The LaryngoscopeLippincott Williams & Wilkins, Inc., Philadelphia© 2001 The American Laryngological,Rhinological and Otological Society, Inc.

Accuracy of Acoustic RhinometryMeasurements

Ozcan Cakmak, MD; Huseyin Celik, PhD; Tan Ergin, MD; Levent Sennaroglu, MD

Objectives: To identify the factors that influencethe accuracy of acoustic rhinometry measurementsrecorded with commercially available equipment.Study Design: A simple model was used which con-sisted of a metal pipe and cylindrical inserts. Theseinserts comprised various lengths, and aperture di-mensions were comparable to, or smaller than, thenasal valve areas of both adults and children. Meth-ods: Accuracy of the acoustic rhinometry techniquewas evaluated by comparing the measured and actualcross-sectional areas. The results were discussed interms of the calculated acoustic transmission, reflec-tion, and attenuation coefficients of the pipe modelvariations. Results: Reducing the inner diameter ofthe insert increased the degree of measurement er-ror. As the length of the insert was increased, themeasured cross-sectional area gradually decreased,approaching the actual area of the experimental pas-sageway. For larger inserts, level of error was nothighly dependent on passageway length comparedwith the narrower inserts. Conclusion: Our resultsshow that both the cross-sectional area and passage-way length of the narrow segment are the most sig-nificant factors that influence the accuracy in acous-tic rhinometry measurements. Key Words: Acousticrhinometry, accuracy, nasal valve.

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INTRODUCTIONFor decades, rhinologists have been trying to find an

objective means of assessing the nasal airway that can beapplied to a broad spectrum of patients. Recently, Hilberget al.1 introduced acoustic rhinometry (AR) as a useful toolfor measuring the dimensions of the nasal cavity.

Acoustic rhinometry analyses soundwaves that arereflected within the nasal cavity. Acoustic pulses, whichare generated by a spark, pass through the wave tube andenter the nasal passage through the nosepiece of the AR

device. The sound is reflected as the waves impact struc-tures in the passage. These reflected waves are detectedby a microphone and are then amplified, low-pass-filtered,and digitized. Finally, the processed data are convertedinto an area–distance plot using a computer.1

Acoustic rhinometry is a quick, painless, noninva-sive, and reliable method that can be performed easily andrequires minimal patient cooperation. It is potentiallyuseful for characterizing the geometry of the nasal cavity,for quantifying the dimensions of nasal obstructions, andfor assessing results of surgery and response to medicaltreatment. However, certain factors inherent to the phys-ics and hardware involved in the technique affect theaccuracy of AR. Although this new method has beenwidely used in clinical trials, to date only a few studieshave investigated its limitations.2,3 If a clinical examina-tion is done without considering these limitations, thedata can easily be misinterpreted.

Our aim in this study was to identify factors that influ-ence the accuracy of AR measurements recorded with com-mercially available equipment. To carry out the investiga-tion, we used a simple model consisting of a metal pipe thatwas fitted with cylindrical inserts of varied lengths andvaried aperture dimensions, the latter being comparable tothose of the human nasal valve. The results are discussed interms of the calculated acoustic transmission, reflection, andattenuation coefficients of the pipe model variations.

THEORYThe AR instrument we used is capable of producing and

detecting soundwaves in the frequency range of 100 to 10,000 Hz.A 10-kHz low-pass filter was used to limit the highest frequency.The speed of sound in air at 20°C and at atmospheric pressure isapproximately 34,300 cm/s; therefore, the shortest wavelength (l)produced by the AR instrument is 3.43 cm. The cross-sectionalarea of the nasal airway should be smaller than l2; therefore,when analyzing AR measurements, there is no need to considerdiffraction and interference effects. In other words, AR works onthe basis of the rules of reflection. In the section below, weexpress the transmission and reflection coefficients of sound-waves propagated in two different media. We then apply theseexpressions to the reflection, transmission, and attenuation coef-ficients for soundwave propagation in cylindrical pipes. Finally,we consider how these formulae apply to the experimental ARresults.

