Patent Publication Number: US-2022211295-A1

Title: Device for measuring a user&#39;s oxygen-consumption

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     There is provided a measuring device. In particular, there is provided a device for determining a user&#39;s oxygen-consumption. 
     Description of the Related Art 
     A conventional oxygen consumption (“VO2”) monitor device may use a pump to draw air away from the user&#39;s air stream. The device may further include a desiccation system, a relatively large mixing chamber, and an oxygen sensor. It may be undesirable for the user to have attached to their face the entirety of a conventional VO2 monitor due to the excessive vibration, weight, and noise. To mitigate against this, such assemblies may be split into two parts: a face mask for flow measurement, and an external box located either in a backpack or table-top unit with a tube connecting the two parts. The mixing chamber is typically needed to stabilize a gas sample prior to analysis, and/or to remove physical vibration caused by a pump. 
     Such assemblies may thus require a relatively large number of parts and may be bulky as well as expensive. 
     There may accordingly be a need for an improved device that overcomes the above disadvantages. 
     BRIEF SUMMARY OF INVENTION 
     There is accordingly provided a device for measuring a user&#39;s oxygen-consumption. The device includes a venturi, which may be called and in this description will hereafter be referred to as a venturi tube. The venturi tube has a first tapered portion, a second tapered portion that is more tapered compared to the first tapered portion, and a constriction between said portions thereof. The device includes at least one pressure sensor in communication with the first tapered portion of the venturi tube. The device includes an oxygen sensor in communication with the first tapered portion of the venturi tube. 
     There is also provided a device for measuring a user&#39;s oxygen-consumption according to a further aspect. The device includes a venturi tube. The venturi tube has a constriction and is shaped to promote laminar flow through an exhale-receiving portion thereof. The device includes at least one pressure sensor in communication with the constriction and the exhale-receiving portion of the venturi tube. The device includes a desiccant tube in communication the exhale-receiving portion of the venturi tube. A drying agent surrounds the tube in this example. The device includes an oxygen sensor. The desiccant tube is between and in communication with the oxygen sensor and the exhale-receiving portion of the venturi tube. 
     There is further provided a method of calibrating one of the above devices to obtain an ambient oxygen sensor value. The oxygen sensor emits an oxygen sensor signal. The method includes normalizing the oxygen sensor signal with ambient pressure and temperature to inhibit drift caused by changes in elevation and environment. The method may further include normalizing the oxygen signal with relative humidity to inhibit drift caused by changes in elevation and environment. The method includes purging the venturi tube by having a user take two or more slow, large-volume inhales of air through the device successively without exhaling through the device. The method includes measuring and storing via a processor the ambient oxygen sensor value thereafter. 
     There is yet further provided a device for measuring a user&#39;s oxygen-consumption. The device includes a replaceable venturi tube having a proximal end connectable to a breath-receiving member and a distal end through which air enters during inhalation. The device includes a sensor assembly comprising two parts hingedly connected together and between which the venturi tube is selectively received. 
     There is also provided a kit for measuring a user&#39;s oxygen-consumption. The kit includes a plurality of replaceable venturi tubes of different shapes, with the kit thus being customizable to desired test conditions and criteria. Each venturi tube has a proximal end connectable to a breath-receiving member and a distal end through which air enters during inhalation. The kit includes a sensor assembly to which respective ones of the venturi tubes are selectively received. 
     There is additionally provided a device for measuring a user&#39;s oxygen-consumption. The device includes a tubular member with a first tapered portion through which an exhalation of air enters into the device, a second tapered portion, and a constriction between the portions thereof. The devices includes a flow sensing mechanism in communication with the first tapered portion of the tubular member. The device includes an oxygen sensor in communication with the first tapered portion of the tubular member. The device is configured such that the oxygen sensor is passively supplied a portion of the exhalation of air by means of positive or negative differential pressure referenced between the first tapered portion and at least one of ambient air and the constriction of the tubular member. 
     There is yet additionally provided a device for measuring a user&#39;s oxygen-consumption. The device includes a tubular member with a first portion through which an exhalation of air enters into the device, a second portion, and a region of reduced effective cross-sectional area relative to that of and positioned between said portions thereof. The device includes a flow sensing mechanism in fluid communication with the first portion of the tubular member. The flow sensing mechanism passively samples the exhalation of air by means of positive or negative differential pressure referenced between the first portion of the tubular member and at least one of ambient air and said region of reduced cross-sectional area. The device includes an oxygen sensor in fluid communication with the first portion of the tubular member. The oxygen sensor passively samples the exhalation of air by means of positive or negative differential pressure between referenced the first portion of the tubular member and at least one of ambient air and said region of reduced cross-sectional area. 
     There is further provided a device for measuring a user&#39;s oxygen-consumption. The device includes first and second portions through which an exhalation of air passes. The device includes a region of reduced cross-sectional area relative to that of and positioned between the portions of the device. The device includes a flow sensing mechanism and an oxygen sensor in communication with the first portion of the device. The oxygen sensor is supplied the exhalation of air by means of positive or negative differential pressure referenced between the first portion of the device and one of ambient air, the region of reduced cross-sectional area and the second portion of the device. 
