Mucociliary Clearance

Overview

• Murray & Nadel's Textbook of Respiratory Medicine; Fishman's Pulmonary Diseases and Disorders

Airway Surface Liquid (ASL) - Two-Layer System

1. Mobile mucus layer (gel layer) - composed primarily of secreted polymeric mucins. Water accounts for ~98% of its mass; mucins only ~0.5% (yet form the structural backbone). The two major secreted mucins are MUC5AC and MUC5B - both are exceedingly large glycoproteins (up to 3 × 10⁶ Da) that polymerize into long chains and branched networks. MUC5AC forms branched covalent networks; MUC5B forms end-to-end polymers.
2. Periciliary layer (PCL / sol layer) - stationary layer immediately surrounding the cilia, containing membrane-tethered mucins and glycoconjugates. Cilia beat within the PCL; their tips contact the overlying gel layer during the power stroke, propelling it.

• Fishman's Pulmonary Diseases and Disorders, p. 326-345

Mucus Composition and Secretory Cells

• Goblet cells produce thick, carbohydrate-rich secretions.
• Submucosal glands (lined by mucinous and serous cells) also contribute and become hypertrophic in chronic bronchitis.
• Seromucinous glands and goblet cells are the main contributors in the nose.
• K.J. Lee's Essential Otolaryngology; Fishman's

Ciliary Structure and Beat Mechanics

• Each multiciliated cell has hundreds of cilia arranged on its apical surface.
• The ciliary axoneme has the classic 9+2 microtubule structure with inner and outer dynein arms - dynein ATPase motors generate the sliding force between microtubules.
• Beat pattern: asymmetric two-phase cycle
  • Fast, forward power stroke - extended cilium sweeps through the gel layer, propelling mucus proximally.
  • Slower, backward recovery stroke - cilium bends close to the cell surface, moving through the lower-viscosity PCL to minimize backward drag on mucus.
• Cilia beat in metachronal waves - sequential (not synchronized) activity produces a coordinated wave along the airway epithelium.

Regulation of Ciliary Beat Frequency (CBF)

• Increased intracellular calcium → increased CBF
• Increased nitric oxide (NO) → increased CBF
• ATP released extracellularly activates P2Y2 receptors → drives mucin secretion, ion channel opening, and increased CBF; subsequent dephosphorylation to adenosine activates A2b receptors for sustained hydration signals (purinergic signaling cascade)
• Hyperviscous mucus → reduced CBF and efficiency
• Murray & Nadel's, p. 4145-4160

Direction of Mucociliary Transport

• In the lungs: movement is from peripheral airspaces toward the mouth (distal-to-proximal).
• In the nose: mucus travels along the nasal mucosa at 2-10 mm/h toward the nasopharynx.
• In the Eustachian tube/middle ear: cilia transport the mucous blanket from the tympanic orifice toward the nasopharynx. This is an active process - not gravity-dependent.
• Planar cell polarity establishes the directional orientation of cilia. Wnt signaling pathways are involved. The direction is developmentally programmed - surgical reversal of a tracheal segment does NOT reverse cilia beat direction.
• Ciliated cells are most numerous in the trachea and lobar bronchi, decreasing progressively distally.
• Murray & Nadel's; Cummings Otolaryngology

Particle Filtration

• Particles >12 µm are filtered in the nose.
• Particles depositing in ciliated airways are trapped in mucus and cleared centrally.
• If MCC is impaired, coughing becomes the backup clearance mechanism.
• If both MCC and cough fail: retained secretions produce airway obstruction and amplify inflammatory processes.

Evaluation of Mucociliary Transport

• K.J. Lee's Essential Otolaryngology

Diseases Impairing Mucociliary Clearance

Primary Ciliary Dyskinesia (PCD)

• Congenital, genetically heterogeneous disorder of dynein arms or other ciliary components → loss of ciliary movement.
• Leads to mucus stasis → bronchiectasis, sinusitis, and near-universal otitis media.
• In males: infertility (immotile spermatozoa).
• May cause situs inversus / dextrocardia (role of monociliated cells in embryogenesis - Kartagener syndrome when PCD + situs inversus).
• Nasal NO is markedly reduced.