Presented at “The Nose 2000...And Beyond” in Washington, DC,September 20–23 2000.

From the Otorhinolaryngology Department (O.C., T.E.), Baskent Uni-versity Faculty of Medicine, Adana Dr. Turgut Noyan Hospital, Adana,Turkey; and the Departments of Physics (H.C.) and Otorhinolaryngology(L.S.), Hacettepe University, Beytepe, Ankara, Turkey.

Editor’s Note: This Manuscript was accepted for publication January16, 2001.

Send Correspondence to Ozcan Cakmak, MD, Bestekar Sokak, No: 70/C,06680, Kavaklidere, Ankara, Turkey. E-mail: Ozcakmak@hotmail.com

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Transmission and Reflection of Soundwaves atthe Interface Between Two Fluids

The general expressions for the sound power transmission(at) and reflection (ar) coefficients for plane acoustic waves trav-elling from one fluid medium to another at normal incidence tothe interface are given by4,5:

at 5 1 2 ar 5 4R1R2/~R1 1 R2!2 (1)

where R1 5 p1c1 and R2 5 p2c2 are the characteristic impedancesof the two media; pi and ci are density of media and speed ofsound, respectively.

The characteristic impedances of air and water can be takenas 430 kgm-2s-1 and 1.5 3 106 kgm-2s-1, respectively. By substi-tuting these values into Equation 1, the values of 0.001 and 0.999can be obtained for at and ar. The transmission coefficient forplane acoustic waves passing from a gas into a solid is approxi-mately 10-4, and that from a gas to a liquid is roughly 10-3 (i.e., thereflection coefficients at the air/liquid and air/solid interfaces areessentially equal to one). Therefore, a solid surface and a liquidsurface both act as a reflecting mirror for acoustic waves ofnormal incidence. This indicates that nasal fluid will influenceAR measurements. In other words, if a viscous fluid covers thewalls of the nasal passage, the measured cross-sectional area willindicate that the canal is narrowed.

Transmission and Reflection of SoundwavesTraveling Through Cylindrical Pipes

The model variations used in the present work were con-structed from a cylindrical brass pipe (Fig. 1). The cross-sectionalareas and lengths of the inserts were chosen in line with the actualdimensions of the human nasal cavity, and with the dimensions ofsimilar inserts that have been used by other investigators.2,3

For all the models used in this work A1 5 A3 5 1.131 cm2,whereas the cross-sectional area A2 and the length b of the insertsare taken to be variable. The transmission coefficient (at) and thereflection coefficient (ar) for plane acoustic waves propagatingthrough a three-stage pipe of cross-sectional areas A1, A2, and A3

are given by4,6:

at 5 1 2 ar

54

~ A3/A1 1 1!2 Cos2~2pfb/c! 1 ~A2/A1 1 A3/A2!2 Cos2~2pfb/c!

(2)

where f is the frequency and c is the speed of sound in air.The transmission coefficient at as obtained from Equation 2

is plotted in Figure 2 as a function of frequency. The resultsobtained for at of models with different values of A2 are shown onthe same diagram. The illustration shows that, for the insertswith a small cross-sectional area, the transmission coefficient ofhigh-frequency sound waves is small. These results clearly indi-cate that relatively higher degrees of error will be expected whenmeasuring inserts of a smaller cross-sectional area.

To study the variation of the transmission coefficient withcross-sectional area A2, it is necessary to calculate the average ofat over the frequency range provided by the AR instrument, using

at~ A2! 51

9900 E100

10000

at~ A2, f !df (3)

All calculations were made using Mathcad8 mathematical soft-ware (Mathead 2000 Professional, Mathsoft Inc., USA). The re-sults obtained for at(A2) are shown in Figure 3. The transmissioncoefficient increases as the cross-sectional area of the insert en-larges. It should be noted that the behavior is approximatelylinear at small values of A2, whereas there is a deviation fromlinearity at higher values of A2, and the relationship tends tosaturate when A2 5 A1 5 A3.

