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Alterations in nasal airway resistance following superior repositioning of the maxilla
Alterations in nasal airway resistance following superior repositioning of the maxilla
-w
Dr. Turvey
Timothy A. Turvey, D.D.S.,* David J. Hall, D.D.S., MS.,** and Donald W. Warren, D.D.S., Ph.D.*** Chapel
Hill,
N.
C.
Superior repositioning of the maxilla is a contemporary surgical procedure used to correct a variety of dentofacial deformities, including vertical maxillary excess. Concern for the effect of this procedure on nasal respiration is warranted, since superior repositioning of the maxilla may decrease the volume of the nasal cavity. In this study pre- and postoperative nasal-resistance values were obtained for 52 patients who underwent superior repositioning of the maxilla by the LeFort I downfracture procedure. Of these 52 patients, 24 underwent segmental osteotomies and 28 underwent one-piece superior repositioning. Results indicate that the long-faced persons for whom superior repositioning of the maxilla is recommended usually have pretreatment nasal-resistance values within previously reported normal ranges. Superior repositioning of the maxilla, with or without involvement of the nasal floor, usually results in decreased nasal resistance.
Key words: Nasal resistance, respiratory mode, long-face syndrome, LeFort I osteotomy, superior repositioning of the maxilla
T
he refinement of maxillary surgical techniques since the late 1960s and the subsequent increase in their use are of considerable interest to surgeons and orthodontists. Superior repositioning procedures that appear to reduce the volume and possibly the airflow capacity of the nasal airway are of particular concern. Surgeons have designed maxillary surgical techniques that intentionally avoid the nasal cavity and have suggested modifications to previous procedures to avoid possible adverse nasal airway alterations. l-5 The increased use of maxillary surgery has coincided with a renewed interest among orthodontists in the possible influence of respiratory mode upon growth of the orofacial complex. 6-g Impaired nasal respiration and the resulting functional adaptations necessary for oral breathing have been suggested as primary factors causing abnormal facial growtl-~.‘~~‘* If, in fact, decreased capacity for nasal respiration is a primary etiologic factor in the development of facial abnormalities, From the School of Dentistry, University of North Carolina. This work was supported in part by National Institutes of Health Grants DE-04267, DE-02668, DE-05215, and DE-06061 from the National Institute of Dental Research and University Grant I-0-104-4340-VC 647 from the University of North Carolina. *Associate F’rofessor of Oral and Maxillofacial Surgery; Co-Director. Dentofacial Deformity Rogram. **Clinical Associate Professor of Orthodontics; Co-Director, Dentofacial Deformity Program. ***Kenan Professor and Chairman, Dental Ecology.
especially vertical maxillary excess, then corrective surgery that might further increase resistance to nasal airflow seems questionable. The ease with which air passes through the nasal cavity depends primarily upon the resistance of the cavity to airflow. The principles of aerodynamics that determine the movement of air through a tube apply also to the nasal passages. Airflow follows the path of least resistance. Airflow-resistance measurements alone cannot be used to determine the mode of respiration or the relative percentages of oral versus nasal flow; comparison of within-subject resistance values pre- and postoperatively would provide an indication of physical changes that influence nasal airflow. Resistance within the nasal passages is a function of the size, shape, and length of the cavity. Although resistance is influenced by these factors, which may change flow from laminar to turbulent, the primary determinant of the magnitude of resistance is the smallest cross-sectional area of the airway. The location of this constriction can be affected by size of the turbinates, septal deviations, the presence of polyps, adenoidal tissue, the character of the mucosa, and the shape of the anterior nares. Unless a completely subnasal surgical approach is used, a reduction in the volume of the nasal cavity must occur when the maxilla is superiorly repositioned. However, because resistance is a function of the size, shape, and length of the airway, it does not 109
110
Turvey, Hall, and Warren
Am. J. Orthod. February 1984
Fig. 1. LeFort I segmental osteotomy; the paramidline cuts have been placed laterally so that the floor of the nose is a separate segment which is elevated minimally when the maxilla is superiorly repositioned (Group I).
