Cold, Dry Air and Hyperosmolar Challenge in Rhinitis

Transcription

1 1 Cold, Dry Air and Hyperosmolar Challenge in Rhinitis Paraya Assanasen 1, M.D., Robert M. Naclerio 2, M.D. The Department of Otorhinolaryngology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand 1 and The Section of Otolaryngology-Head and Neck Surgery, The Pritzker School of Medicine, The University of Chicago, Chicago, Illinois 2 Address correspondence: Robert M. Naclerio, M.D., Professor and Chief, Section of Otolaryngology-Head and Neck Surgery, The University of Chicago, 5841 S. Maryland Ave., MC 1035, Chicago, IL 60637, Tel: (773) , Fax: (773) rnacleri@surgery.bsd.uchicago.edu

2 2 Introduction Rhinitis implies inflammation of the nasal mucosa. Inflammation is caused by many stimuli including the ambient conditions. The environmental conditions can also act as a trigger of symptoms, particularly in patients with rhinitis of other causes. The interaction of environmental temperatures and humidity, especially dry condition, and nasal inflammation is reviewed in this chapter. Also reviewed is hyperosmolar challenge, which can serve as a surrogate for cold, dry air (CDA) challenge. Many individuals experience symptoms of rhinitis, primarily rhinorrhea and nasal congestion, on exposure to cold windy environments [1]. A burning sensation inside the nose frequently precedes or accompanies these symptoms. Some individuals are exquisitely sensitive to CDA, for example, patients with nonallergic rhinitis react to CDA more vigorously than healthy individuals [2]. There has been interest in the nasal reaction to CDA to understand the physiology of the nose, and to offer better understanding in the mechanisms of lower airway reactions to the same stimulus; i.e., exercise-induced asthma. The prevalence of cold air-induced rhinitis is not clear, but in a 1980/81 survey of 912 police officers in Paris, France, 5.4% reported this problem and they were associated with lower forced expiratory volume in 1 second (FEV 1 ) [3]. The symptom of rhinitis provoked by CDA was considered a possible risk factor or marker for chronic airflow limitation. A database of 206 individuals with objectively confirmed perennial allergic rhinitis and 150 with seasonal allergic rhinitis indicate that cold air is considered a stimulus for nasal symptoms in by 55 and 28 %,

3 3 respectively [4]. Individuals skiing almost uniformly have rhinitis and hence the placement of tissues on the lift lines. Studies demonstrate that nasal inhalation of CDA causes drying of the nasal mucosa, resulting in increased tonicity and osmolarity of nasal secretions [5]. Hyperosmolar stimuli can trigger nerves directly leading to reflex stimulation of the parasympathetic system. In support of this concept, unilateral challenge with CDA led to bilateral cholinergic secretory response via nasonasal reflex and this secretory response could be reduced by atropine [6,7]. When exposed to CDA, the complex nasal vasculature structure performs air conditioning by dilatation of the resistance vessels and increasing blood flow [8]. Passive vasodilatation of the nasal vascular bed in response to CDA is mediated by the parasympathetic system since vasodilatation of nasal vessels can be induced with electrical stimulation of parasympathetic fibers or with exogenous acetylcholine and can be partially inhibited by atropine [9-11]. These effects could lead to increased speed of airflow, increased evaporation of water from nasal mucosal surface and hence increased osmolarity of nasal secretions. Because increasing the osmolarity of the medium surrounding isolated mast cells and other cells in vitro triggers mediator secretion, response to CDA nasal inhalation could also be caused by the release of mediators secondary to an increase in the osmolarity of the mucosal secretions [5].

4 4 The Conditioning Capacity of the Human Nose A major function of the nose is to condition the temperature and humidity of inspired air [12]. In the healthy state, the reserve of nose to perform this function is enormous. Prior investigations of nasal conditioning have led to several observations. First, exhaled air is fully humidified [12]. Second, its temperature is slightly below body temperature because of a mucosal temperature gradient caused by inspiration. This gradient leads to a recovery of heat and water estimated to be 30% of that needed to condition inspired air [13,14]. Inspiring hot dry air interferes with the establishment of the gradient and allows for less recovery of heat and water during expiration [14]. Third, there is wide individual variability in the temperature recorded in the nasopharynx [12-14]. Fourth, despite the wide variability in nasopharyngeal temperature, the relative humidity is 100% [12-14]. Finally, ventilation between 10 and 40 liters has no effect on the temperature and humidity of inspired air [13]. The theoretical model of Hanna and Scherer predicts that the blood temperature distribution along the airway wall, and the total cross-sectional area and perimeter of the nasal cavity, are the two most important parameters of the human air conditioning response [15]. Other factors, such as the thickness of the airway surface liquid, blood perfusion rates, and the thickness of the mucosal - submucosal layers, are thought to be less important within physiologic limits. As discussed below, parts of this model can be supported, but others can not. Part of the importance of nasal air conditioning is its impact on the lower airway. Air that is not fully conditioned when it exits the nasal cavity requires further conditioning by the lower

