INTRODUCTION

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THE NOSE FUNCTIONS TO condition the temperature and humidity of inspired air (6, 7, 13, 14, 19). How the nasal glands, blood vessels, nerves, epithelium, and other resident cells function in concert in health and disease to achieve this goal remains largely unexplored. One end result of nasal conditioning is to prepare air for gas exchange by the alveoli, which occurs at 37°C and 100% relative humidity (RH).

The air conditioning capacity of the nose protects the lower airways by warming and humidifying the air from ambient conditions that range from temperatures from 42 to 48°C and from 0 to 100% RH (17). Nasal conditioning occurs at a resting ventilation of ~5 l/min to sustained flow rates of 20 to 30 l/min before nasal breathing is supplemented with oral breathing (9). The importance of nasal conditioning is exemplified by the work of Shurman-Ellstein et al. (20). Inhalation of the same volume of dry air through the mouth, in contrast to the oronasal route, caused a greater reduction in forced expiratory volume in 1 s in asthmatic patients (20).

At present, the nasal air conditioning process is poorly understood. We undertook the present study to evaluate the influence of inspired air conditions and inspiratory flow rates on nasal air conditioning and used this approach to test the hypothesis that nasal air conditioning is similar in asymptomatic allergic subjects out of their allergy season and normal, nonallergic subjects. Investigations into nasal conditioning of patients with allergic rhinitis are important because of the high prevalence of allergic rhinitis in the US population and its association with lower airway disease (10).

The air-conditioning capacity of the nose can be investigated under different atmospheric conditions. Exposure of the nose to hot, humid air (HHA; 37°C and >90% RH) or cold, dry air (CDA; 0°C and <10% RH) allows assessment of nasal function under two extreme conditions. Similarly temperature and RH measurements can be performed at basal or increased nasal airflow, thereby testing the conditioning capacity of the nose at rest and during increased flow rates, as achieved during moderate exercise. The conditioning property can be investigated in healthy noses as well as in those affected with inflammation, such as allergic rhinitis. The interaction of nasal conditioning and allergic inflammation, with its resultant mucosal hyperreactivity, has not been investigated in detail.

Evaluation of the conditioning capacity of the nose has been hampered by the difficulty of sampling air as it exits the nose. Therefore, we developed a probe to measure the temperature and RH of air exiting the nasal cavity. The probe, equipped with temperature and humidity sensors, is inserted through one nostril into the nasopharynx and continuously samples the airstream immediately after it exits the other nostril. By measuring airstream temperature and RH as it enters the nose and as it exits into the nasopharynx, one can assess the nasal air-conditioning capacity at controlled air temperatures, RHs, and flow rates.

	MATERIALS AND METHODS

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Nasal probe construction. Nasal probes were constructed from a 14-Fr suction catheter (4-mm outside diameter × 15-cm length; Kendall Healthcare Products, Mansfield, MA). Temperature and RH sensors were inserted into the catheter through circular holes 1 cm from the rounded probe tip. The holes were fashioned to accommodate the sensors and to allow circulation of air around them.

Probe insertion. All patients were seated in a chair during the entire study. Using a nasal speculum and a light source, we inspected each nostril for significant septal deviation or inferior-turbinate hypertrophy, which might hinder probe insertion. The more-patent nostril was chosen as the conduit for the probe and was sprayed with two puffs (0.2 ml) of 0.05% oxymetazoline hydrochloride (Nostrilla, Ciba Self-Medication, Woodbridge, NJ), followed by two puffs (0.2 ml) of 4% lidocaine (Roxane Laboratories, Columbus, OH). Ten minutes later, the probe was slowly inserted through the nose into the nasopharynx. To prevent the sensors from contacting nasal secretions during insertion, the probe tip was covered with thin nylon sheeting that was withdrawn after the probe was positioned in the nasopharynx. The rationale for positioning the probe in the nasopharynx is that it samples the end result of nasal warming and humidification. Nasal endoscopy with a flexible nasopharyngoscope was then performed in the same nostril in which the probe was inserted, for confirmation of its position and sensor orientation. Because the effects of lidocaine, oxymetazoline, and probe insertion on the conditioning capacity of the nostril are currently unknown, we sealed the "probe" nostril with a wax plug. Thus the probe sensors detected inspired-air conditioning by the unmanipulated nostril.

