Acoustic rhinometry in healthy humans: accuracy of area estimates and ability to quantify certain anatomic structures in the nasal cavity

OBJECTIVES: We evaluated the accuracy of acoustic rhinometry (AR) measurements in healthy humans and assessed the ability of AR in quantifying the dimensions of the paranasal sinuses and certain anatomic structures in the nasal cavity. METHODS: Twenty nasal passages of 10 healthy adults were examined by AR and computed tomography (CT) before and after decongestion. Actual cross-sectional areas of the nasal cavity and actual locations of the nasal valve, the head of the inferior turbinate, the head of the middle turbinate, the ostia of the frontal and maxillary sinuses, and the choana were determined from CT sections perpendicular to the curved acoustic axis of the nasal passage. RESULTS: The AR-measured cross-sectional areas in the anterior nasal cavity were in reasonable agreement with the corresponding areas determined from CT, whereas AR consistently overestimated the passage areas at locations posterior to the paranasal sinus ostia. The nasal valve was identified as a pronounced minimum on the AR area-distance curve. However, AR did not discretely identify the head of the inferior turbinate, the head of the middle turbinate, or the choana. CONCLUSIONS: The local minima on the AR area-distance curve beyond the nasal valve are caused by acoustic resonances in the nasal cavity, and do not correspond to any anatomic structure. The AR area overestimation beyond the paranasal sinus ostia is due to the interaction between the nasal cavity and the paranasal sinuses, rather than to sound loss into the sinuses. Acoustic rhinometry provides no quantitative information on ostium size or sinus volume in either non-decongested or decongested nasal cavities.     

Semi-automatic segmentation of computed tomographic images in volumetric estimation of nasal airway

The objective of this study was to determine nasal cavity volumes and cross-sectional profiles from segmented coronal high-resolution computed tomography (HRCT) images. Pathological mucosal changes and congenital sinonasal variants were quantitated and three-dimensional (3D) images for determining sinonasal airway diseases evaluated by using the new semiautomatic segmentation software, Anatomatic. Anterior to posterior cross-sectional profiles of the sinonasal airway were obtained from acoustic rhinometry and segmented coronal HRCT images and compared in five patients having complaints of nasal obstruction and chronic sinusitis. Results showed that accurate volumes of air spaces in the nasal cavity and paranasal sinuses were obtained. When compared, the cross-sectional profiles of the nasal cavities obtained from acoustic rhinometry and the segmentation technique were similar in the anterior portion, but differed in the posterior portion. The results obtained by coronal HRCT and segmentation were more reliable than those produced with acoustic rhinometry. 3D images acquired from segmented images were found to help make a good pre-operative assessment of the whole sinonasal compartment. Segmentation and volumetric analysis using the Anatomatic technique also proved to be well suited to the evaluation of the nasal cavity and paranasal sinus geometry in patients with sinonasal diseases. Received: 5 March 1998 / Accepted: 9 June 1998     

Acoustic rhinometry and paranasal sinuses: a systematic study in models, anatomic specimens, and in vivo

OBJECTIVE/HYPOTHESIS: Acoustic rhinometry (AR) evaluates the cross-sectional areas (CSA) of the nasal cavity through acoustic reflections. The aim of this study was to test whether the paranasal sinuses are a cause for the measurement of increased CSA in the posterior cavum of the nose. STUDY DESIGN:: Experimental study to evaluate the influence of paranasal sinus volume on AR measurements in two anatomic nose models, an anatomic specimen, and seven individuals. METHODS: The paranasal sinus volume was systematically reduced by filling of the maxillary sinus with saline. The paranasal sinus ostia were enlarged in the models and the anatomic specimen by infundibulotomy and supraturbinal fenestration, with AR repeated thereafter. RESULTS: No modification of the posterior area-distance curve was found in the models, the specimen, and the individuals after changing the volume of the maxillary sinus with unmodified anatomy of the paranasal sinus ostia. The apparent CSA measured in the posterior cavum after infundibulotomy and supraturbinate fenestration in the models and the specimen increased with the volume of the paranasal sinuses. CONCLUSION: Regular anatomy provided, AR reveals reproducible measurements that correspond with the actual CSA up to the ostia of the paranasal sinuses. Untypical large openings to the paranasal sinuses (e.g., after paranasal sinus surgery) appear to contribute to the inaccuracy of AR by overlapping paranasal sinus CSA with the posterior part of the area distance curve.     