necessarily follow that a measurable increase in airway resistance will occur. l2 Although decreases in nasal airway resistance following rapid maxillary expansion have been reported,13, l4 data describing the effect of superior repositioning of the maxilla upon nasal resistance are not available. The development of instrumentation and techniques for measurement of pressures and airflow associated with breathing provides the opportunity to measure nasal resistance under these circumstances. The purpose of this study was to determine how superior repositioning of the maxilla affects the nasal airway. Specific objectives of this study were to (1) evaluate presurgical nasal resistance in patients requiring superior repositioning of the maxilla in order to test the hypothesis that nasal airway resistance is a common feature in excessive vertical development of the lower third of the face; (2) obtain measurements of nasal airway resistance following superior repositioning of the maxilla to establish whether consistent changes in nasal resistark follow such surgical procedures; and (3) determine the relationship between the type of surgical procedure and changes in nasal resistance. METHODS Surgical sample
Patients scheduled for superior repositioning of the maxilla were selected through the Dentofacial Deformity Program at the University of North Carolina. Fifty-two persons with long-face morphology consented to participate in this study. There were 9 male and 43 female patients ranging in age from 14 to 56 years (mean, 23.7 years; SD, 0.8179). All patients
were treated by the LeFort I downfracture procedure. I5 Three variations of this operation were represented. Fifteen patients (Group I) had a segmental osteotomy in which an attempt was made to place the paramidline cuts far enough laterally so that the floor of the nose was a separate segment which was elevated minimally. The purpose was to produce the smallest change possible in the internal anatomy of the nose (Fig. 1). Nine patients (Group II) had a segmental osteotomy in which the paramidline cuts were placed more medially and, therefore, involved more elevation of the nasal floor (Fig. 2). Since the locations of the cuts relative to the midline were not actually measured in either group, it is possible that no significant anatomic difference between the two segmental procedures really existed. Twenty-eight patients (Group III) underwent a onepiece osteotomy which elevated the nasal floor with the maxilla. In the patients of all three groups, a portion of the inferior aspect of the nasal septum was routinely removed to avoid bending the septum when the maxilla was repositioned. One patient in Group III required removal of the inferior turbinates so that the nasal floor could be elevated without impingement. In addition, septal exostoses were removed, if present. The surgical techniques for septum removal and turbinectomy have been described in detail elsewhere.16 Evaluation of oral-nasal pressure and nasal airflow
Nasal resistance was calculated from the parameters of differential oral-nasal pressure and nasal expiratory airflow using a modification of Ohm’s law. Nasal resistance (R) is defined as the pressure drop across the nose (A p) &vided by the volume rate of nasal airflow (6),
Alterations
Volume 85 Number 2
in nasal airway resistance
111
Fig. 2. LeFort I segmental osteotomy; the paramidline cuts are placed medially so that elevation of more of the nasal floor occurs when the maxilla is superiorly repositioned (Group II).
Fig. 3. Diagram of equipment used to measure nasal airway resistance.
(R = a). This equation and the measurement technique hive previously been described by Watson and associates. l7 Drop in nasal pressure was measured with a differential pressure transducer (Statham 283 TC). Separate polyethylene catheters, approximately 30 cm in length and 1.5 mm in diameter, were attached to both the high and low sides of the pressure transducer. The high-side catheter was placed in the subject’s orpharynx as far posteriorly as could be tolerated, and the low-side catheter was placed in the nasal mask. Tygon tubing, approximately 15 cm in length and 1.5 mm in diameter, was also attached to the mask. This tubing directed the airflow through a heated pneumotachograph (Fleisch) which measured volume rate of nasal airflow. Masks were selected to adapt well to each subject’s face, so that the nose (but not the mouth) was covered. Care was taken to avoid leakage or obstruction of nasal airflow. Signals from both the pressure and flow transducers were amplified and then recorded on a directreadout recorder (Honeywell “Visicorder” 1508).
The equipment used is illustrated diagrammatically in Fig. 3. Subjects were seated, and the mask and catheters were placed in the proper positions. Each subject was asked to breathe in through the mouth, close the lips around the oral catheter, and breathe out through the nose,. A regular pattern of such breathing was established, and simultaneous recordings of pressure and flow were obtained. Flow was calibrated with a rotameter at 250 cc per second, and pressure was calibrated at 2 cm of H,O with a water manometer. Between four and eight determinations at each examining session were made for every subject. Using the recordings obtained, nasal resistance was calculated at a flow rate of 250 cc per second. This flow rate was chosen to minimize the effect of turbulence and to allow comparison with the results of other studies. It also is compatible with normal respiratory patterns of breathing. Pre- and postoperative comparisons were always made at the same rate of airflow, since resistance is flow-dependent when turbulence is pres-
112
Tuwey,
Hull,
and
Am. .I. Or&d. Fehruary 1984
Warren
I. Reliability of nasal-resistance measurement technique (25 patients) Wilcoxon matched-pairs signed rank test (a = 0.05)
Ill. Changes in nasal resistance by direction of change
Table
Measurement 1 Measurement 2 Difference (2-l)
Table
Mean
Median
Range
SD
3.51 2.87 -0.64
2.69 2.19 -0.50
0.51-9.68 0.73-I 1.50
0.73 0.58
Calculated 2 value 0.74; p > 0.05. There is no significant difference between which indicates that the method is reliable
measurements 1 and 2, and reproduceable.