"Sniff" test. To ensure that the probe sensors retained an adequate response time when positioned in the nasopharynx, the subject forcefully inhaled room air through the nose with the mouth closed. This maneuver created an airflow transiently exceeding 100 l/min. A rapid change in both temperature and RH readings during the sniffs reflected adequate response times for the studies presented here.

Exposure conditions. Preconditioned air was delivered through a nasal continuous positive airway pressure mask (Respironics, Murrysville, PA) firmly applied to the face. A spacer was also placed to avoid pressure from the mask over the nasal bridge. A second probe, similar to the one in the nasopharynx, was positioned within the mask for measuring the temperature and RH of inhaled air before its entry into the nose. For CDA challenges, dry air from compressed air tanks was chilled by passage at prechosen flow rates through copper tubing submerged in refrigerated ethanol (FTS Systems, Stone Bridge, NY). CDA was directed into the nasal mask through flexible rubber tubing; air flowing into the mask then entered the patent nostril and exited through the mouth. The precise temperature delivered to the nose depended on the flow rate and averaged ~19°C at 5 l/min to 10.5°C at 10 l/min and 0.8°C at 20 l/min. For delivery of HHA challenges, air from the compressed air tank was passed through a bubble humidifier immersed in a hot water bath. In this way, air at 37°C and >90% RH was delivered to the nasal mask.

Data handling. During CDA and HHA challenges, temperature and RH values were collected simultaneously by the sensors located in the mask and in the nasopharynx. Water content of air (WC) is a function of its temperature and RH, and was computed (2) from temperature and RH as where WC is in milligrams per kilogram; T and RH are the temperature and relative humidity values of air at 760 mmHg, respectively; and D is the density of air (1.2 g/l at 20°C). Total water lost by the nasal mucosa [water gradient (WG)] during a 15-min challenge was calculated from the difference in water contents of inspired and nasopharyngeal air, the flow rate, and the challenge duration (15 min).

Subjects. Eleven healthy, nonallergic subjects were recruited for this study on the basis of the absence of a history of chronic or frequently recurrent nasal symptoms and negative skin-prick testing to seasonal and perennial allergens. Twenty-two seasonally allergic subjects with positive skin prick testing were also studied outside their allergy season (Table 1). They were asymptomatic and taking no medications for their nasal symptoms within the 1 mo before the study. During their allergy season, 19 subjects used over-the-counter antihistamines and/or decongestants, 2 used prescription nonsedating antihistamines, and 1 used intranasal steroids. In studies not using all subjects, the age and gender were similar to the group as a whole. Exclusion criteria included a history of perennial allergic or nonallergic rhinitis and the presence of nasal symptoms suggestive of a common cold at the time of study. All subjects underwent nasal endoscopy before and after probe placement. This demonstrated no mucosal or structural abnormalities. The study was approved by the Institutional Review Board at the University of Chicago, and all subjects gave informed, written consent before participation.

Study design. On presentation to the laboratory, the subjects rested for 15 min before the initiation of the experiment so that their noses adjusted to the room temperature and RH in the laboratory, which were usually 22°C and <10% RH. We prospectively assigned allergic and nonallergic subjects randomly to breathe HHA and CDA on two separate visits. We also tested the reproducibility of the response to CDA challenge in both groups by repeating the CDA challenge on separate days two times in allergic subjects and three times in nonallergic subjects. All visits were separated by at least 48 h to avoid potential effects of one challenge on another.

