Abstract:
Apparatus and methods for generating repeatable closure of a volume measurement chamber are provided. More particularly, in one embodiment of the present invention, a dual articulating hinge is used to affix a chamber door to a volume measurement chamber, providing repeatable closure of a chamber door. In another embodiment of the invention, a laterally compliant magnetic latch is used to fasten a chamber door to a volume measurement chamber. In a third embodiment, a chamber door lid is mounted to a hinge bar via a ball joint, allowing the chamber door lid to self center about the chamber opening.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to apparatus and methods for providing repeatable volume within an enclosed chamber. More specifically, the present invention provides apparatus and methods for providing repeatable door closure in a plethysmographic chamber to enhance the accuracy of body composition measurements.  
         BACKGROUND OF THE INVENTION  
         [0002]    The assessment of body composition, including measurement of fat and fat-free mass, provides physicians with important information regarding physical status. Excess body fat has been associated with a variety of disease processes, such as cardiovascular disease, is diabetes, hypertension, hyperlipidemia, kidney disease, and musculoskeletal disorders. Low levels of fat free mass have been found to be critically adverse to the health of certain at-risk populations, such as the elderly, infants, and those suffering from muscle wasting diseases.  
           [0003]    Assessment of body composition has also been found to be useful in the context of evaluating and improving athletic performance. Generally, athletes require a high strength to weight ratio to achieve optimal athletic performance. Because body fat adds weight without a commensurate increase in strength, low body fat percentages have been emphasized within many athletic fields. However, too little body fat can result in deterioration of both health and athletic performance. Thus, accurate measurement of body composition has been found extremely useful in analysis of athletic performance.  
           [0004]    A variety of methods are currently used in the assessment of body composition. One common method is a skinfold measurement, typically performed using calipers that compress the skin at certain points on the body. While non-invasive, this method suffers from poor accuracy on account of variations in fat patterning, misapplication of population specific prediction equations, improper site identification for compressing the skin, poor fold grasping, and the necessity for significant technician training to administer the test properly.  
           [0005]    Another method employed is bioelectric impedance analysis (“BIA”). Bioelectric impedance measurements rely on the fact that the body contains intracellular and extracellular fluids that are capable of conducting electricity. By passing a high frequency electric current through the body, BIA determines body composition based on the bodies, measured impedance in passing current, and the known impedance values for human tissue. However, the accuracy of this method is greatly affected by the state of hydration of the subject, and variations in temperature of both the subject and the surrounding environment.  
           [0006]    The most common method currently used when precision body mass measurements are required is hydrostatic weighing. This method is based upon the application of Archimedes principle, and requires weighing of the subject on land, repeated weighing of the subject under water, and an estimation of air present in the lungs of the subject using gas dilution techniques. However, hydrodensitometry is time consuming, typically unpleasant for the subjects, requires significant subject participation such as repeated, complete exhalation of air from the subject&#39;s lungs, requires considerable technician training and, due to the necessary facilities for implementation, is unsuitable for clinical practice. Further, its application to populations who would particularly benefit from body-mass measurement, such as the obese, elderly, infants, or cardiac patents, is precluded by the above concerns.  
           [0007]    One technique offering particular promise in performing body mass measurement is the use of plethysmography. Plethysmographic methods determine body composition through application of Boyle&#39;s law to the differentiation in volume between the volume of an empty measurement chamber, and the volume of the chamber with the subject to be measured inside. Examples of this technique are disclosed in U.S. Pat. No. 4,369,652 issued to Gundlach, U.S. Pat. No. 5,450,750 issued to Abler, U.S. Pat. No. 4,184,371 issued to Brachet, and U.S. Pat. No. 5,105,825 issued to Dempster. This procedure, in contrast to hydrodensitometry, generally does not cause anxiety or discomfort in the subject, and due to the ease and non-invasiveness of the technique, can readily be applied to populations for whom hydrodensitometry is impractical.  