Effects of anatomical variations of the nasal cavity on acoustic rhinometry measurements: a model study

BACKGROUND: The goal of this study was to assess how anatomic variations of the nasal cavity affect the accuracy of acoustic rhinometry (AR) measurements. METHODS: A cast model of a human nasal cavity was used to investigate the effects of the nasal valve and paranasal sinuses on AR measurements. A luminal impression of a cadaver nasal cavity was made, and a cast model was created from this impression. To simulate the nasal valve, inserts of varying inner diameter were placed in the model nasal passage. To simulate the paranasal sinuses, side branches with varying neck diameters and cavity volumes were attached to the model. RESULTS: The AR measurements of the anterior nasal passage were reasonably precise when the passage area of the insert was within the normal range. When the passage area of the insert was reduced, AR measurements significantly underestimated the cross-sectional areas beyond the insert. The volume of the paranasal sinus had limited effect on AR measurements when the sinus ostium was small. However, when the ostium size was large, increasing the volume of the sinus led to significant overestimation of AR-derived areas beyond the ostium. CONCLUSION: The pathologies that narrow the anterior nasal passage result in the most significant AR error by causing area underestimation beyond the constriction. It also appears that increased paranasal sinus volume causes overestimation of areas posterior to the sinus ostium when the ostium size is large. If these physical effects are not considered, the results obtained during clinical examination with AR may be misinterpreted.     

Acoustic rhinometry: the bat principle of the nose]

All cross-sectional areas of the upper airway can be measured by an acoustic signal using the acoustic reflection technique, or acoustic rhinometry. The plane of the cross-sectional areas measured was determined in nasal models. The isotemporal layers were found to be nearly parallel to the nasal valve. The acoustically measured cross-sectional areas correlated with the cross-sectional areas of cuts from nasal models. After digitizing these cuts, a CAD software calculates cross-sectional areas in all orientations and at all distances. The difference between the measured and calculated cross-sectional areas is up to 3% in the nasal cavity and up to 17% in the nasopharynx. The hypothesis that the cross-sectional areas measured lie nearly parallel to the nasal valve was confirmed. The normal rhinometric curve shows the minimal cross-sectional area (I-notch) to lie at the nasal isthmus. The second narrowest segment of the nasal cavity lies at the head of the inferior concha and septal concha (C-notch). Characteristic examples of patients with turbinate hypertrophy, choanal atresia, enlarged adenoids, and septal deviations are presented. Acoustic rhinometric curves can only be interpreted in combination with the rhinoscopic findings because different pathological conditions can produce similar curves. Recording of reliable and reproducible data by acoustic rhinometry demands that the connection between the rhinometer and the nose does not distort the valve area. When we used two different nose pieces (1.2 and 1.5 cm outer diameter) the cross-sectional areas in the anterior third of the nose of only 28% of the patients was measured correctly.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acoustic rhinometry: an explanation of some common artefacts associated with nasal decongestion

The nasal cavities of 51 healthy volunteers were examined using acoustic rhinometry before and after nasal decongestant. Several specific dimensions were studied, which included the minimum cross-sectional area, and three volumes corresponding to the anterior, middle and posterior regions of the nasal airway. An average acoustic rhinometry trace was constructed for the whole group of subjects, before and after decongestion, from data extracted from the raw data files written to the computer hard disk for each subject. A 27.5% (P < 0.0001) increase in the minimum cross-sectional area was observed, with no shift in its position. The greatest increase in nasal dimensions was seen in the anterior and middle parts of the nose, however, significant changes were also seen in the posterior nasal cavity and post nasal space. There are a number of possible sources of artefact. First, confusion of the first and second minima may produce apparent movement of the minimum cross-sectional area following nasal decongestion. Second, a postulated change in the acoustic path length may lead to apparent changes in volume in certain regions of the nose. Third, a variable and uncontrollable degree of sound energy loss will occur into the opposite nasal cavity beyond the posterior border of the septum. An apparent increase in the dimensions of this region will be seen as the opposite cavity decongests. We feel that all users of the acoustic rhinometer need to be aware of these potential sources of artefact, and attention needs to be focused on an agreed definition of the components of the acoustic rhinometry trace.     

