Intra- and intersession reliability of acoustic rhinometry in measuring nasal cross-sectional area.

Abstract

We evaluated the intrasession and intersession reliability of acoustic rhinometry in measuring nasal cross-sectional areas in 10 subjects. Subjects were measured under three conditions: with a Breathe Right nasal strip in place, with a sham strip in place, and with no strip in place. Two sets of three measurements were taken 1 week apart. The intrasession reliability both with and without the Breathe Right strip was very good (intraclass correlation coefficient [ICC] [2,1]: 0.97 and 0.98, respectively). The intersession reliability with and without the Breathe Right strip was not nearly as good (ICC [2,1]: 0.62 and 0.67). The Breathe Right strip increased the mean nasal cross-sectional area by 0.10 [cm.sup.2] (17.4%). We conclude that acoustic rhinometry is a reliable way to measure nasal cross-sectional area during a single session of multiple tests, but it is not as reliable across sessions. We also determined that the Breathe Right nasal strip significantly increases nasal cross-sectional area.

Introduction

The Breathe Right nasal strip (CNS, Inc.; Minneapolis) is an adhesive strip that contains two parallel plastic springs. It is available in two sizes: small/medium and medium/large. When properly applied to the outside of the nose, the springs lift the nasal walls and widen the nasal valve. [1] CNS claims that such an opening of the nasal cavities leads to a 30% reduction in nasal airway resistance. [2,3] The company says that these strips reduce oxygen consumption, improve ventilation, reduce heart rate, and improve cardiorespiratory efficiency, all of which "instantly" reduce the amount of energy expended to breathe. [1,2]

Many researchers have attested to the validity with which acoustic rhinometry illustrates areas of potential obstruction, congestion, and septal abnormalities. [4-7] It has also been shown to be an effective way of measuring nasal cross-sectional area. [3,8,9] Furthermore, Silkoff et al reported that the measurement of nasal cross-sectional areas by acoustic rhinometry is reliable across sessions. [10] However, they did not report which specific intraclass correlation coefficient (ICC) they used in their study, as we have (2,1), and no other report of intrasession reliability has been published. Also, there has been no published report attesting to the ability of Breathe Right nasal strips to produce a reliable increase in nasal cross-sectional area.

The purpose of our study was threefold: (1) to determine the intra- and intersession reliability of acoustic rhinometry, (2) to determine its intra- and intersession reliability in measuring the nasal cross-sectional area with the Breathe Right nasal strip in place, and (3) to determine if the Breathe Right strip increases nasal cross-sectional area significantly better than sham strips or no strips.

Subjects and methods

We used a 1 x 3 repeated-measures factorial design for this study. The repeated independent variable was treatment; the three variables were no strip (control), a sham strip, and the Breathe Right strip. The dependent variable was the cross-sectional area of each nostril.

Ten subjects (mean age: 24.1 years; mean height: 5 ft., 7 in.; mean weight: 152.5 lbs.) participated in this study. All subjects were graduate students at Indiana State University.

Nasal cross-sectional area was measured with the Eccovision Acoustic Rhinometry System (E. Benson Hood Laboratories; Pembroke, Mass.). The rhinometer was properly calibrated according to the manufacturer's guidelines. [11]

The nasal cross-sectional area of both the left and right nostril was measured in each patient under three conditions in the following order: with no strip in place (control), with a sham strip in place, and with the Breathe Right strip in place. The sham strip was similar to the Breathe Right strip except that it did not contain the two springs. Three consecutive measurements were made under each condition. The same investigator performed all measurements.

The Breathe Right and sham strips were fitted across the nose in accordance with the instructions in the manufacturer's package insert. [12] The correct size of the rhinometer nose tip was determined by holding the tip to the nostril and making sure that the tip formed a seal with the nostril without distorting the shape of the nasal cavity. The nose tip was then placed on the wave tube, and a seal was made with the subject's nostril. The subject was instructed to sit up straight, inhale, and hold his or her breath during the measurement of each nostril.

Seven days after the initial testing, another set of measurements was made under the same conditions. These new measurements served as the basis for the intersession comparison.

The ICC (2,1) was used to calculate the intra- and intersession reliability of the nasal cross-sectional measurements in each of the three conditions. [13] Changes in nasal cross-sectional area induced by the Breathe Right nasal strip were determined according to one-way repeated-measures ANOVA and Bonferroni corrected pairwise comparisons. A probability of p[less than]0.05 was considered to be statistically significant.

Results

The intrasession reliability both with and without the Breathe Right strip was very good (ICC [2,1]: 0.97 and 0.98, respectively) (table). The intersession reliability with and without the Breathe Right strip was not nearly as good (ICC [2,1]: 0.62 and 0.67, respectively).

The nasal cross-sectional area was significantly larger with the Breathe Right strip in place than it was under both control (p[less than]0.001) and sham conditions (p = 0.001) (figure). The Breathe Right strip increased nasal cross-sectional area by 0.10 [cm.sup.2] (17.4%). There was no significant difference in measurements of cross-sectional areas between the sham and control conditions (p = 0.073).

Discussion

The results of this study demonstrate that the intrasession reliability of acoustic rhinometry to measure nasal cross-sectional area was much better than its intersession reliability. Roithmann et al reported similar findings regarding the reproducibility of acoustic rhinometry measurements overtime. [14] They observed that when subjects were retested at weekly intervals, there was a variability of 17% in the total minimum cross-sectional area. Silkoff et al recorded average variability coefficients of 8.1 and 9.7% for right and left nostrils over five sessions. [10] They did not report intrasession reliability because their methodology required that they keep measuring the cross-sectional area until they recorded four measurements that varied by less than 10%.

