Rhinomanometry

ontinuing

Medica

druciation

This continuing medical education self-assessment program is sponsored by The American Academy of Aillergy and Immunology.

Rhinomanometry Michael

J. Schumacher,

m----_-e--MB, FIRAW ITkxvz, Ariz.

The sensation of obstruction to airflow in the nose is a common symptom, affecting most patients8with rhinitis. In these patients it is highly variable in severity, reflecting physiologic changes and pathologic responses to inhaled or ingested allergens, chemical irritants, drugs, or cold dry air. Nasal obstruction may also be relatively fixed, caused by the prese:nce of a foreign body or anatomic abnormalities, such as sepltal deviation, polyps, tumors, or granulomatoas infiltrates. The subjective sensation of nasal obstruction is very difficult to quantify in clinical practice unless the obstruction is nearly complete. Furthermore, perception of nasal obstruction varies considerably, often bearing no direct relationship to the actual resistance to airflow in the nose. Mouth breathing, particularly in children, does not always signify severe nasal obstruction, and the oronasal distribution of ventilation in patients with rhinitis may not correlate with the degree of nasal obstruction.‘, ’ In the clinical assessment of airway patency, the “sniff test” is umeliable in patients whose nares readily display alar collapse. Thus, an objective technique for measurement of obstruction to nasal airflow is useful. RMM implies the measurement of the difference in

Fromthe Department of Pediatrics, University of Arizona Health! Sciences Center, Tucson, Ariz. Reprint requests: M. J. Schumacher, MB, Dept. of Pediatrics., University of Arizona Health Sciences Center, Tucson, AZ

85124.

,Abbreviations used

RMM: Rhinomanometry NAIR: Nasal airway resistance

transna,sal pressure that drives the flow of air through thgenas,al cavities. Thus, the technique requires simultaneous measurement of the transnasal gradient and the rate of nasal airflow. It is confused with nasal peak expiratory flow rate determinations, a method that provides no i~fo~a~~o~ on the pressure or driving force producing the peak expiratorly flow. The transnasal pressure difference is measured between the nasopharynx and the external nares. Pressure and flow data obtained during respiration are usually represented as a curve plotted on Cartesian coordinates or as a variable derived from pressure and flow differentials in the curve. These derived variables include NAR (commonly abbreviated Rn), nasal conductance, and work of breathing. PRESISURE-FLOW CURVES Airflow in the nose is probably never lamilaar, even in unobstructed respiration with normal tidal volumes. Turbulent airflow facilitates the deposition of large particles that contaminate inspired air, increasing fhe efficiency of particle trapping in the nasal cavity. Particularly during inspiration, turbulence of airflow is aided by the position of the narrowest cross-sectional area of the nose at the nasal valves, a short distance

during inspiration and closed in ~~pirati~u~ as illustrated in Fig. 1, inspiratory alar collapse may be responsible.7 Problems caused by phase shift may be overcome in curve-fitting studies by applying the formula NAR = K, + K2iV = K, - K,,V where Kzi and K, are inspiratory and expiratory constants, respectively.6 This formula for fitting to the entire pressure-flow loop has the advantage of closely approximating the pressure-flow curves near zero flow, whereas fitting to the acceleration phases of inspiratory or expiratory segments of the curve often cause considerable errors at low flow rates. FIG. 1. Pressure-flow loop from one normal breath (dotted line) with Rohrer equation curves fitted separately to the acceleration phases of inspiration (top right) and expiration (bottom left,l Ordinate is pressure and abscissa is flow. Irregular plots above and below abscissa are residual differences between the fitted curve and the data, multiplied by 10. Note differences between inspiratory and expiratory loops. Alar collapse in this patient is reflected in the open inspiratory loop.