Cystic Fibrosis (CF)

• Defective CFTR (chloride channel) → reduced chloride secretion into airway lumen + increased ENaC-mediated sodium absorption (worsened by inflammatory proteases) → mucus dehydration → hyperviscous mucus → impaired MCC.
• Airway secretions contain mucus + DNA and actin from dead neutrophils (neutrophil extracellular traps).
• Treatments: hypertonic saline (osmotic gradient draws water into lumen), inhaled mannitol, recombinant DNase (dornase alfa), CFTR modulators.

Acquired causes

• Tobacco smoking, influenza, and other upper respiratory viruses (ciliated cells may take 1 month to regenerate after viral damage).
• Bacterial infection (endotoxin release + inflammatory pathways damage cilia).
• Chronic bronchitis: goblet cell hyperplasia in distal airways, submucosal gland hypertrophy.
• Chronic sinusitis, middle ear effusions: hyperviscous secretions reduce CBF.
• Murray & Nadel's; Cummings Otolaryngology; Fishman's

Nasal Cycle

Definition and Mechanism

• The changes are driven by vascular activity - specifically, alterations in the volume of blood in capacitance vessels (venous sinusoids) of the nasal mucosa.
• The cycle is alternating: as one side congests, the other decongests, such that total nasal resistance remains relatively constant.
• Duration: every 2-12 hours (Heetderks' original observation: mean ~2.5 hours; Scott-Brown's range: 4-12 hours).
• Demonstrable in up to 80% of adults but not easy to demonstrate in children.
• Scott-Brown's Otorhinolaryngology; Cummings Otolaryngology

Control: Autonomic Nervous System

• Parasympathetic (vagal) overactivity → vasodilation of sinusoids → nasal congestion.
• Sympathetic tone → vasoconstriction → decongestion.
• High CO₂ in inspired air (rebreathing) → increases nasal resistance; hyperventilation reverses this.
• Drugs that block noradrenaline action → congestion (increased resistance).
• Antihistamines have anticholinergic (anti-parasympathetic) effects → increase sympathetic tone → improve nasal airway.
• Hormonal changes (puberty, pregnancy) affect the nasal mucosa and the cycle.

Factors Affecting the Nasal Cycle

Clinical Significance

Paradoxical Nasal Obstruction

• On the deviated (obstructed) side, patients learn to subconsciously habituate to the steady-state increased resistance.
• The normal (open) side varies with the cycle; when it enters the congested (turgescent) phase, the patient perceives obstruction on what appears to be the clinically wider side.
• This is paradoxical nasal obstruction - the patient complains of the side that looks more patent on examination.
• This unilateral turbinate enlargement is often a normal variant and must not be misinterpreted as pathological.
• Surgical correction must address both the deviated septum AND the hypertrophied turbinate.

Unilateral Turbinate Enlargement

• Cummings Otolaryngology, p. 3048-3052

Nasal Cycle and Olfaction

• Cummings Otolaryngology, p. 900

Summary Comparison

• Murray & Nadel's Textbook of Respiratory Medicine
• Fishman's Pulmonary Diseases and Disorders
• Cummings Otolaryngology - Head and Neck Surgery
• Scott-Brown's Otorhinolaryngology Head & Neck Surgery, Vol. 1
• K.J. Lee's Essential Otolaryngology

Otitis Media with Effusion (OME)

Definition

Otitis media with effusion: amber-colored effusion behind an intact tympanic membrane with a small bubble near the light reflex. - Shambaugh Surgery of the Ear