5 5 airways [16]. This fact has been amply demonstrated and relates to minute ventilation, tidal volume, and the temperature and water content of the inspired air [17]. Transferring this function from the nose to other parts of the airway for prolonged periods of time may alter airway physiology. This notion is supported in part by several lines of evidence: epidemiological studies by Annensi et al. showed that subjects reporting nasal sensitivity to CDA had a more rapid decline in FEV 1 over five years compared to those without such sensitivity [18]; inhalation of the same volume of dry air through the mouth, in contrast to the oronasal route, causes a greater reduction in FEV 1 in asthmatics [19]; temperature changes can affect ciliary activity in vitro; and subjects requiring a tracheotomy or endotracheal intubation require protracted periods of time for the trachea to adapt to humidifying inspired air [12]. Also studies of changes in the lower airways of elite athletes who exercise in cold environments for prolonged periods of time. Exposure to unconditioned air not may not only adversely affects the lower airway mucosa, but also has been shown to affect the nose itself. It is well established that nasal congestion is a physiologic response to breathing cold air [20]. Prolonged exposure of rats to cold environments results in nasal mucosal damage, with decreased goblet cells and intraepithelial glands as well as fibrotic changes [21]. Fibrotic changes have been suggested to occur in asthma and would be expected to interfere with water movement [22]. Intermittent exposure of guinea pigs to cold air induces upregulation of muscarinic receptors and increased responsiveness to methacholine and antigen provocation, but not to histamine [23]. The use of nasal continuous positive airway pressure (CPAP), which involves high flows of dry air, for treatment of sleep apnea leads to significant rhinitis, which is in part reduced by heated humidification of the inspired air.

6 6 Additionally, subjects, who had a total laryngectomy and hence are no longer passing air through their nose, undergo structural changes in their nasal mucosa [14]. These lines of evidence suggest that the mucosa of the upper and lower airway changes in response to the airconditioning demands dictated by the environment. When air is inspired through the nose, not only the warming but also the humidification process lead to mucosal surface cooling, [24] because vaporization of water from the epithelial lining fluid into the airstream requires heat. With water leaving the epithelial lining fluid, transient increases in the osmolarity of this fluid is also expected. With increasing ventilation rates through the nose or when the ambient air is at much lower than room air temperature (and, consequently, water content), the nasal heat and water losses are increased and the cooling, as well as the drying effects on the nasal mucosa are greater. This poses a stress on the mucosa and probably activates a number of compensatory mechanisms. The anatomy of the nasal mucosa is of major importance in the ability of the nasal passages to condition air while retaining mucosal heat and water homeostasis. One of the characteristic mucosal structures is the dense, subepithelial capillary network. These capillaries have fenestrations that are polarized toward the luminal surface [25]. Blood flow through this network provides heat and the fenestrae probably facilitate water transportation into the interstitium, the epithelial cells and the epithelial lining fluid. Another important structural element of the nasal submucosa is the venous sinusoids, which lie below the subepithelial capillary network. These blood vessels have the ability to rapidly pool large volumes of blood because they are supplied by many arteriovenous anastomoses and because their draining veins