from the external nares. Predominant sites of obstruction to airflow in the normal nose are at this point and at the pyriform aperture of the bony cavum.3 Turbulence is further increased by the complex shape of superior, middle, and inferior turbinates that increase the surface area of the lateral walls of the nose. Thus, the relationship between pressure and flow is never linear and approximates to a quadratic equation, as suggested by Rohrer: P = K,V + K2V2 where P is the transnasal pressure gradient, V is the flow rate, and K, and K, are constants that describe the slope and shape of the pressure-flow curve, respectively. Inspiratory segments of the curve have been demonstrated to fit to this equation.4 Computer-aided data acquisition has demonstrated that inspiratory and expiratory segments of the nasal pressure-flow curve differ significantly in most subjects and that a modified ohrer’s equation is suitable only when it is fitted separately to the inspiratory and expiratory loops (Fig. l).” Careful inspection of pressure-flow curves demonstrate that most of them are, in fact, open loops in which the acceleration and deceleration phases are separated. These differences were demonstrated in mathematics modeling experiments to be due to a slight delay in the increment in flow when an increressure is applied.6 Study of a number of normal individuals and patients with rhinitis demonstrates that the degree of openness of the loop, that is, the degree of phase shift, varies considerably from one patient to another. When the loop is wide open

PHYSIOLOGIC PERTURBAT PRESSURE-FLOW RELATIO In the normal nose, NAR is highest in infancy, being approximately six times higber than adult values.8-10Resistance falls progressively during childhood with growth of the maxillary bones and tends to be higher in female than in male subjects.“. ‘* Nasal patency may also be affected by genetic and racial influences on the shape of the maxillae and the cartilaginous portion of the nose.” Although a high arched palate is not always associated with increased NAR, separation of the longitudinal suture of the maxilla by orthodontic procedures designed to eliminate molar crossbite reduces NAR. 13,I4 Physiologic variation in nasal potency is determined mainly by the degree of congestion of capacitance blood vessels in the submucosa of the middle and inferior turbinates. These sinusoidal vessels constrict cyclically under sympathetic neural control. This results in simultaneous and opposite changes in NAR in each of the nasal cavities, with a cycle length of 2 to 4 hours, easily demonstrable in 60% to 70% of normal individuals.‘5s I6 Resistance to airflow on the congested side is affected by posture, resistance being maximal in the supine horizontal position and minimal in the upright sitting position.“, I8 In the recumbent lateral position, resistance in the inferior, dependent side is higher than in the superior side, possibly from autonomic reflexes arising from the dependent shoulder.” Neck vein compression also In patients with allergic rhinitis, NA by exercise, during which sinusoidal decongestion results from increased sympathetic nerve discharge2” Voluntary isocapnic hyperventilation has no effect on NAR in normal subjects.” NAR may be reduced by breath holding or rebreathing that increases arterial CO, corIce~trations, leading to alae nasi activation.” The idea that nasal decongestion is the cause of decreased resistance during CO2 inhalation23 has not been confirmed by critical studies. NAR is usually less during inspiration than

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in expiration5. 24 partly because of alae nasi function.22z 25 Activation of alae nasi muscles dilates the nasal vestibules, increasing the effective crosssectional diameter at the nasal valve, which is near the point of maximum physiologic obstruction in the nose. These muscles serve to splint the cartilaginous region of the nose, particularly during rapid inspiration, as in sniffing. Failure of this splinting effect in facial nerve palsies can cause inspiratory alar collapse. CALCULATION

OF NAR AND

Pressure

I

OTHER

NAR can be calculated from the slope of the pressure-flow curve at any given point on the curve. Nasal conductance is the reciprocal of this value. Mathematically, NAR is derived from the tangent to the curve calculated at an arbitrary point on the curve and is expressed as kilopascals per liter per second or centimeters of water per liter per second (Fig. 2). During any given breath, this value increases with increasing airflow because turbulence is a flowdependent phenomenon. The nonlinear relationship between pressure and flow has two implications. One is the inability to derive NAR simply from the ratio of instantaneous values of pressure and flow. NAR must be calculated from the ratio of the differentials, APIA+. The pressure-flow curve also implies that an arbitrary reference value must be used for a pressure gradient or flow rate at which to measure NAR (or conductance). When the arbitrary flow rate at which the NAR is measured is too high, it may not be possible to measure NAR in the severely obstructed nose because of difficulties in achieving high flow rates. If an arbitrary pressure value chosen for NAR measurement is too high, then it may be impossible to measure NAR in patients who have widely open nasal airways and very low pressure gradients at all points along the pressure-flow curve. These problems can be overcome by measuring the slope of the curve near zero flow. Although this method may be applied to all pressure-flow curves, it measures NAR at a point in the respiratory cycle where there is little or no subjective sensation of nasal obstruction. A suitable compromise applicable to most posterior RMM tests could use a reference flow rate of 0.25 L/set or a pressure gradient of 0.05 kPa (5 mm H,O). Because resistances are higher with anterior RMM, an arbitrary flow rate of 0.1 L/set or a pressure gradient of 0.15 kPa would be suitable for most curves. Resistances in normal adults measured by posterior RMM at 0.25 Lisec are usually in the range 0.08 kPa/L/sec to 0.25 kPa/L/sec. Obstructive symptoms are usually perceived at levels >0.3 kPalLisec.

