Patent Publication Number: US-6213959-B1

Title: Morphometric modeling system and method

Description:
This application is a continuation of U.S. Ser. No. 09/061,020 filed Apr. 15, 1998, now U.S. Pat. No. 6,048,322. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention relates in general to the preliminary screening for a sleep-related breathing disorder and, more particularly, to a tool for use in obtaining measurements of the oral cavity. 
     BACKGROUND OF THE INVENTION 
     The obstructive sleep apnea syndrome (OSAS) is a sleep disorder in which the patient exhibits breathing pauses during sleep, resulting in excessive daytime sleepiness, sleep fragmentation, and intermittent hypoxia. Patients suffering from the disorder have a greater risk of developing diurnal hypertension, myocardial infarction, ventricular failure, pulmonary hypertension, cardiac dysrhythmias and stroke. In addition to health problems, OSAS significantly reduces the effectiveness and alertness of the individual during the day which adversely effects the individual&#39;s lifestyle and increases the risk of injury to the individual and others from motor vehicle and work-related accidents. 
     OSAS is typically diagnosed by polysomnographic testing. This procedure involves monitoring the patient overnight to record brain activity, eye movements, chin and leg muscle movements, cardiac rhythm, snoring intensity, oronasal airflow, respiratory muscle effort, and blood oxygen saturation. The test is time consuming, labor intensive and expensive. Thus, a method of screening patients to reliably determine whether or not they may be at risk for OSAS reduces the number of patients who are unnecessarily subjected to polysomnographic testing. More importantly, earlier diagnosis and treatment of OSAS would be promoted because the screening results would eliminate the reluctance of a physician to prescribe polysomnographic testing for those patients who do not exhibit dramatic OSAS symptoms. 
     Mathematical formulas have been developed to clinically predict whether a patient is likely to suffer from OSAS. These mathematical models primarily rely on measurements of body mass index and neck circumference, two factors which are indicative of the obesity of the patient. Obesity is one of the important risk factors for OSAS. However, not all patients who suffer from OSAS are obese. Although prior mathematical models have combined the body mass index and neck circumference measurements with oxygen saturation levels, witnessed apneas and questionnaire data, these mathematical models are of little use in screening patients who are not obese. A system of screening patients without relying on whether or not they are obese would ensure that further testing is prescribed for all patients at risk for OSAS independent of their body weight. 
     Another significant risk factor in the development of OSAS is craniofacial dysmorphism (disproportionate craniofacial anatomy). Abnormalities associated with craniofacial dysmorphism include a reduction in the upper airway caliber which makes the airway susceptible to collapse during sleep. Abnormalities in craniomandibular morphology, such as a narrow or posteriorly displaced mandible, are often found in OSAS patients. Another abnormality commonly found in OSAS patients is a highly arched palate. A system of quickly and accurately detecting the presence of a narrow or posteriorly displaced mandible and/or a highly arched palate would facilitate the assessment of a patient&#39;s OSAS risk. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide a system of screening patients for OSAS. 
     It is a further object of the present invention to provide a tool which may be used to measure the oral cavity of a patient. 
     It is another object of the present invention to provide a measurement tool which may be used to easily, accurately and quickly obtain measurements of the palatal height, the spacing between the second molars, and the overlap between the upper and lower incisors. 
     It is yet another object of the present invention to provide a system for converting measurements of the oral cavity and other patient data into a morphometric model value which may be used to predict whether further testing of the patient for OSAS is warranted. 
     A more general object of the present invention is to provide a measurement tool which may be efficiently and inexpensively manufactured, and which is suitable for either disposal after a single use or sterilization to permit the tool to be reused. 
     In summary, the present invention provides a tool for measuring the oral cavity. The tool includes first and second measuring members pivotally coupled together for relative pivotal movement of the measuring members about a pivot axis. The first measuring member includes a first leg portion positioned forwardly of the pivot axis and a dial portion with graduations provided thereon. The second measuring member includes a second leg portion positioned forwardly of the pivot axis and a pointer. The second leg portion moves relative to the first leg portion and the pointer moves across the dial upon relative pivotal movement of the first and second measuring members to designate the first graduations and indicates a first measured value indicative of the spacing between the leg portions. One of the measuring members also has second graduations provided thereon in the form of a linear scale such that the second graduations provide a measurement indicative of the spacing between two members, for example the size of the overlap between the upper and lower right central incisors. The measurement tool also includes a support member positionable in the oral cavity of a patient, with the patient biting on upper and lower bite surfaces of the support member. The support member is formed with an opening shaped to slidably receive and support the first leg portion and a slot offset from the opening. The slot is shaped to receive the second leg portion, with the second leg portion being movable within the slot as the second measuring member is pivoted relative to the first measuring member. 