7 7 (cushion veins) can contract and stop blood outflow [26]. Blood pooling leads to engorgement of the nasal mucosa and this increases the airstream contact surface. There is no agreement on which structural element of the nasal mucosa mainly contributes to water transportation and air humidification. The abundance of seromucus submucosal glands, especially in the anterior portions of the nasal cavity, suggests that their secretions could provide most of the water needed for humidification [27]. Also, with a bidirectional breathing pattern (inhalation and exhalation through the nose), heat and water losses are smaller because a substantial percentage, approximately 30%, of the heat and water supplied to the airstream at inspiration is passively returned to the mucosa at expiration, as long as expiration also takes place through the nose and at resting respiratory rates [12,14]. Cauna has contended that the role of humidification belongs to water from the fenestrated subepithelial capillaries, which continuously diffuses through the epithelium [28]. However, Ingelstedt, who injected fluorescein intravenously in normal humans, was not subsequently able to detect it in their nasal secretions [29]. Fluorescein is supposed to freely move across capillaries into the adjacent tissues and its absence in these experiments suggested that transudation does not occur. Fluorescein, however, may not cross the nasal basement membrane and diffuse between epithelial cells. Osmotic drives generated by water loss during the inspiratory phase may move water from intraepithelial spaces into the airway lumen [30]. At basal conditions, no osmotic drive for water to reach the lumen is generated by the apical surface of nasal epithelium, which predominantly absorbs sodium ions [31]. However, hypertonicity of the pericilliary fluid, which may occur as a result of water loss into the airstream, may lead to

8 8 reduction of sodium absorption followed by induction of chloride secretion [31]. Agents that induce camp also increase chloride secretion. These include α 2 - and β-agonists and prostaglandins E 1, E 2 and F 2α. In addition, bradykinin, adenosine, eosinophil major basic protein, substance P and mast cell mediators have shown similar effects [32,33]. From this list, it becomes evident that sympathetic and neuropeptide-containing nerve activation as well as allergic or nonallergic inflammation can increase chloride secretion leading to osmotic water diffusion into the airway lumen. It is also worth noting that methacholine-induced human nasal secretions are hyperosmolar (approx 340 mosm/kg H2O) [34,35] and that, in vitro, acetylcholine induces a large secretory flow of both sodium and chloride [31] suggesting that cholinergic stimulation also results in the generation of an osmotic drive to provide water to the airway surface. Evidence for hyperosmolarity occurring because of water loss from nasal surface An experimental model of nasal provocation with CDA was developed in 1985 [36]. The measurement of osmolarity of the nasal secretions was done using 2 methods. First, nasal lavages with a solution of known osmolarity can be measured before and after the provocation. It measures change of secretion osmolarity indirectly since nasal secretions are diluted to an unknown extent by the lavage solution. Second, dry-filter paper disc can be placed on the nasal mucosa before and after the provocation to collect the sample of secretions. It measures osmolarity of undiluted secretions and is more accurate. However, adequate secretions to saturate discs (at least = 8 μl) may not always be present in subjects with normal noses.

9 9 Using these techniques, nasal inhalation of CDA leads to hypertonicity of nasal lining fluid [5, 37]. Secretions produced by inhalation of hot (40-45 C) dry air through the nose were more hyperosmolar compared to the respective CDA challenge [38]. Hot dry air is expected to induce more water loss than CDA. These studies suggest that hydration of nasal mucosa and water loss caused by CDA challenge is an important factor to determine the osmolarity of nasal secretions. Individuals who do not develop a symptomatic response to CDA do not have increased post CDA osmolarity [5] indicating that they have greater capacity to achieve osmotic homeostasis. No change of number of epithelial cells in nasal lavage fluids was observed after CDA provocation in non-responders, while the number of epithelial cells in nasal lavage fluids increased six fold immediately after CDA provocation in CDA-reactive individuals. It is possible that the epithelial detachment occurs as a result of mucosal desiccation due to inability to compensate dry-air-induced water loss [39]. Human model for the study of dry-air and hyperosmolar challenge Model of nasal challenge with dry air or with hyperosmolar stimuli (hypertonic saline, mannitol) has helped to understand the pathophysiology of CDA and hyperosmolar stimuli-induced nasal inflammation. This model allows quantitative assessments of the release of inflammatory mediators during the nasal inflammatory response [40]. The effects of medication on the clinical response and inhibition of mediator release have also been examined with this model. Nasal provocation involves direct exposure of CDA or direct application of hyperosmolar stimuli to the nasal mucosa and observing the response both objectively and subjectively. It can be performed easily and frequently.