FIG. 2. Diagrammatic representation of a pressure-flow curve from one breath. Airway resistance is derived from the tangent to the curve at a reference flow lx) or pressure (y). The tangent is the same as the differential ratio

APiAif.

Nasal power may also be determined by RllM.26 It varies throughout the respiratory cycle and, at any given moment, is proportional to the product of the pressure gradient and flow rate. Similarly, work of breathing is proportional to the pressure gradient and the volume of air moved, making it dependent on tidal volume and the ventilation rate. Therefore, use of power or work of breathing as a measure of nasal obstruction requires standardization of tidal volume and ventilation rate. Work of breathing is sometimes expressed as work per unit volume, for example, as joules per liter,27 and increases linearly with ventilation.28 The slope of this linear plot of work per liter against minute volume of respiration is equivalent to average NAR. This method of deriving average NAR, which usually requires computer-assisted RMM equipment, is reported to be relatively i~depe~d~~t of ventilation rates. This may prove to be an acceptable alternative to measurement of NA arbitrary point on the pressure4 RHINOMANOMETRIC

METH

Three devices are common to all ~biuomanomet~c systems: a differential pressure transducer for measurement of the transnasal pressure gradient, a pneumotachometer, and a second pressure transducer connected to the pneumotachometer for measurement of nasal airflow.29 The pressure transducers require careful selection for sensitivity in the range of pressures to be encountered, and they require testing for symmetry and linearity of response. The pneumotach-

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OscilloscoDe

X-Y Recorder .3. Diagram illustrating electrical connections of pressure and flow transducers (7IJ in anterior or posterior RMM in a noncomputerized system. After amplification by carrier amplifiers (AI, the signals may be displayed as pressure-flow curves on an oscilloscope screen. For calcuiation of resistance, the slope of the curve may be measured with a graticule attached to the oscilloscope screen, but an X-Y recorder for more accurate measurement of angles on the hard copy is preferable.

ometer, chosen for the range of airflow to be studied, requires initial calibration with an accurate rotameter system. Usually, the pressure and flow transducers are each connected to a carrier amplifier. In the initial setup of the equipment, the flow channel should be calibrated with an inclined water manometer, and the pressure channel, with a vertical Utube water manometer. The outputs from each of the carrier amplifiers may be displayed on a variety of devices, such as a very high speed X-Y recorder, a mcasu~ement-plotting system, or a storage oscilloscope (Fig. 3). If the signals are digitized and processed by a computer, they may also be displayed on a video monitor screen. Pressure and flowmonitoring tubing should be kept short and equal in length to reduce the possibility of hysteresis and phase-shift artifacts. T TECHNIQUES ressure and flow relationships in the nose can be measured by anterior RMM, posterior RMM, and forced oscillation. Both active and passive methods have been described for anterior RMM, whereas posterior RMM is active. In active anterior RMM, nasal airflow and pressure gradients are measured across the left or right nasal cavity during normal respiration to develop pressure-flow curves. In passive anterior M, a constant strearn of air is blown into the nose while pressure differences between the external nares and the nasopharynx are monitored.” In forced oscillation methods, a sine wave is superimposed on the pressure-flow curve, the frequency of the sine wave

FIG. 4. Transducer connections for measuring airway resistance in the right nasal airway by anterior ~~~. The /efi nasal airway is occluded for pressure measurements, and the right airway connected to a ~ne~m~tacbometer for flow measurements. A mouth tube is not required for this method.

being chosen to correspond with the natural resonance of the respiratory tract. Resistance measured by this method (acoustic impedance) is dependent on the frequency of oscillation in the 5 to 15 Hz range3’ and can be affected by artifacts.32 These methods do not elicit exactly comparable results and differ from one another in the complexity of equipment required aad the degree of cooperation required by the patient. Anterior