     There is yet also provided a device for measuring a user&#39;s oxygen-consumption. The device includes a venturi tube shaped to receive therethrough an exhalation of air. The device includes an oxygen sensor and at least one of a flow sensor and a pressure sensor. Each said sensor is in fluid communication with the venturi tube and passively samples the exhalation of air via a positive or negative pressure differential referenced between the venturi tube and ambient air or referenced between two longitudinally spaced-apart regions of different cross-sectional area of the venturi tube. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention will be more readily understood from the following description of preferred embodiments thereof given, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a top, right side perspective view of a facemask with an oxygen-consumption measuring device coupled thereto, the device including a venturi tube and a sensor assembly extending about the venturi tube; 
         FIG. 2  is a top, left side perspective view of the device of  FIG. 1 , with the sensor assembly being shown in an open position and positioned above the venturi tube; 
         FIG. 3  is a top, right side perspective view of the venturi tube of  FIG. 2 ; 
         FIG. 4  is a distal end elevation view of the venturi tube of  FIG. 3 ; 
         FIG. 5  is a proximal end elevation view of the venturi tube of  FIG. 3 ; 
         FIG. 6  is a cross-sectional view taken along lines  6 - 6  of the venturi tube shown in  FIG. 4 ; 
         FIG. 7  is a cross-sectional view taken along lines  7 - 7  of the venturi tube shown in  FIG. 4 ; 
         FIG. 8  is a top, right side perspective view of the device of  FIG. 1 ; 
         FIG. 9  is a schematic diagram of the device of  FIG. 1  showing the process of exhalation through the device; 
         FIG. 10  is a schematic diagram of the device similar to  FIG. 9  showing the process of inhalation through the device; 
         FIG. 11  is a cross-section view taken along lines  11 - 11  of the facemask and the device of  FIG. 1 , the facemask and the device being shown partially in fragment; 
         FIG. 12  is a top, right perspective view of the sensor assembly of the device of  FIG. 1 , with the venturi tube thereof being removed; 
         FIG. 13  is a front elevation view of the sensor assembly of  FIG. 12 ; 
         FIG. 14  is a rear elevation view of the sensor assembly of  FIG. 12 ; 
         FIG. 15  is a top, left side cross-sectional view taken along lines  15 - 15  of the sensor assembly of  FIG. 12 ; 
         FIG. 16  is a top, right side perspective view of the sensor assembly of  FIG. 12 , with an outer shell of a first part of the sensor assembly being removed to reveal a circuit board cover, and a battery and circuit board of the device mounted onto the circuit board cover; 
         FIG. 17  is a top, right side perspective view of the sensor assembly similar to  FIG. 16 , with the battery now also being removed to reveal additional features of the circuit board of the device; 
         FIG. 18  is a first side elevation view of the circuit board of  FIG. 17 ; 
         FIG. 19  is a second side elevation view of the circuit board of  FIG. 18 ; 
         FIG. 20  is a top, right side perspective view of the sensor assembly similar to  FIG. 17 , with the circuit board now additionally being removed to reveal the outer side of the circuit board cover, the circuit board cover including an environmental sensor inlet and pressure sensor inlets; 
         FIG. 21  is an outer side elevation view of the first part of the sensor assembly of  FIG. 20 , with channels and sample ports thereof being shown in ghost, and with the ends of the venturi tube of  FIG. 1  also being shown and the rest of the venturi tube being not show; 
         FIG. 22  is a cross-sectional view taken along lines  22 - 22  of the device of  FIG. 8 , with sectional aspects of the venturi tube being shown in ghost to reveal the inner side elevation view of an oxygen sensor cover of a second part of the sensor assembly of the device; 
         FIG. 23  is a cross-sectional view taken of the second part of the sensor assembly of the device similar to  FIG. 22 , with sectional aspects of the second part of the venturi tube being shown in ghost to reveal oxygen sensor cover ports and oxygen passageways connected thereto; 
         FIG. 24  is a cross-sectional view taken of the second part of the sensor assembly of the device similar to  FIG. 23 , with sectional aspects of the second part of the venturi tube being shown in ghost to reveal desiccant tubes of the device as well inner-plate flow channels linking the desiccant tubes to oxygen sensor ports, each of the desiccant tubes being surrounded by a drying agent; 
         FIG. 25  is a front, inner side perspective view of the second part of the sensor assembly of the device, with the oxygen sensor cover being removed to better reveal the oxygen sensor and related components including an oxygen sensor holster plate; 
         FIG. 26  is a top, front, inner side perspective view of the oxygen sensor and the oxygen sensor holster plate of  FIG. 25 ; 
         FIG. 27  is a top, rear, inner side perspective view of the oxygen sensor and the oxygen sensor holster plate of  FIG. 25 ; 
         FIG. 28  is a top, front, outer side perspective view of the oxygen sensor and the oxygen sensor holster plate of  FIG. 25 ; 
         FIG. 29  is a graph showing output data from a differential pressure sensor of the device, the output data showing changes in differential pressure while the user inhales through the device; 
         FIG. 30  is a graph showing output data from an environmental sensor of the device, the output data showing changes in absolute pressure while a user inhales through the device; 
         FIGS. 31A to 31D  are flow charts showing various algorithms and communication means for the device of  FIG. 1 ; 
         FIG. 32  is a distal end elevation view of a venturi tube according to a second embodiment; 
         FIG. 33  is a proximal end elevation view thereof; 
         FIG. 34  is a cross-sectional view taken along lines  34 - 34  of the venturi tube shown in  FIG. 32 ; 
