The relationship between nasal airway size and nasal-oral breathing

The relationship between nasal airway size and nasal-oral breathing Donald W. Warren, D.D.S., Ph.D.,* W. Michael Hairfield, D.D.S.,‘* Debra Seaton, D.M.D., MS.,*** Kathleen E. Morr, M.S.,**** and Lynn R. Smith, B.S.,***** Chapel Hill, N.C.

Most clinicians agree that impaired nasal breathing results in obligatory mouth breathing. Some believe that mouth breathing influences dentofacial growth; others disagree. The term mouth breathing is confusing because total mouth breathing rarely occurs. A combination of nasal and oral breathing is more usual. The purpose of the present study involving 116 adult subjects was to (1) assess the relationship between nasal impairment and nasal-oral breathing, (2) determine the switching range from nasal to nasal-oral breathing, and (3) quantify the term mouth breathing. The pressure-flow technique was used to estimate nasal airway size; inductive plethysmography was used to assess nasal-oral breathing in normal and impaired breathers. Analysis of the date showed a Pearson rank correlation of 0.545 (P < 0.001) between nasal area and nasal-oral respiration. Ninety-seven percent of subjects with a nasal size CO.4 cm* were mouth breathers to some extent. About 12% of subjects with an adequate airway were assumed to be habitual mouth breathers. The findings indicate that the switching range from nasal to nasal-oral breathing is very narrow (0.4-0.45 cm’). These results also confirm our contention that in adults an airway ~0.4 cm* is impaired. (AM J ORTHOD DENTOFAC ORTHOP 1966;93:289-93.)

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ost clinicians agree that impaired nasal breathing results in obligatory mouth breathing. ‘-I3 While many believe that mouth breathing influences dentofacial growth,‘4-23 others disagree.‘2,24-26Much of the controversy stems from differences in the definition of nasal airway impairment and confusion over what the term mouth breathing really means. For example, an open-mouth posture does not always produce oral breathing. 27 Furthermore, those who mouth breathe usually nose breathe to some degree also.27 This study is the sixth in a series of investigations concerning upper airway breathing in normal and nasally impaired populations. Our research is motivated by the need for a more objective assessment of airway impairment and a better definition of the term mouth breathing.

From the School of Dentistry, University of North Carolina at Chapel Hill. Supported in part by Grants DE06957, DE07105, DE06061, DEO0129, and DE02668, N.I.D.R. *Kenan Professor and Director, Oral-Facial and Communicative Disorders Program, Department of Dental Ecology and the Dental Research Center. **Assistant Professor, Department of Dental Ecology and the Dental Research Center. ***Clinical Assistant Professor, Department of Dental Ecology and the Dental Research Center. ****Associate Professor. Department of Dental Ecology and the Dental Research Center. *****Clinical Instructor, Department of Dental Ecology and the Dental Research Center.

We have recently reported two new approaches for monitoring the upper airway during breathing. One technique provides an estimate of nasal cross-sectional size’* and the other provides an assessment of percent nasal respiration. 29 The purpose of the present study was to combine both techniques to determine the relationship between nasal airway size and percent nasal respiration. Such data would show the ranges at which persons would manifest nasal or combined nasal and oral respiration and, in turn, would identify more precisely the dimensions of nasal airway impairment. METHOD

The nasal airway and percent nasal respiration were assessed in 116 adult subjects. The sample included patients referred from otolaryngology with the clinical diagnosis of impaired nasal respiration and patients from dental clinics of the School of Dentistry. A diverse population in terms of nasal respiration was desired. Measurement of nasal cross-sectional

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The pressure-flow technique was used to estimate the smallest cross-sectional area of the nasal airway. Details of the procedures used have been reported previously. ** The assumption made with this approach is that the smallest cross-sectional area of a structure can be estimated if the differential pressure across the structure is measured simultaneously with the rate of airflow 289

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through it. The reliability of this procedure has been verified in a number of laboratories.30,3’ The nasal pressure drop was measured by a differential pressure transducer connected to two catheters. The first catheter was positioned midway fin the subject’s oropharynx and the second catheter was placed within the nasal cap. Nasal airflow was measured by a heated pneumotachograph connected to a well-adapted nasal cap. Each subject was asked to breathe normally in and out of the nose. The resulting pressure and tirflow measurements were transmitted to a microcomputer and associated hardware for recording and analysis.