RM

Anterior RMM is a convenient technique because it requires very little patient cooperation. In this method, NAR is measured in one side of the nasal cavity only, because the airflow on the co~~alat~raI side of the nose must be obstructed to monitor nasopharyngeal pressure (Fig. 4). Pressure-flow curves in the nasal cavity being assessed can be measured either by applying tubes to the skin surrounding each nostril for measurement of flow and pressure, respectively, or through sealing a small tube into one nosttil to measure nasopharyngeal pressure and measuring airtlow through the other nares by means of a closely fitting face mask. In the former method, the ends of the monitoring tubes must be molded and applied

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without deforming the nose or allowing air leaks. In the latter method, the nose is less likely to be deformed by the instrumentation, and both methods suffer from inhibition of alae nasi function that occurs when the external nares are instrumented. If the cartilaginous portion of the nose or the nasal valve is deformed by upward displacement of the tip of the nose or by insertion of a large bore tube into the nose, falsely low resistances will be obtained because of deformation of a critical resistive component of the nasal anatomy. Anterior RMM cannot be used if a septal perforation is present. Nasal patency assessedby this technique is affected by nasal cycling in most normal adults. If measurements by anterior RMM are confined to one side of the nose and only a few measurements are made, it may be difficult to determine whether the sinusoids are physiologically constricted or dilated on that side. As the usual duration of the nasal cycle is only 2 to 4 hours, prolonged sequential measurements of NAR on only one side of the nose could also be misleading. Therefore, it is important to measure resistance on both sides of the nose, particularly if the response to a challenge procedure or a therapeutic intervention is being assessed during a period of time. Theoretically, the resistance to total airflow through both sides of the nose is a function of resistance to flow on each side separately, expressed as the sum of the conductances on the left and right sides: 1/ NAR (total) = l/NAR (left) + l/NAR (right). However, the total NAR, as measured by posterior RMM, has been demonstrated to be significantly different from the reciprocal of the sum of the reciprocals of the left and right NAR, as measured by anterior RMM.33 Thus, it is not possible to compute accurately total NAR from the left and right NAR with anterior rhinomanometric methods. Study of a mechanical model of the nasal airways has suggested that the cause of the discrepancy may be resistive components in the nasopharynx, distortion of the nares by instrumentation, and air leaks.34

In posterior RMM, a face mask may be fitted with a pneumotachometer for monitoring airflow through both nasal cavities simultaneously and for monitoring anterior nasal pressure. Pharyngeal pressure is monitored with an oral tube (Fig. 5). A short oral tube is usually adequate for monitoring pharyngeal pressure, provided that the patient can be trained to keep the soft palate elevated and the upper surface of the tongue well down and away from the palate, allowing free communication between the oropharynx and the oral cavity. Although the diameter or length of the oral tube is not critical, a cuffed tube or an oral tube

Pressure Transducer FIG. 5. Transducer connections for posterior RMM with a skin diver’s face mask and pneumotachometer fixed to the face plate of the mask. In certain applications, the oral tube may be extended to the hypopharynx.

9 mm in diameter may be more successful for patients who have difficulty in controlling their oropharynx and soft palate. If the patient is able to tolerate extension of the oral tube into the pharynx, artifacts can be minimized. An additional advantage of a pharyngeal catheter is that it can be extended to the tip of the epiglottis, allowing study of resistance to airflow in the entire supraglottic upper airway. A mask that covers eyes, mouth, and nose, such as an aviator’s mask, is ideal for posterior R cause it does not distort the cartilaginous portion of the nose but has the disadvantage of a large dead space and limited access of the oral tube in patients who have difficulty with the procedure. A skin diver’s face mask that covers the eyes and nose only is more convenient, and it does not deform the nose or obstruct airflow, provided that the lower rim of the mask is placed on the vermilion border of the upper lip. An alternative to measurement of airflow by a face mask fitted with a pneumotachometer is a “head-out” displacement-type body plethysmograph that incorporates a large laminar flow element.35.36Transducers and other electronic equipment for posterior ~~~ are similar to that needed for anterior Ran and require similar calibration procedures. In posterior RMM, it is essential that the pressureflow curves are displayed in real time, because pressure artifacts caused by malposition of the pharynx and tongue cannot be detected by any other means. Display of the curve is also useful for detection of air leaks and obstruction of the mouth tube. It is necessary e of to establish that a smooth pressure-flow curve artifacts is being achieved before calculation of hrer constants to describe the curve or calculation of NAR. Approximately 20% of normal individuals have insufficient palatal control to ahow pressure-flow re-