Changes in Nasal Airway Dimensions in Infancy

Thirty-nine infants, previously examined as neonates, were re-examined at 1 year of age with continuous wide-band noise acoustic rhinometry using a specific probe optimized for infants, to determine the dimensional growth and maturation of nasal airway geometry in otherwise healthy infants. During the first year of life, the acoustically determined dimensions of the nasal airways increased significantly. The total minimal cross-sectional area increased by 67% (0.21cm²     

Nasal airway volume and resistance to airflow

BACKGROUND: In modern rhinological practice and research, rhinomanometry and acoustic rhinometry are widely used. The goal of this study was to determine whether there is correlation between rhinomanometrically derived nasal airflow resistances and acoustic rhinometrically derived nasal airway volumes. METHODS: To achieve the goal, a prospective cross-sectional study of a total of 316 patients complaining of nasal obstruction was performed. Resulting data were compared by means of Spearman rank 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 states showed significant negative correlation unilaterally 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.     

Study and application of a mathematical model for the provisional assessment of areas and nasal resistance, obtained using acoustic rhinometry and active anterior rhinomanometry

Nasal resistance (NR) depends on the geometrical features and tortuosity of the nasal airway and on the air flow. Knowing the longitudinal distribution of cross-sectional areas (CSAs) in the nasal cavity (which can be obtained using acoustic rhinometry) and the laminar nasal resistance (obtainable by processing the rhinomanometric results), it is possible to calculate, utilizing a mathematical model elaborated on the basis of fluid dynamics, the differential nasal resistance (NRdiff) and the cumulative nasal resistance (NRcum), thus localizing the position at which the highest resistance is concentrated and the related longitudinal distribution. Using a mathematical model, we integrated the sigmoid curves DeltaP/Q of rhinomanometry with the cross-sectional areas obtained using acoustic rhinometry, thus obtaining the normal distribution of differential and cumulative nasal resistances. Afterwards, we empirically reduced the cross-sectional areas corresponding to the head, body, tail and the whole inferior turbinate, recalculating the differential and cumulative nasal resistance distribution curves. The results show that reduction of up to 50% of cross-sectional areas does not substantially affect the resistivity role of the nasal valve, while greater reductions move the highest resistivity point to an area at the junction of the body and the head of the inferior turbinate. The study of the differential nasal resistance trend curves as a function of the reduction of cross-sectional areas shows that the resistance variation of the body and the whole inferior turbinate prevail with reductions of up to 40%, while the variation of cross-sectional areas of the body bordering the inferior turbinate head is predominant with higher reductions. The cross-sectional areas of the nasal airway cavity with highest resistivity are mainly located in an anterior position, where the differential nasal resistances are higher, but there are substantial variations produced by reducing the cross-sectional area of the posterior nasal airway. A similar model can produce provisional values for the results obtainable with functional nasal surgery.     

Anterior turbinectomy: experimental and clinical study

INTRODUCTION: Minimal cross-sectional areas situated at the anterior end of the inferior turbinate have the most influence on nasal patency. To improve persistent nasal obstruction, 2 types of inferior turbinectomies--conventional complete resection including the anterior and posterior mucosa and anterior resection of the anterior mucosa--were conducted and preoperative and postoperative nasal patency and stuffy sensation were compared and analyze. OBJECTS AND METHODS: Cases undergoing 2 types of turbinectomies between July 1997 and March 2000 numbered 63--conventional in 32 (64 sides) and anterior in 31 (62 sides). Anterior, posterior, and total nasal volume and minimal cross-sectional area were evaluated pre- and postoperatively using an acoustic rhinometer. The stuffy sensation was similarly evaluated by the visual analog scale (VAS). RESULTS: All nasal volumes showed postoperative increase under conventional treatments. Anterior and posterior volumes significantly increased under anterior treatment. Comparing the results of postoperative volume posterior volume was significantly larger under conventional treatment than under anterior treatment. Stuffy sensation significantly improved by VAS in both types of turbinectomy, with no significant difference between them. CONCLUSION: Anterior treatment to solely increase nasal volume at the minimal cross sectional area showed equal postoperative improvement in VAS under conventional treatment.     