10 10 Nasal provocation of the human nasal mucosa has several advantages. First, the human nasal mucosa is the organ where the disease occurs. Second, it examines the organ in its entirety, not isolating any single element, as occurs in vitro. Third, animal models do not always mimic the human condition. Fourth, the nasal model is a simple, safe, reliable, and reproducible tool for the evaluation of the effectiveness and possible mode of action of drugs used in the treatment of nasal inflammation. Onset of action and duration of drug can also be evaluated. The model of nasal CDA challenge Togias developed is characterized by: (a) breathing air through a nasal CPAP mask placed over the nose; (b) subfreezing air temperatures ( 0 º to -10º C); (c) moderately high airflow (around 26 l/ min); and (d) a minute duration of challenge [36]. Subjects were asked to inhale through the nose and exhale through the mouth to maximize the potency of the stimulus. Nasal inhalation of warm and moist air (around 37ºC, 100% relative humidity) was used as a negative control. Braat and colleagues [41] used -10º C with a relative humidity of < 10% air via purpose-designed nose cap. The dosage was increased in steps by analogy with the histamine series as follows: 12.5, 25, 50, 100, 200, and 400 L. This involved CDA provocation steps of 1, 1, 2, 4, 8, and 16 min with a flow of 12.5 for the first step and 25 L/min for the following steps. With this model, they could differentiate patients with nonallergic noninfectious perennial rhinitis from control subjects. Hyperosmolar challenge of the nose involves the instillation of 10 ml of hyperosmolar mannitol solution (around 800 mosmol/ kg) into the nose (in the form of a nasal lavage), where it remains for 10 seconds [37,42] before being expelled. This can lead to nasal symptoms (burning is the most prominent symptom) and histamine release in returned nasal lavage fluids. One can access

11 11 the capacity of the nasal mucosa to correct acutely the hypertonic load by measuring the osmolarity of the mannitol solution before instillation and after expelling it from the nose [37]. Hypertonic saline spray with increasing concentrations (0.9% to 22% NaCl solutions) have been used in a stepwise protocol for hyperosmolar challenge in the nose [43,44]. Furthermore, localized hyperosmolar nasal provocation can be done by applying filter paper disc soaked with NaCl solution on the septal or conchal mucosa. [45,46]. For experimental research, quantitative measurements with high reproducibility are essential [47]. The interpretation of the results demands basic knowledge of the techniques employed as well as study design. All provocation studies require careful subject selection, and the disease state and the symptomatic status of the subject must be clearly defined by subjective and objective parameters. The selected subjects should be free of other underlying diseases and of the need for medications that may confound the interpretation of results. Assessment of the response A. Subjective: The subjective assessment of symptoms by the subject is valid. Symptoms produced after nasal challenge can be recorded by different techniques, such as symptom scores or visual analog scale. Congestion, rhinorrhea, pruritic score are easy to assess by the subjects and yield valuable information. Counting sneezes by investigator provides an objective symptom index. In addition to symptom scores, at least one objective measurement of the nasal response should be considered.

12 12 B. Objective: 1. Nasal airway resistance (NAR): Nasal congestion is one of the cardinal symptoms of nasal inflammation and the major symptom of the cold air-induced rhinitis. Rhinomanometry measures NAR by quantitatively measuring nasal airflow and pressure. Active anterior rhinomanometry is recommended and most frequently used because it is well-tolerated by the patients. Unfortunately, the correlation between the objective and subjective response is weak. 2. Nasal peak inspiratory flow: It is the simplest technique for detecting changes in nasal patency for repeated measurements before and after nasal challenge. It can also be done at home to monitor the symptom of nasal congestion or the response of the treatment over a more prolonged time period. 3. Nasal Volume: The geometrical cross-sectional area and nasal volume can be measured using acoustic rhinometry. 4. Nasal secretions: Several methods have been used to collect and quantify nasal secretions: suction, blowing, dripping, lavage, and absorption. Blown secretions can be quantified by weighing of handkerchiefs. Amount of nasal secretions can also be obtained by the placement of discs on the nasal mucosa for a fixed period of time. Discs used for secretion collection are first kept in Eppendorf tubes, and the disc-tube combinations are weighed before collection of secretions. After the collection, the discs are replaced in the Eppendorf tubes and weighed. The precollection weight is then subtracted from the postcollection weight to determine the weight of secretions generated in a fixed period of time [48]. The luminal surface of nasal mucous membrane is lined with an epithelial lining fluid (ELF). Nasal lavage samples ELF from a large mucosal area, whereas discs sample those secretions from a localized area. Importantly,

