Portuguese Version

Year:  2004  Vol. 70   Ed. 4 - (9º)

Artigo Original

Pages: 500 to 503

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Acoustic rhinometry as diagnostic method

Author(s): Edilson Zancanella1,
Wilma T. Anselmo Lima2

Keywords: Key words: acoustic rhinometry, nasal obstruction.

Abstract:
Introduction: The clear and objective evaluation of nasal patency has been reason for investigation for more than 100 years. The development of trustworthy objective methods of measure has been slow, and even with some attempts, none has been generallly accepted, remaining for the majority of the rhinologists the diagnoses based on clinical history and on rhinoscopy. Acoustics Rhinometry is a technique to measure the relation between the transversal area and the distance of the nasal cavity. Objective: To study the nasal patency through acoustics rhinometry in regular patients. Study Design: Clinical prospective. Material and Methods: We evaluated twenty patients aged 16 to 60. All of them underwent acoustics rhinometry examination before and after nasal decongestion, and the measures of MCA (minimum transversal area) and the distance have been analyzed. Results: Average values of MCA 0,59 before and 0.60 after decongestion were found. Conclusion: We concluded that acoustics rhinometry is an objective, simple, fast, reproducible, trustworthy, non-invasive method diagnostic for evaluation of nasal patency in patients with chronic nasal obstruction.

INTRODUCTION

Nose is the olfaction sense, the sentinel of the lower respiratory tract because it is the first to retain and fight against inhaled allergens. For this reason, nasal breathing is of utmost importance, because it acts as primary sensorial receptor, influencing cell oxygenation of all body parts and helping to maintain homeostasis in the frequent contact with foreign antigens.

The air that penetrates into the nose follows a path that is thought be like a tube, up to reaching rhinopharynx. In the way, there is wide variation in the diameter of the tube, comprising two main points of resistance of air-nasal flow common to the anatomy: the nasal valve and the mucosa cover of the nasal cavity 1.

For over 100 years, researchers have shown interest in assessing air nasal tract. In other words, it has undoubtedly happened owing to the fact that nasal obstruction is a common complaint of patients. However, the development of objective methods and reliable measures has been slow and even after different attempts, none has been generally accepted; most rhinologists base their diagnosis on clinical history and rhinoscopy data 2.

Even counting on detailed clinical history and appropriate physical examination, diagnosis may be incomplete, hindering treatment. Nasal endoscopy complemented by information provided by Computed Tomography (CT scan) also allows more specific anatomical diagnosis of the nasal cavity and nearby structures. Both are excellent means for diagnosis and objective follow-up of treatment. However, quantification of nasal obstruction cannot be measured by any of these methods 3.

Computed rhinomanometry and acoustic rhinometry are the current methods more specifically directed to assessing nasal permeability 4.

Computed rhinomanometry consists of an objective measure of nasal airways made by the correlation between pressure and transnasal flow. It is a dynamic test that allows assessment of nasal resistance 5.

Acoustic rhinometry is a technique that allows measurement of the correlation between the transversal area and the distance of the nasal cavity 6. It is a static test that uses a probe that transmits and receives sound from the electronic source to the nostrils 7.

The acquisition of the device Rhinometrics SRE2000/SRE2001 by the Division of Rhinosinusology, Department of Ophthalmology, Otorhinolaryngology and Head and Neck Surgery, Medical School, Ribeirão Preto - USP, allowed the conduction of the present study to systematize nasal objective investigation in ENT practice and to compare obtained data with the international literature.

Acoustic Rhinometry

Acoustic Rhinometry is a technique that enables measurement of the correlation between the transversal section of the nasal cavity and the distance in the nasal cavity. The method is based on the analysis of the sound reflected in the nasal cavity taking into account sound properties in the incidence of nasal cavity based on the reflection of sound waves 6.