         FIG. 35  is a cross-sectional view taken along lines  35 - 35  of the venturi tube shown in  FIG. 32 ; 
         FIG. 36  is a distal end elevation view of a venturi tube according to a third embodiment; 
         FIG. 37  is a proximal end elevation view thereof; 
         FIG. 38  is a cross-sectional view taken along lines  38 - 38  of the venturi tube shown in  FIG. 36 ; 
         FIG. 39  is a cross-sectional view taken along lines  39 - 39  of the venturi tube shown in  FIG. 36 ; 
         FIG. 40  is a schematic diagram of an oxygen-consumption measuring device according to a fourth embodiment; 
         FIG. 41  is a top, right side perspective view of a facemask with an oxygen-consumption measuring device coupled thereto according to a fifth embodiment, the device including a venturi tube and a sensor assembly extending about the venturi tube; 
         FIG. 42  is a rear, top, side perspective view of the device shown in  FIG. 41 ; 
         FIG. 43  is a front elevation view of the device shown in  FIG. 42 ; 
         FIG. 44  is a cross-sectional view taken along lines  44 - 44  of the device shown in  FIG. 43 ; 
         FIG. 45  is a cross-sectional view taken along lines  45 - 45  of the device shown in  FIG. 43 ; 
         FIG. 46  is a schematic diagram of the device of  FIG. 41 ; and 
         FIG. 47  is a schematic diagram of an oxygen-consumption measuring device according to sixth embodiment; and 
         FIG. 48  is a schematic diagram of an oxygen-consumption measuring device according to a seventh embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings and first to  FIG. 1 , there is shown a device  50  for measuring a user&#39;s oxygen-consumption. As seen in  FIG. 8 , the device includes a top  52 , a bottom  54 , a rear  56 , a front  58 , a right side  60  and a left side  62 . The front, rear, top and bottom of the device  50  extend between the sides of the device. The top  52  and bottom  54  of the device extend from the front  58  and rear  56  of the device. 
     As seen in  FIG. 2 , the device  50  includes an asymmetrical, replaceable tubular member, in this example a venturi, which may be referred to and herein after described as a venturi tube  64 . Referring to  FIG. 3 , the venturi tube has a proximal end  66  through which a user&#39;s exhalations of air enter into the device. The proximal end of the venturi tube  64  aligns with the rear  56  of the device  50  seen in  FIG. 1 . The venturi tube includes a pair of spaced-apart, radially-outwardly extending flanges  68  and  70 , flange  68  of which is adjacent to the proximal end thereof. As seen in  FIG. 3 , flange  68  includes a plurality of circumferentially spaced-apart, arced shaped recesses  72  in this example. The venturi tube  64  includes an annular groove  74  positioned between flanges  68  and  70 . 
     Referring to  FIG. 1 , the rear  56  of the device  50  is connectable to a breath-receiving member, in this example a facemask  76  shaped to cover a user&#39;s mouth and nose. In this example, the facemask is an off-the-shelf component of a 7450 V2-type which may be purchased at Hans Rudolf, Inc., having an address of 8325 Cole Parkway Shawnee, Kans., 66227, United States of America. However, this is not strictly required and other types facemasks or mouth and/or nose engagement mechanisms may be used in other embodiments, such as a snorkel mouthpiece with a nose clamp, for example. 
     The facemask has a central aperture  78 . As seen in  FIG. 11 , the facemask  76  includes a pair of spaced-apart, inwardly-extending, annular male members  80  and  82  positioned adjacent to the central aperture of the mask. Groove  74  of the venturi tube  64  is shaped to selectively receive male member  82  in this example between flanges  68  and  70 . Flange  68  is shaped to at least partially extend between male members  80  and  82 . In this manner, the venturi tube  64 , and thus the device  50 , selectively couples to the facemask  76 . 
     As seen in  FIG. 3 , the venturi tube  64  has a distal end  84  spaced-apart from the proximal end  66  thereof. The distal end of the venturi tube receives air therethrough during inhalation by the user. The venturi tube  64  includes an outwardly-extending flange  86  which aligns with the distal end  84  and which extends towards the proximal end of the venturi tube. Flange  86  has indicia  88  thereon indicating the size of the venturi tube shown, in this example displaying the word “MEDIUM”. 
     Still referring to  FIG. 3 , the venturi tube  64  includes a top  90 , a bottom  92 , a right side  94  and a left side  96 . The top, bottom, right and left sides of the venturi tube extend between the proximal end  66  and distal end  84  of the venturi tube. The sides  94  and  96  of the venturi tube  64  extend from the top  90  to the bottom  92  of the device. As seen in  FIG. 4 , the venturi tube  64  has a laterally-extending, cross-sectional first or vertical plane  89  and a laterally-extending, cross-sectional second or horizontal plane  91  which extends perpendicular to the vertical plane. 
     As seen in  FIG. 3 , the venturi tube  64  includes an outer surface  98  extending between the flanges  70  and  86 . The outer surface of the venturi tube is oval-shaped in cross-section. 
     As seen in  FIG. 7 , the venturi tube  64  includes a pair of spaced-apart orientation tabs  93  and  95  located adjacent to flange  86 . The tabs extend outwards from the outer surface  98  of the venturi tube. Tab  93  extends towards the right side  94  of the venturi tube and tab  95  extends towards the left side  96  of the venturi tube. The tabs are generally rectangular prisms in shape in this example. 
     As seen in  FIG. 6 , the venturi tube has a height H between its flanged ends  86  and  70  thereof that extends in the vertical direction between the top  90  and bottom  92  of the venturi tube  64 . As seen in  FIG. 7 , the venturi tube  64  has a width W between its flanged ends  68  and  84  that extends between sides  94  and  96  of the venturi tube. The height H of the venturi tube seen in  FIG. 6  is greater than the width W of the venturi tube seen in  FIG. 7  in this example. 