     Additional objects and features of the invention will be more readily apparent from the following detailed description and appended claims when taken in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front plan view of a measurement tool in accordance with the present invention, shown with the tool in an open position. 
     FIG. 2 is an enlarged end view taken substantially along line  2 — 2  in FIG.  1 . 
     FIG. 3 is a front plan view of the measurement device of the tool of FIG.  1 . 
     FIG. 4 is a schematic view of the measurement tool of FIG. 1, shown measuring the palatial height of the oral cavity. 
     FIG. 5 is a schematic view of the measurement tool of FIG. 1, shown measuring the distance between the left and right molars. 
     FIG. 6 is a schematic view of the measurement tool of FIG. 1, shown measuring the overlap of the upper and lower incisors. 
     FIG. 7 is a diagram of the processing system of the present invention. 
     FIG. 8 is graphical depiction of the number of patients per morphometric model number. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiment of the invention, which is illustrated in the accompanying figures. Turning now to the drawings, wherein like components are designated by like reference numerals throughout the various figures, attention is directed to FIGS. 1-3. 
     Tool  10 , constructed in accordance with the present invention, is particularly suitable for quickly and accurately measuring the oral cavity of a patient. In general, the tool  10  includes a measurement device  12  and a support member  14  which cooperates with the measurement device  12  as shown particularly in FIGS. 1 and 2 and described in more detail below. As shown particularly in FIGS. 1 and 3, the measurement device  12  includes a pair of measuring members  16  and  18  which are pivotally coupled together at pivot axis P. The measuring members  16  and  18  may be coupled together by any suitable pivot or fastener  20  which permits relative pivotal movement of the two members  16  and  18 . In the illustrated embodiment, a screw and anchor nut are used to secure the measuring members  16 ,  18  together, although it is to be understood that other suitable fasteners may also be employed. In this embodiment, the interior diameters of the holes (not shown) formed through the measuring members are greater than the maximum exterior diameter of the fastener  20  so that the pivoting of the measuring members is not significantly restricted by friction. However, in other embodiments of the invention the relative sizes of the pivot and the holes formed through the measuring members  16 ,  18  may be selected so that the measuring members  16 ,  18  are substantially held in place by friction until a positive force is applied to one of the members. The frictional forces would hold the measuring members  16 ,  18  in position, allowing the device  12  to be handled for reading and recording the measurement without unintentional movement of the measuring members  16 ,  18 . Bushings, bearings or other devices may also be employed if desired, although such devices would increase the complexity of the device  12  and the cost of manufacture. 
     The first measuring member  16  has a leg portion  24  positioned forwardly of the pivot axis P. The leg portion  24  includes a tapered front end  26  which accommodates the profile of the relaxed tongue and facilitates insertion of the leg portion  24  into the support member  14  as described below. The narrow tip  28  of the front end  26  also facilitates use of the device  12  as a caliper to measure the distance between the second molars on the left and light sides of the oral cavity. The measuring member  16  also includes a dial portion  30 . In the illustrated embodiment, outer edge  32  of the dial portion  30  has an arcuate shape since the measuring member  18  travels in a circular path. However, it is to be understood that the dial portion may also have other shapes within the scope of this invention. The arcuate extent of the dial portion  30  is about 90°, but may be increased or decreased to meet the needs of a particular application. A series of graduations, generally designated  34 , are provided on the dial portion  30 . The graduations  34  may be etched into the dial portion  30 , printed on the dial portion or applied using other suitable means. 
     In the illustrated embodiment, the graduations identify the angle θ between the measuring members  16 ,  18 . The dial portion  30  may also include graduations in which the angular measurement has been converted into a measurement of the linear distance between the tip  28  and the front end of the measuring member  18 , allowing the height or width measured using the device  12  to be immediately identified without further calculation. If desired, the graduations may designate both the angles and the converted linear measurement. 