Nasal obstruction following septorhinoplasty: how well does acoustic rhinometry work?

Septorhinoplasty aims to improve not only the esthetic appearance but also breathing function of the nose. Although the esthetic improvement can be judged by the patient and the surgeon easily, evaluation of nasal breathing is more complicated. Besides the subjective symptom scores given by the patient, some objective methods have been developed. One of the most widely used of these objective methods is acoustic rhinometry, which gives valuable information about the cross-sectional areas and volumes of the nasal airway as a function of distance from the nostril. Since the introduction of acoustic rhinometry, many papers were reported regarding its efficiency with some conflicting conclusions. Septorhinoplasty has the potential to narrow the nasal airway, especially if it includes lateral osteotomies and hump reduction. We aimed to evaluate the role of rhinoplasty on nasal obstruction with the help of subjective symptom scores and acoustic rhinometry. The study consisted of 26 patients who underwent septorhinoplasty. Before and after surgery, the symptom scores and findings of acoustic rhinometry were collected both before and after decongestion of the nasal mucosa. Symptom scores decreased on both sides, which were statistically significant (p < 0.05), however, the changes in cross-sectional areas of the nasal airway were not statistically significant (p > 0.05). The correlation between the symptom scores and acoustic rhinometry findings was not significant for all levels. The effect of septorhinoplasty on nasal airway and some important maneuvers to protect against nasal obstruction are discussed.     

Accuracy of measurement of acoustic rhinometry applied to small experimental animals

Nasal obstruction is one of the major symptoms of allergic rhinitis. In the study of the mechanism of nasal obstruction, experiments on animal are useful. In adult humans, acoustic rhinometry has been used to evaluate nasal obstruction by determining nasal cavity dimensions in terms of cross-sectional areas as a function of the distance from the nostril. We modified the equipment used on humans to assess dimensions of nasal airway geometry of small experimental animals. The purpose of this study was to investigate the accuracy of measurement of the modified acoustic rhinometry applied to small experimental animals using nasal cavity models and guinea pigs. Measurement of the nasal cavity models (made of cylindrical silicone tubes) showed that the acoustic rhinometry estimated 85.5% of actual area and 79.0% of actual volume. In guinea pigs, nasal cavity volume determined by the acoustic rhinometry was 73.7 +/- 20.0% of actual volume. The actual volume was estimated by impression material instilled into the nasal cavity of the animals (IM volume), and volume determined by acoustic rhinometry significantly correlated with IM volume. Furthermore, there was a significant negative correlation between the volume and nasal airway resistance in guinea pigs. Measurement of the nasal airway resistance is the method frequently used in the evaluation of the nasal obstruction in guinea pigs. These results suggest that acoustic rhinometry is useful in evaluating nasal obstruction in small experimental animals.     

Acoustic rhinometry: a study of transient and continuous noise techniques with nasal models.

The objective of this study is to compare the properties of two of the most frequently used acoustic rhinometers: the EcoVision (Hood Laboratories, USA) using the transient technique, and the Rhin2100 (RhinoMetrics, Denmark) using the continuous wide-band technique. In the wide-band rhinometer (Rhin2100), the transient analog signals of traditional rhinometers (EcoVision), are replaced by a digitally produced continuous wide-band noise signal. Tubular models and a plastic model produced by stereolithography (SLA), representing the true replicate of the nasal anatomy, were used to compare the accuracy of the two rhinometers. The effect of increasing angling (0-50 degrees) between the sound wave tube and the cavity was evaluated in a tubular model. The curves obtained with the two rhinometers showed close similarity, and the acoustically derived volumes correlated well with the volumes of tubular (% error < 4%) as well as the complex nasal model (% error < 10.5%). Both rhinometers underestimated the minimum cross-sectional area (MCA) of the complex nasal model (mean % error complex model: Rhin2100 = -7.6%, EcoVision = -13%). The effect of increasing the angle between the nose adapter and the tubular models was small for both rhinometers (CV < 3% for MCA and CV < 1% for volumes). The similar, and in general, high accuracy of the two rhinometers evaluated, particularly in the complicated geometry of the SLA model, is an indication of the reliability of both. The small effect of changing the angle between the nose adapter and the models was unexpected and very encouraging. Nevertheless, some minor differences in performance and capabilities of the two rhinometers might influence interpretation and comparison of results. Further comparisons in a clinical setting are under current investigation.     

