Immediate postural responses to total nasal obstruction

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Immediate postural responses to total nasal obstruction Luc P. M. Tourne, DDS, MS," and James Schweiger, DDS, MS b Mechelen, Belgium, and Duluth, Minn. Twenty-five nasal breathing adults were radiographically examined before and after their nasal respiratory pattern had been artificially eliminated for a period of 1 hour. Six angular and six linear variables were measured to determine the extent of the postural reflexive behavior of the cranium, mandible, hyoid bone, tongue, and lips. All subjects coped in their own individual way with the environmental impact. The most generalized findings were parting of the lips (p < 0.05), a drop in mandibular position (p < 0.001), and a downward movement of the hyoid bone (p < 0.05). Cranial extension did not reach statistical significance (p = 0.06). The relevance of these findings relative to primate experiments and human clinical research is discussed. If the same postural reactions are maintained over a long-term period, they may be instrumental in influencing the vertical craniofacial growth pattern. (Am J Orthod Dentofac Orthop 1996;110:606-11 .) Nasa l respiratory impairment has been asso- ciated with a deviant vertical craniofacial growth pat- tern for at least a century. An increase in anterior face height 1-3 and in gonial angle, 4 along with a decrease in facial prognathism, ''4'5 are commonly described fea- tures. The morphologic changes may be induced by an alteration in craniofacial muscle recruitment or by a soft tissue stretching mechanism. 6'7 These functional responses, in turn, could be elicited by postural reflex- ive mechanisms that facilitate passage of air through the oropharynx. 8 This environmental concept of verti- cal craniofacial growth has been corroborated by some clinical studies that have indeed found associations between nasorespiratory impairment and postural vari- ables. 9"1~ However, controversy still remains about the validity of contemporary methods for quantifying the oronasal breathing ratio H'12 and the cause and effect relationship between oronasal breathing, postural be- haviors, and skeletal structure. 13-15 In addition, with the exception of the studies of Vig and Showfety 16 and of Hellsing, 17 the postural reactions after nasal obstruc- tion have never been experimentally studied in human beings. This article is the first attempt tO radiographi- cally measure the nature and the extent of those reflexes within a controlled experimental setting. METHODS AND MATERIALS A group of 25 adults (14 women and ! l men) participated in the study. The ages ranged from 23.7 years to 39.9 years, with a mean of 29.4 years. None of the subjects reported having had any difficulty breathing through the nose. Observa- Study approved by the Committee on the Use of Human Subject~ in Research, University of Minnesota and the Committee on the Use of Ionizing Radiation, Department of Environmental Health and Safety, University of Minnesota (study license number 22-00218-29). ~In private practice, Mechelen, Belgium. bin private practice, Duluth, Minn. Reprint requests to: Dr. L. Tourne, 38 Steenweg, 2800 Mechelen, Belgium. Copyright �9 1996 by the American Association of Orthodontists. 0889-5406/96/$5.00 + 0 8/1/65469 )) Tv __ i s ~ - - , " J ,n -Tv eZt b a~('--~'~7 ~J I \ I Fig. 1. Landmarks and postural measurements. For details see Tables I and II. tion of the subjects revealed that all had lip contact at rest. A preexperimental reference lateral cephalometric radiograph was taken with each subject standing with their head held in a natural position as obtained by the "self-balancing method." 18 With this method, a self-balance position is achieved by hav- ing each subject tilt their head backward and forward with decreasing amplitude until the most neutral and comfortable position is reached. The natural rest position of the mandible was standardized by having the subject pronounce the word Mississippi, at the end of which the radiograph was exposed. A standard x-ray cephalometric control unit was used. To avoid the use of a head holder and earrods, it was necessary to construct a special film holder to allow film placement in an alternative position. According to the technique of Moorrees and Kean, ~9 a weighted metal chain was suspended in front of the x-ray cassette to register a gravity-determined true vertical 606 American Journal of Orthodontics and Dentofacial Orthopedics Tourne and Schweiger 607 Volume 110, No. 6 reference line on each radiograph. Each subject's nose was then blocked with a nose clip of the type commonly used by swimmers. After a 1-hour period, the same technique was used to take a second lateral cephalogram of the nasally obstructed subject. The cephalograms were traced and appropriate land- marks identified (Table I, Fig. I) to construct 11 postural variables describing the position of the craniofacial, cervical, and hyoid structures (Table II, Fig. 1). These measurements were