The method involves a recently introduced device that monitors ventilation in a noninvasive way-and provides the opportunity to measure oral-nasal respiration without enclosing the head or body in an airtight box .29 The respiratory inductive plethysmogmph used in fhis study has been described by Cohen and associates,32 Watson,33 and Sackner.% Briefly, the device consists of two transducers tkat record the relative movements of the abdomen and thoracic cage during respiration. Two Teflon-coated wires, sewn into lightweight elastic material, are fastened with Velcro around the upper chest and abdumen. The transducers are attached to frequency oscillators that connect to a calibration system. Each transdueer measures changes in inductance that are proportional to changes in horacic cage and abdoininal volumes. Breathing changes the mean c&s-sectional area of the coils and the inductance changes .&at result are converted into proportional voltages.

size and percent nasal breathing.

The rib eage and abdominal signals are then calibrated aiaitit a known volume by having the sGbje&s breathe into a spirometer. The sum of the caIib&ed signals (thoracic and -abdominal) i-sequivalent to~ti4iaJ volume. Calibration is automatically performed by a software program that aiso provides automatic validation of the calibration proeed~es. After comph&g the calihzation procedures, th& subjects are asked to count from 60 to 70 t@%re recording data. owe believe this distraction and the fact that no information concerning breading is provided present a better free-breathing environmet becat& tli;e attention of the sub&+ is not focused on respiration. Subjects are motitored for approGmately 2 &&es after phonation to ensure a normal breathing p&eti. Separation of the oral and nasal components of tidal volume is accomp&+hed by placing a sm@ll pal ep, over the nose and connecting it through a tube to &i integrating pneutiotachograph, which measures n&al air volume. If-the ratio of nasal/ tidal volume is mtiltiplied by 100, a percentage of nasal breathing -is obtained.

Spearman’s rank correlation coefficient was cpmputed to-determine the strength of tie relations&ip between area-and percent nasal breathing. This is a nsnparametric measure of association in which thO&es for area are ass@ned a rank among themselves a& similarly for percent nagal brf#&ilg. Cam* is determified by the difference in ranks for each subject . The values of Spearman’s co&G&fall between- - 1 and 3 in which 0 implies no correlati@, -4 imp&s-

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Fig. 2. A more nonlinear relationship results when probable habitual mouth breathers are removed. The data demonstrate a vertical pattern for nasal airway adequacy and a horizontal pattern for impaired nasal breathers. The switching range is narrow, beginning at ~0.5 cm’. At 0.4 cm’, almost all adults become nasal-oral breathers.

absolute negative correlation, and 1 implies absolute positive correlation. The Spearman correlation coefficient for area vs. percent nasal breathing was 0.545, which is significantly different from 0 (P < 0.001). This indicates that there is a relationship between the two variables-that is, as cross-sectional area increases, percent nasal breathing tends to increase. The data were then subgrouped according to percent nasal breathing (Fig. 1). Subjects who demonstrated a percent nasal breathing of 80 and above were classified as nasal breathers. In fact, some subjects scored slightly above 100%. This reflects measurement error associated with this respirometric technique. Although we have reported a mean error of approximately 5%,29 errors as great as 10% are not uncommon. Mouth breathing was defined by means of the following criteria. Subjects scoring between 60% and 80% were classified as predominantly nasal breathers. Those falling in the 40% to 60% subgroup were considered mixed oral-nasal breathers. The 20% to 40% subgroup comprised the predominantly oral breathers and those in the 0 to 20% subgroup were considered to be oral breathers. These are arbitrary classifications but appear to be reasonable. The data were further categorized into nasal areas 30.4 cm* and CO.4 cm’. Tthese categories are based on our previous reports indicating that in adults a nasal cross-sectional area CO.4 cm2 constitutes nasal airway impairment.'2.13.35-37