           [0008]    However, to the present, plethysmographic methods have demonstrated problems with accuracy. For example, failure to take into account differences in compressibility of air in the chamber as opposed to air in the lungs of the subject can result in significant variability in measurements. Although some effort has been made to address these considerations, as disclosed by Dempster, U.S. Pat. No. 5,105,825, the greatest practical impediment to widespread application of plethysmography is the necessity for repeatable, precise volume within the measurement chamber.  
           [0009]    As noted by Gundlach, et al., “The Plethysmometric Measurement of Total Body Volume,” Human Biology, Vol. 38, No. 5, p.783-99, large variations in measured body composition occur based on small changes of volume in the measurement chamber, due to nonrepeatability in the closing action employed for measurement chambers. Variability in closure pressure, and various stresses and strains in both the chamber door and chamber wall for plethysmographic chambers likewise contribute to the inaccuracy of body composition measurements. While current plethysmographic systems have to a certain degree been able to provide mechanical stability with respect to the method of ingress and egress necessary to generate accurate measurements, such systems are typically very complex, expensive, and labor-intensive to manufacture.  
           [0010]    In view of the foregoing drawbacks, it would be desirable to provide apparatus and methods for accurate, non-invasive determination of body mass.  
           [0011]    It would further be desirable to provide apparatus and methods for providing repeatable door closure in a plethysmographic chamber to ensure accurate, precise volume measurements.  
           [0012]    It would further be desirable to provide robust, inexpensive, and easy to manufacture systems for providing repeatable door closure in a plethysmographic chamber.  
         SUMMARY OF THE INVENTION  
         [0013]    It is an object of the present invention to provide apparatus and methods for accurate, non-invasive determination of body mass.  
           [0014]    It is another object of the present invention to provide apparatus and methods for providing repeatable door closure in a plethysmographic chamber to ensure accurate, precise volume measurements.  
           [0015]    It is still another object of the present invention to provide robust, inexpensive, and easy to manufacture systems for providing repeatable door closure in a plethysmographic chamber.  
           [0016]    These and other objects of the present invention are accomplished by providing systems and methods for generating repeatable, accurate door closure in a plethysmographic chamber.  
           [0017]    One embodiment of the apparatus and methods of the present invention comprises one or more dual-articulating hinges mounted to closable means of entry for a plethysmographic chamber, said hinges providing repeatable, solid location of the means of entry upon closure.  
           [0018]    A second embodiment of the present invention involves the use of one or more laterally compliant magnetic latches for fastening the means of chamber entry to the chamber wall.  
           [0019]    A third embodiment of the apparatus and methods of the present invention comprises a spring loaded, self-aligning door that likewise generates repeatable door closure. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The foregoing and other objects of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:  
         [0021]    [0021]FIG. 1A is a representation of a plethysmographic chamber in which embodiments of the present invention operate;  
         [0022]    [0022]FIG. 1B is a representational view of the plethysmographic chamber of the present invention with the chamber door in the open position;  
         [0023]    [0023]FIG. 2A is an exploded view of the dual-articulating hinge of the present invention;  
         [0024]    [0024]FIG. 2B is a cross-sectional view of the dual-articulating hinge of the present invention;  
         [0025]    [0025]FIG. 3A is an exploded view of the laterally compliant magnetic latch of the present invention;  
         [0026]    [0026]FIG. 3B is a cross-sectional view of the laterally compliant magnetic latch of the present invention in the closed position;  
         [0027]    [0027]FIG. 4 is a representation of the infant sized plethysmographic chamber of the present invention; and  
         [0028]    [0028]FIG. 5A is an exploded view of the spring-loaded, self-aligning door of the present invention;  
         [0029]    [0029]FIG. 5B is a cross-sectional view of the door assembly of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    Referring to FIG. 1A, a representational view of the plethysmographic chamber in which embodiments of the present invention operate is described.  