Reduction rhinoplasty and nasal patency: Change in the cross-sectional area of the nose evaluated by acoustic rhinometry

The feeling of nasal patency is related to the dimensions of the nasal cavity. After aesthetic reduction rhinoplasty, the cross-sectional areas of the nose may decrease critically. In this study, acoustic rhinometry, a new method based on acoustic reflections, was used to evaluate the internal dimensions of the nasal cavity in 37 patients before reduction rhinoplasty and again 6 months after surgery. The internal dimensions of the nasal cavity—especially the anterior dimensions—were reduced after rhinoplasty. Compared with the preoperative values, the minimum cross-sectional area (at the nasal valve) decreased by 22% (totally) to 25% (unilaterally) (P = .000), and the cross-sectional areas at the piriform aperture decreased by 11% to 13% (P = .02).     

A human study model for nitric oxide research in sinonasal disease

Sinus nitric oxide (NO) measurements present a novel and promising approach to help overcome difficulties and confounding variables associated with nasal NO measurements such as the nasal cycle, ostial patency, and individual contribution to total NO production of each sinus. Conflicting results reported on nasal NO measurements in various sinonasal diseases are presumed to originate from the variable diffusion of sinus NO into the nose where it is measured. This study presents a novel technique and research method for direct measurement of sinus NO. The authors' original technique of individual, non-destructive catheterization of the sinuses through their natural ostia is developed and refined to allow accurate measurements of NO produced in the sinuses. Our study indicates that reproducible catheterization of the sinuses through their natural ostia can be performed in the clinical research setting under local and topical anesthesia. The model can be used to test the effects of various conditions on nasal and sinus NO production in a variety of disease models and the variables affecting sinonasal gas exchange can be differentially studied. Volunteer healthy adult human subjects without nasal allergies are used. An endoscopic nasal exam with topical anesthesia followed by in vitro allergy testing is performed to determine eligibility. Sinus computerized tomography (CT) scans are used to delineate anatomic features and to calculate paranasal sinus volumes. Continuous flow sinus air sampling and NO measurement with a chemiluminescence analyzer is obtained through polyethylene tube catheters (PEC) placed endoscopically into an aerated major paranasal sinus. Catheters are introduced through natural ostia under local and topical anesthesia. Nasal and differential sinus NO measurements are performed.     

Objective computerized determination of the minimum cross-sectional area of the nasal passage on computed tomography

OBJECTIVES/HYPOTHESIS: Current methods that measure cross-sectional areas of the nasal passage on computed tomography (CT) do not determine the minimum cross-sectional area that may be an important factor in nasal airway resistance. Objective measurement of the dimensions of the nasal passage may help in the diagnosis, as well as the choice and evaluation of surgical treatment for upper airway insufficiencies. STUDY DESIGN: Retrospective and clinical study. METHODS: Software was developed that automatically calculates the minimum cross-sectional area of the nasal passage on CT. RESULTS: Evaluation shows that the minimization algorithm in the software reliably calculates the position and orientation of the oblique plane on which the minimum cross-section lies. CONCLUSION: The developed method may be used for objective and observer-independent evaluation of surgical treatment options.     

Nasal airway volumetric measurement using segmented HRCT images and acoustic rhinometry

Semiautomatic segmentation methods using High Resolution Computed Tomography (HRCT) or Magnetic Resonance Imaging give accurate and reproducible volumetric measurements in various intracranial diseases. In this prospective study, for the first time in literature, with the help of a new semiautomatic segmentation technique and coronal HRCT, we correlated the volumes and cross-sectional areas of the nasal cavity with those obtained by clinical acoustic rhinometry in 14 patients with chronic sinusitis. The measurements obtained by both techniques showed statistically significant correlations between volumes in the anterior and middle parts, but statistically poor correlations between the volumes in the posterior part of the nasal cavity. Coronal HRCT and our new microcomputer applicable semiautomatic segmentation software proved compatible with daily clinical practice. Based on the promising results of our study, we recommend the use of this technique in the validation studies of acoustic rhinometry and in complicated cases as a complementary examination in the evaluation of nasal cavity.     