     Referring to  FIG. 6 , the venturi tube  64  includes an annular first inner surface  99  that extends from the proximal end  66  towards the distal end  84  thereof. The venturi tube includes an annular second inner surface  100  that extends from the distal end  84  towards the proximal end  66  thereof. The inner surfaces  99  and  100  of the venturi tube are in fluid communication with each other. The venturi tube  64  includes a constriction  102  interposed between the inner surfaces thereof. The constriction may also be referred to as a throat of the venturi tube. As seen in  FIG. 5 , the constriction  102  is generally circular in cross-section in this embodiment. The constriction has a width C W  and a height C H . The width and height of the constriction  102  are generally equal in size to each other in this embodiment. 
     The first inner surface  99  of the venturi tube  64  tapers in the vertical plane  89  in this example from the proximal end  66  of the venturi tube to the constriction  102 . The first inner surface of the venturi tube defines a first tapered portion or exhale-receiving portion  104 . The venturi tube  64  is shaped to promote laminar flow through the exhale-receiving portion thereof. As seen with references to  FIGS. 5 to 7 , the exhale-receiving portion  104  of the venturi tube  64  in this example is circular in shape at the proximal end  66  of the venturi tube. As seen in  FIG. 7 , the exhale-receiving portion of the venturi tube has a flared section  105  adjacent to the proximal end  66  of the venturi tube. The exhale-receiving portion  104  of the venturi tube  64  has a substantially constant diameter that is oval-shaped in cross-section thereafter in this example in the horizontal plane  91  as the exhale-receiving portion of the venturi tube  64  extends past the flared portion  105  and to the constriction  102 . 
     As seen in  FIG. 6 , the second inner surface  100  of the venturi tube  64  tapers in the vertical plane  89  in this example from the distal end  84  of the venturi tube to the constriction  102 . As seen in  FIG. 7 , the second inner surface of the venturi tube also tapers in the horizontal plane  91  from the distal end of the venturi tube to the constriction. The second inner surface  100  of the venturi tube defines a second tapered portion or inhale-receiving portion  106 . The inhale-receiving portion of the venturi tube  64  is more tapered compared to the exhale-receiving portion  104  of the venturi tube in this example. As seen with reference to  FIGS. 4, 6 and 7 , the inhale-receiving portion  106  of the venturi tube is generally circular in cross-section in this example. 
     As seen in  FIG. 7 , the venturi tube  64  includes a pair of proximal sample ports  108  and  110 . The sample ports extend through the venturi tube from the outer surface  98  to the inner surface  99  of the venturi tube. The proximal sample ports  108  and  110  are positioned near the proximal end  66  of the venturi tube and adjacent to the flared section  105  of the exhale-receiving portion  104  of the venturi tube. The ports are thus in fluid communication with the exhale-receiving portion of the venturi tube. Port  108  is positioned adjacent to the right side  94  of the venturi tube  64  and port  110  is position adjacent to the left side of the venturi tube. Referring to  FIG. 3 , the proximal sample ports are positioned between the top and bottom of the venturi tube  64  in this example, as seen by port  108  positioned between top  90  and bottom  92 . 
     As seen in  FIG. 7 , the venturi tube  64  includes a pair of constriction sample ports  112  and  114 , which may also be referred to as throat sample ports. The sample ports extend through the venturi tube from the outer surface  98  to the inner surface  99  thereof. The constriction sample ports  112  and  114  are positioned adjacent to, align with and are in fluid communication with the constriction  102  of the venturi tube. Port  112  is positioned adjacent to the right side  94  of the venturi tube  64  and port  114  is position adjacent to the left side of the venturi tube. Referring to  FIG. 3 , the constriction sample ports are positioned between the top and bottom of the venturi tube  64  in this example, as seen by port  112  positioned between top  90  and bottom  92 . 
     Still referring to  FIG. 3 , the venturi tube  64  includes in this example a pair of spaced-apart laterally-extending flow channels  116  and  118 . The flow channels extend from the right side  94  to the left side  96  of the venturi tube  64 . Flow channel  116  is adjacent to the top  90  of the venturi tube and flow channel  118  is adjacent to the bottom  92  of the venturi tube in this example. Channels  116  and  118  align adjacent and to the right of the constriction ports  112  in this example from the perspective of  FIG. 3 . As seen in  FIG. 6 , channels  116  and  118  are separated from and not in communication with the main air stream flowing through constriction  102  of the venturi tube  64 . 
     As seen in  FIG. 8 , device  50  further includes a sensor assembly  120 . The sensor assembly includes two parts  122  and  124  hingedly connected together. Referring to  FIG. 12 , parts  122  and  124  of the assembly  120  include housings  126  and  127 . The housings include outer shells  128  and  129 , respectively. The outer shells  128  and  129  include arcuate-shaped front walls  130  and  131 , respectively. The front walls align adjacent to the front  58  of the device  50 . 
     The walls  130  and  131  have centrally positioned recessed portions  117  and  119 , respectively, which face each other and which extend radially outwards. The recessed portions are generally rectangular prisms in shape in this example. The recessed portions  117  and  119  are shaped to receive the orientation tabs  93  and  95  of the venturi tube  64  seen in  FIG. 7 . The tabs and recessed portions so shaped and positioned thus promote the correct orientation of the venturi tube relative to the outer shells  128  and  129 . 