         [0031]    Plethysmographic chamber  20  is composed of chamber wall  22 , chamber door  24 , hinge  26 , latch  28 , and plethysmographic measurement components  30 . Chamber wall  22  and chamber door  24  may be constructed of any suitably rigid material, such as plywood, molded fiberglass, aluminum, etc. Further, chamber door  24  may contain transparent panels constructed of a translucent material such as glass, plexiglass, or polycarbonate.  
         [0032]    As can be seen more clearly in FIG. 1B, a representation of the chamber of the present invention with the chamber door in the open position, dual-articulating hinge  26  permanently affixes chamber door  24  to chamber wall  22 , and allows chamber door  24  to open and close, providing for entry of the subject to be measured into chamber  20 .  
         [0033]    Laterally compliant magnetic latch  28 , located on the opposite side of chamber  22  from hinge  26 , fastens chamber door  24  to chamber wall  22  when chamber door  24  is in the closed position.  
         [0034]    Further, upon closure of chamber door  24 , gasket  32 , affixed about the circumference of chamber door  24 , is inflated to a fixed pressure, creating a seal between chamber door  24  and chamber wall  22 .  
         [0035]    Although one hinge and one latch are shown in the illustrations of FIGS. 1A and 1B, one of ordinary skill in the art would recognize that multiple hinges and/or multiple latches could be used in accord with the present inventions.  
         [0036]    Further, one of skill in the art would recognize that the dual articulating hinge and magnetic latch of the present invention could be used either in combination with or separately from each other in accord with the present inventions. In the preferred embodiment, two hinges are used to create stability across the plane of closure between door  24  and wall  22 , in conjunction with two laterally compliant latches.  
         [0037]    Referring now to FIG. 2A, an exploded view of the dual articulating hinge of the present invention is described. Inner hinge leaf  34  is connected to hinge coupling strut  36  at hinge  38  by means of hinge pin  40 . Rotational movement about hinge  38 , therefore, provides a first degree of articulation. Hinge coupling strut  36  is connected to outer hinge leaf  42  at hinge  44  by means of hinge pin  46 . Rotational movement about hinge  44  defines a second degree of articulation.  
         [0038]    In order to accurately and repeatedly define the clearance between chamber door  24  and chamber wall  22 , a spacer  48  is coupled to inner hinge leaf  34 . When chamber door  24  is closed, spacer  48  makes contact with contact point  50  on outer hinge leaf  42 , thereby defining the distance between chamber door  24  and chamber wall  22 . Preferably spacer  48  is adjustable, to allow for user selectable setting of the clearance between chamber door  24  and chamber wall  22 . For example, spacer  48  could be a bolt whose height can be adjusted by tightening or loosening the bolt into a threaded insert  51  in the inner hinge leaf  38 .  
         [0039]    Referring now to FIG. 2B, a cross-sectional view of the dual-articulating hinge of the present invention is described. As set forth above, when chamber door  24  is in the process of being closed, spacer  48  makes contact at a contact point  50  on outer hinge leaf  44 .  
         [0040]    In the preferred embodiment, contact point  50  is a roller bearing mounted on hinge pin  46 . As door  24  is closed, and spacer  48  makes contact with the roller bearing, the roller bearing can rotationally pivot about hinge pin  46 , and therefore is able to lessen stress in the plane of closure while bearing the load presented at spacer  48 .  
         [0041]    Further, it is preferred that some tension be applied in the degree of articulation defined by hinge  46  to provide more repeatable door closure position, and to minimize scrubbing of gasket  32 . In the preferred embodiment, hinge spring  56  is mechanically coupled to hinge coupling strut  36  by means of retaining screw  52 , which passes through both the bore of hinge spring  56  and through gap  58  in hinge coupling strut  36 , and is coupled directly to upper hinge leaf  42 . As door  24  is being closed, upper hinge leaf  42  rotates in the degree of articulation defined by hinge  44 . Spring  56  is, therefore, compressed by the head of retaining screw  52  on account of the rotation about hinge  44 , providing for greater repeatability of door closure. Alternatively, a washer  57  can be used in conjunction with retaining screw  52  to compress spring  56 .  