     The measuring member  16  also includes a second series of graduations, generally designated  36 . The graduations  36  provide a linear scale which may be used to measure the spacing between two members, such as the overlap between the upper and lower right central incisors. In the illustrated embodiment, the graduations  36  are provided along the straight edge  38  of the dial portion, extending inwardly from the outer edge  32  such that the outer edge may be positioned directly against the lower right central incisor. The curvature of the outer edge  32  accommodates the profile of the gums of the lower central incisors and the lower lip. It is to be understood that the graduations may also be positioned in other locations on the measuring member  16  such as along the inner edge  40  of the dial portion. Although not shown, the graduations  36  may also be provided on the second measuring member  18  instead of member  16 . The graduations  36  may be applied using printing, etching or other suitable techniques. 
     The second measuring member  18  includes a leg portion  42  positioned forwardly of the pivot axis P. The leg portion  42  is of substantially the same length as the leg portion  24 . The leg portions  24 ,  42  each have a length of about 70 mm to 80 mm, for example 75 mm. The leg portion  42  is tapered to a narrow tip  44  which is substantially centered on the central axis of the measuring member  18 . 
     The member  18  includes a pointer portion  46  spaced from the leg portion  42 . The pointer portion  46  has a pointed end  48 , the apex  50  of which coincides with the central axis of the measuring member. The apex  50  moves along the graduated curve  35  and designates one of the graduations  34  to indicate the angle θ between the leg portions  24  and  42 . The pointer  46 , which is transparent, is provided with a line  52  extending inwardly from the apex  50  along the central axis of the member  18  to facilitate the identification of which of the graduations  34  is designated by the pointer  46 . It is to be understood that the pointer portion  46  may have other configurations suitable for pointing to one of graduations  34 . For example, the length of the pointer portion  46  may be increased such that the line  52  extends across the graduated curve to provide the primary means of reading the designated graduation. With this modification, where the apex  50  is not used to identify the designated graduation, the end of the pointer portion  46  may be blunt, curved to follow the arcuate edge  32  of the dial portion  30 , or have other shapes. 
     The support member  14  is shown in FIGS. 1 and 2. One function of the support member  14  is to provide a biting block which is inserted between the upper and lower jaws of the patient and used to hold the jaws in a partially open position. This is to standardize the jaw opening across patients, which coincides with a 20 degree angle (not shown) between the tips of the upper and lower central incisors with the axis of the angle at the mandibular condyle. The support member  14  includes upper and lower bite surfaces  60  and  62  which are contacted by the patient&#39;s upper and lower central incisors, respectively, when the support member  14  is clamped between the upper and lower jaws. The support member  14  is positioned so that upper and lower bite surfaces  60  and  62  are parallel to the horizontal plane of the upper surfaces of the teeth on the lower jaw. In the illustrated embodiment, the bite surfaces  60 ,  62  have a width greater than the width of the body of the support member  14  to maximize the surface area of the bite surfaces  60 ,  62  while still allowing visualization of the oral cavity and reducing the amount of material required to form the support member  14 , thereby reducing the cost of manufacture. However, it is to be understood that the upper and lower bite surfaces  60 ,  62  may be coextensive with the remainder of the support member  14  if desired. The bite surfaces  60 ,  62  have a width of about 15 mm to 25 mm, for example 21 mm, although in other modifications of the invention the width of the bite surfaces  60 ,  62  may be larger or smaller. The height of the support member  14  is about 35 mm to 45 mm, for example 40 mm, opening the mouth a sufficient amount to measure the palate height with the device  12 . However, it is to be understood that the height of the support member  14  may be decreased to measure the oral cavity of children, for example. 
     Another function of the support member  14  is to support the measuring members  16 ,  18  so that a reliable and accurate measurement of the palate height may be obtained. The support member includes a bore  64  formed through the support member  12 . The bore  64  is shaped to slidably receive the leg portion  24  of the first measuring member  16  and support the leg portion  24  in position during the measurement. The tapered front end  26  of the leg portion  24  facilitates insertion of the leg portion  24  into the bore  64 . In the illustrated embodiment, the bore  64  follows the shape of the exterior of the leg portion and is slightly larger than the leg portion  24  such that the leg portion  24  may be easily slid into place, but vertical and side-to-side movement of the leg portion  24  within the bore  64  is limited. However, it is to be understood that the size of the bore  64  relative to the leg portion  24  may be increased provided the bore  64  continues to support the device  12  in the proper position. 