The physical principle of the technique is that the sound in a tube, or in the airways, is reflected by changes in acoustic impedance caused by changes to the tube dimension. Changes in area of the transversal section are proportional to changes in acoustic impedance as a result of the propagation of the unidimensional wave. If the affecting wave is compared to the reflected wave it is possible to determine changes to the section area. Taking into account the time of interval between the input and the reflected waves and sound speed, it is possible to define the distance to a specific change of area 8.

The clinical value of acoustic rhinometry is its capability to measure the dimensions of the nasal cavity in terms of curve, correlating the section area with the distance. This curve describes the permeability of the nasal airway, giving the impression of what the obstruction level is. The method allows assessment of measures before and after the use of decongestants, assessing whether the cause of nasal obstruction is mainly skeletal or mucosal. Acoustic Rhinometry may be used as a diagnostic and follow-up tool, both in rhinology and in rhinosurgery 9.

Acoustic Rhinometer consists of a unit in which we couple probe and microcomputer with specific software for the conduction of the test. The distal extremity of the probe is connected to an adapter to be placed close to the nostril. The sound wave produced by the device is audible and between frequencies of 100 and 10,000 Hz. The test is quick, non-invasive, assessing one nostril at a time. The recording of the exam is made by a graphic called Rhinogram, presenting separated measures on the right and on the left, correlating distance with transversal area.

MATERIAL AND METHODS

We assessed 40 nasal fossas in 20 patients aged between 20 and 60 years. The patients were seen in the Ambulatory of Otology, and in addition to not having nasal complaints, their anterior rhinoscopy and nasofibroscopy were absolutely normal.

All patients were submitted to directed clinical history, emphasizing nasal complaints. We assessed them with anterior rhinoscopy, rigid nasofibroscopy and acoustic rhinometry before and after use of vasoconstrictor. The study was authorized by the Ethics Committee.

Equipment

We used equipment SR2000 by Rhinometrics, Denmark, and nasal adapters of varied sizes according to nostril size of the patient.

Rhinometric Assessment

We conducted the acoustic rhinometry without vasoconstrictor and 15 minutes after application of two jets of efenedrin 0.5% in each nostril.

The test was conducted in an acoustically treated environment, observing all factors that ensured test accuracy, according to the standardization of the International Committee for Acoustic Rhinometry:

a) patient remained 30 minutes in a room with air conditioned at 21°C of temperature before the measurement;

b) temperature and air humidity were maintained at 21°C and 50% to 60%, respectively;

c) stabilization of the head of the patient;

d) positioning of the wave tube;

e) use of vaseline to prevent leaks;

f) control of breathing.

In order to ensure test accuracy, each exam comprised at least three curves of each nostril. After each measure the nasal adapter was removed from the nostril, reconnected and a new measure was made.

The results were considered appropriate if variability coefficient was below 10%.

Based on recorded curves, we defined mean curve of each nostril of patients. Values of mean curves were analyzed.

All exams were conducted by the same observer.

Statistical Analysis

The statistical analysis was conducted in each group isolated, trying to characterize the sample through an exploratory analysis between data without vasoconstrictor and with vasoconstrictor. We defined the mean of measurements of each analyzed item, with calculation of standard deviation and confidence interval of 95%.

We applied the T paired test comparing values of the groups without vasoconstriction and with vasoconstriction, with values of significance below 0.05.

Analyses were made manually and using SPSS software.

RESULTS

We analyzed 20 patients, 16 women and 4 men, mean age of 33 years, 95% Caucasian and 5% Asian-descendents. All patients were asymptomatic concerning the nasal obstruction complaint and did not present septum deviation or inferior concha hypertrophy. Values found in each item were: ATM 1 (minimum transversal area), distance 1, volume 1 - before vasoconstriction and after vasoconstriction: ATM 2, distance 2 and volume 2; we presented the variation between measures and standard deviation. We tried to evidence differences between the measurements, observing an increase in ATM after vasoconstriction, with reduction of distance 1. We observed increase in volumes 1 and 2 after vasoconstriction.