13 13 collection of nasal secretion is useful for the assessment of both cellular and biochemical changes in nasal secretions and change in the osmolarity of nasal secretion. 5. Biological markers: Biological markers can be measured in collected secretions to understand the underlying pathophysiology. These include histamine and other mast cell-associated mediators, cytokines, plasma protein, and glandular secretory products. It is important to know the stability of each marker after recovery, as well as the validity of each measurement when interpreting changes in the levels of these markers. The amount of markers obtained reflects their levels on the mucosal surface, which may not be the true amount of released substances. However, the level of mediators obtained at fixed time intervals best reflects the total amount of the mediator collected. 6. Cells: Cells can be obtained from the nasal cavity by multiple techniques. The epithelial layer can be scraped or brushed. Nasal scrapings and brushing allow mucosal sampling from a wide area of the nasal cavity and provide a lot of epithelial cells. However, it does not provide information on the submucosa. Blown secretion are simple and painless to collect, but are dependent on the spontaneous exfoliation of both epithelial and inflammatory cells. The specimen reflects activity only in the upper level of the nasal mucosa and yields low cellularity. Nasal lavage is also a useful method for providing cell for the study. This technique samples the entire nasal cavity and reflects changes in the upper mucosa only. Nasal biopsy provides information about structural elements and cellular contents of the epithelial layer and the deeper submucosa. A wide range of histochemical or immunohistochemical techniques can be employed for light microscopy to provide more detailed evaluation of the cellular content. Alternatively, samples may be processed specifically for either transmission or scanning electron microscopy and subjected to protein and message analysis.

14 14 Comparison between dry-air and hyperosmolar challenge Hyperosmolar provocation in the human nose activates nasal glands as shown by increased mucin and lysozyme [44] and TAME esterase [42,49] in nasal secretions. However, plasma extravasation has not been demonstrated [44,49]. Sanico et al [46] showed that unilateral stimulation of nasal mucosa using filter paper discs soaked with hyperosmolar stimuli resulted in bilateral secretory response. Pretreatment of the ipsilateral to the hyperosmolar challenge site with topical anesthetic (lidocaine) inhibited both the ipsilateral and the contralateral secretory response to the unilateral hyperosmolar challenge. This demonstrates that hypertonic stimulus can activate sensory nerves and induce central reflexes with efferent glandular responses in the nasal mucosa. Furthermore, repetitive, unilateral application of capsaicin for several days before hyperosmolar challenge inhibited both the ipsilateral and the contralateral secretory response [45], indicating that these responses are produced by capsaicin-sensitive fibers. These fibers carry neuropeptides which are responsible for neurogenic inflammation. Hyperosmolar provocation resulted in release of histamine and leukotriene C 4 [42], generating the hypothesis that hyperosmolarity leads to mast cell activation and inflammatory mediator release. Human lung mast cells release inflammatory mediators upon exposure to a hyperosmolar medium, in vitro [50,51] without the stimulus being toxic to the cells. However, mast cell tryptase cannot be detected following hyperosmolar nasal challenge [49]. The similarities between the nasal response to hyperosmolar stimulus and that to CDA are as follows:

15 15 1. Individuals who develop nasal symptoms after CDA challenge are more responsive to challenge with hyperosmolar mannitol. [37] 2. CDA provocation in the CDA-sensitive subjects can activate nasal glands as shown by increased levels of kallikrein and lysozyme [49,52] in nasal secretions 3. In cold-air-sensitive individuals, CDA activates sensory nerve endings and produces central secretory reflex: unilateral CDA challenge leads to bilateral secretion and pretreatment of the side ipsilateral to the CDA challenge site with topical anesthetic (lidocaine) inhibited both the ipsilateral and the contralateral secretory response [7] 4. CDA provocation in the CDA-sensitive subjects lead to mast cell activation as indicated by elevations of tryptase [49], histamine, prostaglandin D2, immunoreactive sulphidoleukotrienes [36,53]. It is believed to occur by dry-air-induced hyperosmolarity of nasal secretions. The difference between the nasal response to hyperosmolar stimulus and that to CDA is that plasma extravasation as shown by increased albumin levels [35] and bradykinins [36] in returned nasal lavage fluid have been demonstrated after CDA challenge, but not after hyperosmolar challenge. Late phase responses after nasal provocation with CDA were shown [54]. Eight of 12 CDAreactive individuals who had early symptom and mediator release in lavage fluids demonstrated late recurrence of symptoms and late peaks of histamine and TAME esterase activity, which are similar to those observed after allergen challenge of subjects with allergic rhinitis. Unfortunately, no one has examined the occurrence of late response after nasal challenge with hyperosmolar stimuli.