Measurements were also made as a function of the length bof the insert by taking its cross-sectional A2 as a parameter. Tocompare the calculated results with the experimental data, it isnecessary to calculate the average of the transmission coefficientresults over the AR frequency:

at~b! 51

9900 E100

10000

at~b, f !df (4)

Figure 4 shows the transmission coefficient at as a function of bfor chosen values of A2. For small values of A2, the transmissioncoefficient first rapidly declines, but then levels off and shows ashoulder at b>1.7 cm. For larger values of A2, at(b) exhibits awide and shallow minimum, the location of which shifts tosmaller b as A2 increases. Although the cross-sectional area of thepassage A2 is fixed, the initial decrease of the transmission coef-ficient with increasing insert length would yield a measuredvalue of A2 which is lower than the actual value. These resultsshow that length of passage constriction affects accuracy whenmeasuring cavities with small cross-sectional areas.

Fig. 1. The dimensions of the modelpipe apparatus, which consisted of threecylindrical parts. The left end is con-nected to the nosepiece of the acousticrhinometer. The length and diameter ofeach part are shown. Here A1 5 A3 51.131 cm2; A2, ai, bi, and xi are variable.

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Absorption of Soundwaves Within CylindricalPipes

Soundwaves lose energy as they pass through a medium.The losses that occur as a result of internal friction and heatconduction in a viscous boundary layer attenuate the soundwavestravelling in a pipe.4,7 The intensity of the attenuated sound wavecan be expressed by

I 5 Ioexp(22ax) (5A)

where Io is the initial intensity of the sound wave, a is theattenuation coefficient, and 2x is the distance travelled throughthe pipe by the wave. The attenuation coefficient a (in units ofneper/m) of a soundwave in a cylindrical pipe is a function of bothwave frequency and pipe diameter:

a 52ac Îphf

r(5B)

Fig. 2. The transmission coefficient as afunction of the frequency of sound-waves. Each curve is labeled with thediameter (ai) of the insert aperture (a2 50.2 cm, a3 5 0.3 cm, a4 5 0.4 cm, a5 50.5 cm, a6 5 0.6 cm, a7 5 0.7 cm, a8 50.8 cm, a9 5 0.9 cm, a10 5 1.0 cm).

Fig. 3. The frequency-average of thetransmission coefficient versus thecross-sectional area A2 of the insertaperture.

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Here h, a, c, f, and r are the shear viscosity coefficient, diameterof the pipe, speed of sound, wave frequency, and density of airin the pipe, respectively. Using these values, h 5 3.5 3 10-5

kgm-1s-1, c 5 343 ms-1, and r 5 1.21 kgm-3 for dry air at 20°C,Equation 5B can be written as a 5 5.52 3 10-5 = / a.

The attenuation coefficient of soundwaves travelling in airis proportional to the square of frequency, a 5 2 3 10-11 2. Forsoundwaves of 10 kHz frequency propagating in air at standardconditions a 5 0.002 neper/m, whereas for soundwaves of thesame frequency travelling in an air-filled tube a 5 0.55 neper/m.

To interpret the experimental data, it is necessary to calcu-late the average of the relative intensity (I/I0) over frequenciesfrom 100 to 10,000 Hz using:

I/I0 5 ~1/9900!E100

10000

exp(211 3 1025 3 Îf/a)df (5C)

A value of 0.75 is obtained for the average relative intensityof the reflected soundwaves in a pipe 1 cm in diameter and 20 cmlong. In other words, the energy of the reflected soundwave de-creases by 25%. In principle, AR measures the intensity of thereflected soundwave and converts the results to yield the cross-sectional area of the pipe. According to the above calculations, ifthe attenuation of soundwaves in the nasal airway is not takeninto account, the cross-sectional area measured by AR would beconsistently overestimated.