The difference between the means for each measurement, before and after vasoconstriction, presented ATM 1- 0.007; ATM 2 - 0.06; Dist1 - 0.2; Dist2 - 0.003; Vol1 - 0.01 and Vol2 - 0.33. These values were within the confidence interval of 95%, evidencing an acceptable variation of 5% among analyses.

DISCUSSION

Objective assessment of nasal permeability has been made and discussed by many authors 10-14,18,20,21,23. The wide range of variables presented at the execution of Acoustic Rhinometry has required standardization of all items related to reproducibility and accuracy of exam, which have been highlighted and well defined (Rhinology, Supplement 16, Dec. 2000) 19,22. The execution of the exams in our study followed all relevant guidelines and we tried to review them during the conduction of the tests.

The use of different devices and different ways to present measures has also hindered immediate comparison of parameters. We emphasize that in all studied groups, we used the mean measures of nasal fossas.

We compared our results with those by:

-Hilberg et al. (1990)14, who studied 34 patients in Denmark and obtained ATM 0.72 and Dist 2.28 and after vasoconstriction, ATM 0.96 and Dist 1.68;

-Lenders & Pirsig (1990)15 in a study with 134 Caucasian patients presenting ATM 0.73;

-Grymer et al. (1991)9 studied 82 Caucasian patients and obtained ATM 0.73 and after vasoconstriction, 0.92;

-Morgan et al. (1995)16 studied 60 patients divided into Caucasians - ATM 0,69 - Dist 1.08 and after vasoconstriction, ATM 0.76 - Dist 0.93, Asian-descendents ATM 0.63 - Dist 1.61 and after, ATM 0.81 - Dist 0.86, and African-descendents ATM 0.87 - Dist 0.94 and after, 0.97 - 0.76, respectively;

-Roithmann et al. (1995)13 who studied 51 nasal cavities in Canada and presented ATM 0.62 and after vasoconstriction, 0.67;

-Gurr et al. (1996)11 studied 20 Anglo-Saxon patients with ATM 0.70, Dist 1.12 and Vol 4.69 and after vasoconstriction, ATM 0.76, Dist 0.96 and Vol 5.55, and 20 Indian patients with ATM 0.70, Dist 1.37 and Vol 4.52 and after vasoconstriction, ATM 0.77, Dist 1.09 and Vol 4.83.

We did not find in the literature data relative to exams executed with the same parameters as the Brazilian ones, but we believe that the predominance of Caucasian patients in our study (83%) should not be used as a parameter to compare to Caucasian or Anglo-Saxon patients. Morgan et al. (1995)16 concluded that racial differences influence nasal internal geometry and should be taken into account in the interpretation of acoustic rhinometry data.

Even so, values found for ATM 0.59 and after vasoconstriction ATM 0.60 are within the interval described by Hilberg et al. (2000)14: 0.60 0.18.

The influence of many different factors in nasal functioning has a key role in the correct assessment of its permeability. The need to standardize all items related to these possible alterations will result in objective and reliable data for the conduction of acoustic rhinometry.

We believe that Standardization 2000 has added a lot to the execution of this test and data produced based on it has now further reliability.

We also emphasize the importance of studying different populations to produce parameters for different racial groups. For this reason, we think we have contributed to the appropriate assessment of the Brazilian population thanks to the data resultant from our study.

The comparison of data collected - normal ATM1 0.59, after vasoconstriction 0.60 - allows objective comparison.

CONCLUSION

Acoustic rhinometry is the correct method to assess the nasal region, presenting objective, reproducible and reliable data.

It is a quick method, easy to conduct after training, that has clear rules concerning execution and requires strict compliance with its standardization.

We evidenced some numeric differences in our analyzed sample, ATM1 0.59 - after vasoconstriction, 0.60 transforming it into an objective parameter of comparison.

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