How does the physiology of the nose impact respiratory health and what treatments are available for nasal disorders?

Nasal Physiology and Its Impact on Respiratory Health

The nose serves as a critical first-line defense mechanism in the respiratory system, functioning as both a filter and air-conditioner, with disorders of nasal physiology significantly impacting overall respiratory health and requiring targeted treatments based on specific pathophysiology. 1

Physiological Functions of the Nose

The nose performs several essential functions that contribute to respiratory health:

• Air conditioning: Warms, humidifies, and filters inspired air before it reaches the lower airways
• Mucociliary clearance: Removes particles and pathogens through coordinated ciliary action
• Defense mechanisms: Provides both physical and immunological barriers against pathogens
• Sensory functions: Detects irritants and triggers protective reflexes

Nervous System Components

The nasal cavity has a complex nervous system that includes:

• Sensory nerves: Generate sensations (like pruritus) and trigger motor reflexes (like sneezing)
• Parasympathetic nerves: Control secretory glands and vasodilation
• Sympathetic nerves: Regulate vasoconstriction and nasal patency 2

This neural network allows rapid responses to physical and chemical stimuli, essential for defensive and homeostatic functions.

Impact on Respiratory Health

The physiological connection between the nose and lower airways is significant:

• United airway concept: The nose and bronchial tree function as an integrated system
• Nasal disorders can trigger or worsen lower airway conditions: Particularly bronchial hyperresponsiveness and asthma 3
• Neurogenic inflammation: Release of neuropeptides from sensory nerves can promote inflammation throughout the respiratory tract 2

Nasal-Bronchial Relationship

Research demonstrates that:

• Nasal conditions frequently coexist with asthma
• Treatment of nasal disorders often improves asthma control
• Neural reflexes from the nose can influence bronchial physiology 3

Common Nasal Disorders

Rhinitis

Rhinitis is characterized by inflammation or irritation of nasal mucosa with symptoms including:

• Nasal obstruction
• Rhinorrhea (runny nose)
• Sneezing
• Nasal itching

Types of Rhinitis:

1. Infectious rhinitis:

   • Usually viral, lasting up to 10 days
   • Part of common cold syndrome

2. Allergic rhinitis:

   • Caused by IgE-mediated response to allergens
   • Can be seasonal (pollens) or perennial (dust mites, molds, animal dander)
   • Symptoms often include itching and ocular manifestations 4

3. Non-allergic rhinitis:

   • Response to irritants, temperature and humidity changes
   • Non-specific nasal hyperreactivity
   • Often lacks inflammatory markers 4

Rhinosinusitis and Nasal Polyposis

These conditions represent more complex nasal pathologies that can significantly impact respiratory health and quality of life 3.

Treatment Approaches

For Allergic Rhinitis:

1. Allergen avoidance: Reduction of environmental allergen exposure
2. Pharmacotherapy:
   • Second-generation antihistamines: Effective for rhinorrhea, sneezing, and itching but less so for congestion
   • Intranasal corticosteroids: Most effective for all symptoms including nasal congestion
   • Decongestants: Provide short-term relief of nasal obstruction but should be limited to avoid rebound congestion 4
3. Immunotherapy: Allergen vaccines or sublingual tablets for long-term management

For Non-allergic Rhinitis:

• Avoidance of triggers
• Intranasal corticosteroids
• Anticholinergics for rhinorrhea
• Saline irrigation

For Infectious Rhinitis:

• Symptomatic treatment
• Saline irrigation
• Short-term decongestants if needed

Clinical Considerations and Pitfalls

• Avoid prolonged use of nasal decongestants: Can lead to rhinitis medicamentosa (rebound congestion) after several days of use 4
• Consider systemic conditions: Nasal symptoms may be manifestations of systemic illnesses including immunodeficiencies, inflammatory disorders, and hematologic diseases 5
• Neural hyperresponsiveness: Can occur even without visible inflammation, explaining symptoms in non-allergic rhinitis patients 2
• Unified treatment approach: Addressing both upper and lower airway disease simultaneously often yields better outcomes 3

Understanding the complex physiology of the nose and its impact on overall respiratory health is essential for effective management of nasal disorders and their systemic effects.