     The support member  14  also includes a slot  66  shaped to slidably receive the leg portion  42  of the second measuring member  18 . Slot  66  is also used to align support member  14  between the upper and lower jaws. Support member  14  is positioned so that slot  66  is aligned with the grooves between the two central incisors of the upper and lower jaws. As shown particularly in FIG. 2, the slot  66  is positioned vertically above the bore  64 , and the central axis of the slot is offset from the central axis of the bore  64 . Since the position of the device  12  within the support member  14  is controlled by the bore  64 . the slot  66  is substantially wider than the leg portion  42  such that the leg portion  42  may move without contacting the side walls of the slot  66 . With this configuration, the variations in the size of the leg portion  42  or the exact position of the leg portion  42  relative to the measuring member  16  can be accommodated. However, it is to be understood that the size of the slot  66  may be increased or decreased within the scope of this invention. 
     The device  12  and support member  14  are formed of a material which is suitable for insertion into the oral cavity of the patient, such as plastic or acrylic. In the preferred embodiment, the second measuring member is transparent such that the graduations  34  on the dial portion  30  may be viewed through the pointer portion  46 . The first measuring member may also be transparent. 
     FIGS. 4-6 show the use of the tool  10  of this invention to measure the oral cavity. FIG. 4 shows the measurement of the palatal height (P), or the distance between the dorsum of the tongue at the median lingual sulcus to the highest point of the palate. In FIG. 4, the support member  14  is gripped between the upper and lower jaws. The leg portion  24  of the measuring member  16  is passed through the bore  64  and rests on the tongue (not shown). As the leg portion  24  of the measuring member  16  is advanced forward in bore  64 , the measuring member  18 , with the leg portion  42  positioned in the slot  66 , is automatically pivoted clockwise relative to the measuring member  16  until the pointed end  44  of the leg portion contacts the palate. This occurs because, as measuring member  16  advances forward in bore  64 , the leg portion  42  of measuring member  18  slides along the lower edge of slot  66 , resulting in an increase in angle θ. The size of the opening between the leg portions  24  and  42 , in the form of angle θ or the linear distance between the pointed end  44  and the tip  28 , is indicated by the pointer portion  46  which designates the appropriate one of the graduations  34 . The value associated with the designated graduation, which represents the palatal height P, is noted. 
     FIG. 5 shows the measurement device  12  measuring the width of the mandible. As shown in FIG. 5, the spacing between the mesial surfaces of the crowns of the second molars is measured to determine the mandibular intermolar distance (Mn), and the process is repeated with the upper jaw to determine the maxillary intermolar distance (Mx). These measurements are obtained by inserting the leg portions  24 ,  42  of the device  12  into the oral cavity and positioning the tip  28  on one of the second molars and the end  44  on the opposite second molar. The distance separating the tip  28  and end  44 , in the form of the angle θ between the leg portions  24 ,  42  or the linear distance between the tip and end, is determined by reading the graduation on the dial portion  30  which is identified by the pointer portion  46 . 
     FIG. 6 shows the tool  10  measuring the overjet or overlap between the upper and lower incisors (OJ). Specifically, the horizontal overlap of the crowns of the upper and lower right central incisors is measured. This measurement is obtained by positioning the second graduations  36  adjacent to the overlap. With the device  12  of the present embodiment, where the graduations  36  are positioned on the edge  38  of the measuring member  16 , the outer edge  32  of the dial portion  30  is positioned against the surface of the lower right central incisor and the graduation  36  located adjacent to the tip of the upper right central incisor is noted. 
     Once these data are obtained, the morphometric model value (MMV) for the patient is obtained using the following formula:        MMV   =       [     P   +     (       M                 x     -   Mn     )     +     3      OJ       ]     +       3        [     Max        (       BMI   -   25     ,   0     )       ]            NC   BMI                         
     where: 
     P: palatal height in millimeters (FIG. 4) 
     Mx: maxillary intermolar distance in millimeters (FIG. 5) 
     Mn: mandibular intermolar distance in millimeters (FIG. 5) 
     OJ: incisor overjet in millimeters (FIG. 6) 
     NC: neck circumference in centimeters, measured at the level of the cricothyroid membrane 
     BMI: body mass index, defined as weight in kilograms divided by the square of height in meters. 
     In addition to the oral cavity measurements P, Mx, Mn and OJ, enclosed within the first set of brackets for illustrative purposes, the above formula also incorporates data indicative of the patient&#39;s obesity if the body mass index is greater than 25 kg/m 2 . As discussed above, obesity is an important risk factor for the development of OSAS. If a patient is not obese, for the purposes of this analysis the body mass index is no greater than 25, craniofacial dysmorphism is the sole factor for determining the patient&#39;s risk for OSAS. Using this system as a basis for screening patients prior to prescribing further testing, the amount of craniofacial dysmorphism which must be present to signal that further testing is needed varies independently from whether a patient is obese or not. 
     If the patient is not obese (i.e., BMI≦25), the second half of the formula automatically becomes zero, and the equation reduces to the first half of the formula: 
     