Experimental ProcedureA transient signal acoustic rhinometer (Ecco Vision, Hood

Instruments, Pembroke, MA) was used to perform the acousticmeasurements. In this particular rhinometer, the processedbandwidth was in the frequency range of 100 to 10,000 Hz.9 Asimple metal pipe of 1.2 cm inner diameter and 12 cm in lengthwas used for all the experiments. Measurements were takenusing 72 cylindrical metal inserts incorporating nine differentinner diameters (ai 5 0.2 cm, 0.3 cm, 0.4 cm, 0.5 cm, 0.6 cm, 0.7cm, 0.8 cm, 0.9 cm, and 1.0 cm) and eight different lengths (bi 5

0.25 cm, 0.50 cm, 0.75 cm, 1.0 cm, 1.25 cm, 1.5 cm, 1.75 cm, and2.0 cm). The distance (xi) from the nosepiece of the rhinometer tothe insert was adjusted precisely (Fig. 1). The different variationsof the model were designed so there was secure contact betweenthe model and the nosepiece of rhinometer to prevent acousticleakage, and all AR measurements were repeated at least fivetimes to ensure that the results were reproducible. The collecteddata were analyzed and plotted using Origin software (version6.0; Micrococal Software Inc., USA). We evaluated the accuracy ofthe AR technique by comparing the measured and actual cross-sectional areas of the inserts of different aperture size and pas-sage length. The percentage error for each individual measure-ment was calculated using

Error 5 Smeasured area 2 actual areaactual area D3 100 (6)

EXPERIMENTAL RESULTSWe found that the AR measurements varied accord-

ing to where the opening of the insert was located insidethe edge of the pipe. Measurements were taken with ap-erture of the cylindrical insert placed at x1 5 2 cm, x2 5 4cm, x3 5 6 cm, and x4 5 8 cm from the front end of the pipeat x 5 0 (see Fig. 1). Figure 5A and B shows the results ofAR measurements obtained with insert apertures locatedat x1 5 2 cm and x4 5 8 cm inside the pipe. We analyzedthe data obtained for inserts with apertures of variousdiameters placed at different locations in the pipe, andcalculated the error in the measured cross-sectional areaaccording to aperture size using Equation 6. The percent-age error calculated for selected insert locations is plottedin Figure 5C as a function of the actual cross-sectionalarea. This graph shows that there was a high degree oferror when inserts with small cross-sectional area weremeasured, and that the magnitude of the error was not

Fig. 4. The frequency-average of thetransmission coefficient versus thelength b of the insert. Each curve is la-beled with the diameter (ai) of the insertaperture (a2 5 0.2 cm, a3 5 0.3 cm, a45 0.4 cm, a5 5 0.5 cm, a6 5 0.6 cm, a75 0.7 cm, a8 5 0.8 cm, a9 5 0.9 cm, a105 1.0 cm).

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highly dependent on insert aperture location. The relativeintensity of the reflected sound waves (Equation 5C) trav-elling in a pipe 1.2 cm in diameter and 6 cm in length was0.964. This shows that there is an approximately 4% dif-ference between the results of measurements when theaperture is placed at xi 5 2 cm and xi 5 8 cm inside thepipe.

Intensity measurements were also made using in-serts with apertures of fixed diameter but variable lengthlocated at a given position in the pipe. Figure 6A and Bshows the measurement results at two selected aperturediameters and various insert lengths. The area-versus-distance curve, which corresponds to the measured cross-sectional area (A2) of the aperture, exhibits a deep trough.As the length of the insert is increased, the measuredcross-sectional area gradually decreases, approaching theactual area of the experimental passageway. Further in-crease in the length of the insert to more than approxi-mately 1.75 cm produces the start of a second trough,which corresponds to a marked increase in the acoustictransmission coefficient (Fig. 4).

We calculated the level of error in the measuredvalues of A2; Figure 6C shows the distribution of error forselected insert lengths as a function of actual area A2.There was a large degree of error in the measurements forsmall-area inserts. For inserts of length b .0.75 cm, we

found that error was essentially independent of b for in-sert areas greater than approximately 0.2 cm2. In otherwords, when the experimental passageway of a largecross-sectional area was measured, error did not changesignificantly as insert length changed (Fig. 4).