II. Pretreatment nasal resistance, longface patients planned for surgical correction of vertical maxillary excess
Table
Nasal (Normal) (Moderate) (High)
resistance l-4.5 4.6-9.9 IO-50
No. of patients
(cm H,OiLisec) Mean SD Mean SD Mean SD
2.65 .99 7.2 1.93 23.86 13.39
12 (23%) 7 (14%)
ent. Postsurgical nasal-resistance measurements were obtained one year after surgery. Data to test the reliability and reproducibility of the measuring technique were obtained on a series of twenty-five patients who were undergoing orthodontic treatment in preparation for surgery. Nasal airway resistance was evaluated on two different occasions at least 6 months apart, but before surgery. A standard error of + 1.46 was calculated by the Dahlberg method, SE =
2 d’ where d equals the difference be(N-l)’ tween the two recorded values and N equals the sample size. As the data are considerably skewed to the right, this represents an overestimate of the magnitude of the method error. As a further test of reliability, the same data were subjected to the Wilcoxon matched-pairs signed rank test, and again no significant difference was found between the two data sets (p > 0.05) (Table I). nasal
3.94 1.62 1.90
5.51 1.61 3.59
7.51 1.54 3.80
2.14 0.17 1.84
Of the 14 patients whose resistance remained unchanged or increased postsurgically, most demonstrated normal preoperative nasal resistance when either the mean or median value was considered. This represents a homogeneous sample when compared to the 38 patients who demonstrated decreased nasal resistance postsurgically. The group that showed decreased nasal resistance postsurgically had a wide range of presurgical values, and this accounts for the moderately high mean resistance. Since this group’s presurgical resistance had a wide range, the median resistance (3.80 cm H,O/Llsec) more accurately reflects the group’s nasal airway resistance.
33 (63%)
The skewed distribution and wide range of values for the total sample can be seen clearly. The median pretreatment resistance for the 52 patients is 3.46 cm H,O/Llsec.
RESULTS Presurgical
Mean SE Median
resistance
Presurgical nasal-resistance values are shown in Table II. The skewed distribution and wide range of values for the total sample can be seen clearly. The 52
patients had a median nasal resistance of 3.46 cm H,O/L/sec. When grouped according to nasal-resistance values (Table II), these patients fell into three nonoverlapping groups. Thirty-three (63%) had nasal-resistance values between 1 and 4.4 cm H,O/L/sec, falling within an approximately normal range; 12 (23%) had values between 4.5 and 9.9 cm H,O/L/sec; and 7 (14%) had very high values, ranging from 10 up to 50 cm H,O/L/sec. Nasal-resistance
changes
following
surgery
When the change from pre- to postoperative resistance was compared on an individual basis, it was observed that resistance decreased in 38 patients and stayed the same or increased in 14. Six of the 7 patients who had extremely high resistance presurgically showed a dramatic drop to normal levels; the seventh patient in this group showed essentially no change (23.3 preoperatively, 24.1 postoperatively), and this patient was noted to have asthma. Eleven of the 12 patients with preoperative resistance in the 4.5 to 9.9 range showed a decrease to normal values after surgery, while in the twelfth the values remained the same (9.2 preoperatively, 10.6 postoperatively). Only one patient who had normal values before surgery showed an increase to above the normal range postsurgically (from 3.6 to 9.2). Mean changes in those in whom resistance decreased and those in whom it did not are shown in Table III. The effect of the various surgical procedures is shown in Table IV. The Wilcoxon signed rank test was used to test the hypothesis that there was no difference between preoperative and postoperative measurements.
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airway
resistance
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Table IV. Change in nasal resistance following superior repositioning of the maxilla by type of
maxillary osteotomy N Group 1* Group II** Group III*** Combined *Group I-Segmental, **Group II-Segmental, ***Group III-One-piece
15 9 28 52
Mean decrease in resistance postop 5.8 8.4 0.7 3.5
SD 3.2 4.1 0.4 1.2
Wilcoxon sign rank test HO*: D@erence (pre.-post.) = 0 p p p p
< 0.01 < 0.05 >>O.lO < 0.01
(NS)
paramidlme cuts lateral. paramidline cuts medial. maxillary osteotomy.
At (Y= 0.05, this null hypothesis was rejected for Groups I and II and for all groups combined but was accepted for Group III. It is interesting to note that nasal resistance decreased by about the same amount in Group II, in which no attempt was made to avoid elevating the nasal floor, as in Group I, in which elevation of the nasal floor was minimized. DISCUSSION The meaning of nasal resistance
The meaning of nasal airway resistance must be clearly understood so that the findings are not misinterpreted. The value obtained when pressure drop across the nasal airway is divided by flow rate is defined as nasal resistance. In this study, as in previous work using this technique, resistance was obtained by measuring the pressure gradient at the same flow rate before and after treatment. Resistance values in our sample were established at a flow rate of 250 cc per second. As long as flow remains laminar, resistance will remain constant. However, when flow rate increases sufficiently to create turbulence, the resistance value will increase with, and vary with, airflow rate in a nonlinear relationship. By comparing presurgical and postsurgical resistance at the same flow rate, we eliminate possible changes in resistance due to flow rate. Although respiratory mode, defined as the proportionality between nasal and oral breathing, cannot be determined from nasal-resistance measurements, it is reasonable to assume that, given sufficiently high nasal resistance to airflow, a shift toward oral respiration occurs. The range of resistance values at which this shift occurs is not definitely known and presumably differs to some degree among individual patients and physiologic demands. Watson, Warren, and Fisher17 suggested a value of 4.5 cm H,O/L/sec as the approximate point at which the change toward oral respiration begins. This was based on the finding that at about this value 77% of the subjects studied demonstrated subjective signs of mouth breathing.17 It must be emphasized that the change from oral to nasal breathing, however,