         [0042]    Further, as one of ordinary skill in the art would recognize, other methods of providing tension in the degree of the articulation in order to facilitate repeatable door closure can be used in accordance with the present invention. For example, a torsion spring can be used in conjunction with hinge  44  to provide the desired tension in the second degree of articulation. Alternatively, a leaf spring could be used in conjunction with upper hinge leaf  42  to generate the required tension.  
         [0043]    Referring back to FIG. 2A, it is preferable that hinge spring  56  be precompressed to minimize the effort necessary to close door  24 . Thus, in a preferred embodiment, a pair of adjustable set screws,  58  and  59 , are mounted through hinge coupling strut  36 , such that set screws  58  and  59  make contact with upper hinge leaf  42 , thereby setting a minimum gap between coupling strut  38  and upper hinge leaf  42 , and precompressing hinge spring  56 . This precompression of hinge spring  56  makes door closure easier, and also assists in minimizing scrubbing of the gasket  32 .  
         [0044]    Alternatively, one of ordinary skill in the art would recognize that the structure and function of hinge  42  and hinge coupling strut  36 , defining the second degree of articulation, could be performed by a leaf spring solidly affixed to upper hinge leaf  42  at one end, and terminating at hinge  38  (which defines the first degree of articulation) at the other end, and still remain within the scope of the invention.  
         [0045]    Referring now to FIG. 3A, a detailed view of the magnetic latch of the present invention is described. Magnetic latch  28  is comprised of a first latch member  60  and a second latch member  62 .  
         [0046]    In a preferred embodiment, first latch member  60  is affixed to chamber door  24 , and second latch member  62  is affixed to chamber wall  22 , such that when door  24  is in the closed position, latch  28  fastens chamber door  24  to chamber wall  2 : 2 . Alternatively, first latch member  60  can be located on chamber wall  22  and second latch member  62  can be located on chamber door  24 .  
         [0047]    First latch member  60  consists of latch face plate  64 , roller ball  66 , sleeve  68 , and latch mount  69 . Roller ball  66  is housed in sleeve  68 , which in turn is housed within the surface of latch face plate  64 . Latch face plate  64  is coupled to latch mount  69 , which is used to mount first latch member  60  to the plethysmographic chamber. In a preferred embodiment, first latch member  60  further comprises a plate  70 , which is coupled between roller ball  66  and latch mount  69 . Plate  70  is preferably made of the same hardened material as roller ball  66 .  
         [0048]    Sleeve  68  is made of rubber or other similarly pliant compound that allows for rotational movement of roller ball  66 . Roller ball  66  is made of any suitably hard metal which will not deform under the stresses imparted by contact between first latch member  60  and second latch member  62 , such as carbide or hardened steel. Any such deformation in roller ball  66  would hinder the ability of magnetic latch  28  to maintain lateral compliance.  
         [0049]    Second latch member  62  is comprised of magnet housing  72 , magnet outer pole piece  73 , magnet coil  74 , magnet inner pole piece  76 , and insert plate  78 . Insert plate  78  is made of similarly hard material as roller ball  66 . Alternatively, the insert plate could be comprised of a hardened case surrounding the end of magnet inner pole piece  76  proximal to latch member  60  when latch  28  is in the closed position. The combination of magnet outer pole piece  73 , magnet coil  74 , magnet inner pole piece  76  form an electromagnet  79 , the magnetic force of which serves to couple second latch member  62  and first latch member  60 .  