     As best seen in  FIG. 14 , the outer shells  128  and  129  include arcuate-shaped rear walls  132  and  133 , respectively. The rear walls align adjacent to and with the rear  56  of the device. The front and rear walls of the outer shells include inner and outer peripheral edges. This is seen by inner peripheral edge  134  and outer peripheral edge  136  for rear wall  132  of outer shell  128  and by inner peripheral edge  135  and outer peripheral edge  137  for rear wall  133  of outer shell  129 . The inner peripheral edges of the front and rear walls of the outer shells have a curvature that is less than that of the outer peripheral edges of the front and rear walls of the outer shells in this example. The inner peripheral edges  134  of the front and rear walls of outer shell  128  face the inner peripheral edges  135  of the front and rear walls of outer shell  129  in this example. 
     Referring to  FIG. 12 , the outer shells  128  and  129  include curved outer walls  138  and  139 , respectively. The outer walls are arcuate-shaped in lateral cross-section in this example. Outer wall  138  of outer shell  128  extends between and is integrally formed with the front wall  130  and rear wall  132  of the outer shell in this example. The outer wall  138  aligns with the side  60  of the device  50  and extends from the top  52  to the bottom  54  of the device in this example. Outer wall  139  of outer shell  129  extends between and is integrally formed with the front wall  131  and rear wall  133  of the outer shell in this example. The outer wall  139  aligns with the side  62  of the device  50  and extends from the top  52  to the bottom  54  of the device in this example. 
     As seen in  FIG. 12 , the outer shells  128  and  129  have first or upper ends  148  and  150 , respectively, which align with the top  52  of the device  50 . The outer shells  128  and  129  have second or lower ends  154  and  156 , respectively, which align with the bottom  54  of the device  50 . In this example, the upper ends  148  and  150  of the outer shells hingedly couple together via a hinge mechanism  152 . 
     As seen in  FIG. 2 , the sensor assembly  120  has an open position in which the parts  122  and  124  thereof are angled outwards from each other. In this case, the lower ends  154  and  156  of the outer shells  128  and  129 , respectively, are spaced-apart from each other when the sensor assembly is in the open position. The hinge mechanism  152  enables the sensor assembly  120  to be moveable from the open position to a closed position seen in  FIGS. 8 and 12 to 14 , for example. As seen in  FIG. 13 , the lower ends  154  and  156  of the outer shells  128  and  129  are adjacent to each other when the sensor assembly is in the closed position. Parts  122  and  124  of the sensor assembly  120  when in the closed position form an aperture  158 . The aperture is oval-shaped in cross-section in this example. As seen with reference to  FIGS. 2 and 8 , the aperture is shaped to receive the annular outer surface  98  of venturi tube  64  as the sensor assembly  120  moves to the closed position. In this manner, the venturi tube is thus selectively received between the two parts  122  and  124  of the sensor assembly. 
     The selectively opening and closing of the sensor assembly enables a user to selectively replace the venturi tube  64 . This may thereby effectively result in a device  50  in which all parts that directly touch the user&#39;s air stream are replaceable. The device so configured may thus allow multiple people to use the same device without sharing or exchanging germs. 
     As seen in  FIG. 15 , the sensor assembly  120  includes a latch mechanism  160  located adjacent to the bottom  54  of the device  50 . As seen in  FIG. 21 , the latch mechanism is centrally disposed between the rear  56  and front  58  of the device. Referring back to  FIG. 15 , the latch mechanism includes a male member, in this example in the form of a hook  162 . The hook in this example is coupled to and extends from lower end  154  of outer shell  138  in this example. The latch mechanism  160  further includes a female member, in this example in the form of a grooved seat  164  positioned adjacent to the lower end  156  of outer shell  139 . Grooved seat  164  is shaped to selectively receive hook  162 . In this manner, the parts  122  and  124  of the sensor assembly may selectively couple together in the closed position of the sensor assembly seen in  FIG. 15 . 
     Still referring to  FIG. 15 , the outer shells  128  and  129  include openings  142  and  143 , respectively, which extend between outer walls  138  and  139 , respectively. Housings  126  and  127  include inner planar members, in this example a circuit board cover  144  and an oxygen sensor cover  145 , respectively. The circuit board cover is shaped to be received within opening  142  of outer shell  138 . The oxygen sensor cover  145  is shaped to be received within opening  143  of outer shell  139 . 
     The covers  144  and  145  have curved inner surfaces  146  and  147  that face each other in this example. As seen in  FIG. 13 , the inner surfaces of the covers are arcuate-shaped in cross-section and extend between the top  52  and the bottom  54  of the device  50 . As seen in  FIG. 12 , recessed portions  117  and  119  of walls  130  and  131  are adjacent to inner surfaces  146  and  147  of the covers  144  and  145 , respectively. 
     As seen in  FIG. 14 , the inner surface  146  of cover  144  of housing  126  has a curvature that is substantially similar to and aligned with the inner peripheral edges  134  of the front and rear walls of the outer shell  128 . The curvature of inner surface  146  of the cover is less than that of the outer wall  138  of the housing in this example. Similarly, the inner surface  147  of cover  145  of housing  127  has a curvature that is substantially similar to and aligned with the inner peripheral edges  135  of the front and rear walls of the outer shell  129 . The curvature of inner surface  147  of the cover is less than that of the outer wall  139  of the housing in this example. Aperture  158  is enclosed by the inner surfaces  146  and  147  of covers  144  and  145  in this example. As seen with reference to  FIGS. 2 and 8 , the inner surfaces of the covers abut the outer surface  98  of the venturi tube  64  when the sensor assembly  120  is in the closed position. 