probably occurs over a range of values. Equipment for determining respiratory mode has recently been developed but was not used in this study .18 The use of nasal decongestant sprays prior to the recording of nasal resistance (not done in this study) reduces the resistance value in some persons by as much as 45 to 50%. The variable effect of pharmacologic agents on patients has been eliminated with our investigation, since we precluded the use of these agents. Since some investigators have routinely used decongestants, ls this source of variation between studies should be kept in mind when results are compared. Other factors that must be considered in an explanation of the results concerning nasal airway resistance are the alterations of the nasal septum, the nasal crest of the maxilla, and the inferior turbinates. In all cases, a portion of the nasal septum was excised to permit superior repositioning of the maxilla without bowing the septum. In one case removal of the inferior turbinates was necessary. These maneuvers may have increased the size of the nasal passageway and, therefore, decreased the nasal airway resistance. Our clinical observations indicate that superior repositioning of the maxilla results in flaring of the nostrils. As the external nares change in shape from narrow slits presurgically to a more ovoid form (become more circular) postoperatively, the area of the opening increases, and it is the cross-sectional area which most affects the magnitude of nasal-resistance. It is quite possible that the decrease in nasal resistance observed in our present sample is due to widening of the nares and opening of the liminal valve. It is also possible that the decrease in nasal resistance reported to occur after rapid palatal expansion13 is also produced by changes in dimensions of the nares. Further studies to examine this issue are in progress. Nasal resistance in relation to the long-face condition
Our data indicate that the long-faced patients for whom superior repositioning is recommended generally
114
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Turvey, Hall, and Warren
have pretreatment nasal-resistance values within the previously reported range of normal. The faces of these patients are characterized by narrow alar bases, lip incompetency at repose, excessive exposure of gingiva upon smiling, excessive lower facial heights, and steep mandibular plane angles. 2o Only 36% (19) of our subjects had nasal-resistance values above 4.5 cm H,OIL/ sec. This suggests that restriction of the nasal airway is not a major cause of the anatomic condition. However, no definite conclusions about mouth breathing as an etiologic factor can be made. Further studies will be necessary, although it seems appropriate to suggest that mouth breathing is not necessary in most of these patients-a point made also in a recent review of the research in this area.” Superior repositioning of the maxilla, with or without involvement of the nasal floor, almost always results in decreased nasal airway resistance. Only one patient in this series of 52 persons showed a postsurgical increase in resistance to above normal values, while 17 of the 19 who had high nasal resistance presurgically had normal values postsurgically. It is probable that the postoperative decrease in nasal airway resistance is associated with changes at the external nares and liminal valve. This explains why nasal resistance decreased about the same way in patients who had segmental osteotomies with elevation of the nasal floor as in patients who had less change in internal nasal anatomy. There appears to be no reason to prefer one segmental procedure over the other when one is considering effect on the nasal airway. We have no data on the resistance values in patients who have buckling of the nasal septum, since in our surgical procedures care was taken to avoid this. Our observation that nasal resistance decreased in both groups in which segmental osteotomies were performed but remained essentially the same in the group that underwent one-piece osteotomies is best explained by the relatively low pretreatment nasal resistance in the latter group of patients. Since nasal resistance in the normal range was not affected by the surgery in most instances, the mean change in the one-piece osteotomy group, which contained a relatively large number of patients with pretreatment normal values, was small. CONCLUSIONS
We conclude that superior repositioning of the maxilla does not increase resistance to nasal breathing, whether or not the surgical procedure elevates the floor of the nose. Concern about the respiratory effects of this surgical procedure appears unwarranted.
REFERENCES ’1. Wolford LM, Epker BN: The combined anterior and posterior maxillary osteotomy: a new technique. J Oral Surg 33: 842-851, 1975. 2. Bell WH: LeFort I osteotomy for correction of maxillary deformities. J Oral Surg 33: 412-426, 1975. 3. Hall DH, Roddy SC: Treatment of maxillary alveolar hyperplasia by total maxillary alveolar osteotomy. J Oral Surg 33: 180-188, 1975. 4. Epker BN, Wolford LM: Middle third facial osteotomies: their use in the correction of acquired and developmental dentofacial and craniofacial deformities. J Oral Surg 33: 491-5 14, 1975. 5. Hall DH, West RA: Combined anterior and posterior maxillary osteotomy. J Oral Surg 34: 126-188, 1976. 6. Linder-Aronson S, Backstrom A: A comparison betweenmouth and nose breathers with respect to occlusion and facial dimensions. Odontol Revy 11: 343-376, 1960. 7. Linder-Aronson S: Adenoids: their effect on mode of breathing and nasal airflow and their relationship to characteristics of facial skeleton and the dent&ion. Acta Otolaryngol Suppl 265, pp. 1-132, 1970. 8. Rubin RM: Facial deformities: a preventable disease? Angle Orthod 49: 98-103, 1979. 9. Subtelny JD: Oral respiration: facial maldevelopment and corrective dentofacial orthopedics. Angle Orthod 50: 147-164, 1980. 10. Harvold EP, Vargervik D, Chierici G: Primate experiments on oral sensation and dental malocclusions. AM J ORTHOD 63: 494-508, 1973. 11. Woodside DG, Linder-Aronson S: The channelization of upper and lower face heights compared to population standards in males between ages 6 to 20 years. Eur J Orthod 1: 25-40, 1979. 12. Montgomery WM, Vig PS, Staab EV, Matteson SE: Computed tomography: a three-dimensional study of the nasal airway. AM J ORTHOD
76: 363-375,
13. Hershey HG, Stewart resistance associated ORTHOD
69: 274-284,
1979.