       
           MMV=P+ ( Mx−Mn )+3 OJ   
       
     
     The remaining formula indicates OSAS risk based only on the degree of craniofacial dysmorphism since the patient is not obese. Thus, the formula can be used for screening all patients for OSAS, including those whom are obese, not obese, and those with or without craniofacial dysmorphism. 
     As is diagrammatically illustrated in FIG. 7, a computer  74  (e.g., programmed calculator, software program) is preferably used to compute the model value number. The user inputs the necessary data, in the preferred embodiment the palatal height P, maxillary intermolar distance Mx, mandibular intermolar distance Mn, the incisor ovedjet OJ, the neck circumference NC, and the body mass index BMI. With the tool  10  of the illustrated embodiment, the graduations  34  identify the angle between the leg portions  24 ,  42  in degrees. Computer  74  is configured to receive the values for P, Mx and Mn in degrees and convert these values into a linear distance using stored information on the measurement device  12 . As discussed above, in other modifications of the invention the graduations may identify the values for P, Mx and Mn in millimeters, in which case the computer  74  would be configured to receive the linear measurements and calculate the morphometric model value therefrom. The computer  74  produces an output indicating the morphometric model value for the patient. The computer  74  may be programmed to compare the calculated morphometric model value with the target value and indicate when the calculated value is equal to or greater than the target value such that further testing is required. Alternatively, the user may personally evaluate the calculated model number and the need for further testing for OSAS. 
     EXPERIMENTAL DATA 
     Three hundred patients underwent traditional testing by polysomnography to determine whether they had OSAS. These patients were also evaluated using measurements equivalent to those obtained from morphometric measurement tool  10  and system of the present invention, with the first equation being used to calculate the morphometric model value. The results are summarized in the following table. 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                   
                 PATIENTS 
               
               
                   
                 PATIENTS 
                 WITHOUT 
               
               
                 CHARACTERISTIC 
                 WITH OSAS 
                 OSAS 
               
               
                   
               
             
            
               
                 Men/women 
                 203/51 
                 21/25 
               
               
                 Age (y) 
                 48.1 ± 12.4 
                 40.2 ± 14.0 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                   
                   
                 PATIENTS 
               
               
                   
                   
                 PATIENTS 
                 WITHOUT 
               
               
                   
                 CHARACTERISTIC 
                 WITH OSAS 
                 OSAS 
               
               
                   
                   
               
             
            
               
                   
                 Epworth Sleepiness Scale score 
                 11.5 ± 5.7 
                  7.5 ± 5.9 
               
               
                   
                 Weight (kg) 
                 101.9 ± 25.8 
                 68.7 ± 9.9 
               
               
                   
                 Height (cm) 
                 174.3 ± 9.4  
                 171.8 ± 8.7  
               
               
                   
                 Body Mass Index (kg/m 2 ) 
                 33.6 ± 8.5 
                 23.2 ± 2.6 
               
               
                   
                 Neck Circumference (cm) 
                 41.7 ± 4.7 
                 34.5 ± 3.4 
               
               
                   
                 Maxillary Intermolar Distance 
                 42.0 ± 3.6 
                 39.8 ± 3.8 
               
               
                   
                 (mm) 
               
               
                   
                 Mandibular Intermolar Distance 
                 39.8 ± 3.8 
                 37.8 ± 3.4 
               
               
                   
                 (mm) 
               
               
                   
                 Palatal Height (mm) 
                 52.4 ± 4.1 
                 48.0 ± 4.4 
               
               
                   
                 Overjet (mm) 
                  3.9 ± 2.0 
                  3.3 ± 1.5 
               
               
                   
                 Respiratory Disturbance Index 
                  40.7 ± 42.8 
                  0.8 ± 0.8 
               
               
                   
                 (events/h) 
               
               
                   
                 Minimum Oxygen Saturation 
                  79.5 ± 12.7 
                 95.1 ± 3.0 
               
               
                   
                 (%) 
               
               
                   
                 Morphometric Model Value 
                  95.3 ± 21.2 
                 61.6 ± 6.2 
               
               
                   
                   
               
            
           
         
       
     
     In general, patients with morphometric model values of 70 or more had OSAS, while patients with values less than 70 did not exhibit evidence of OSAS. Thus, a target value of 70 was selected. FIG. 8 shows the number of patients having each morphometric value, with the hatched areas representing the non-OSAS group. As shown in FIG. 8, a smaller number of patients with a model number of less than 70, six total, had OSAS. The model value of the majority of these patients was between 65 and 70. Thus, patients with model values between 65 and 70 should not be automatically dismissed as being without OSAS solely on the basis of their model value. Instead, other factors such as the patient&#39;s symptoms and known sleep problems as well as questionnaire data should be considered and a subjective determination made of whether further testing is necessary. Further, the practitioners subjective opinion that the patient may have OSAS should not be completely ignored for patients with a model value of less than 65. 
     The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best use the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.