     Referring to  FIG. 20 , circuit board cover  144  has an outer surface  166  opposite its inner surface  146 . The outer surface of the cover is substantially rectangular in shape in this example. The device  50  includes a pair of inlets, in this example pressure sensor inlets  168  and  170 . The pressure sensor inlets extend through the cover  144  from the inner surface  146  towards the outer surface  166  thereof. The pressure sensor inlets  168  and  170  are positioned between the rear  56  and front  58  of the device  50  in this example. Sensor inlet  170  is positioned adjacent to the bottom  54  of the device in this example, and sensor inlet  168  is positioned adjacent to and above sensor inlet  170  from the perspective of  FIG. 20 . As seen in  FIG. 21 , pressure sensor inlet  168  is positioned below proximal sample port  108  of the venturi tube  64  in this example. Pressure sensor inlet  170  is position below constriction sample port  112  in this example. 
     Still referring to  FIG. 21 , cover  144  includes a pair of conduits, in this example channels  172  and  174 . The channels are in communication with, recessed relative to and extend inwards relative to the inner surface  146  of the cover. Channel  172  extends between pressure sensor inlet  168  and proximal sample port  108  of the venturi tube  64 . In this manner, pressure sensor inlet  168  and proximal sample port  108  are thus in fluid communication with each other via channel  172 . Channel  174  extends between pressure sensor inlet  170  and constriction sample port  112  of the venturi tube  64 . In this manner, pressure sensor inlet  170  and constriction sample port  112  are thus in fluid communication with each other via channel  174 . Channels  172  and  174  are also shown schematically in  FIG. 9 . The channels are positioned so that the sample ports are of equal distance from the air stream. 
     Referring back to  FIG. 21 , cover  144  includes an additional conduit, in this example channel  175  in communication with, recessed relative to and extending inwards relative to the inner surface  146  of the cover. Channel  175  extends between constriction sample port  112  of the venturi tube  64  and laterally-extending flow channel  116  of the venturi tube. In this manner, constriction sample port  112  and channel  116  are thus in fluid communication with each other via channel  175 . 
     As seen in  FIG. 9 , the device  50  includes a flow sensing mechanism, in this example a pressure sensor, in this case a differential pressure sensor  176 . The differential pressure sensor in this example is an off-the-shelf product, in this case an AMS5915-type pressure sensor that may be purchased at Analog Microelectronics GmbH, having an address of An der Fahrt 13, 55124 Mainz, Germany. However, this is not strictly required and other types of pressure sensors may be used in other embodiments. 
     The pressure sensor  176  is in fluid communication with the constriction  102  of the venturi tube  64  via constriction sample port  112 , channel  174  and pressure sensor inlet  170 . The pressure sensor is in fluid communication with the exhale-receiving portion  104  of the venturi tube  64  adjacent to the proximal end  66  of the tube via proximal sample port  108 , channel  172  and pressure sensor inlet  168 . The pressure sensor  176  in this example measures the difference in pressure at inlets  168  and  170  and emits a pressure sensor signal in response thereto. The pressure sensor  176  so configured measures the flow rate through the venturi tube  64  as well as the breath state, namely, a no breath state, an inhale-breath state, or an exhale-breath state. 
     Referring to  FIG. 20 , cover  144  further includes an environmental sensor inlet  178 . The environmental sensor inlet extends from the outer surface  166  towards the inner surface  146  of the cover. As seen in  FIG. 21 , the environmental sensor inlet  178  is aligned and in communication with constriction sample port  112 . However, this is not strictly required, and the sensor inlet may alternatively align with and be in communication with constriction sample port  114  as seen in  FIGS. 9 and 10 . Referring back to  FIG. 20 , the environmental sensor inlet  178  is positioned adjacent to the front  58  of the device  50  in this example. As seen with reference to  FIGS. 21 and 22 , the environmental sensor inlet is positioned adjacent to and aligns with the constriction  102  of the venturi tube  64  in this example. Referring to  FIG. 20 , the environmental sensor inlet  178  is positioned between the top  52  and bottom  54  of the device  50  in this example. 
     As seen in  FIG. 9 , the device  50  includes an environmental sensor  180 . The environmental sensor in this example is an off-the-shelf product, in this case a BME280-type environmental sensor which may be purchased at Bosch Sensortec GmbH, having an address of Gerhard-Kindler-StraBe 9, 72770 Reutlingen/Kusterdingen, Germany. However, this is not strictly required and other types of environmental sensors may be used in other embodiments. As seen in  FIG. 9 , the environmental sensor  180  has a port  181  connected to and in fluid communication with the constriction port  114  via conduit  183  in this example. 
     The environmental sensor  180  outputs an absolute pressure signal as shown in  FIG. 30 . During an inhale seen in  FIG. 10 , the differential pressure sensor  176  is subject to turbulence seen in  FIG. 29  that is absent in the environmental sensor&#39;s pressure output seen in  FIG. 30 . The device  50  is thus configured to use the change in the environmental sensor&#39;s absolute pressure output to determine the inhale flow. This circumvents signal noise which may otherwise occur in the differential pressure sensor signal during inhales. Referring to  FIG. 9 , flow through the device  50  is thus measured bi-directionally via the differential pressure sensor  176  for exhalations and breath state detection, and via the environmental sensor  180  for inhalations. The environmental sensor also outputs temperature and relative humidity data for flow calculations and oxygen sensor signal correction. 