Epidemiology

• Most common cause of acquired hearing loss in children.
• Point prevalence on screening: up to 20% of children.
• Peak incidence around 1 year of age; by age 3, nearly all children have experienced at least one episode.
• OME in most children is mild and resolves spontaneously; it becomes clinically significant when bilateral, persistent, or occurring during critical developmental windows.
• Cummings Otolaryngology

Risk Factors

Pathophysiology

1. Eustachian Tube Dysfunction (Classic Model)

• Pressure equalization (ventilation) of the middle ear
• Mucociliary clearance of secretions toward the nasopharynx
• Protection of the middle ear from nasopharyngeal pathogens

• Smaller in diameter
• More horizontal in orientation (vs. the adult 45° angle)
• More compliant/flexible
• More susceptible to dysfunction from lymphoid tissue (adenoids) at the nasopharyngeal orifice

• Inflammatory causes: allergic disease, LPR/GERD, viral URTIs (mucosal edema)
• Anatomic causes: cleft palate (abnormal tensor/levator veli palatini insertion), synechiae from surgery, nasopharyngeal masses
• Functional causes: ciliary dysmotility (smoking-related, syndromic)
• Mechanical obstruction: prominent adenoid tissue, nasopharyngeal masses

2. Biofilm / Chronic Inflammation Model (Emerging Evidence)

• Protect bacteria from host defenses and antibiotics
• Allow bacterial communication via hormonal (quorum sensing) signals
• Persist subclinically, secreting endotoxins and exotoxins

• Post (2001): demonstrated H. influenzae biofilms in a chinchilla model by SEM
• Hall-Stoodley (2006): confocal laser-scanning microscopy found biofilms in mucosal biopsies of 92% of children with chronic OME, vs. 0% of controls
• Coates (2008): transmission electron microscopy demonstrated intracellular bacterial infection of middle ear mucosal epithelial cells in OME

Inflammatory Cascade in OME

• Early mediators: arachidonic acid metabolites, histamine, platelet-activating factor, adhesion molecules
• Key cytokines: TNF-α and IL-1β are the primary drivers; also IL-6, IL-8 (pro-inflammatory); IL-2, IL-4, IL-5, IL-10, IFN-γ (immunoregulatory); TGF-β and IL-10 (downregulation)
• Mucosal response: proliferation of lining + secretion of mucus; basal cells differentiate into goblet and ciliated cells → thick, tenacious mucoid effusion rich in mucins
• The mucin content primarily determines effusion viscosity (children tend toward more mucoid; adults more serous effusions)
• Shambaugh Surgery of the Ear; Cummings Otolaryngology

Clinical Features

Diagnosis

Otoscopy

• Amber (yellow/orange) effusion visible behind an intact tympanic membrane
• Air-fluid level or air bubbles may be present
• TM appears dull, retracted, or with decreased mobility
• On pneumatoscopy (Siegle speculum): limited or no TM excursion

Audiometry

• Flat conductive hearing loss (air-bone gap)

Tympanometry

• Type B (flat) curve - no tympanometric peak
• Normal ear canal volume (distinguishes from perforation, where ECV is high)
• Absent stapedial reflexes

Imaging (CT/MRI)

• Opacification of middle ear and mastoid air cell spaces
• No erosion of mastoid septa or cortical bone (distinguishes from coalescent mastoiditis or cholesteatoma)

Natural History and Consequences

• Most OME resolves spontaneously within several months.
• Prolonged bilateral OME → conductive hearing loss → speech and language delay, particularly if occurring during critical developmental periods (first 2-3 years).
• Long-term OME (untreated) can lead to:
  • TM atrophy and atelectasis
  • Ossicular fixation and erosion
  • Retraction pockets → risk of cholesteatoma
  • Tympanosclerosis

Management

1. Watchful Waiting

• First-line approach for most children.
• OME resolves spontaneously in the majority within 3 months.
• Hearing should be monitored during this period.