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Printef

Computer

Oscilloscope

r/ 0

Plotter

FIG. 6. Diagram illustrating components of a computerized system suitable for anterior or posterior RMM demonstrating pressure and flow transducers (TD) connected to carrier amplifiers (A), an anaiogue-to-digital converter t’ADC,J, a computer, a digital-to-analogue converter (DAC), and an oscilloscope. For certain applications, the computer may be programed to display curves on the cornputer monitor screen, dispensing with the need for a DAC and oscilloscope.

cordings consistently free of artifacts. It is important to check for unilateral nasal obstruction before undertaking repeated recordings during a period of several hours because near total obstruction on one side of the nose may have the effect of measurement of NAR in the contralateral side only, producing curves similar to those obtained by anterior RMM. In these circumstances, the nasal cycle would strongly affect the reproducibility of nasal pressure-flow curves, leading to high amplitude cycling of resistance.37 erized RMM Determination of NAR by measurement of the slope of the pressure-flow curve at any point can be done by displaying the curve on an X-Y recorder or on a storage oscilloscope fitted with a Collins graticule (Warren Collins, Inc., Braintree, Mass.). This method is slow and may be subject to parallax errors. Therefore, computerization of the RMM system is desirable.5 In an ideal system, the computer should sample the curve every 10 msec and, for single-point resistance determinations, should calculate the slope by regression analysis with at least two points on either side of the reference flow or pressure value. The software could also include a program for calculation of Rohrer constants or for determining average resistance from work per liter and ventilation rate. tine clinical purposes, a computerized anFor M system does not require visualization of terior the pressure-flow curve during the performance of the respiratory maneuvers. For research applications or for posterior RMM under all circumstances, a comsystem must include a method for display of the pressure-flow curve (Fig. 6). An ideal system

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should include a true 16-bit microcomputer with several I/O ports, 640 K of memory, a Q-bit analogueto-digital converter, sufficient disk space to store complete pressure-flow curve data, a chronometer, and a printer. A computerized system allows accurate and fast recording of resistances and should be programed to allow identification of artifacts and their exclusion from data for computer analysis. Programs could also provide electronic storage of large numbers of data points on each NAR curve, and interactive software could allow the control of the progress of a nasalchallenge experiment according to a predete~i~~d protocol. Applications

of RMM

For routine clinical evaluation of patients with rhinitis, RMM may not be particularly useful because of the considerable overlap in NAR found in normal subjects and subjects with rhinitis. However, assessment of nasal patency becomes more ~~fo~ati~e when it is studied repetitively during a period of time to test the effect of acute exposure to allergens, seasonal variation in prevalence of allergens to which the patient is sensitive, and correlation with the severity of symptoms, as reported by the patients. Repeated evaluation by RMM is also a valuable objective method for studying efficacy of intranasal therapy with mast cell stabilizers, including cromolyn, topical corticosteroids, and mediator antagonists. When NAR is studied in a given patient repeatedly during a period of time, it is important to study the patient at the same time of day because of the diurnal variation in NAR, known to be highest at night and in the early morning. Oral or inhaled decongestant therapy should be stopped before RMM. Effects of oral antihistamines on RMM testing may be unpredictable. Although combined oral H1- and HZ-antihistamine therapy is known to reduce the congestive effect of topical histamine challenge, oral Ha-antihistamine treatment alone may increase NAR in the normal ~~~halle~g~d nose. 36 Measurement of unilateral NAR by anterior R is useful in evaluating some patients with anatomic obstruction and can provide objective data to evaluate efficacy of surgical intervention, such as ~~ino~Ias~~, septal correction, turbinectomy, and polypectomy. In septal deviation, the patient may be unaware of the constant obstruction caused by septal en~roaebment on one side of the nose and may complain of inte~itte~t obstruction on the opposite side during the congestive phases of nasal cycling on that side, sometimes termed “paradoxical nasal obstruction.“38 NA fluenced by encroachment on the anterior nasal airway by septal deviation and mucosal ~ongestio*, particularly when septal protrusions or congestion is at or near