BL, Warren with rapid
DW: Changes in nasal airway maxillary expansion. AM J
1976.
14. Wertz RA: Changes in nasal airflow incident to rapid maxillary expansion. Angle Orthod 38: l-11, 1968. 15. Bell WH, Proffit WR, White Rp: Surgical correction of dentofacial deformities. Philadelphia, 1980, W.B. Saunders Company, chaps. 8 and 13. 16. Turvey TA: Management of the nasal apparatus in maxillary surgery. J Oral Surg 31: 331-335, 1980. 17. Watson RM, Warren DW, Fisher ND: Nasal resistance skeletal classification and mouth breathing in orthodontic patients. AM J ORTHOD
54: 367-379,
1968.
18. Gurley WH, Vig PS: A technique for the simultaneous measurement of nasal and oral respiration. AM J ORTHOD 82: 33-41, 1982.
19. Solow B, Greve E: Craniocervical angulation and nasal respiratory resistance, nasorespiratory function and craniofacial growth. In McNamara JA (editor): Nasorespiratory function and craniofacial growth. Ann Arbor, 1979, University of Michigan Center for Human Growth and Development, pp. 87-l 19. J, Bell WH, Epker BN, Mishelevich 20. Schendel SA, Eisenfield DJ: The long-face syndrome-Vertical maxillary excess. AM J ORTHOD
70: 398-408,
1976.
21. O’Ryan FS, Gallagher CM, LaBanc JP, Epker BN: The relation between nasorespiratory function and dentofacial morphology: a review. AM J ORTHOD 82: 403410, 1982.
-w
Dr. Turvey
Timothy A. Turvey, D.D.S.,* David J. Hall, D.D.S., MS.,** and Donald W. Warren, D.D.S., Ph.D.*** Chapel
Hill,
N.
C.
Superior repositioning of the maxilla is a contemporary surgical procedure used to correct a variety of dentofacial deformities, including vertical maxillary excess. Concern for the effect of this procedure on nasal respiration is warranted, since superior repositioning of the maxilla may decrease the volume of the nasal cavity. In this study pre- and postoperative nasal-resistance values were obtained for 52 patients who underwent superior repositioning of the maxilla by the LeFort I downfracture procedure. Of these 52 patients, 24 underwent segmental osteotomies and 28 underwent one-piece superior repositioning. Results indicate that the long-faced persons for whom superior repositioning of the maxilla is recommended usually have pretreatment nasal-resistance values within previously reported normal ranges. Superior repositioning of the maxilla, with or without involvement of the nasal floor, usually results in decreased nasal resistance.
Key words: Nasal resistance, respiratory mode, long-face syndrome, LeFort I osteotomy, superior repositioning of the maxilla
T
he refinement of maxillary surgical techniques since the late 1960s and the subsequent increase in their use are of considerable interest to surgeons and orthodontists. Superior repositioning procedures that appear to reduce the volume and possibly the airflow capacity of the nasal airway are of particular concern. Surgeons have designed maxillary surgical techniques that intentionally avoid the nasal cavity and have suggested modifications to previous procedures to avoid possible adverse nasal airway alterations. l-5 The increased use of maxillary surgery has coincided with a renewed interest among orthodontists in the possible influence of respiratory mode upon growth of the orofacial complex. 6-g Impaired nasal respiration and the resulting functional adaptations necessary for oral breathing have been suggested as primary factors causing abnormal facial growtl-~.‘~~‘* If, in fact, decreased capacity for nasal respiration is a primary etiologic factor in the development of facial abnormalities, From the School of Dentistry, University of North Carolina. This work was supported in part by National Institutes of Health Grants DE-04267, DE-02668, DE-05215, and DE-06061 from the National Institute of Dental Research and University Grant I-0-104-4340-VC 647 from the University of North Carolina. *Associate F’rofessor of Oral and Maxillofacial Surgery; Co-Director. Dentofacial Deformity Rogram. **Clinical Associate Professor of Orthodontics; Co-Director, Dentofacial Deformity Program. ***Kenan Professor and Chairman, Dental Ecology.
especially vertical maxillary excess, then corrective surgery that might further increase resistance to nasal airflow seems questionable. The ease with which air passes through the nasal cavity depends primarily upon the resistance of the cavity to airflow. The principles of aerodynamics that determine the movement of air through a tube apply also to the nasal passages. Airflow follows the path of least resistance. Airflow-resistance measurements alone cannot be used to determine the mode of respiration or the relative percentages of oral versus nasal flow; comparison of within-subject resistance values pre- and postoperatively would provide an indication of physical changes that influence nasal airflow. Resistance within the nasal passages is a function of the size, shape, and length of the cavity. Although resistance is influenced by these factors, which may change flow from laminar to turbulent, the primary determinant of the magnitude of resistance is the smallest cross-sectional area of the airway. The location of this constriction can be affected by size of the turbinates, septal deviations, the presence of polyps, adenoidal tissue, the character of the mucosa, and the shape of the anterior nares. Unless a completely subnasal surgical approach is used, a reduction in the volume of the nasal cavity must occur when the maxilla is superiorly repositioned. However, because resistance is a function of the size, shape, and length of the airway, it does not 109
110
Turvey, Hall, and Warren
Am. J. Orthod. February 1984
Fig. 1. LeFort I segmental osteotomy; the paramidline cuts have been placed laterally so that the floor of the nose is a separate segment which is elevated minimally when the maxilla is superiorly repositioned (Group I).
