The Normal Nasal Cycle
The nasal cycle is a physiologic phenomenon occurring in 70-90% of healthy individuals, characterized by alternating congestion and decongestion of the nasal venous sinuses on opposite sides of the nose over several hours, while total nasal resistance remains relatively constant. 1, 2
Defining Characteristics
The cycle consists of reciprocal changes between the two nasal cavities: as one side becomes congested, the contralateral side simultaneously decongests, maintaining overall nasal airflow at a constant level. 1, 3
Prevalence is approximately 70-90% in the general population, with the classic 1977 Mayo Clinic study documenting a clearly defined nasal cycle in 72% of 50 healthy subjects using rhinomanometry. 1, 3
Each cycle includes a working phase and a resting phase: the resting phase allows for rehydration and regeneration of the nasal mucosa. 1
Cycle Duration and Variability
The typical cycle duration ranges from several hours, with individual cycles varying based on multiple physiologic factors. 1, 2
Factors that influence cycle length include: age, body position, physical activity level, mucociliary clearance rates, and time of day. 1
The cycle characteristically lengthens during sleep, representing a circadian variation in this autonomic process. 1
Physiologic Mechanism
The nasal cycle is mediated by alternating congestion and decongestion of nasal venous sinuses, controlled by autonomic nervous system regulation with the hypothalamus serving as the central regulator. 2, 4
Rhinomanometric definition: A resistance change of at least 20% between the right and left nasal passages over a 30-minute period (two consecutive 15-minute measurements) that reverses at least once during monitoring. 3
Clinical Significance
Most individuals are unaware of the nasal cycle because total nasal resistance remains fairly constant despite unilateral changes, as the combined resistance is less than either individual passage alone. 3
The nasal cycle serves important respiratory defense functions: (a) alternating the work of air conditioning between passages to prevent mucosal fatigue, (b) generating plasma exudate that physically cleanses epithelium and provides antibodies and inflammatory mediators, and (c) maintaining airway patency during inflammatory responses to infection. 2
Mucociliary clearance is significantly affected by the nasal cycle: clearance from the patent nostril is approximately 2.5 times faster than from the obstructed side, which has practical implications for intranasal drug delivery. 5
Pattern Classification
Four nasal cycle patterns have been described: (1) classic alternating pattern, (2) parallel pattern (both sides change together), (3) irregular pattern, and (4) acyclic (no discernible pattern). 4
The pattern of nasal cycle does not correlate with subjective nasal obstruction symptoms or the presence of local nasal inflammation on cytology. 4
Assessment Methods
Long-term rhinoflowmetry enables assessment of the circadian course and alternating cyclic changes of the nasal mucosa throughout the day and night. 1
Active posterior rhinomanometry with continuous monitoring (typically at 15-minute intervals over 7+ hours) is the gold standard research method for documenting the nasal cycle. 3