When we applied a gelatinous material to the innerwall of the inserts, the measurements reflected a narrow-ing of the lumen. The extent of the observed effect wasdependent on the amount of material applied (Fig. 7).

DISCUSSIONSince Sondhi and Gopinach9 first described acoustic

pulse-response analysis in 1971, studies have shown thatit is difficult to quantify cross-sectional areas distal to anarrow aperture using AR. The calculation of each areadata point depends on the result of more proximal areacalculations because of marching algorithms.10 Acousticpulses lose power as they contact and pass through nar-rowed regions, and this makes it difficult to assess theactual areas of the more posterior sections of the nasalpassages. This is potentially problematic because the nar-rowest part of the nasal passage, the nasal valve area, islocated in the anterior portion of the nasal cavity.1,2 For-tunately, the nasal valve region is the most important partof the nasal passage in terms of its role in respiratoryphysiology and is of most interest to the rhinologist.11,12

Fig. 5. (A) Insert cross-sectional area and the measured area by ARas a function of aperture location inside the pipe. The insert isplaced at xi 5 2 cm from the left end of the pipe. The differentsymbols refer to datasets collected for different aperture diametersfor insert length b 5 1 cm. (B) Measured area by AR as a function ofaperture location inside the pipe. The insert is placed at xi 5 8 cmfrom the left end of the pipe. The different symbols refer to datasetscollected for different aperture diameters for insert length b 5 1 cm.(C) Percentage error in the measurements of area A2. The differentsymbols refer to datasets generated by different insert locationsinside the pipe.

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Minimal changes in the cross-sectional area of thenasal valve can produce significant changes in nasal re-sistance.13 Any method used to assess this key region is oflittle value if it is not accurate. The normal range for areain the nasal valve region in adults is 0.4 to 0.6 cm2, and in6-year-old children it is 0.21 6 0.05 cm2.14–16 In thisstudy, the areas of the cylindrical inserts used approxi-mate, or are smaller than, the nasal valve areas of adultsand children (range, 0.031–0.875 cm2). This will allowimitation of the normal anatomy and pathologies of thisregion.

Hamilton and colleagues3 highlighted some factorsthat limit the accuracy of AR. They constructed a simpletube model in which the main cylinder remained constantand an insert of fixed length (1 cm) with a constricted areawas modified to represent areas of 0.07 to 0.95 cm2. Theseauthors found that AR measurements of versions withlarger minimal cross-sectional areas (greater than 0.4cm2) had less than a 10% error, and that the level of errorrose gradually as the degree of constriction increased, to amaximum error of 40% for the smallest cross-sectionalarea measured. Buenting et al.2 also investigated the ac-curacy of AR measurements by inserting cylindrical in-serts of 1-cm length and 2 to 9 mm inner diameter withina simple rigid pipe model. Similar to the findings of Ham-

ilton and coworkers, they found that when the diameter ofthe aperture was less than 6 mm (area 5 0.28 cm2), themeasured area was overestimated by 10%.

In our study, when 1-cm long inserts were measured,the result was less than 10% error for actual cavity areaslarger than 0.385 cm2, and up to 70% error for an actualpassageway area of 0.071 cm2. As this indicates, the de-gree of error was high when we measured passages withsmall cross-sectional areas (i.e., passages of small aper-ture size). The measured cross-sectional area depends onthe transmission coefficient (Fig. 3), with a decrease in theintensity of transmitted soundwaves corresponding to adecrease in the cross-sectional area. The transmission co-efficients of high-frequency soundwaves are small for pas-sageways of a small cross-sectional area (Fig. 2). Thisrelationship clearly explains the source of the relativelyhigher degrees of error that are generated when measur-ing small-area passageways. The transmission coefficientincreases nonlinearly as the cross-sectional area of thepassage expands (Fig. 3). The nonlinear behavior of thetransmission coefficient must be considered in the ARalgorithm.