     As mentioned above, the pressure sensor output is used for breath state detection and exhale flow calculations. The pressure sensor  176  is used to detect breath state by means of a zero-crossing check of the differential pressure sensor output with consideration to the sensor&#39;s signal noise threshold. If the breath state is in an exhale direction, the differential pressure sensor output is used to compute the instantaneous flow rate between data samples. If the breath state is in an inhale direction, the difference between the environmental sensor pressure output and ambient pressure is used to compute an instantaneous flow rate between data samples. Ambient pressure is the last environmental sensor pressure output where no breathing has occurred. The instantaneous flow volume between data samples is calculated using each gap&#39;s instantaneous flow rate. When the breath state returns to no breathing, all of the instantaneous flow volumes for the completed breath segment are summed. This sum is known by those skilled in the art as tidal volume (Tv(L)). Breath segment frequency is then calculated using the following formula: (segment Rf)=30 s/(breath segment time(s)). The ventilation (Ve) of the breath segment is calculated using the following formula: Ve (L/min)=(breath segment frequency)×(breath segment tidal volume (L)). For each pair of inhale and exhale segments, average breath segment frequency (Rf), Tv, and Ve are determined as the final flow metrics for the whole breath. 
     As seen in  FIG. 16 , the device  50  includes a circuit board  182 . The circuit board mounts to the outer surface  166  of cover  144  via a pair of spaced-apart fasteners, in this example screws  184  and  186 . The circuit board has an inner side  187 , best seen in  FIG. 19 , which faces the outer surface  166  of the cover seen in  FIG. 16 . Differential pressure sensor  176  and environmental sensor  180  couple to the inner side of the circuit board  182  in this example. 
     As seen in  FIG. 18 , the device  50  includes a processor, in this example a microprocessor  190  coupled to the outer side  188  of the circuit board. In this case, the microprocessor is an off-the-shelf component of a NRF51422-type which may be purchased at Nordic Semiconductor ASA, having an address of P.O. Box 436, Skøyen, 0213, Oslo, Norway. However, this is not strictly required and other types of processors may be used in other embodiments. The microprocessor  190  operatively couples with the differential pressure sensor  176  and environmental sensor  180  seen in  FIG. 19  and receives data therefrom. The circuit board  182  connects to the analog output of the oxygen sensor by the means of two wires in communication with the two thru-hole connections labeled “OXYGEN SENSOR CONNECTION”. 
     As seen in  FIG. 18 , the device  50  further includes a USB connector  192  coupled to the outer side  188  of the circuit board  182 . The USB connector is operatively connected to the microprocessor and enables selective uploading of data from the processor to a remote server or computer, for example. As seen in  FIG. 16 , the device  50  additionally includes a battery  194  for supplying power thereto. In this example, the battery is a lithium-polymer rechargeable type battery; however, this is not strictly required and other types of batteries or power sources may be used in other embodiments. The battery operatively connects to the microprocessor  190 . 
     The device  50  includes an on/off switch, in this example in the form of an on/off plunger switch  196  coupled to the circuit board  182 . The switch is configured to cut off power to the device upon the switch being pushed inwards towards the circuit board. 
     As seen in  FIG. 15 , a pair of spaced-apart flanges  198  and  200  extend inwards from the front wall  130  of outer shell  128 . The flanges are shaped to receive battery  194  therebetween. 
     The oxygen sensor cover  145  includes an outer side  202  opposite the inner surface  147  thereof. The cover includes a pair of spaced-apart upper and lower receptacles  204  and  206  and a central receptacle  208  between the peripheral receptacles in this example. The receptacles are situated along the outer side  202  of the oxygen sensor cover  145 . 
     As seen in  FIG. 22 , cover  145  includes a conduit, in this example a cover plate flow channel  210  that is in communication with, recessed relative to and outwardly extending relative to the inner surface  147  of the cover. The cover further includes a first oxygen sensor cover plate port  212  that extends from the inner surface  147  of the cover through to the outer side  202  of the cover seen in  FIG. 15  in this example. Referring to  FIGS. 21 and 22 , constriction sample port  112  seen in  FIG. 21  is thus in communication with oxygen sensor cover plate port  212  seen in  FIG. 22  via channel  175  of the circuit board cover  144  seen in  FIG. 21 , flow-channel  116  of the venturi tube  64  seen in  FIG. 22 , and channel  210  of the oxygen sensor cover  145  seen in  FIG. 22 . 
     As seen in  FIG. 24 , the device  50  includes in this example a pair of spaced-apart desiccant plates  214  and  216  adjacent to the rear  56  and front  58  of the device. The plates are generally rectangular prisms in this example and operatively couple to the outer side  202  of the oxygen sensor cover  145  seen in  FIG. 15 . 
     Referring back to  FIG. 24 , plate  214  includes a first or upper conduit extending therein, in this example a channel  218  which is adjacent to the top  52  of the device  50 . The channel is in fluid communication with the oxygen sensor cover plate port  212  seen in  FIG. 23 . 
     Still referring to  FIG. 23 , the oxygen sensor cover has a second oxygen sensor cover plate port  220  that is in fluid communication with proximal sample port  110  seen in  FIG. 22 . Referring back to  FIG. 23 , plate  214  includes a second or lower conduit extending therein, in this example a channel  222 . The channel is adjacent to the bottom  54  of the device  50  and is in fluid communication port  220 . 
