with the normal function of the ear canal, tympanic membrane, and ossicular chain is crucial for accurate diagnosis and appropriate treatment.

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