**2. Understanding of nasal cycle**

The nasal cycle is an alternating one, with the total resistance in the nose remaining constant. The nasal cycle's value becomes evident when one considers that the function of the nose is to warm, humidify, and filter nasally inspired air. These humidifying and filtering functions are dependent on the presence of moist respiratory epithelium. The presence of two nasal fossae or chambers that function in an alternating pattern prevents excessive drying, crusting, and infection, which are the likely results of a static passage that is open to constant airflow, especially in desert regions. This cycle was believed to be an ultradian rhythm seen in people with normal health.

The swap of predominant nasal airflow between two nostrils determines the nasal patency, "why" we breathe from any one nostril at any point of time, there is no conclusive scientific evidence to answer. The "how" is explained by the presence of sympathetic and parasympathetic nerves that clog the nasal mucosa. When the sympathetic nerves in one nostril become active that nostril decongests. In this biorhythm, if the sympathetic nerves of the one nostril drop, immediately the parasympathetic nerves take over, so that the other nostril congests. This cycle, which is controlled by the autonomic nervous system as described above, had a mean duration of two and a half hours. The periodic congestion and decongestion of cavernous tissue of the nasal mucosa is the cause for nasal cycle [1]. Nasal cycle rhythm pattern is considered to be controlled by the central regulator located in the hypothalamus resulted in the bilateral vasoconstriction of the nasal mucosa [2].

Breathing through alternate nostrils showed effects on brain hemisphere symmetry on EEG topography [3]. There is a significant difference of airflow between left-nostril and right-nostril breathing. Effect of this cycle and manipulation through forced nostril breathing on one side on the endogenous ultradian rhythms of the autonomic and central nervous system [4]. In addition changes in the amount of blood flowing through the cavernous tissues of the nasal conchae was, the way in which the nasal cycle was described [5]. The normal nasal cycle rhythm is disturbed in diseased case, the nasal cycle dominance have been investigated with autism in children [6]. The effect of unilateral nostril breathing is associated with EEG amplitude in contralateral hemisphere [7, 8]; it is reported that left uninostril breathing is associated with enhanced spatial abilities and right uninostril breathing is associated with enhanced verbal abilities [9, 10].

ranges from fraction of seconds to even several years. The cycle exists less than a day (~24 hours) is referred as ultradian cycle (e.g., neuron activity, heart rate, respiration rate, rapid eye moment during sleep), equal to a day as circadian cycle (e.g., sleep-wake cycle) and greater than a day as

The airflow pattern during breathing in both the nostrils will not be same in most of the time. Only one nostril will be dominant for the particular time period, later the dominance shift to other nostril, and this cycle continuous from one nostril to other. This swapping of airflow from one nostril to another for a short duration is called nasal cycle Nasal cycle last for about 25 minutes–4 hours, it varies from person to person; even for the same person, the time periods varies from cycle to cycle. Since the duration of nasal cycle is less than 24 hours, it is classified under ultradian cycle. This chapter completely deals with the analysis of nasal airflow

The nasal cycle is an alternating one, with the total resistance in the nose remaining constant. The nasal cycle's value becomes evident when one considers that the function of the nose is to warm, humidify, and filter nasally inspired air. These humidifying and filtering functions are dependent on the presence of moist respiratory epithelium. The presence of two nasal fossae or chambers that function in an alternating pattern prevents excessive drying, crusting, and infection, which are the likely results of a static passage that is open to constant airflow, especially in desert regions. This cycle was believed to be an ultradian rhythm seen in people with normal health.

The swap of predominant nasal airflow between two nostrils determines the nasal patency, "why" we breathe from any one nostril at any point of time, there is no conclusive scientific evidence to answer. The "how" is explained by the presence of sympathetic and parasympathetic nerves that clog the nasal mucosa. When the sympathetic nerves in one nostril become active that nostril decongests. In this biorhythm, if the sympathetic nerves of the one nostril drop, immediately the parasympathetic nerves take over, so that the other nostril congests. This cycle, which is controlled by the autonomic nervous system as described above, had a mean duration of two and a half hours. The periodic congestion and decongestion of cavernous tissue of the nasal mucosa is the cause for nasal cycle [1]. Nasal cycle rhythm pattern is considered to be controlled by the central regulator located in the hypothalamus resulted in the bilateral vasoconstriction of the nasal mucosa [2].

Breathing through alternate nostrils showed effects on brain hemisphere symmetry on EEG topography [3]. There is a significant difference of airflow between left-nostril and right-nostril breathing. Effect of this cycle and manipulation through forced nostril breathing on one side on the endogenous ultradian rhythms of the autonomic and central nervous system [4]. In addition changes in the amount of blood flowing through the cavernous tissues of the nasal conchae was, the way in which the nasal cycle was described [5]. The normal nasal cycle rhythm is disturbed in diseased case, the nasal cycle dominance have been investigated with autism in children [6]. The effect of unilateral nostril breathing is associated with EEG amplitude in contralateral hemisphere [7, 8]; it is reported that left uninostril breathing is associated with enhanced spatial abilities and right uninostril breathing is associated with enhanced verbal abilities [9, 10].

pattern from both the nostrils at healthy and different diseased states.

infradian cycle (e.g., menstruation cycle).

24 Pathophysiology - Altered Physiological States

**2. Understanding of nasal cycle**

The exact relationship between uninostril breathing and cerebral hemispheric activity is not known. But, some of the previous studies explain the effect of hyperventilation by the nose on EEG activity in the cortex proposes that it is produced by a neural reflex mechanism in the superior nasal meatus [11].

In this study, the most interesting factor of characteristics of airflow in both the nostrils was analyzed extensively. Airflow in one nostril will be greater and other will be lesser, the nostril with greater quantity of airflow is called as dominant nostril. This dominance will exists only for limited duration (approx. 25 minutes–4 hours), later the dominant airflow found to be exists in the other nostril. This swapping of dominant airflow between one nostril to another is called as nasal cycle as illustrated in **Figure 1**. Graph indicating alteration of left and right dominant airflow measured at every 15 minutes for the period of 12 hours.

Previous study on nasal cycle elaborates the cause for this oscillatory function in different view that nasal cycle is regulated by the autonomic nervous system, such that unilateral sympathetic dominance in one nostril causes vasoconstriction and decongestion, while simultaneously parasympathetic dominance in the other nostril causes vasodilatation and congestion [6].

It is proposed that the periodic congestion and decongestion of nasal venous sinusoids may provide a pump mechanism for the generation of plasma exudate, which is an important component of respiratory defense [12]. Nasal cycle also reported to be regulated by the alternating lateralization of plasma catecholamine's [12].

The nasal cycle is not only observed in human nose, it is also found in rabbit and rat [13], the domestic pig [14], the cat [15], and the dog [16] and seems to be a common phenomenon in all mammals and other animals.