         [0050]    Referring now to FIG. 3B, a cross sectional view of the laterally compliant magnetic latch in the closed position is described. At the proximal end of second latch member  62  is an approximately planar surface comprised of insert plate  78 , and proximal ends of magnet outer pole piece  73 , magnet coil  74 , and magnet inner pole piece  76 . The term approximately planar in this instance means that all of the proximal end surfaces of magnet outer pole piece  73 , magnet coil  74 , magnet inner pole piece  76 , and insert plate  78  are parallel with respect to each other and to the plane of closure (defined below), but that one or more of these surfaces may be offset such that the planar end of second latch member  62  is not a perfectly flat surface.  
         [0051]    When latch  28  is in the closed position, the junction formed between latch face plate  64  of first latch member  60 , and the approximately planar surface at the proximal end of second latch member  62  defines the plane of closure for magnetic latch  28 . Although first latch member  60  and second latch member  62  are held together by the magnetic force of electromagnet  79 , the surfaces of first latch member  60  and second latch member  62  only make contact with each other where roller ball  66  makes contact with insert plate  78 , to allow for rotational movement by roller ball  66 . This capability of roller ball  66  to rotate with respect to insert plate  78  relieves stress in the plane of closure caused by shifting, various stresses and strains on the chamber, deviations in chamber door shape, and differing application of pressure in a closing of the chamber door  24 , while still maintaining compliance with respect to chamber closure volume.  
         [0052]    In an alternative embodiment of the magnetic latch of the present invention, multiple roller balls are mounted in said latch face  68  to ensure lateral compliance.  
         [0053]    Referring to FIG. 4, a representational view of the infant sized plethysmographic chamber is described. Plethysmographic chamber  86  is comprised of chamber door assembly  88 , chamber  90 , hinge  92 , and door frame  94 .  
         [0054]    In FIG. 5A, an exploded view of the self aligning chamber door of the present invention is presented. Door assembly  88  is comprised of hinge bar  98 , ball joint  100 , spring  102 , door lid  104 , seal  106  and door frame  94 . Hinge bar  98  is mounted at one end of the chamber door frame  94  by means of hinge  108 . When door assembly  88  is in the closed position, it is fastened to door frame  94  by means of magnetic latch  110 .  
         [0055]    In a preferred embodiment, door lid  104  is mounted pivotally to hinge bar  98  by means of ball joint  100 . Further, door lid  104  is spring loaded about ball joint  100 . Alternatively, door lid  104  could be mounted using any type of pivotal joint, such as a universal joint, a pointed pin in a drilled point, or a short spring, so long as the door lid can move pivotally with respect to the hinge bar.  
         [0056]    Referring now to FIG. 5B, a cross sectional view of door frame  94  and door assembly  88  is described. Seal  106  is mounted about the inner circumference of door lid  104 . When door assembly  88  is in the closed position, door lid  104 , which is symmetrical with respect to ball joint  100 , automatically self centers on standoffs  112 - 114  located about the rim of door lid  104 , on account of door lid  104  being able to move pivotally with respect to hinge bar  98 . In the preferred embodiment, three standoffs are used to provide for the greatest stability and repeatability of closure.  
         [0057]    Seal  106  makes contact with door frame  94  about the circumference of door frame  94 . As shown in FIG. 5B, the shape of the inner surface of door lid  104  can also be tapered to form a better seal with door frame  94 . Further, spring  102 , mounted about ball joint  100 , applies a known force to compress seal  106  against door frame  94 . On account of the self centering of door lid  104 , and the known force applied to door lid  104  by spring  102 , repeatable closure of door assembly  88  is obtained, providing repeatable volume measurements for chamber  86 .  
         [0058]    In a preferred embodiment of the present invention, a shock absorber  118  can be used to mount ball joint  100  to hinge bar  98 . This shock absorption minimizes startling motions of door lid  104  when opening or closing door assembly  88 .  
         [0059]    Although the foregoing embodiments are discussed in the context of plethysmographic systems, one of ordinary skill in the art would recognize that these closure methods and apparatus would be equally useful in any chamber for which repeatable door closure is required.  
         [0060]    Further, while preferred illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.