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the floor of the nose.39.4o The most critical area is between the caudal end of the nasal cartilages and the anterior end of the inferior turbinate bones. In complex septal defmmities, the septum may also appear to deviate to one side only, whereas it actually obstructs on the other side posteriorly in an area hidden from the examiner. However, studies with simulated septal abnormalities demonstrate that large septal spurs, deviations, and mucosal congestion within the cavum may have little effect on NAR.39 These studies.also suggest that nasal polyps, tumor, or granulomatous infiltration may not strongly affect NAR in the decongested nose. Since certain skeletal abnormalities may be relieved by decongestant therapy, and some mucosal alterations may be unaffected by decongestants, RMM performed before and after nasal decongestion is not an infallible method for differentiating between mucosal and skeletal abnormalities.41 Posterior RMM may be helpful in evaluating patients with sleep apnea. In patients with obstructive sleep apnea and seasonal allergic rhinitis, there is evidence of increased frequency and duration of sleep apnea during periods when NAR measured before and after sleep is increased.42 In obese patients with obstructive sleep apnea, NAR measured while the patient is awake and in the sitting position is higher than in control subjects. NAR in these patients was increased further when it was measured in the recumbent position.4” Resistance measurements in patients with sleep apnea and pharyngeal obstruction caused by obesity, adenotonsillar hypertrophy, or pharyngeal paralysis require pressure monitoring at the tip of the epiglottis so that the entire upper airway above the larynx is tested. RMM may not be necessary in identification of adenotonsillar hypertrophy as a cause of sleep apnea in children because clinical criteria alone correlate well with tbe outcome of surgery in these patients. RMIvI is particularly useful in following the progress of nasal challenge tests with mediators of the allergic response, allergens, or chemical irritants. Mediators known to decrease nasal patency in RMM tests are histamine,41 methacholine,44 leukotriene D,,45, 46 and substance P.47Nasal challenge with serotonin induces itching, sneezing, and hypersecretion, and stimulates substance P release, but does not increase NAR in patients with allergic rhinitis.48 Although most patients with allergic rhinitis respond to nasal allergen challenge with a progressive increase in NAR, some subjects have sneezing and rhinorrhea without a significant decrease in nasal patency. Therefore, the response to nasal allergen challenge should be assessed by scoring of rhinorrhea and sneezing in addition to use of RMM. Typically, NAR must be measured for a 1.5 to 30minute period before introduction of any materials into the nasal cavity. Further resistance mea-

surements are necessary after deposition of d&tent or placebo, repeating the measurements every 5 minutes for a further 15 to 20 minutes. If the patient has a stable baseline before the diluent challenge and the resistance after diluent does not increase by >3O%, the patient can be considered stable enough to begin provocation testing with allergens, mediators, or irritants.4gxSo Starting doses of provocative substances are usually chosen to be lower than levels expected to change resistance in the most sensitive subject. At 15 to 20minute intervals, the dose is increased by a standard increment, usually threefold to fivefold, continuing the dosage increases until the NA >lOO% (i.e., doubling), as compared with the average of the postsaline baseline values. During allergen-challenge tests, clear watery rhinorrbea and sneezing commonly occur before substantial increases in resistance. When resistances increase to mm-e than three times the control values, profuse rhinorrhea, repeated sneezing, and a moderate to severe sensation of obstruction is normally present.

CONCLUSIONS Identification and quantification of nasal airflow obstruction by RMM is becoming a useful investigative tool in the practice of allergy and otorhinola~y~gol~gy. Although RMM has not yet found a place in the POUtine evaluation of the patient with rhinitis, the increasing commercial availability of rhinQmaR~meters will help to define specific indications for its use im allergic rhinitis and allied conditions. As with pulrn~~a~function testing of patients with asthma, repeated evaluation by RMM during a period of time is far more informative than a single determination. The method is clearly useful in studying nasal responses to challenge tests and has been established as a means of evaluating success of surgery for relief of nasal obstruction. RMM is also becoming important in the investigation of patients with obstructive sleep apnea. Among the variety of RMM methods available, anterior RMM is the simplest and easiest to perform but is subject to artifacts from nasal ~~st~~~~tat~on and is complicated by effects of nasal cycling. Posterior RMM has neither of these disadvantages but may be difficult to perform in some patients and requires expensive equipment. ~Qmp~te~2atio~ of RMM has increased reproducibility of results and allowed convenient calculation of ~hysi~l~gic~lly relevant data. REFERENCES 1. Chadha TS, Birch S, Sackner MA. Oronassl distribution of ventilation during exercise in normal subjects and patients with asthma and rhinitis. Chest 1987;92:1037.