According to these categories and subgroupings, 34

of 35 subjects demonstrating an airway size ~0.4 cm* were oral breathers to some extent. Twenty-two were mixed, predominantly oral, or oral; 12 were predominantly nasal. Only one was classified as a nasal breather. On the other hand, 54 of 81 subjects demonstrating a nasal cross-sectional area aO.4 cm2 were found to be nasal breathers and another 11 subjects were predominantly nasal. Only 16 were mixed, predominantly oral, or oral breathers. Similarly, of those classified as nasal breathers, 54 of 55 subjects had a nasal airway size 20.4 cm2. DISCUSSION

The data generated from this study demonstrate that percent nasal breathing is mildly correlated with nasal cross-sectional size-that is, larger nasal airways are generally associated with greater amounts of nasal breathing. The considerable variability observed in the data reflects a variety of factors. The population consisted primarily of nasal and nasal-oral breathers. Only two of the 116 subjects were total oral breathers. Many were obligatory nasal-oral breathers and a few were habitual nasal-oral breathers. The habitual nasal-oral breathers undoubtedly skew the data somewhat. Most habitual breathers can be identified and the data adjusted if certain assumptions are accepted. One assumption is that persons with an airway CO.4 cm2 are obligated to mouth breathe. The present data support this. Another assumption is that persons with an airway in the 0.4 to 0.5 cm* range may be

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obligatory or habitual mouth breathers, but differentiation is not possible. The basis for considering that some may be obligatory mouth breathers stems from the observations of McCaffrey and Kern”’ on persons with unilateral nasal impairment-namely, thatpersons with unilateral impairment often demonstrate symptoms of breathing distress. The 0.4 to 0.5 cm2 borderline growp may include a few such persons. In addition, since airway resistance is flowdependent, because of the development of turbulence, there may be some persons in this borderline range who breathe at a high enough rate of flow to produce symptoms of distress. Because we cannot differentiate with confidence those obligated to mouth breathe from those who are habitual mouth breathers in this range, none should be eliminated from the data pool. Variability within this borderline group may thus be caused by morphologic or behavioral factors. Therefore, only 11 subjects can be defined as probable habitual mouth breathers. Each has an airway >0.5 cm’, two are predominantly oral breathers, four are mixed, and five are predominantly nasal breathers. Fig. 2 illustrates the revised data with the probable habitual mouth breathers removed on the basis of these subsequent, but not unreasonable, assumptions. A nonlinear relationship consisting of a relatively narrow vertical pattern associated with the nasal breathers and a wider horizontal pattern associated with the nasal-orai breathers becomes apparent. The vertical pattern has a range of approximately 0.5 to 1.O cm’, which probably accounts for much of the scatter within the adequate group. The fact that nasal airway adequacy represents an approximate twofold range in size is one source of scatter of the data and this could be labeled anatomic variability. The scatter of the horizontal pattern reflects such factors as tongue carriage, mandibular position, velar length and size, pillar drape, amount of tonsillar mass, and magnitude of nasal resistance. AH of the above influence oral airway resistance and affect oral airflow volume in obligatory mouth breathers--that is, when a person becomes obligated to mouth breathe, the actual percentage of oral breathing will be determined by combinations of factors relating tathe morphology and function of oral, pharyngeal, and nasal structures. in addition, some of the scatter could result from induced variability caused by experimental disturbance of the system. There are three conclusions to be drawn from the present data. One involves our contention that a nasal airway CO.4 cm’ constitutes impairment in adults.‘2~“s‘“7Approximafely 97% of the subjects in this