then compared for each subject's initial and final radio- graphs. Because a head holder was not used, magnification variations between initial and final radiographs were possible. To correct for this, differences in preexperimental and postex- perimental sella-nasion distances were expressed as a percent- age ratio of the preexperimental distance. This intraindividual correction factor was subsequently used to adjust all postex- perimental linear measurements. Because angular values do not change with magnification variations, no corrective factors were applied to those values. The subject's postural adaptation was calculated by the differences between the preexperimental and postexperimen- tal values. All variables were tested for statistical significance by a paired t test. The level of significance was determined at p < 0.05. To look for associations between the different postural reflexes, a Pearson correlation coefficient was cal- culated between all variables. METHOD ERROR Intraexamincr reliability was assessed by retracing eight randomly selected radiographs and calculating the pooled standard deviation among duplicate measurements with Dahlberg's formula. 2~ It ranged from 0.001 mm (i-i) to 0.33 mm (c3-h) for the linear measurements and from 0.3 ~ (hyoid plane angle) to 0.47 ~ for the angular measurements. All these were well within the acceptable range. To avoid extra radiation for the subjects, the reproduc- ibility of the postural reflexes was not assessed in this study. The reliability of the natural head posture technique, bow- ever, has been documented in other research. ~a-~9,~ RESULTS Table III shows the descriptive statistics and the significance of the difference between prenasal and postnasal blockage values. Positive and negative val- ues are assigned as appropriate, depending on whether there was an increase or decrease in the value mea- sured. There was a significant opening of the lips (t7 = 0.016) and a mandibular postural adaptation with a backward rotation (sn-MP) and increased mouth opening (i-i) (p < 0.001) (Fig. 2). The vertical drop in hyoid position (MP-h) just obtained statistical signifi- cance (p =0.049). Extension of the head (sn-TV) showed a tendency towards significance (p = 0.06). However, individual differences in amount and mode of adaptation were remarkable (see ranges in Table III). Head extension (sn-TV) was a common postural reflex, but six subjects actually flexed their head after nasal blockage. Analogously, although most subjects .l . . . . l I Ct t" { �9 I I S j l I ~Y .'" ~, I j .~ r ! , . X , j , . . ' \ i ~ t ~' ' , . I I I / Fig. 2. Overlay tracing of before (solid line) and after (broken line) cephalograms of subject with marked postural response. Superimposition is on c4, so that depicted changes are con- glomerate of cervical, craniocervical, and mandibular postural reactions. Notice marked craniocervical extension, parting of lips, lower tongue position, and drop of hyoid bone relative to mandibular border. showed a drop in mandibular position (sn-MP, i-i), some exceptions (n = 3) could be noted. Hyoid posi- tion was also variable: The hyoid inclination became steeper in about half of the subjects (n = 12) and it dropped relative to the mandible (MP-h) in 16 subjects. A drop in tongue position (n = 16) was not uniform. Whereas the majority of the subjects (n = 17) showed an increased craniocervical extension (cvt-sn), only seven showed a decrease in cervical lordosis (opt-cvt). Statistically significant correlations between pos- tural adaptations are displayed in Table IV. An increase in crania/extension (sn-TV) can be partly explained by an increase in craniocervical extension (r = 0.66, p < 0.001), and it seems to carry the mandible with it (r=--0.87, p < 0.01) to such a degree that the steeper mandibular position created by the mouth opening (r( i- i /sn-MP) = 0.74, p < 0.01) can be totally negated by this effect: sn-MP change can be positive while MP-TH change can be negative. The hyoid bone, however, does not totally follow this mandibular movement and, as a consequence, increased cranial extension is associated with greater opening in hyoid plane angle (r = 0.56, p < 0.01). A lowering in tongue position (t-MP) is partially associated with a drop in hyoid position (h-MP) (r = -0.56, p < 0.01). 