necessarily follow that a measurable increase in airway resistance will occur. l2 Although decreases in nasal airway resistance following rapid maxillary expansion have been reported,13, l4 data describing the effect of superior repositioning of the maxilla upon nasal resistance are not available. The development of instrumentation and techniques for measurement of pressures and airflow associated with breathing provides the opportunity to measure nasal resistance under these circumstances. The purpose of this study was to determine how superior repositioning of the maxilla affects the nasal airway. Specific objectives of this study were to (1) evaluate presurgical nasal resistance in patients requiring superior repositioning of the maxilla in order to test the hypothesis that nasal airway resistance is a common feature in excessive vertical development of the lower third of the face; (2) obtain measurements of nasal airway resistance following superior repositioning of the maxilla to establish whether consistent changes in nasal resistark follow such surgical procedures; and (3) determine the relationship between the type of surgical procedure and changes in nasal resistance. METHODS Surgical sample
Patients scheduled for superior repositioning of the maxilla were selected through the Dentofacial Deformity Program at the University of North Carolina. Fifty-two persons with long-face morphology consented to participate in this study. There were 9 male and 43 female patients ranging in age from 14 to 56 years (mean, 23.7 years; SD, 0.8179). All patients
were treated by the LeFort I downfracture procedure. I5 Three variations of this operation were represented. Fifteen patients (Group I) had a segmental osteotomy in which an attempt was made to place the paramidline cuts far enough laterally so that the floor of the nose was a separate segment which was elevated minimally. The purpose was to produce the smallest change possible in the internal anatomy of the nose (Fig. 1). Nine patients (Group II) had a segmental osteotomy in which the paramidline cuts were placed more medially and, therefore, involved more elevation of the nasal floor (Fig. 2). Since the locations of the cuts relative to the midline were not actually measured in either group, it is possible that no significant anatomic difference between the two segmental procedures really existed. Twenty-eight patients (Group III) underwent a onepiece osteotomy which elevated the nasal floor with the maxilla. In the patients of all three groups, a portion of the inferior aspect of the nasal septum was routinely removed to avoid bending the septum when the maxilla was repositioned. One patient in Group III required removal of the inferior turbinates so that the nasal floor could be elevated without impingement. In addition, septal exostoses were removed, if present. The surgical techniques for septum removal and turbinectomy have been described in detail elsewhere.16 Evaluation of oral-nasal pressure and nasal airflow
Nasal resistance was calculated from the parameters of differential oral-nasal pressure and nasal expiratory airflow using a modification of Ohm’s law. Nasal resistance (R) is defined as the pressure drop across the nose (A p) &vided by the volume rate of nasal airflow (6),
Alterations
Volume 85 Number 2
in nasal airway resistance
111
Fig. 2. LeFort I segmental osteotomy; the paramidline cuts are placed medially so that elevation of more of the nasal floor occurs when the maxilla is superiorly repositioned (Group II).
Fig. 3. Diagram of equipment used to measure nasal airway resistance.
(R = a). This equation and the measurement technique hive previously been described by Watson and associates. l7 Drop in nasal pressure was measured with a differential pressure transducer (Statham 283 TC). Separate polyethylene catheters, approximately 30 cm in length and 1.5 mm in diameter, were attached to both the high and low sides of the pressure transducer. The high-side catheter was placed in the subject’s orpharynx as far posteriorly as could be tolerated, and the low-side catheter was placed in the nasal mask. Tygon tubing, approximately 15 cm in length and 1.5 mm in diameter, was also attached to the mask. This tubing directed the airflow through a heated pneumotachograph (Fleisch) which measured volume rate of nasal airflow. Masks were selected to adapt well to each subject’s face, so that the nose (but not the mouth) was covered. Care was taken to avoid leakage or obstruction of nasal airflow. Signals from both the pressure and flow transducers were amplified and then recorded on a directreadout recorder (Honeywell “Visicorder” 1508).