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2. Chowanetz W, Schott J, Jany B. Nasal admixture during mouth breathing in awake normal subjects. Bull Eur Physiopathol Respir 1987;23:125. 3. Haight JSJ, Cole P. The site and function of the nasal valve. Laryngoscope 1983;93:49. 4. Cockcroft DW, MacCormack DW, Tar10 SM, Hargreave FE, Pengelly LD. Nasal airway inspiratory resistance. Am Rev Respir Dis 1979;119:921. 5. Schumacher MJ, Gaines JA, Bescript B Computer-aided rhinometry: analysis of inspiratory and expiratory nasal pressuretlow curves in subjects with rhinitis. Comput Biol Med 1985;15:187. 6. Schumacher MJ, Games JA. Mathematical modelling of pressure Aow curves from posterior rhinometry [Abstract]. J ALLERGYCLIN IMMtJNOL 1986;77:241. 7. de Bonilla JSD, McCaffrey TV, Kern EB. The nasal valve: a rhinomanometric evaluation of maximum nasal inspiratory flow and pressure curves. Ann Otol Rhino1 Laryngol 1986;95:229. 8. Polgar 6, Kong GP. The nasal resistance of newborn infants. J Pediatr 1965671557. 9. Polgar G. Opposing forces to breathing in newborn infants. Biol Neonate 1967;ll:l. IO. Stocks J, Godfrey S. Nasal resistance during infancy. Respir Physiol 1978;34:233. 11. Ghaem A, Martineaud JP. Determination de la resistance nasale chez des sujets normaux a l’aide de deux techniques de rhinomanomttrie. Bull Eur Physiopathol Respir 1985;21: 11. 12. Hoshino T, Togawa K, Nishihira S. Statistical analysis of changes of pediatric nasal patency with growth. Laryngoscope I988;98:219. 13. Hershey HG, Stewart BL, Warren DW. Changes in nasal airway resistance associated with rapid maxillary expansion. Am J Orthod 1976;69:274. 14. Hartgerink DV, Vig PS, Abbott DW. The effect of rapid maxillary expansion on nasal airway resistance. Am J Orthod Dentofacial Orthop 1987;92:38 1. 15. Heetderks DR. Observations on the reaction of normal nasal mucous membrane. Am .I Med Sci 1927;174:231. 16. Kern EB. Rhinomanometry. Otolaryngol Clin North Am 1973;6:863. 17. Hasegawa M. Nasal cycle and postural variations in nasal resistance. Ann Otol 1982;91:112. 18. Rundcrantz I-I. Postural variations of nasal patency. Acta Otolaryngol 1969;68:435. 19. Rao S, Potdar A. Nasal airflow with body in various positions. J Appl Physioi 1970;28:162. 20. Richerson HB, Seebohm PM. Nasal response to exercise. J Allergy 1968;41:269. 21. Olson LG, Strohl KP. The response of the nasal airway to exercise. Am Rev Respir Dis 1987;135:3561 22. Strom KP, O’Cain CF, Slutsky AS. Alae nasi activation and nasal resistance in healthy subjects. J Appl Physiol: Respir Envir Exercise Physiol 1982;52: 1432. 23. Da&more NS, Eccles R. Changes in human nasal resistance associated with exercise, hyperventilation, and rebreathing. Acta Otolaryngol 1977;84:416. 24. Kenyon GS. Phase variation in nasal airways resistance assessed by active anterior rhinometry. J Laryngol Otol 1987;101:910. 25. Cole P, Haight JSJ, Love L, Oprysk D. Dynamic components of nasal resistance. Am Rev Respir Dis 1985;132:1229. 26. Walker SB, Shapiro GG, Biemran CW, Morgan MS, Marshall SG, Furnkawa CT, Pierson WE. Induction of eustachian tube dysfunction with histamine nasal provocation. J ALLERGYCLIN IMMWOL 1985;76:158. 27. Cole P, Niinimaa V, Mintz S, Silverman F. Work of nasal

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