608 Tourne and Schweiger American Journal of Orthodontics and Dentofacial Orthopedics December 1996 Table I. Definition of less common landmarks c2: e3: c4 c2t rgn h gh t OPT CVT Most inferior and posterior point on the corpus of the second cervical vertebra Most iufer~or and anterior point on the corpus of the third cervical vertebra Most inferior and posterior point on the corpus of the fourth cet'vical vertebra Most posterior and superior point on the dorsal side of the odontoid process (Retrognathion) most inferior and posterior point on the mandibular symphysis (Hyoidale) most anterior and superior point on the body of the hyoid bone Most posterior and superior point on the greater hum of the hyoid bone Most superior point of the tongue (Odoutoid process tangent) the posterior tangent to the odontoid process through c2 and c2t (Cervical vertebra tangent) line connecting cervical landmarks c4 and c2t Table II. Definition of postural measurements Angles sn-TV sn-MP MP-TH h pl ang OPT-CVT CT-sn Distances MP-h i-i t-MP c3-h ha-c4 stu-stl The angle formed by lines sella-nasion and the extracranial true vertical line. The angle between sella-nasion and the mandibular plane (go-gn) The angle formed by the mandibular plane and the extraeranial true horizontal line (Hyoid plane angle) the posterior angle formed by lines h-gh and c3-rgn The angle formed by lines OPT and CVT The angle formed by lines CVT and sn Perpendicular distance from hyoidale to the mandibular plane Vertical distance between upper and lower incisal edges Perpendicular distance from t to the mandibular plane Distance from c3 to hyoidale Distance from basion to c4 Vertical distance between upper and lower lip Table III. Descriptive and comparative statistics of the observed changes Variable I Number of observations t Minimum Maximum Mean Standard deviation sn-TV 25 -8.0 12.0 1.72 4.38 sn-MP 25 -2.0 4.5 1.54 1.68 MP-TH 25 -11.0 10.0 -0.48 4.76 h pl ang 21 -14.0 13.0 1.07 7.11 OPT-CVT 24 -9.0 3.5 0.13 2.50 CVT-sn 25 -7.0 8.5 1.36 4.03 MP-h 25 -8.0 l 1.5 1.77 4.28 i-i 25 -3.5 10.3 3.37 3.55 t-MP 24 -12.7 12.7 -1.66 6.01 c3-h 25 -5.5 4.0 0.19 2.19 ba-c4 25 --4.0 3.5 -0.17 1.97 stu-stl 24 -7.5 9.0 2.35 4.44 Significance 1.96 0.061 * 4.58 American Journal of Orthodontics and Dentofacial Orthopedics Tourne and Schweiger 600 Volume 110, No. 6 Table IV. Significant correlations between postural changes sn-TV 1.00 sn-MP 1.00 MP-TH --0.868** 1.00 h pl ang 0.558** -0.492* OPT-CVT CVT-sn 0~657"* MP-h i-i 0.740** 0.426* c3-h t-MP h pl ang 1.00 0.713"* 0.533* ] OPT-CVT1CVT-sn ) MP-h 1.00 0.446* 1.00 -0.456* 1,00 -0.558** *p < 0.05; **p < 0.01; ***p < 0.001. anteroposterior diameter of the pharynx at this level. 33 Nevertheless, this tendency toward positional hyoid instability should be taken into account with interpre- tation of the data. In addition, a lateral cephalogram can only give a momentary picture of the dynamic reflexive adaptation process and is not necessarily representative of that patient's behavior. This may explain why in some persons actual decreases in mandibular opening and lip separation were noted (Table III). Significant controversy exists in the orthodontic publications concerning the validity of different meth- ods used to assess a person's mode of breathing. 'z Although it has not been proven quantitatively in this study, the fact that all subjects were able to breathe effortlessly through their nose with their lips contact- ing for an extended period of time is good clinical proof of a nasal breathing pattern during that observa- tion period, To eliminate any doubt about the oronasal percentage ratio of the airflow, the nasal passages were totally blocked during the experiment. Because the structures lying above the level of the palate are largely fixed, compensatory functional respi- ratory adaptations will occur at the level of the orophar- ynx. 36 Several descriptions of those postural reflexes have previously been based on clinical observations, without an attempt to objectively measure oronasal res- piratory ratio and without quantification of the postural changes. 37-4~ Moreover, cross-sectional studies that found significant correlations between postural vari- ables and degree of nasal resistancC 2 cannot, by their nature, show any cause and effect relationship. In longi- tudinal postadenoidectomy studies, 9 the contraction of scar tissue and altered oral sensation may influence head posture. This study has attempted to avoid those pitfalls by its experimental design as described previously. Several postural adaptation mechanisms previously described in the clinical studies were noted in this sample. Parting of the lips with mandibular opening and an increase in freeway space were the most significant findings and it corroborates the reports of Subtelny, 37'3s Bowen and Ba lyeat , 39 Neivert, ~~ and Yip and Cleal l . 43 The lowering of the hyoid position also found in this study has been described previously 26'33"4346 as a mecha- nism to preserve airway patency. Although a lowering of the tongue has been mentioned in several publica- tions, ~'37~39'4~ no statistically significant difference could be found in this study. However, some of the studies had not measured tongue position quantita- tively, 37"s94~ whereas others report that the tongue posi- tion changes predominantly after tonsillectomy. 4s'~'7 Oral mechanical interference has indeed been proven to elicit orofacial postural reflexes. 48 The oral sensory stimulus by mechanical obstruction of the tonsils may be more important for tongue position than the respira- tory pattern on itself. After tonsillectomy, the base of the tongue regains the space previously taken by the tonsils and acquires a more dorsal position without a significant upward relocation. 