16 16 Assessment of the Ability of the Nose to Warm and Humidify Air Nasal Probe: We developed a probe with a thermistor and a humidity sensor that is placed in the nasopharynx by passage through the nose and makes continuous recordings [55]. We selected the nasopharynx for these studies because it represents the end result of nasal conditioning and because the probe can be placed reproducibly in the same location. Although the exact location for conditioning of air within the nose will shift, such a shift occurring before the exiting of air from the nose would not be expected to influence the pharynx or lower airway. We used the inhalation of air at different temperatures, humidities, and flow rates to assess the nasal airconditioning capacity. The technique involves placing a nasal CPAP mask over the probe with head straps. The first probe containing a temperature and humidity sensor was inserted into the nasopharynx, and a second probe containing another temperature and humidity sensor is inserted into the mask and positioned just outside the nasal cavity. Silicone wax was used to provide an airtight seal around the probes where they entered the mask. Air from compressed air tanks was passed through a flow meter into a cold air machine. CDA at 0% relative humidity was then delivered to the patient s nose via the mask at flow rates of 5, 10 and 20 l/ min. The air temperature was approximately 19, 10.5, and 0.8 ºC at 5, 10, and 20 l/ min., respectively. The range of flow rates from 5 to 20 l/min spans flows at rest to values at which most individuals switch from nasal to oronasal breathing [56]. The subjects were instructed to breathe in and out through the mouth. Exposure to each flow rate lasted 22 min. The last 15 min. at each flow rate were used to calculate the water content of the air by the standard formula [55]. The difference between the

17 17 water content of air prior to entry into the nose and that in the nasopharynx is the water gradient (WG) across the nose, which represents the amount of water evaporated by the nose to condition air. Nasopharyngeal temperatures at 5, 10, and 20 l/min for subjects during exposure to CDA were 33.4 ± 0.7 ºC, 30.5 ± 1.1 ºC, and 25.9 ± 1.4 ºC, respectively [55]. The nasopharyngeal temperature fell significantly with increasing flow rates. Furthermore, nasopharyngeal temperatures during CDA were consistently lower than those during exposure to hot, humid air at each flow rate. After CDA exposure, the WG at 5, 10, and 20 l/min. was ± 12.6 mg, ± 32.0 mg, and ± 62.1 mg, respectively. Individuals showed a wide variability in their ability to condition air. This ability does not correlate with baseline nasal airway resistance, nasal volume, nasopharyngeal mucosal temperature or body temperature. Proctor et al. speculated that prior viral infections may have altered the epithelium, thus producing the variability [56]. However, it may reflects an intrinsic capacity of the nasal surface to condition inhaled air. A recent study showed that siblings condition air similarly, suggesting a hereditary component to nasal conditioning (unpublished observation). Surface Temperature: Multiple factors can contribute to the amount of water delivered to inspired air. Among these, the geometry of the nasal cavity and the temperature of the nasal mucosa appear to be key factors [15]. Keck and colleagues measured intranasal temperature at different locations in 50 volunteers after inspiration and found that the greatest increase in temperature was observed in the nasal valve area indicating that most of the air-conditioning

18 18 takes place in the anterior segments of the nose between the nasal valve and the middle turbinate. [57 We studied the effects of raising the nasal mucosal surface temperature by immersion of the feet in warm water. This technique was based on the observations in 1954 by Cole [58]. He showed that the mucosal temperature in the nose increased approximately 2ºC when a fan blew heat from an open flame onto the dorsal skin of subjects. This increase occurred without a concurrent increase in body core temperature. Studies of the microcirculation of skin and its contribution to heat exchange predict that the increase in nasal mucosal temperature after external thermal stimulation is secondary to a neural reflex [59]. Furthermore, elevation of the nasal mucosal surface temperature after warming of the feet was shown by us to occur via a neural reflex [60]. Our method of heating the feet by immersion in a warm water bath reproduced Cole s observation and showed that increased nasal mucosal temperature improved the ability of the nose to condition inspired air without a significant change in the volume of the nasal cavity [61]. These findings are consistent with the theoretical model of heat and water vapor transport across the nose developed by Hanna et al. [15]. Application of a topical vasoconstrictor drug, oxymetazoline, decreases nasal mucosal temperature [62] and the temperature of inspired air at the oropharynx [24]. However, whether or not vasoconstrictors could reduce the WG across the nasal passages is unknown. Application of an alpha-adrenoreceptor antagonist which increased the temperature of nasal mucosa had no impact on the ability of the nose to condition air [62]. Furthermore, we reduced the nasal volume without altering the mucosal temperature by placing subjects in the supine position and studied