Hamilton et al.3 found that actual passage areaswere underestimated in all except the tightest construc-tions, whereas Buenting and colleagues4 found that larger

Fig. 6. (A) Measured area by AR as a function of the insert length.The insert is placed at xi 5 2 cm from the left end of the pipe. Here,insert cross-sectional area A2 5 0.031 cm2. The different symbolsrefer to datasets generated from different aperture diameters ofinsert length b. (B) Measured area by AR as a function of the insertlength. The insert is placed at xi 5 2 cm from the left end of the pipe.Here, insert cross-sectional area A2 5 0.636 cm2. The differentsymbols refer to datasets collected for different aperture diametersof insert length b. (C) Percentage error in the measurements ofcross-sectional area A2. Here bi is the length of the insert.

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cavity areas were consistently underestimated andsmaller ones were always overestimated. In contrast toboth of these reports, our findings indicated that the cross-sectional areas of these experimental passageways arealways overestimated by the AR technique. The overesti-mations in our study can be explained by the absorption ofsoundwaves that occurs within cylindrical pipes. As arule, soundwaves lose some of their energy as they travelthrough a medium. In their study using human centralairway casts, Jackson et al.17 found that internal energylosses introduced negligible error. However, based on thetheoretical considerations and the results obtained in ourwork, we conclude that this attenuation significantly af-fects the accuracy of AR measurements. Specifically, theloss in the intensity of the reflected waves leads to over-estimation of the cross-sectional area of the nasal airway.Therefore, the attenuation of soundwaves within pipesshould also be considered in the AR algorithm.

The use of a wave tube of a different internal diam-eter (1.2 cm in our study, 1.3 cm and not specified in otherstudies2,3) could also explain some of the disparity be-tween the results of the various studies that have beendone. In principle, the diameter (a) of the wave tubeshould not exceed (/1.7 (5 c/1.7f). Below this frequency, itis reasonable to picture the air motion as being parallel tothe pipe axis, but at higher frequencies soundwaves followa zigzag path as they travel down the pipe.18 The relativeintensity of soundwaves depends on both the diameterand length of the wave tube (see Equation 5A) and also onthe position of the receiving microphone. Thus, the dimen-sions of the wave tube and the location of the microphoneused in the investigations are important factors as well.

Buenting et al.2 noted that when the aperture of theinsert was narrower, it was necessary to lengthen thecylinder to preserve the accuracy of measure of the cross-sectional area. In our study, we used inserts of fixed di-

ameter but variable length (b) to clarify what is occurringin this effect. As the length of the insert is increased, themeasured cross-sectional area gradually decreases to thepoint where it approaches the actual cross-sectional areaof the experimental passageway. For inserts of lengthsgreater than 0.75 cm, the error is essentially independentof b for areas above roughly 0.2 cm2 (Fig. 6C). This obser-vation can be explained by considering that the transmis-sion coefficient varies with the length of the constrictedpassage. In our work, as experimental insert length in-creased, the transmission coefficient first droppedsharply, then increased slightly, and eventually stabilized(Fig. 4). While the transmission coefficient dependsgreatly on the length of the insert with a smaller cross-sectional area, this relationship is weak when passage-ways of a larger area are measured. For larger inserts,level of error is less influenced by passageway length,whereas for narrow inserts, measurement error increasesas the passageway becomes shorter (Fig. 4). Our resultsconcur with those of Buenting and colleagues,2 and indi-cate that length of the insert is one of the main influenceson AR accuracy. This is of particular importance in thepediatric population in which, depending on the lengthand cross-sectional area of the nasal valve region, theexaminer should expect less accurate AR measurements.The same consideration applies to cases of nasal pathologythat involve extreme narrowing and shortening of thepassageway, especially the nasal valve area. For example,measurements taken in patients with severe septal devi-ation, polyps, and web or stricture of the anterior nasalcavity would involve a higher magnitude of error.

The error resulting from viscous losses has also beenidentified as a limiting factor in AR measurements.8 Ourfindings indicated that application of gelatinous materialmimicked narrowing of the tube, and that the degree ofthe effect paralleled the amount of substance that was

Fig. 7. The variation in insert area whena gelatinous material was applied to theinner wall of the model.

