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Nasal Airway Volume and Resistance to Airflow

Gehua Zhang, M.D.,* Philip Solomon, M.D.,** Richard Rival, M.D.,** Ronald S. Fenton, M.D.**

From the *Department of Otolaryngology-Head and Neck Surgery, The Third Affiliated Hospital, Sun Yat-Sen University, Guangzhou, GD, China, and **Department of Otolaryngology-Head and Neck Surgery, St. Michael's Hospital, University of Toronto, Toronto, Canada.
Address correspondence and reprint requests to Gehua Zhang, M.D. Department of Otolaryngology-Head and Neck Surgery, The Third Affiliated Hospital, Sun Yat-Sen University, Guangzhou, 510630, China. Email address: gehuazh@hotmail.com

Abstract

Background: In keeping with the concepts of evidence-based medicine, various objective measuring techniques are used for assessment of nasal airway patency. In modern rhinological practice and research, rhinomanometry and acoustic rhinometry are probable the most widely used techniques. The goal of the present study was to determine whether there is correlation between rhinomanometrically derived nasal airflow resistances and acoustic rhinometrically derived nasal airway volumes.

Methods: In order to achieve the goal, a prospective cross-sectional study of a total of 316 patients complaining of nasal obstruction was undertaken. Resulting data were compared by means of Pearson correlations of the total number of patients and of subgroups.

Results: The total number of patients, and most subgroups, in both their untreated and decongested state, bilaterally and unilaterally, demonstrated significant correlation (p < 0.001) between nasal airflow resistances and nasal volumes.

Conclusion: Rhinomanometric nasal airflow resistances and concurrent acoustic rhinometric nasal airway volumes are closely correlated. The combination of the two objective methods provides insight into nasal airflow physiology and nasal airway anatomy. Each method supports the other despite entirely independently derived values and each supplies similar useful information on the features that define nasal patency.

Key Words: Nasal airway, nasal obstruction, nasal volume, nasal patency, objective measurement, rhinomanometry, acoustic rhinometry, nasal resistance, nasal airflow, correlation

Introduction

Experiments performed by Qian1 have demonstrated that the changes in volume by obstruction of the lumen of a length of plastic tubing are closely correlated with changes in the degree of resistance to airflow through it. These artificial means led him to choose acoustic rhinometric volumes in place of rhinomanometric resistances for testing groups of children. However, the present author's review of the literature has not revealed such a correlation in human subjects.

Rhinomanometry employs a dynamic technique in which nasal resistance to respiratory airflow though one or both nasal cavities can be measured during exclusive nasal breathing. Acoustic rhinometry, by contrast, is a static procedure that can provide objective information about nasal airway geometry. These two objective methods of measurement have been independently validated against other objective modalities2-6.

Acoustic rhinographs display successive 'valleys' that correspond with anatomic narrowings in the proximal nasal cavity6-9. Several studies have shown correlation between acoustic rhinometric nasal volumes and CTs and MRIs of the proximal portion of the nasal airway.8,10-12

By comparing the parameters obtained from active anterior rhinomanometry, acoustic rhinometry, and peak expiratory flow rate, Numminen13 found statistically significant correlations between nasal airway volume and minimal cross-sectional area by acoustic rhinometry, and resistance in expiration and inspiration by peak expiratory flow rate, but no correlation was found between other rhinometric measurements. Research published by Naito3 reached a similar conclusion.

The aim of our study was to compare nasal airway volumes by acoustic rhinometry with nasal airflow resistances by rhinomanometry in patients complaining of nasal obstruction, and to determine whether these two diverse forms of objective measurements supported each other, whether nasal airflow resistance change was predictable by nasal airway volume change, or if acoustic rhinometry and rhinomanometry provided entirely independent values.

Materials and Methods

Study Design

A prospective cross-sectional study was conducted with 316 consecutive patients complaining of nasal obstruction, who were referred to the Nasal Airflow Laboratory of St. Michael's Hospital, Toronto, from October 2006 to March 2007. Criteria for inclusion of patients in the study were (1) age greater than 18 years old, (2) with the complaint of nasal obstruction at least 6 months duration, (3) absence of acute upper respiratory tract infection in the preceding two weeks, (4) absence of significant systemic disease, (5) absence of nasal polyps. Nasal medications were discontinued for 24 hours prior to the study.

The Ethics Committee of the Hospital approved the study, and informed consent was obtained from all patients.