2. Medical Therapy

• Antibiotics: modest short-term benefit; not routinely recommended due to side effects and resistance concerns.
• Intranasal corticosteroids: may reduce adenoid size and ET inflammation; modest effect.
• Antihistamines/decongestants: not recommended (no evidence of benefit).
• Autoinflation (e.g., Otovent device): may help in cooperative older children.

3. Surgical Management - Tympanostomy Tubes

• Bilateral OME with hearing loss persisting ≥3 months
• Bilateral OME with associated speech/language delay or developmental concerns
• Bilateral OME with at-risk children (cleft palate, Down syndrome, permanent hearing loss, autism, etc.)
• Recurrent AOM with MEE

Tympanostomy Tubes (Ventilation Tubes / Grommets)

A ventilation tube seated in the tympanic membrane, acting as a surrogate for the dysfunctional Eustachian tube. - Cummings Otolaryngology

Mechanism of Action

• Provide middle ear ventilation - equalize middle ear pressure with atmospheric pressure, bypassing the dysfunctional ET
• Allow drainage of MEE through the external canal
• Reverse and prevent re-accumulation of MEE
• Create a less favorable environment for microbial growth
• Enable topical treatment of subsequent AOM episodes with antibiotic eardrops directly through the tube (avoiding systemic antibiotics)

Types of Tubes

• Shepard tubes: 93% extruded by 2 years
• Armstrong tubes: 80% extruded by 2 years
• Reuter-Bobbin: 66% by 2 years
• Goode T-tubes: only 31% extruded by 2 years

Surgical Technique

• Anesthesia: almost always general anesthesia (face mask) in children; IV access often not required for uncomplicated cases.
• Nitrous oxide can be used - it enhances instrumentation by expanding gases within the middle ear.
• A myringotomy incision is made (typically in the anteroinferior quadrant), MEE is aspirated, and the tube is placed.
• Procedure is brief (minutes per ear).

Indications - AAO-HNS Guidelines

• OME: tubes recommended for bilateral OME with documented hearing loss persisting ≥3 months, or OME of any duration in at-risk children.
• rAOM with MEE present in at least one ear at time of assessment: tubes recommended as an option.
• rAOM without MEE: tubes not recommended by 2013 AAO-HNS guidelines (AAP guidelines allow tubes as an option after failed preventive/medical treatments).

Postsurgical Follow-up

• First visit: 2-3 months after surgery (otoscopy + audiometry)
• Ongoing: every 6-12 months thereafter, or sooner if problems arise
• Monitor for tube patency, extrusion, TM changes

Complications and Sequelae

Management of Otorrhea

• First-line: ototopical fluoroquinolone drops (e.g., ciprofloxacin) - more effective and cost-effective than oral antibiotics; aminoglycoside drops avoided due to potential ototoxicity.
• If no resolution in 2 weeks: culture from tube opening to guide therapy.
• If yeast predominant: topical clotrimazole.
• Persistent/recurrent otorrhea: consider tube removal (biofilm formation on tube may perpetuate drainage).

Prevention of Immediate Postoperative Otorrhea

• Multiple saline washouts (NNT 7)
• Single application of antibiotic-corticosteroid drops intraoperatively (NNT 13)
• Single application of 6% ciprofloxacin otic suspension intraoperatively

Adenoidectomy as Adjunct

• Adenoids serve as a nasopharyngeal reservoir for respiratory pathogens and may obstruct ET function.
• Meta-analysis of 10 RCTs: adenoidectomy (alone or with tubes) most beneficial in children <2 years with rAOM.
• Benefit is modest and must be weighed against surgical risk.
• Re-insertion of a second set of tubes: adding adenoidectomy at this point is supported by evidence and reduces the need for further sets.

Special Populations

Summary: OME vs. AOM

• Shambaugh Surgery of the Ear
• Cummings Otolaryngology - Head and Neck Surgery
• Scott-Brown's Otorhinolaryngology Head & Neck Surgery, Vol. 2
• Harrison's Principles of Internal Medicine, 22nd ed.
• K.J. Lee's Essential Otolaryngology