category were noted to be mouth breathers to some extent and obligatory mouth breathing is consistent wiih a definition of impairment.“5”x The second conclusion is that the switching range from nasal to nasal-oral breathing is fairly narrow. Ex cept for the 11 subjects subsequently classified as habitual mouth breathers, the change from nasal to nasaloral breathing was an on-off phenomenon with little variability. Finally, the data indicatethat the term mouth breathing should be used with some caution since even impaired nasal breathers demonstrate a wide range of nasal-oral volumes with each breath. Although some may be oral breathers, many are predominantly oral, mixed, or even predominantly nasal breathers. Perhaps, the inability to link respiratory behaviors to dentofacjalgrowth stems from this inconsistent and variable response among subjects. The present findings suggest that we focus out artention on exaggerated postural responses to impairment. When impaired nasal respiration results in postural changes of the head and neck,“g-J’ and changes in tongue and mandibular placement,” unfavorable dentofacial development may occur. We believe the stimulus for exaggerated postural responses may relate to morphologic features of the oropharynx.” REfEREN.CES 1. Hastings S. James W. Discussion on mouthbreathing and nasal obstruction. Proc R Sot Med 1932:25:1343. 2. Balyeat RM, Bowen R. Facial and dental deformities due to perennial nasal allergy in childhood. Orthod Dent Child Int J 1934:20:445-55. 3. Ballenger WL, Ballenger HC. Diseases of the nose, throat and ear. 8th ed. Philadelphia: Lea & Febiger, L943:124. 307-9. 4. Ballard CF. The aetiology of malocclusion. An assessment. Dent Pratt 1957;8:42. 5. Ballard CF. Gwenn-Evans E. Discussion on the mouthbreather. Proc R Sot Med 1958;51:279-85. 6. Backlund E. Facial growth and the significance of oral habits. mouthbreathing, and soft tissues for malocclusion. Acta Odontoi Stand 1963;2l(suppl 36):1-139. 7. Ricketts RM. Respiratory obstruction syndrome. AM J Orcrnot? 1968:54:495-507. 8. Watson RM, Watren DW, Fischer ND. Nasal resistance, skeletal classification and mouth breathing in orthodontic patients. 4hj J ORTHOD 1968:54:367-79. 9. Linder-Aronson S. Effects of adenoidectomy on the dentition and facial skeleton over a period of fivi~years. Trans Eur Urthod Sot 1973: 177-86. 10. McCaffrey TV, Kern EB. Clinical cvatuation of nasal obstruction: a study of 1,000 patients. Arch Otolaryngol 1975;105: 542-5. 11. Linder-Aronson S. Adenoids: their effect on mode of breathing and nasal airflow and their relationship tocharacterisims of the facial skeleton and the dentition. Acta Otolaryngol 1979: 265(suppl): l-132.