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added (Fig. 7). This result is in line with the fact thatliquids act as a mirror for sound waves (see Equation 1). Itfollows that to obtain more accurate measurements, thenasal cavity should be cleared of nasal secretions beforeAR examination.

CONCLUSIONThe anatomy of the human nose is complex, and the

amount of space in the nasal cavity can vary greatly. Theaccuracy of AR measurements is highly dependent onnasal passage anatomy, especially that of the narrowestsection, and on the specifications of the AR instrumentused. Our results show that cross-sectional area and pas-sageway length are the factors that most significantlyinfluence accuracy in AR. These two parameters should beconsidered together when estimating error in AR findings.When the cross-sectional area and length of the narrowestpart of the passage are relatively small and short, respec-tively, there is a higher probability of measurement error.Every clinician who uses AR equipment should be awareof the factors that affect the accuracy of these measure-ments, because results from many patients may includeconsiderable error. Although the method is potentiallyuseful in practice, there is also risk of misinterpretation.

The results of the model calculations presented inthis work suggest that there is a need for further improve-ment in the design of AR equipment and related computersoftware.

AcknowledgmentThe authors thank Prof. Dr. M. Cankurtaran for his

valuable consultation and his critique of the manuscript.

REFERENCES1. Hilberg O, Jackson AC, Swift DL, Pedersen OF. Acoustic

rhinometry; evaluation of nasal cavity geometry by acous-tic rhinometry. J Appl Physiol 1989;66:295–303.

2. Buenting JE, Dalston RM, Smith TL, Drake AF. Artifacts

associated with acoustic rhinometric assessment of infantsand young children: a model study. J Appl Physiol 1994;77:2555–2563.

3. Hamilton JW, Cook JA, Philips DE, Jones AS. Limitations ofacoustic rhinometry determined by a simple model. ActaOtolaryngol 1995;115:811–814.

4. Kinsler LE, Frey AR, Coppens AB, Sanders JV. Fundamen-tals of Acoustics, 3rd ed. New York, Toronto: John Wileyand Sons Inc., 1982.

5. Biltz J. Elements of Acoustics. London: Butterworths, 1964.6. Seto WW. Theory and Problems of Acoustics. Schaum’s Out-

line Series in Engineering. New York, San Francisco:McGraw-Hill Book Co, 1971.

7. Meyer E, Neumann EG. Physical and Applied Acoustics. NewYork, London: Academic Press, 1972.

8. Djuspesland PG, Qian W, Furlaott H, Rotnes JS, Cole P,Zamel N. Acoustic rhinometry: a study of transient andcontinuous noise techniques with nasal models. Am J Rhi-nol 1999;13:323–329.

9. Sondhi MM, Gopinach B. Determination of vocal tract shapefrom impulse responsing at the lips. J Acoust Soc Am1971;49:291–299.

10. Marshall I. Impedance reconstruction methods for pulse ref-lectometry. Acoustica 1992;76:118–128.

11. Kasperbauer JL, Kern EB. Nasal valve physiology. Implica-tions in nasal valve surgery. Otolaryngol Clin North Am1987;20:699–719.

12. Haight JSJ, Cole P. The site and the function of the nasalvalve. Laryngoscope 1983;93:49–55.

13. Chaban R, Cole P, Naito K. Simulated septal deviations. ArchOtolaryngol Head Neck Surg 1988;114:413–415.

14. Masing H. Experimentelle untersuchungen uber die stro-mung im nasenmodell. Arch Klin Exp Ohren NasenKehlkopheilkd 1967;189:59–70.

15. Bridger P. Physiology of nasal valve. Arch Otolaryngol 1970;92:543–553.

16. Warren DW, Hairfield WM, Dalston ET. Effect of age onnasal cross-sectional area and respiratory mode in chil-dren. Laryngoscope 1990;100:89–93.

17. Jackson AC, Olson DE. Comparison of direct and acousticalarea measurements in physical models of human centralairways. J Appl Physiol 1980;48:896–902.

18. Hall DE. Basic Acoustics. New York, NY: John Wiley & SonsInc, 1987.

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