The equipment used is illustrated diagrammatically in Fig. 3. Subjects were seated, and the mask and catheters were placed in the proper positions. Each subject was asked to breathe in through the mouth, close the lips around the oral catheter, and breathe out through the nose,. A regular pattern of such breathing was established, and simultaneous recordings of pressure and flow were obtained. Flow was calibrated with a rotameter at 250 cc per second, and pressure was calibrated at 2 cm of H,O with a water manometer. Between four and eight determinations at each examining session were made for every subject. Using the recordings obtained, nasal resistance was calculated at a flow rate of 250 cc per second. This flow rate was chosen to minimize the effect of turbulence and to allow comparison with the results of other studies. It also is compatible with normal respiratory patterns of breathing. Pre- and postoperative comparisons were always made at the same rate of airflow, since resistance is flow-dependent when turbulence is pres-
112
Tuwey,
Hull,
and
Am. .I. Or&d. Fehruary 1984
Warren
I. Reliability of nasal-resistance measurement technique (25 patients) Wilcoxon matched-pairs signed rank test (a = 0.05)
Ill. Changes in nasal resistance by direction of change
Table
Measurement 1 Measurement 2 Difference (2-l)
Table
Mean
Median
Range
SD
3.51 2.87 -0.64
2.69 2.19 -0.50
0.51-9.68 0.73-I 1.50
0.73 0.58
Calculated 2 value 0.74; p > 0.05. There is no significant difference between which indicates that the method is reliable
measurements 1 and 2, and reproduceable.
II. Pretreatment nasal resistance, longface patients planned for surgical correction of vertical maxillary excess
Table
Nasal (Normal) (Moderate) (High)
resistance l-4.5 4.6-9.9 IO-50
No. of patients
(cm H,OiLisec) Mean SD Mean SD Mean SD
2.65 .99 7.2 1.93 23.86 13.39
12 (23%) 7 (14%)
ent. Postsurgical nasal-resistance measurements were obtained one year after surgery. Data to test the reliability and reproducibility of the measuring technique were obtained on a series of twenty-five patients who were undergoing orthodontic treatment in preparation for surgery. Nasal airway resistance was evaluated on two different occasions at least 6 months apart, but before surgery. A standard error of + 1.46 was calculated by the Dahlberg method, SE =
2 d’ where d equals the difference be(N-l)’ tween the two recorded values and N equals the sample size. As the data are considerably skewed to the right, this represents an overestimate of the magnitude of the method error. As a further test of reliability, the same data were subjected to the Wilcoxon matched-pairs signed rank test, and again no significant difference was found between the two data sets (p > 0.05) (Table I). nasal
3.94 1.62 1.90
5.51 1.61 3.59
7.51 1.54 3.80
2.14 0.17 1.84
Of the 14 patients whose resistance remained unchanged or increased postsurgically, most demonstrated normal preoperative nasal resistance when either the mean or median value was considered. This represents a homogeneous sample when compared to the 38 patients who demonstrated decreased nasal resistance postsurgically. The group that showed decreased nasal resistance postsurgically had a wide range of presurgical values, and this accounts for the moderately high mean resistance. Since this group’s presurgical resistance had a wide range, the median resistance (3.80 cm H,O/Llsec) more accurately reflects the group’s nasal airway resistance.
33 (63%)
The skewed distribution and wide range of values for the total sample can be seen clearly. The median pretreatment resistance for the 52 patients is 3.46 cm H,O/Llsec.
RESULTS Presurgical
Mean SE Median
resistance
Presurgical nasal-resistance values are shown in Table II. The skewed distribution and wide range of values for the total sample can be seen clearly. The 52
patients had a median nasal resistance of 3.46 cm H,O/L/sec. When grouped according to nasal-resistance values (Table II), these patients fell into three nonoverlapping groups. Thirty-three (63%) had nasal-resistance values between 1 and 4.4 cm H,O/L/sec, falling within an approximately normal range; 12 (23%) had values between 4.5 and 9.9 cm H,O/L/sec; and 7 (14%) had very high values, ranging from 10 up to 50 cm H,O/L/sec. Nasal-resistance
changes
following
surgery
When the change from pre- to postoperative resistance was compared on an individual basis, it was observed that resistance decreased in 38 patients and stayed the same or increased in 14. Six of the 7 patients who had extremely high resistance presurgically showed a dramatic drop to normal levels; the seventh patient in this group showed essentially no change (23.3 preoperatively, 24.1 postoperatively), and this patient was noted to have asthma. Eleven of the 12 patients with preoperative resistance in the 4.5 to 9.9 range showed a decrease to normal values after surgery, while in the twelfth the values remained the same (9.2 preoperatively, 10.6 postoperatively). Only one patient who had normal values before surgery showed an increase to above the normal range postsurgically (from 3.6 to 9.2). Mean changes in those in whom resistance decreased and those in whom it did not are shown in Table III. The effect of the various surgical procedures is shown in Table IV. The Wilcoxon signed rank test was used to test the hypothesis that there was no difference between preoperative and postoperative measurements.
Volume 85 Number 2
Alterations
in nasal
airway
resistance
113
Table IV. Change in nasal resistance following superior repositioning of the maxilla by type of
maxillary osteotomy N Group 1* Group II** Group III*** Combined *Group I-Segmental, **Group II-Segmental, ***Group III-One-piece
15 9 28 52
Mean decrease in resistance postop 5.8 8.4 0.7 3.5
SD 3.2 4.1 0.4 1.2
Wilcoxon sign rank test HO*: D@erence (pre.-post.) = 0 p p p p
< 0.01 < 0.05 >>O.lO < 0.01
(NS)
paramidlme cuts lateral. paramidline cuts medial. maxillary osteotomy.