46 The reflexive behavior of the hyoid bone was significantly correlated with tongue position (r= --0.56, p < 0.01). This reciprocally positional relation- ship has been described by BrodiC 9 and StepovichY Unexpectedly, no statistically significant differences were found for head extension (sn-TV) and craniocer- vical extension (cvt-sn). A larger sample size might have proven sn-TV to become significantly different as its p value was close (p = 0.06). The postural reactions may have increased also with increased duration of the experiment as Vig 16 showed maximum postural activ- ity after about 2 hours of nasal blockage. Vig's findings of about 3.5 ~ cranial extension after a 1-hour period is about 2 ~ more than found in this study (1.7~ Hellsing et al. '~ also found a more pronounced head posture change, comparable to Vig's data. A different measur- ing method in Vig's and Hellsing's experiments may possibly account for the difference. The clinical pub- lished works tend to support the concept of respiratory 610 Tourne and Schweiger American Journal of Orthodontics and Dentofacial Orthopedics December 1996 influence on cranial extension. No data on individual postural behavior have been described in clinical ad- enoidectomy or tonsillectomy studies, but the presur- gical and postsurgical group means indicate a decrease in head extension of about 2.5 ~ after adenoidectomy. 9 However, in the subgroup with a marked reduction of nasal respiratory resistance, the craniocervical angle was reduced by almost 5~ 9 In contrast, after applica- tion of an intranasal corticosteroid in children with asthma and perennial rhinitis, Wenzel et al.5o reported an effective reduction in craniocervical angulation of about 1 ~ relative to a placebo group. The same small statistically nonsignificant reduction has been noticed by Behlfelt 1 year after tonsillectomy. 46 This postural response, however, does not seem to have a clearly beneficial effect on airway patency. Although Hells- ing 5' reported an increased cross-sectional dimension of the pharynx with extension of the head, Weber, 52 as well as Peters, 53 could not find a difference in nasal resistance. No significant difference in cervical lordosis (opt- cvt) was found, but when it occurs, it may indirectly help airway patency because weak correlations were shown between a decreased change in lordosis and an increased distance between the cervical spine and the hyoid bone (r = -0.46, p < 0.05). A decreased change in cervical lordosis is weakly associated with a de- creased change in craniocervical extension (r--0.45, p < 0.05). Typically described is an association be- tween decreased lordosis and increased craniocervical extension. 23 However, the latter association may be found within certain craniofacial morphologic sub- groups, 23 as they have not been concomitantly de- scribed as postural airway reflexes. 9'5~ Hellsing 51 has indeed found that increased craniocervical extension in itself leads to an increase in cervical lordosis, but found a negative correlation coefficient between the changes of the two postural variables. Harvold et al. 54 and Miller et al. 55 described the early postural adaptations of primates adapting to complete nasal blockage. The animals showed continu- ous or rhythmic lowering of the mandible. Their tongue and lips altered shape in a variety of configu- rations, along with a rhythmic or continuous change in position. Electromyographic (EMG) changes in dorsal tongue fibers, suprahyoid, genioglossus, and orbicu- laris otis muscles were found? 5 Because the animals coped in different ways with nasal obstruction, the dentoalveolar distortions were not uniform and differ- ent types of malocclusions resulted, s4 However, the skeletal changes noticeable after 1 year of nasal ob- struction were uniform in that all animals showed an increase in facial height, mandibular plane angle and gonial angle. 54 The same dramatic craniofacial and oral muscle behavioral change was not noticed in the human experimental group. The reason for this may be the anatomic difference between the human and the pri- mate oropharyngeal anatomy. 55 An oral airway passage is structurally easier accomplished and less life threat- ening in the human being, obviating the need for excessive muscle recruitment? 6 As such, human adap- tation to oral respiration requires only a small adjust- ment in mandibular position to maintain a patent oral respiratory tract. Nasal obstruction in human subjects leads to a decrease in postcervical and anterior tempo- ral muscle tone and only to a weakly significant and very temporary increase in suprahyoid muscle EMG activity. 17 This and the observed individual variations in response may explain why clinical longitudinal studies did not show the same dramatic and consistent impact on the craniofacial growth pattern. 46'57's8 CONCLUSION The aim of this study was to contribute to our under- standing of the initial postural reactions to nasal obstruction. 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