19 19 this effect on nasal conditioning capacity. Contrary to the theoretical model, in the supine position, subjects were less able to condition CDA compared with the upright position [63]. Based on these observations, the theoretical model of Hanna and Sherer is only partially supported [15]. It is quite possible that surface temperature and nasal volume may be only partial factors responsible for water transportation capacity across the nasal mucosa. There are many complex factors (e.g. electrolyte transportation across the nasal mucosa, nasal potential differences, tight junction transport, or aquaporin function) which have not been accessed. Nasal inflammation: With our ability to measure nasal conditioning, we next studied the influence of allergic inflammation on the air conditioning capacity of the nose. We previously showed that subjects with seasonal allergic rhinitis out of season had a reduced ability to warm and humidify air compared with normal subjects [55]. The reason for the difference is not apparent. We next studied the effect of allergic responses induced by either seasonal exposure or nasal challenge with antigen on nasal conditioning of CDA. Allergic response caused by either seasonal exposure or allergen challenge, specifically the late-phase response, increased the ability of the nose to condition inspired air [64]. The allergen challenge-induced observation was subsequently confirmed by another group of investigators in subjects with perennial allergic rhinitis [65]. A critical question remains: How does allergic inflammation improve the ability of the nose to condition inspired air? We considered the two major theoretical contributors to conditioning; nasal geometry and surface temperature. Allergic inflammation does not appear to affect surface temperature under resting conditions [64], but the effect on surface temperature under stress

20 20 condition e.g. CDA inhalation is unknown.. Rozsasi et al. [65] found that temperature on both sides of the nose increased non-significantly after nasal allergen challenge with no correlation to changes in nasal perimeter and patency. In the opposite direction, a study demonstrated that treatment of the nose with topical glucocorticosteroids for 2 weeks decreases the ability of the nose to condition air in nonsmoking subjects with asthma [66]. These studies demonstrate that allergic inflammation increases nasal air-conditioning, which is probably related to inflammatory products that alter ionic transportation across the epithelium, leading to better water transport. Patients with AR and asthma have been shown to have stronger nasal responsiveness to CDA compared with patients with rhinitis alone. This observation demonstrated that, compared with rhinitis alone, the presence of asthma and rhinitis signifies a higher degree of functional abnormality of the entire airway [52]. We have shown that subjects with asthma had a decreased ability to condition air [67]. The more severe the asthma, the worse was the ability of the nose to condition air, indicating that the reduced nasal conditioning capacity of subjects with asthma may adversely affect the lower airway. Parasympathetic Nervous System: The parasympathetically driven glands in the nose, approximately 45,000 per nasal cavity, are the major contributors to the volume of surface secretions [27]. Blocking the parasympathetic system with anticholinergic agents reduces rhinorrhea [68]. Local application of atropine sulfate significantly inhibited rhinorrhea and TAME esterase activity in nasal lavage fluids, suggesting that parasympathetic neuronal activity occurs during the nasal response to CDA [35]. A commercially available anticholinergic treatment for excessive rhinorrhea is ipratropium bromide. We were concerned that, while

21 21 ipratropium bromide treated the rhinorrhea, it might worsen the ability of the nose to condition air. It had been shown that subcutaneous injection of 1 mg atropine decreases the ability of the nose to humidify air [69]. However, application of homatropine or ipratropium bromide to the nasal surface did not impair its humidification function [70,71]. We also studied the effect of treatment with ipratropium bromide on the ability of the nose to condition CDA. Ipratropium bromide improved the conditioning of inspired air, as demonstrated by an enhancement of the water supplied to inhaled air during its passage across the nasal cavity despite the fact that the secretory response measured after the end of cold air exposure was decreased [72]. This experiment suggests that glandular secretion is not a major contributor to nasal condition and blocking secretions does not adversely affect the ability of the nose to warm and humidify air. Mechanism of CDA-induced rhinitis CDA challenge to the nose led to mast cell and glandular activation [49,52] and plasma extravasation [35] (Figure 1). This was only observed in cold-air-sensitive individuals, but not in the non-sensitive controls and correlated well with the development of nasal symptoms. Nasal reaction caused by bidirectional nasal breathing of cold dry air (inhaled and exhaled through the nose) is qualitatively similar to that induced when air is only inhaled through the nose and exhaled through the mouth. [48].