Statistical analysis. Statistical analysis was performed with parametric statistics. Multiple, repeated measurements were compared by ANOVA, and post hoc analysis was performed by using Fisher's test of least significant difference. Comparison of results within the same group of subjects undergoing different exposures was done by paired t-test. Nonpaired comparisons (e.g., allergic vs. nonallergic subjects) were performed with the nonpaired t-test. Two-tailed P values  0.05 were considered to indicate significance. The data are presented as means ± SE.

	RESULTS

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Sniff test. To ensure that the temperature and RH sensor continued to function after placement in the nasopharynx, subjects were asked to breathe room air and perform the sniff test periodically during the experiment. The data from a representative patient are shown in Fig. 1. Room air at 22°C, 30% RH was warmed up in the nasopharynx to 32°C when the subject was quietly breathing. With forceful inhalation, the temperature dropped briefly to 22°C and was then restored back to 32°C. The RH tracing behaved in a similar manner. At rest, the RH in the nasopharynx was 100%. With forceful inhalation, there was a brief drop in the RH to between 10 and 20%, followed by its restoration to 100%. This maneuver shows the adequacy of time responses for our studies. Sniffs performed during and after CDA or HHA exposures showed similar results.

View larger version (22K): [in this window] [in a new window]   Fig. 1.   Data from a representative subject performing "sniff" test. Temperature and relative humidity in nasopharynx are shown during inhalation of air at room temperature for a time interval of ~8 min. Dips in both nasopharyngeal temperature and relative humidity are seen in response to vigorous inhalations, verifying functioning of probe sensors.

Exposure to HHA. Eleven nonallergic and 8 allergic subjects were subjected to HHA (37°C; >90% RH) at flow rates of 5, 10, and 20 l/min, each lasting 22 min. The mean nasopharyngeal temperatures at 5, 10, and 20 l/min were 35.7 ± 0.24, 36.0 ± 0.3, and 35.9 ± 0.4°C, respectively (Fig. 2). There was no statistically significant difference in nasopharyngeal temperatures at the three flow rates (P = 0.56) and no difference between allergic and nonallergic subjects (P > 0.05).

View larger version (10K): [in this window] [in a new window]   Fig. 2.   Nasopharyngeal temperature after exposure to 3 flows of cold, dry air (CDA) and hot, humid air (HHA) as depicted on x-axis. , Results after HHA; , results after CDA. Values are means ± SE of 19 patients. * P < 0.05 vs. 5 l/min.  P < 0.05 vs. 10 l/min. ** P < 0.01 vs. responses after HHA.

Exposure to CDA. Eleven nonallergic and 8 allergic subjects were exposed to CDA at flow rates of 5, 10, and 20 l/min. The tracing from one individual is shown in Fig. 3. The temperature in the mask dropped from 31 to 26°C and then plateaued at ~23°C. The nasopharyngeal temperature changed from 36 to 32°C. Increasing the flow to 10 l/min lowered the mask temperature to 10°C, and the nasopharyngeal temperature decreased to 25°C. At a flow of 20 l/min, the mask temperature decreased to 5°C and the nasopharyngeal temperature to 20°C. RH in the mask was consistently at 0% and that in the nasopharynx at 100% with all three flows in all subjects.

View larger version (22K): [in this window] [in a new window]   Fig. 3.   Representative data from 1 nonallergic subject after exposure to CDA. The y-axis reflects temperature and relative humidity, and x-axis is time. Subject was exposed to 3 increasing flows of CDA (5, 10, and 20 l/min) for a total duration of 22 min each. RH(NP), relative humidity in the nasopharynx; RH(MK), relative humidity of inhaled air as measured in mask applied to patient's nose; T(NP), nasopharyngeal temperature; T(MK), temperature of inhaled air in mask.

