Nasal cycle


The cycle consists of alternate nasal blockage between passages. The cycle has been known by Yogis since antiquity although Kayser gave it its first physiological description in 1895. The changes are produced by vascular activity, particularly the volume of blood on the venous sinusoids (capacitance vessels). Cyclical changes occur between four and 12 hours; they are constant for each person.The nasal cycle can be demonstrated in over 80 percent of adults, but it is more difficult to demonstrate in children. It is present in early childhood. The physiological significance is uncertain but, in addition to a resistance and flow cycle, nasal secretions are also cyclical with an increase in secretions in the side with the greatest airflow. Various factors may modify the nasal cycle and include allergy, infection, exercise, hormones, pregnancy,fear and emotions, including sexual activity.

The autonomic nervous system controls the changes; vagal overactivity may cause nasal congestion. High levelsof CO2 in the inspired air produced by rebreathing may also reduce the nasal resistance. This reverses following hyperventilation. Drugs, which block the action of noradrenaline, cause nasal congestion. The anticholinergic effects of antihistamines can block the parasympathetic activity and produce an increase of sympathetic tone, hence an improved airway. Times of hormonal changes, such as puberty and pregnancy, affect the nasal mucosa. These are probably mediated directly on the blood vessels.

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