Roithmann et al found a variability of 5% during minute-to-minute measurements, much less than the 17% variability for week-to-week measurements. [14] In another study, Roithmann et al reported a one-session variability coefficient of less than 10%. [15]

In our study, we found that the Breathe Right nasal strip increased nasal cross-sectional area by 17.4%. A similar increase (21%) was reported by Portugal et al. [3] They found that the increase was consistently seen at the level of the nasal valve, which is the area of greatest nasal resistance. Therefore, when Breathe Right strips are correctly applied, they should decrease the amount of nasal airway resistance. Ng et al also found that the Breathe Right strips significantly increased nasal cross-sectional area. [16] Gosepath et al noted increases of 9 and 37% in nasal cross-sectional area at two different planes. [9] They speculated that the "strips may enhance nasal ventilation by mechanical changes in nasal geometry." This claim needs to be studied further.

The intersession reliability of acoustic rhinometry in our study was not as great as its intrasession reliability. At this time, there is no standardized method for measuring nasal cross-sectional area, so differences between measurements are likely. [17] These differences can occur because of nasal mucosal variations over time, [14] the subject's posture, [14] or a poor positioning a of the acoustic rhinometer so that it distorts the dimensions of the nasal cavity or fails to form a good seal with the nostril. [14,17] We made every effort to control this variable among subjects and between trials, but some variability did occur, as was reflected in our reliability coefficients. To decrease the effects of the nasal cycle, our subjects were measured at approximately the same time of day at both testing sessions. Also, we used an average of three measurements so that errors could be minimized. Tomkinson and Eccles have recommended a standardized procedure that might reduce the variability of measurements as we ll as establish a norm for rhinometer operators to follow. [17]

We conclude that acoustic rhinometry is a reliable way of measuring nasal cross-sectional area during a single testing session. We also conclude that nasal cross-sectional area measurements by acoustic rhinometry with the Breathe Right strip in place are very reliable. The intersession reliability of rhinometry both with and without the Breathe Right strip in place was considerably less. As individual operators become more experienced in using rhinometers, their reliability over time should improve.

Our study also demonstrates that the Breathe Right nasal strip reliably and significantly increases nasal cross-sectional area.

Acknowledgment

The authors thank CNS, Inc., for its donation of the Breathe Right and sham strips that were used in this study. We also thank Barry Long, MD, and his office staff for making their acoustic rhinometer available for our use.

References

(1.) CNS Inc. What does a Breathe Right nasal strip do? Available at www.breatheright.com/de. Accessed June 14, 2001.

(2.) CNS Inc. Proof positive. Available at www.breatheright.com/ae/ael.asp. Accessed June 14, 2001.

(3.) Portugal LG, Mehta RH, Smith BE, et al. Objective assessment of the breathe-right device during exercise in adult males, Am J Rhinol 1997;11:393-7.

(4.) Lenders H, Pirsig W. Diagnostic value of acoustic rhinometry: Patients with allergic and vasomotor rhinitis compared with normal controls. Rhinology 1990;28:5-16.

(5.) Elbrond O, Hilberg O, Felding JU. Acoustic rhinometry: A new method to evaluate the geometry of the nasal cavity and the epipharynx. Am J Rhinol 1991;5:7-9.

(6.) Hilberg O, Jackson AC, Swift DL, Pedersen OF. Acoustic rhinometry: Evaluation of nasal cavity geometry by acoustic reflection. J Appl Physiol 1989;66:295-303.

(7.) Mayhew TM, O'Flynn P. Validation of acoustic rhinometry by using the Cavalieri principle to estimate nasal cavity volume in cadavers. Clin Otolaryngol 1993; 18:220-5.

(8.) Corey JP, Kemker BJ, Nelson R, Gungor A. Evaluation of the nasal cavity by acoustic rhinometry in normal and allergic subjects. Otolaryngol Head Neck Surg 1997;117:22-8.

(9.) Gosepath J, Mann WJ, Amedee RG. Effects of the Breathe Right nasal strips on nasal ventilation. Am J Rhinol 1997;l1:399-402.

(10.) Silkoff PE, Chakravorty S, Chapnik J, et al. Reproducibility of acoustic rhinometry and rhinomanometry in normal subjects. Am J Rhinol 1999;13:l31-5.

(11.) Eccovision Acoustic Rhinometry System [operator's manual]. Pembroke, Mass.: E. Benson Hood Laboratories, 1997.

(12.) Breathe Right Nasal Strip [package insert]. Minneapolis: CNS Inc., 1994.

(13.) Shrout PE, Fleiss JL. Intraclass correlations: Uses in assessing rater reliability. Psychol Bull 1979;86:420-8.

(14.) Roithmann R, Cole P, Chapnik J, Zamel N. Reproducibility of acoustic rhinometric measurements. Am J Rhinol 1995;5:263-7.

(15.) Roithmann R, Cole P, Chapnik J, et al. Acoustic rhinometry in the evaluation of nasal obstruction. Laryngoscope 1995;105:275-81.

(16.) Ng BA, Mamikoglu B, Ahmed MS. Corey JP. The effect of external nasal dilators as measured by acoustic rhinometry. Ear Nose Throat J 1998;77:840-4.

(17.) Tomkinson A, Eccles R. Acoustic rhinometry: Do we need a standardized operating procedure? Clin Otolaryngol 1996;21:284-7.

Table. Nasal cross-sectional area
([cm.sup.2]) across sessions (mean
[+ or -] SD)
                     Session 1               Session 2
Control        0.5652 [+ or -] 0.1757  0.5775 [+ or -] 0.1904
Sham           0.5887 [+ or -] 0.1558  0.5605 [+ or -] 0.1612
Breathe Right  0.6637 [+ or -] 0.1509  0.6880 [+ or -] 0.1946

[Graph omitted]