WG. The WG across the nose was calculated for all three flow rates in subjects (n = 19) after HHA and CDA exposure. After HHA inhalation, the WG at 5, 10, and 20 l/min was 23.3 ± 12.5, 52.2 ± 31.8, and 159.2 ± 66.7 mg, respectively (Fig. 4). ANOVA and post hoc analysis showed a significant difference between WG at 5 and 20 l/min (P < 0.05), as well as between 10 and 20 l/min (P < 0.05) flow rates. After CDA challenge, the WG at 5, 10, and 20 l/min. was 297.6 ± 12.6, 509.1 ± 32.0, and 794.1 ± 62.1 mg, respectively (Fig. 4). Again, ANOVA and post hoc analysis showed that the WGs at 10 and 20 l/min were significantly higher than that at 5 l/min (P < 0.05) and that the WG at 20 l/min was significantly higher than that obtained at 10 l/min (P < 0.05).

View larger version (12K): [in this window] [in a new window]   Fig. 4.   Water gradient across the nasal cavity after exposure to either HHA or CDA at 3 flow rates (5, 10, and 20 l/min). Values are means ± SE of 19 subjects. * P < 0.05 vs. 5 l/min.  P < 0.05 vs. 10 l/min. ** P < 0.01 vs. CDA values at same flow rates.

Reproducibility. The reproducibility of the nasal response to CDA challenge was studied in eight nonallergic subjects on three separate visits (Table 2). During all three visits, there were flow-dependent significant increases in the WG across the nose. After CDA challenge, the mean total WG values for the three visits were not statistically different (P = 0.56) (Fig. 5). The coefficient of variation (%) (SD/mean × 100%) of total WG obtained during the three visits ranged between 5.1 and 33.8% and averaged 14.7%. The reproducibility of the CDA challenge was also studied in eight allergic subjects during two CDA visits (Table 3). On each visit, there were flow-dependent significant increases in the WG across the nose, and the mean total WG was similar on each visit (P = 0.8145; Fig. 5). The coefficient of variation of total WG in these patients ranged between 1.2 and 22.3% and averaged 8.8%.

View larger version (21K): [in this window] [in a new window]   Fig. 5.   Reproducibility of CDA response in nonallergic (A) and allergic (B) subjects. Nasal responses of nonallergic subjects (n = 8) to 3 repeated CDA challenges and those of allergic subjects (n = 8) to 2 repeated CDA challenges are depicted as individual data. Solid bars, means ± SE of the group. Total water gradient across nasal mucosa after all 3 exposure flow rates (5, 10, and 20 l/min) is depicted. There was no significant difference between total water gradients across nasal mucosa in either of the groups on the repeated visits, establishing reproducibility of the response.

Allergic vs. nonallergic subjects. The response to CDA inhalation was compared between 11 nonallergic subjects and 22 allergic subjects. Allergic subjects had significantly lower nasopharyngeal temperatures than did nonallergic subjects at 5 l/min (31.7 ± 0.5 vs. 34.6 ± 0.9°C, respectively; P = 0.0004) and 10 l/min (28.2 ± 0.5 vs. 32.2 ± 1.5°C, respectively; P = 0.003). When allergic were compared with nonallergic subjects, there was a significant difference in WG values obtained at 5 and 10 l/min as well as in the total WG (Fig. 6).

View larger version (15K): [in this window] [in a new window]   Fig. 6.   Comparison of response to CDA challenge of allergic subjects out of allergy season (n = 22) and nonallergic (n = 11) subjects. Left, means ± SE of water gradient across the nose at each of the exposure flow rates. , Response of allergic subjects; , response of nonallergic subjects. Right, total water gradient across nasal cavity for all 3 flow rates of CDA. Solid bars represent means ± SE of individual data points. * P < 0.05 and ** P < 0.01 vs. allergic subjects.

	DISCUSSION

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Our capacity to measure the ability of asymptomatic allergic and nonallergic individuals to warm and humidify air in the nasopharynx is novel. Our demonstration of a difference in the ability of these groups to perform this function is exciting. Unfortunately, we have no knowledge of how inflammation or hyperreactivity affects nasal air conditioning. On the basis of a theoretical model, Hanna and Scherer (12) predict 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. Allergic inflammation would be predicted to affect both parameters. Because the allergic individuals were asymptomatic and outside their allergy season, we do not know the state of inflammation in their nasal mucosa nor the blood flow and shape of the nasal cavities at the time of testing. Endoscopic evaluation of the nasal cavity showed no evidence of inflammation in the allergic subjects or differences compared with the nonallergic, normal subjects.