22 22 Water Homeostasis Cold, Dry Air Heat Osmolarity desiccation Epithelial shedding Nasal Mucosal Temperature Mucosal dysfunction Mast Cell Activation changes in epithelial ion transport Sensorineural stimulation Nasal Epithelium Arteries Subepithelial Capillary Blood Flow Glandular activation Capillaries Vascular engorgement Sinusoids Veins Nasal Symptoms Figure 1 Pathophysiology of CDA-induced rhinitis CDA inhalation stimulates sensory nerves and generates a cholinergic secretory response. Sensory nerve activation of CDA was shown by the production of central secretory reflex. The cholinergic secretory response was demonstrated by the reduction of contralateral secretory response after ipsilateral CDA provocation when the contralateral nostril was pretreated with atropine [7]. Furthermore, atropine was shown to reduce rhinorrhea (but not nasal congestion) scores, as well as a bio-marker of glandular activation after CDA challenge, without affecting plasma exudation [35].

23 23 Although nasal reaction to cold air has been found to involve both mast cell activation and sensorineural stimulation, the clinical significance of the former pathway is unknown. For example, a topical antihistamine (azatadine base) had been previously shown to inhibit allergeninduced symptoms and mast cell mediator release in individuals with allergic rhinitis [73]. However, it had no effect on either symptoms or histamine and TAME-esterase release after CDA provocation. [74]. Furthermore, the use of a topical glucocorticosteroid (beclomethasone) for 7 days significantly reduced histamine release, but not in TAME-esterase activity or albumin levels or in symptoms after CDA challenge [34]. These results indicate that histamine may not be essential for the development of the immediate nasal reaction to CDA. The clinical response to CDA seems to be primarily mediated by neural mechanisms with a sensory element which is located in the nasal mucosa and an effector element which is mostly cholinergic. In support of this concept, objective measures of the nasal reaction (decreased nasal patency and secretion weight) to CDA have been successfully reduced with intranasal capsaicin treatment, which defunctionalizes nociceptor c-fibers [75]. Also, nasal atropine and ipratropium bromide have been effective in reducing rhinorrhea in skiers [76]. During cold air breathing, there is loss of heat and water from mucosal surface, resulting in mucosal cooling and hyperosmolarity of nasal secretions. The affect of cooling of the mucosa is unknown. Evidence has shown that hyperosmolarity is a known trigger for mast cell and sensory nerve activation in the human nose. Water loss leading to hypertonicity is more likely to be the key stimuli compared to heat loss.

24 24 One hypothesis of CDA-induced symptoms of rhinitis is that the respiratory mucosa of individuals with CDA sensitivity cannot compensate for the loss of water that occurs on exposure to the stimulus, leading to epithelial damage. Cruz et al found a 6-fold increase in nasal lavage epithelial cells in the CDA-sensitive group after CDA, but not after warm, moist air [39]. This finding shows that epithelial cell shedding accompanies clinical responses to CDA in the human nose, supporting the above hypothesis. Why does cold air-induced rhinitis affect a subgroup of humans more than others. Neither the presence of atopy nor nasal responsiveness to histamine predicted CDA responsiveness [37]. The osmolarity of the epithelial lining fluid was increased after CDA provocation in the CDAsensitive, but not in the insensitive group [5]. In addition, when nasal challenge with a hyperosmolar solution was performed in both groups, CDA-sensitive subjects release significantly more histamine in nasal lavage fluids compared with CDA-insensitive subjects [37]. The underlying difference between CDA-sensitive and insensitive individuals probably relates to the ability of the mucosa to cope with conditions that demand increased water supply to inhaled air or to the epithelial surface, either after the inhalation of dry air or application of a hyperosmolar stimulus. The airway mucosa of CDA-sensitive individuals cannot compensate for the water loss that occurs under extreme conditions, leading to epithelial damage [39] whereas CDA-insensitive individuals have adequate water supply to the epithelial surface under stressful conditions resulting in no reaction to the stimulus. This finding reflects unequal capability of nasal mucosa to interact with environmental temperatures and humidity in individuals. The human model for the study of dry-air and hyperosmolar challenge has shed insights into the pathophysiology of cold air-induced rhinitis.

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