Evaluation with acoustic rhinometry of surgical results in patients undergoing septoplasty

We used acoustic rhinometry to evaluate the surgical results of septoplasty in patients with nasal respiratory insufficiency caused by morphological abnormalities of the nasal septum. Acoustic rhinometry is a relatively new exploration method for the nasal cavity that yields objective spatial measurements. These measurements are the cross sections and volumes of the nasal cavity divided longitudinally into two regions, an anterior region up to 32 mm from the nasal orifices and the posterior region, up to 64 mm from the same point. We studied 45 patients with nasal respiratory insufficiency who had undergone septoplasty. Measurements were made before and after surgery. Our results show a clear increase in nasal sections and volumes after surgery. They confirm the benefits of acoustic rhinometry as a method for quantifying morphological abnormalities of the nasal cavity.     

Changes in the nasal airway by transverse distraction of the maxilla]

OBJECTIVE: To investigate nasal airway changes through transverse maxillary distraction osteogenesis by means of an objective, reliable, noninvasive investigation technique with special attention to nasal valve changes and widening of the posterior maxilla. PATIENTS AND INTERVENTION: Eight patients with a severe maxillary transversal deficit underwent surgically assisted rapid palatal expansion in local or general anesthesia. Before and after the distraction process, a transnasal series of acoustic measurements of nasal airway profile was performed under topical decongestion. Nasal volume was calculated by integration of the area profile. The cross-sectional area of the nasal valve was also determined. RESULTS: A significant enlargement of nasal volume was recorded in all patients (P < 0.01: Wilcoxon signed rank test). The average increase measured 5 cm3 (23%). The increase in volume was recorded in all parts of the nasal cavity, indicating complete maxillary expansion even in the posterior segment. The nasal valve area raised from 0.56 to 0.70 cm2 (P < 0.01). Six out of eight patients reported striking improvement of nasal patency after maxillary distraction. CONCLUSION: Besides correction of the maxillary arch deformity, rapid palatal expansion contributes to improved nasal patency by resolving nasal valve constriction. Significant widening of the posterior nasal cavity was achieved, indicating a translational pattern of maxillary movement, although the pterygomaxillary junction was not touched in the osteotomy.     

Objective measurement of nasal airway dimensions and resistance using acoustic rhinometry and rhinomanometry in habitual snorers compared with non-snorers

Snorers represent a heterogeneous group that requires adequate assessment before recommending surgical treatment. Most studies of the pathophysiology of snoring and obstructive sleep apnea have emphasized anatomical abnormalities in the oropharyngeal and hypopharyngeal airways. It is still unclear if nasal airway restriction plays an important role in sleep-disordered breathing and there is no general consensus if treatment of nasal pathology should be included in the management of patients with snoring or sleep apnea. The aim of this study was to compare nasal dimensions and airflow resistance of habitual snorers with non-snoring individuals by means of acoustic rhinometry and rhinomanometry. Sixty individuals were enrolled in this analytical cross-sectional study. They were divided in two groups: group A (case) consisted of 30 patients with a main complaint of chronic snoring referred to ear, nose, and throat (ENT) clinic of Hazrat-e-Rasoul University Hospital, Tehran, Iran. Group B (control) consisted of 30 individuals without any complaint of snoring. The subjects were assessed objectively with acoustic rhinometry and rhinomanometry. Nasal dimensions and airflow resistance were recorded for all individuals. The most common site of minimum cross-sectional area (MCA) was at the left concha-notch in both snoring and non-snoring individuals. Significant reduction of cross-sectional area of both isthmus and concha notches was seen in habitual snorers (P < 0.05). The mean total airflow resistances in both pressures of 75 and 150 Pa was higher in habitual snorers. Whereas, these differences were not statistically significant (P > 0.05). The results of our study illustrate that acoustic rhinometry, rhinomanometry may be helpful methods for quantitative assessments of nasal airway respiratory function, and configuration in snorers; especially to evaluate site of MCA, decreased nasal cross-sectional area and increased nasal airflow resistance in habitual snorers which may lead to OSA.