At (Y= 0.05, this null hypothesis was rejected for Groups I and II and for all groups combined but was accepted for Group III. It is interesting to note that nasal resistance decreased by about the same amount in Group II, in which no attempt was made to avoid elevating the nasal floor, as in Group I, in which elevation of the nasal floor was minimized. DISCUSSION The meaning of nasal resistance
The meaning of nasal airway resistance must be clearly understood so that the findings are not misinterpreted. The value obtained when pressure drop across the nasal airway is divided by flow rate is defined as nasal resistance. In this study, as in previous work using this technique, resistance was obtained by measuring the pressure gradient at the same flow rate before and after treatment. Resistance values in our sample were established at a flow rate of 250 cc per second. As long as flow remains laminar, resistance will remain constant. However, when flow rate increases sufficiently to create turbulence, the resistance value will increase with, and vary with, airflow rate in a nonlinear relationship. By comparing presurgical and postsurgical resistance at the same flow rate, we eliminate possible changes in resistance due to flow rate. Although respiratory mode, defined as the proportionality between nasal and oral breathing, cannot be determined from nasal-resistance measurements, it is reasonable to assume that, given sufficiently high nasal resistance to airflow, a shift toward oral respiration occurs. The range of resistance values at which this shift occurs is not definitely known and presumably differs to some degree among individual patients and physiologic demands. Watson, Warren, and Fisher17 suggested a value of 4.5 cm H,O/L/sec as the approximate point at which the change toward oral respiration begins. This was based on the finding that at about this value 77% of the subjects studied demonstrated subjective signs of mouth breathing.17 It must be emphasized that the change from oral to nasal breathing, however,
probably occurs over a range of values. Equipment for determining respiratory mode has recently been developed but was not used in this study .18 The use of nasal decongestant sprays prior to the recording of nasal resistance (not done in this study) reduces the resistance value in some persons by as much as 45 to 50%. The variable effect of pharmacologic agents on patients has been eliminated with our investigation, since we precluded the use of these agents. Since some investigators have routinely used decongestants, ls this source of variation between studies should be kept in mind when results are compared. Other factors that must be considered in an explanation of the results concerning nasal airway resistance are the alterations of the nasal septum, the nasal crest of the maxilla, and the inferior turbinates. In all cases, a portion of the nasal septum was excised to permit superior repositioning of the maxilla without bowing the septum. In one case removal of the inferior turbinates was necessary. These maneuvers may have increased the size of the nasal passageway and, therefore, decreased the nasal airway resistance. Our clinical observations indicate that superior repositioning of the maxilla results in flaring of the nostrils. As the external nares change in shape from narrow slits presurgically to a more ovoid form (become more circular) postoperatively, the area of the opening increases, and it is the cross-sectional area which most affects the magnitude of nasal-resistance. It is quite possible that the decrease in nasal resistance observed in our present sample is due to widening of the nares and opening of the liminal valve. It is also possible that the decrease in nasal resistance reported to occur after rapid palatal expansion13 is also produced by changes in dimensions of the nares. Further studies to examine this issue are in progress. Nasal resistance in relation to the long-face condition
Our data indicate that the long-faced patients for whom superior repositioning is recommended generally
114
Am. J. Orthod. February 1984
Turvey, Hall, and Warren
have pretreatment nasal-resistance values within the previously reported range of normal. The faces of these patients are characterized by narrow alar bases, lip incompetency at repose, excessive exposure of gingiva upon smiling, excessive lower facial heights, and steep mandibular plane angles. 2o Only 36% (19) of our subjects had nasal-resistance values above 4.5 cm H,OIL/ sec. This suggests that restriction of the nasal airway is not a major cause of the anatomic condition. However, no definite conclusions about mouth breathing as an etiologic factor can be made. Further studies will be necessary, although it seems appropriate to suggest that mouth breathing is not necessary in most of these patients-a point made also in a recent review of the research in this area.” Superior repositioning of the maxilla, with or without involvement of the nasal floor, almost always results in decreased nasal airway resistance. Only one patient in this series of 52 persons showed a postsurgical increase in resistance to above normal values, while 17 of the 19 who had high nasal resistance presurgically had normal values postsurgically. It is probable that the postoperative decrease in nasal airway resistance is associated with changes at the external nares and liminal valve. This explains why nasal resistance decreased about the same way in patients who had segmental osteotomies with elevation of the nasal floor as in patients who had less change in internal nasal anatomy. There appears to be no reason to prefer one segmental procedure over the other when one is considering effect on the nasal airway. We have no data on the resistance values in patients who have buckling of the nasal septum, since in our surgical procedures care was taken to avoid this. Our observation that nasal resistance decreased in both groups in which segmental osteotomies were performed but remained essentially the same in the group that underwent one-piece osteotomies is best explained by the relatively low pretreatment nasal resistance in the latter group of patients. Since nasal resistance in the normal range was not affected by the surgery in most instances, the mean change in the one-piece osteotomy group, which contained a relatively large number of patients with pretreatment normal values, was small. CONCLUSIONS
We conclude that superior repositioning of the maxilla does not increase resistance to nasal breathing, whether or not the surgical procedure elevates the floor of the nose. Concern about the respiratory effects of this surgical procedure appears unwarranted.
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