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12. Warren DW, Lehman MD, Hinton VA. Analysis of simulated upper airway breathing. AM J ORTHOD 1984;86:197-206. 13. Hinton VA, Warren DW, Hairfield WM. Upper airway pressures during breathing: a comparison of normal and nasally incompetent subjects with modeling studies. AM J ORTHOD 1986; 89:153-61. 14. Morrison WW. The interrelationship between nasal obstruction and oral deformities. Int J Orthod 1931;17:453-8. 15. Strang RHW. A textbook of orthodontia. 2nd ed. Philadelphia: Lea & Febiger, 1943:144-5. 16. Jennes ML. Corrective nasal surgery in children. Arch Otolaryngol 1963;79: 145-5 I. 17. Reid JM, Donaldson JA. The indications for tonsillectomy and adenoidectomy. Otolaryngol Clin North Am 1970;334-9. 18. Quinn GW. Airway interference and its effect upon the growth and development of the face, jaws, dentition and associated parts. NC Dent .I 1978;60:28-31. 19. Quinn GW. Are dentofacial deformities a preventable disease? NC Dent J 1978;61:5-6. 20. Schulhof RJ. Consideration of airway in orthodontics. J Clin Orthod 1978;12:440-4. 21. Rubin RM. Facial deformity: a preventable disease? Angle Orthod 1979;49:98- 103. 22. Rubin RM. Mode of respiration and facial growth. AM J ORTHOD 1980;78:505-10. 23. Ricketts RM. On early treatment. Part I [JCO interviews]. J Clin Orthod 1979;13:23-38. HF, Leighton BC. A survey of antero-posterior ab24. Humphrey normalities of the jaws in children between the ages of two and five and a half years of age. Br Dent J 1950;88:3. and be25. Leech HL. A clinical analysis of orofacial morphology havior of 500 patients attending an upper respiratory research clinic. Dent Pratt Dent Ret 1958;9:57-68. 26. Vig PS, Sarver DM, Hall DJ, Warren DW. Quantitative evaluation of nasal airflow in relation to facial morphology. AM J ORTHOD 1981;79:263-71. studies of the upper airway: impli27. Warren DW. Aerodynamic cations for growth, breathing and speech. In: McNamara JA, ed. Naso-respiratory function and craniofacial growth. Ann Arbor: 1980. Center for Human Growth and Development, University of Michigan. 28. Warren DW. A quantitative technique for assessing nasal airway impairment. AM J ORTHOD 1984;86:306-14. of nasal 29. Warren DW. Hinton VA, Hairfield WM. Measurement and oral respiration using inductive plethysmography. AM J ORTHOD 1986;89:480-4. 30. Lubker JL. Velopharyngeal orifice area: a replication of analog experimentation. J Speech Hear Res 1969;12:218-22.

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Smith BE, Weinberg B. Prediction of velopharyngeal orifice area: a re-examination of model experimentation. Cleft Palate J 171277-82. Cohen MA, Watson H, Weisshaut R, Scott F, Sackner MA. A transducer for non-invasive monitoring of respiration. In: Statt FD, Raftery EB, Sleight P, Goulding GL, eds. Proceedings of the second international symposium on ambulatory monitoring. New York: Academic Press, 1978. Watson H. The technology of respiratory inductive plethysmography. In: Statt FD, Raftery EB, Goulding GL, eds. Proceedings of the third international symposium on ambulatory monitoring. New York: Academic Press, 1980:537-63. Sackner MA. Monitoring of ventilation without physical connection to the airway: a review. New York: Academic Press 1980;299-319. Warren DW, Hinton VA, Pillsbury HC, Hairfield WM. Effects of size of the nasal airway on nasal airflow rate. Arch Otolaryngol 1987;113:405-8. Hinton VA, Warren DW, Hairfield WM, Seaton D. The relationship between nasal cross-sectional area and nasal air volume in normal and nasally impaired adults. AM J ORTHOD DENTOFAC ORTHOP 1987;92:294-8. Warren DW, Hairfield WM, Seaton D, Hinton VA. The relationship between nasal airway size and nasal airway resistance [submitted for publication]. AM J ORTHOD 1986. Watson RM, Warren DW, Fischer ND. Nasal resistance, skeletal classification and mouth breathing in orthodontic patients. AM J ORTHOD 1968;54:367-79. McNamara JA. Neuromuscular and skeletal adaptations to altered functions in the orofacial region. AM J ORTHOD 1973; 64:578-604. Harvold EP, Tomer BS, Chieici G. Primate experiments on oral respiration. AM J ORTHOD 1981;79:359-72. Solow B, Kreiborg S. Soft-tissue stretching: a possible control factor in craniofacial morphogenesis. Stand J Dent Res 1977; 85505-67. Subtelny JD. Effect of diseases of tonsils and adenoids on dentofacial morphology. Ann Otol Rhino1 Laryngol 1975;84(suppl 19):50-4.

Reprinf requests to: Dr. Donald W. Warren Dental Research Center Building 210H UNC School of Dentistry University of North Carolina at Chapel Chapel Hill, NC 27514

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