The nasal cycle is the alternating congestion and decongestion of the nasal cavities in humans. It is a physiological congestion of the nasal concha due to selective activation of one half of the autonomic nervous system by the hypothalamus. It should not be confused with pathological nasal congestion. The nasal cycle was first described by the German physician Richard Kayser in 1895.[1]
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In 1927 Heetderks[2] spoke about the alternating turgescence of the inferior turbinates in 80% of a normal population. The turbinates in one fossa filled up while the opposite turbinates decongested. This cycle, which is controlled by the autonomic nervous system as described above, had a mean duration of two and a half hours. He further observed and documented that the turbinates in the dependent nasal fossa filled when the patient was in the lateral decubitus (lying down) position. Some postulate that this alternating positional obstruction has the purpose of causing a person to turn from one side to the other while sleeping. The nasal cycle is an alternating one, with the total resistance in the nose remaining constant. In patients with a fixed septal deviation and intermittent nasal obstruction, the interplay of the nasal cycle becomes evident; the sensation of obstruction frequently mirrors the congestion phase.
The nasal cycle should not be confused with pathological nasal congestion: individuals with normal nasal breathing usually do not notice the alternating congestion.[3]
Today, much research about the effect of this cycle and manipulation through unilateral forced nostril breathing exists. Several reviews are freely available.[4]