We developed a means to quantify the ability of the nose to warm and humidify air. The technique involves involves the use of one nostril as a conduit for a catheter containing sensors for continuous sampling of air exiting the opposite nostril. The measurements obtained in the nasopharynx do not determine where the changes occurred during the passage of air through the nasal cavity, but rather they yield the end result of nasal conditioning. The exact location for conditioning of air within the nose may vary in individuals or disease states and may influence nasal function, but it is the air exiting from the nose that would be expected to influence the lower airway. Another reason for sampling the nasopharynx is the ability to place the probe in the same location reproducibly.

The air delivered to the nose for conditioning was controlled. We studied two relatively extreme conditions: HHA (37°C, >90% RH humidity) and CDA (0-5°C, <10% RH). Airflows approximating the range of nasal flows during rest and mild exercise were chosen (9). Unidirectional flow was chosen instead of bidirectional flow as occurs with breathing. This procedure was selected to provide steady-state conditions that might not be reached because of rapid changes that might occur as a result of heat sinks within the nose, the measuring devices, and the air-delivery system. Additionally, the unidirectional flow prevented the mixing of exhaled air from the lungs and reduced the likelihood of HHA from the lungs condensing on the sensors and giving inappropriate assessment of nasal function. This latter phenomenon was of particular concern for the RH sensor.

Although we expected the air to be fully saturated, we needed to ensure that the humidity sensor was functioning. To this end, we developed the sniff test. By forcible inhaling of air through a partially occluded nose, velocities of air estimated to exceed 100 l/min can be obtained for a few seconds. To our advantage, these flow rates exceeded the nasal mucosa's ability to saturate air fully at reduced temperatures, and therefore a drop in RH and temperature was detected by the nasopharyngeal probe, documenting its functionality.

When warm, moist air was breathed (air similar to that in the alveoli), the nose absorbed a little water. Normally, the temperature of the anterior nasal mucosa is 32°C (7). This surface temperature is slightly below that of the inspired air (37°C), and water would be expected to condense on the nasal mucosal surface (13, 14).

Breathing of CDA led to wide individual variability in the temperature recorded in the nasopharynx. Nevertheless, the RH remained at 100%, although the absolute humidity or water content varies with temperature. Furthermore, we demonstrated the reproducibility of these observations by performing repeated measurements on the same individual on different days. Our measurements proved to be fairly reproducible for in vivo human studies.

Similar measurements have been made previously by only a few investigators and were performed only in small numbers of healthy subjects (1, 6, 7, 13, 14, 19). Some studies employed discontinuous sampling techniques, whereas others used invasive techniques, such as cricothyroid membrane puncture in which 5 of 16 subjects fainted as a result of the procedure (13). Our preliminary data measuring temperature and RH after exposure to CDA are consistent with previously published results.

For a full understanding of the ability of the nose to condition air, we must both observe the organ as a whole and examine its individual components. These structural components include a pseudostratified, columnar epithelium with a continuous basement membrane (18); a subepithelial capillary system (5), a distensible, cavernous, vascular network; tubuloalveolar, seromucous glands and goblet cells (21); parasympathetic and sympathetic innervation (16); immunohistochemical evidence of a nonadrenergic, noncholinergic nervous system (3, 4); and the presence of submucosal inflammatory cells. Focusing solely on the individual components of the nose or an isolated element of allergic inflammation may distort the importance of their contribution to overall function. Similarly, focusing solely on the whole response may miss compensatory shifts in the reactivity of the individual components. For example, air may be conditioned to the same extent during an allergic response but only because of a compensatory response in the glands and blood vessels. Our challenge will be to determine the reason for the difference between asymptomatic allergic and nonallergic subjects.