Rhinomanometry

Active posterior rhinomanometry (Toronto System) was employed to measure nasal airflow resistances.14,15 Each patient was seated in a closed head-out body plethysmograph in an air-conditioned laboratory (22-24°C, 50% relative humidity) and instructed to breathe quietly through the nose with the mouth closed. A fine, flexible plastic catheter (Infant Feeding Catheter) was inserted 8-9 cms along the floor of one nasal cavity to the nasopharynx to measure differential transnasal pressures; it was secured by adhesive tape and attached to a transducer. The head-out body plethysmograph measured nasal airflow by displacement of respiratory body volume changes. Pressure and flow were transduced to electrical analog signals, which were digitised, and breathing was monitored by an x/y pressure/flow projection on a computer screen. When breathing was seen to be regular, computer software was enabled to compute and displayed airflow resistance. Five measurements, each of three breaths, were performed, displayed and averaged.14,15 Acoustic rhinometry was then performed.

Acoustic Rhinometry

Acoustic rhinometry (Ecco Vision, Hood, Laboratories, Pembroke, MA. USA) was used to evaluate each nasal cavity separately. Measurements were taken with subjects in a sitting position and they were instructed to hold their breath during the short periods of testing. External nasal adapters were selected for a close fit to each nostril rim and sealed with water-soluble gel while attached to the rhinometer.16 Volume and cross sectional areas of the proximal 6 cms of the nasal cavity were computed and displayed by using of Hood Laboratories software (4.4 version). Each nasal cavity was tested repeatedly to obtain three results in agreement.

Following measurements of the untreated nose, three puffs of topical decongestant (0.1% xylometazoline nasal spray) were applied to each nasal cavity. At least 10 mins expired before rhinomanometric and acoustic rhinometric measurements were repeated.

Statistical Analysis

Pearson correlation analysis was used to evaluate the relationship between nasal airway volume by acoustic rhinometry and nasal airflow resistance by rhinomanometry before and after decongestion both bilaterally and unilaterally. In addition to the total number of patients, subgroups were examined in a similar way. The statistical analysis was done using the SPSS 14.0 version, p values less than 0.05 was considered to indicate statistic significance.

Results

Demographics

Three hundred and sixteen patients consisted of 118 females and 198 males with a mean age of 38.6 years old (ranges, 18 - 81 years). The duration of nasal obstruction was 6 months to 31 years. The ethnicity distribution was Caucasian 247 (78.2%), Asian 47 (14.9%), and African 22 (6.9%).

104 (32.9%) patients' pre-decongestion bilateral nasal resistances were less than 2.5 cms H2O/L/Sec, while 212 (67.1%) patients' exceeded 2.5 cms H2O/L/Sec.

[1 cms H2O/L/Sec (US) = 0.1 P/cm3/Sec (EU)]

112(35.4%) patients' post-decongestion bilateral nasal resistances were less than 1.5 cms H2O/L/Sec, while 204(64.6%) patients' exceeded 1.5 cms H2O/L/Sec.

Correlation Between Nasal Resistance and Nasal Volume in the Total Number of Patients

In these patients, correlations between nasal airflow resistances and nasal airway volumes were compared bilaterally and unilaterally in both the pre-decongested and post-decongested states.

Correlation Between Nasal Resistance and Nasal Volume in Groups

As in previous studies,14,15,17-19 patients were divided into smaller selected groups. The main division was made at 2.5 cmH2O/L/Sec pre-decongestion bilateral nasal resistance and 1.5cmH2O/L/Sec post-decongestion bilateral nasal resistance.

Subgroup 1: Pre-decongestion bilateral nasal resistance <2.5 cmH2O/L/Sec, and post-decongestion bilateral nasal resistance <1.5cmH2O/L/Sec totalled 74 patients. Before and after decongestion the unilateral nasal resistance and unilateral nasal volume had significant correlation (r = -0.45, p < 0.001; r = -0.28, p = 0.001, respectively).

Subgroup 2: Pre-decongestion bilateral nasal resistance <2.5 cmH2O/L/Sec, but post-decongestion bilateral nasal resistance >1.5cmH2O/L/Sec. Only 30 patients were in this group. Before decongestion unilateral nasal resistance and unilateral nasal volume had significant correlation ( r = - 0.32, P < 0.001); however, after decongestion no correlation was found (r = -0.22, p = 0.115).

Subgroup 3: Pre-decongestion bilateral nasal resistance > 2.5 cmH2O/L/Sec, but post-decongestion bilateral nasal resistance < 1.5 cmH2O/L/Sec consisted of 38 patients. Before decongestion the unilateral nasal resistance and unilateral nasal volume had significant correlation ( r = - 0.36, P = 0.003), but after decongestion no correlation was found (r = -0.15, p = 0.238).

