What is the physiology of the nose and paranasal sinuses?

Physiology of the Nose and Paranasal Sinuses

The nose and paranasal sinuses form a complex integrated system that serves critical respiratory functions including air conditioning (warming, humidifying, and filtering), mucociliary clearance, and defense mechanisms, with the osteomeatal complex being the key anatomical region for sinus drainage and ventilation. 1, 2

Primary Functions

Air Conditioning

• Warming and Humidification: The nose conditions inspired air toward a temperature of 37°C and 100% relative humidity before it reaches the lungs 2
• This optimal conditioning is essential for ideal pulmonary gas exchange to prevent desiccation and adhesion of the alveolar capillary bed 3
• The complex three-dimensional structure of the nasal passages facilitates this conditioning process through:
  • Strategic airflow patterns determined by the nasal valve and turbinates
  • Main airstream during inspiration passing through the lower nasal passage 4

Filtration System

• Particle filtration varies by size:
  • Particles >3 μm: Maximum deposition in the anterior part of the nose (nasal valve) 4
  • Particles 0.5-3 μm: Filtered by nasal mucosa and transported by cilia to the nasopharynx
  • Particles <0.5 μm: Low filtration efficiency; these particles more easily pass into the lower respiratory tract 4
• This filtration mechanism provides protection against inhaled particulates and pollutants

Mucociliary Clearance

• The nasal cavity and paranasal sinuses are lined with pseudostratified, columnar, ciliated epithelium covered by a thin mucous layer 1
• In the sinuses, cilia beat in a coordinated fashion toward their natural ostia 1
• This mechanism is crucial for:
  • Removing trapped particles and pathogens
  • Maintaining sinus ventilation and drainage
  • Preventing infection and inflammation

Anatomical Considerations

Osteomeatal Complex

• Critical region where most paranasal sinus ostia drain into the middle meatus and anterior ethmoid 1
• Obstruction in this area significantly reduces clearance and plays a major role in sinusitis pathophysiology 1
• Maintaining patency of this region is essential for normal sinus function

Nasal Cycle

• Physiological alternating congestion and decongestion of the nasal passages 1
• Contributes to the overall efficiency of nasal functions while maintaining consistent airflow

Clinical Implications

• Nasal septal surgery and rhinoplasty can significantly affect the filtration capacity of the nose by altering the structure of the nasal valve and lower turbinates 4
• Evaluation of respiratory functions typically includes assessment of:
  • Mucociliary clearance
  • Nasal airflow patterns
  • Defense mechanisms 5

Pathophysiological Considerations

• Obstruction of the osteomeatal complex is a primary factor in sinusitis development 1
• Different subtypes of non-allergic rhinitis have distinct pathophysiological mechanisms that affect normal nasal and sinus function 5
• Proper wound healing following trauma or surgery is essential for restoring normal physiological function 5

The complex interplay between anatomical structure and physiological function in the nose and paranasal sinuses highlights the importance of maintaining normal airflow patterns, mucociliary clearance, and defense mechanisms for optimal respiratory health.