Subgroup 4: Pre-decongestion bilateral nasal resistance > 2.5 cmH2O/L/Sec, and post-decongestion bilateral nasal resistance > 1.5 cmH2O/L/Sec consisted of 174 patients. Before and after decongestion the unilateral nasal resistance and unilateral nasal volume had significant correlation (r =-0.32, P < 0.001; r = -0.39, p = 0.001, respectively).

Discussion

Modern rhinology includes a variety of objective rhinometric techniques. Rhinomanometry and acoustic rhinometry are probably the most widely used for quantifying nasal patency.

Instead of using a nozzle or a facemask, the Toronto system of active posterior rhinomanometry14,15,17 employs a head-out body plethsmograph which, although cumbersome, it avoids the risk of artifacts that can result from displacement of compliant anterior nasal tissues by displacement of adjoining labial and other mobile facial tissues by a facemask. The head-out body plethysmograph has many different uses, and it accommodates all patients comfortably and independently of body and head size and children prefer it to a facemask.

By contrast with dynamic and physiological rhinomanometry, static acoustic rhinometry is a nonphysiological measure of nasal patency. By means of acoustic reflectance it provides an anatomic profile of the nasal cavity, as both a measure of nasal volume of a predetermined distance beyond the nostril and as cross-section areas within the proximal nasal cavity. It requires minimal patient cooperation, provides readily repeatable results and ease of use.2,5-8,16,20 These two objective techniques are widely used in clinical and research situations and have been independently validated against other objective modalities.

In healthy adults breathing quietly at rest, approximately half the respiratory airway resistance is provided by the nasal airway.21-23 The major proportion of resistance to nasal airflow is contained within 0-5cms of airway lumen between the nostril and the vicinity of the bony cavity entrance.20,21,23 However, the Hood acoustic rhinometry used in our study extends the distance for measurement by a further 1 cm.

Our results have shown that nasal airflow resistance by active posterior rhinomanometry and the nasal airway volume by acoustic rhinometry had significant correlation in the untreated nose (bilateral, r = -0.384, p < 0.001; unilateral, r = -0.395, p < 0.001) and decongested nose (bilateral, r = -0.386, p < 0.001; unilateral, r = -0.359, p < 0.001) in the total number of patients.

Previous studies had indicated that pre-decongestion bilateral nasal resistance 2.5 cmH2O/L/Sec could be considered a reasonable upper limit of patency of a healthy nose. Decongestion demonstrates the extent of mucovascular congestion and residual resistance is structural. Post-decongestion bilateral nasal resistance is greater than 1.5 cmH2O/L/Sec in a structurally obstructed nose. Post-decongestion unilateral nasal resistance measurements are used to determine the site and severity of structural obstructions.14,15,17-19

Our results suggested in pre-decongestion bilateral nasal resistance < 2.5 cmH2O/L/Sec group, 28.8% (30/104) patients had structural obstruction and a majority of patients (71.2%, 74/104) patients were without any structural issue. However, in the pre-decongestion bilateral nasal resistance > 2.5 cmH2O/L/Sec group, 82.1% (174/212) patients had a structural problem, and only a minority of patients (17.9%, 38/212) did not. We consider that in these 38 patients' elevated pre-decongestion bilateral nasal resistance was caused by mucovascular swelling. In this study, subgroup 2 & 3 had no correlation between unilateral nasal resistance and unilateral nasal volume after decongestion. The limited number of only 30-38 patients in these two groups might explain the absence of correlation. A future study of a larger number could possibly provide a different result.

Conclusion

Rhinomanometric nasal airflow resistances have significantly close correlation with acoustic rhinometric nasal airway volumes. The two diverse forms of objective measurement of nasal patency support each other, despite their independent values. The combination of the two objective rhinometric measures provides insight into nasal airflow physiology and nasal airway anatomy. Rhinomanometry and acoustic rhinometry are both useful objective techniques for nasal studies and each provides similar information on nasal patency.

Acknowledgement

As first author I am grateful to Dr. RS Fenton, Otolaryngologist-in-chief, University of Toronto Department of Otolaryngology-Head and Neck Surgery, St Michael's Hospital, Toronto for a generous Research Fellowship grant and use of the department facilities. I also thank Philip Cole, Professor Emeritus for his help in consultation and his review of the manuscript, and Mr. Chris Pritchard for sharing the rhinomanometry recordings.

References

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