     Plate  216  includes a first or upper conduit extending therein, in this example a first u-shaped channel  224  seen in  FIG. 24  adjacent to the top  52  of the device  50 . The plate  216  includes a second or lower conduit extending therein, in this example a second u-shaped channel  226  adjacent to the bottom  54  of the device  50 . 
     As seen in  FIG. 24 , the device  50  includes a pair of desiccants, in this example a pair of desiccant tubes  228  and  230 . In this example, the desiccant tubes are off-the-shelf components of Nafion™-type tubing, which may be purchased at Perma Pure LLC, having an address of 1001 New Hampshire Ave., Lakewood, N.J., 08701, United States of America. However, this is not strictly required and other desiccant tubes and/or other types of desiccants may be used in other embodiments. 
     Desiccant tube  228  extends between channels  218  and  224 . The tube is thus in fluid communication with the constriction  102  of the venturi tube  64  seen in  FIG. 22  via: port  112 , channel  175  and channel  116  seen in  FIG. 21 ; channel  210  and port  212  seen in  FIG. 22 ; and channel  218  seen in  FIG. 24 . As seen in  FIG. 15 , tube  228  is received within and extends along receptacle  204  of the oxygen sensor cover  145  in this example. 
     As seen in  FIG. 24 , desiccant tube  230  extends channels  222  and  226 . The tube is thus in fluid communication with the exhale-receiving portion  104  of the venturi tube  64  seen in  FIG. 22  via: port  110  seen in  FIG. 22 ; and port  220  and channel  222  seen in  FIG. 23 . As seen in  FIG. 15 , tube  230  is received within and extends along receptacle  206  of the oxygen cover  145  in this example. 
     As seen in  FIG. 10 , the device  50  further includes a pair of drying agents  231  and  233  adjacent to and surrounding respective desiccant tubes  228  and  230 . Each of the drying agents is in the form of silicate gel beads in this example. However, this is not strictly required and other drying agents may be used in other embodiments. 
     As seen in  FIG. 15 , the device  50  includes an oxygen sensor  232 . In this example, the oxygen sensor is a passive sensor and is an off-the-shelf component of the galvanic fuel cell type, which may be purchased at Analytical Industries Inc., having an address of 2855 Metropolitan Place, Pomona, Calif., 91767, United States of America. However, this is not strictly required and other types of oxygen sensors may be used in other embodiments. Receptacle  208  of cover  145  is shaped to at least partially receive the oxygen sensor  232  therein. 
     As seen in  FIG. 24 , the oxygen sensor has a pair of oxygen sensor ports  234  and  236  that are in fluid communication with channels  224  and  226 , respectively. As seen in  FIG. 10 , the oxygen sensor  232  is thus in fluid communication with the constriction  102  and the exhale-receiving portion  104  of the venturi tube  64 . As seen in  FIG. 24 , the oxygen sensor is positioned between and in fluid communication with the desiccants tubes  228  and  230 . 
     As seen in  FIG. 25 , the device  50  includes an oxygen sensor micro mixing chamber  238  that is adjacent to and in communication with oxygen sensor ports  234  and  236  seen in  FIG. 24 . The device  50  includes an oxygen sensor electrical output spring connector mechanism  240  through which the oxygen sensor may emit an oxygen sensor signal. 
     As seen in  FIGS. 26 to 28 , the device includes an oxygen sensor holster  242  in this example shaped to receive the oxygen sensor  232  at least in part. As seen in  FIG. 15 , the holster is positioned between the outer shell  139  and oxygen sensor cover plate  145 . The holster  242  is shaped to be selectively removable from the rest of the device  50 . 
     The device  50  so shaped and described herein results in a gas channel flow rate that may be drastically lower than in previous known prior art systems. As a result, by using small desiccant tubes  228  and  230  seen in  FIG. 10 , the device  50  as herein described may desiccate sample gas prior to it reaching the oxygen sensor  232 . 
     In operation and referring to  FIG. 31A , the main routine associated with the device  50  begins with initializing the microcontroller (box  246 ), initializing the sensors (box  248 ), initializing the universal serial bus (USB) and wireless system such as Bluetooth® (box  250 ), and initially setting the current state of the device to idle. Thereafter, the software polls the USB and Bluetooth® communication ports awaiting connection from a parent device. The parent device may be a smartphone or personal computer  255  as seen in  FIG. 31D , for example. Serial communication  252  enables the device  50  to communicate with the parent computer  255 , sharing information such as respiratory data  257 , device information  259 , device error data  261  and device state and settings data  263 . The latter may include venturi size and the like. Respiratory data may include metrics such as Time, Respiratory Frequency, Tidal Volume, Ventilation, Fraction of Expired Oxygen, Fraction of Inspired Oxygen, or Volume of Oxygen Consumed (VO2). The computer  255  will at some point order the software to begin a recording. The software determines the current state of the device (box  252 ): an idle/default state (box  254 ); a calibrating state (box  256 ); or a recording state ( 258 ). If the device is determined to be in an idle/default state, the loop of the routine continues as before (box  260 ). 
     When commanded by the parent device to enter a RECORD state, the software may determine that calibration of the sensors has not yet been performed, and thusly cause the device  50  to enter the calibration state. If the software determines that calibration has already occurred, it may directly enter recording state without re-calibrating. If the device is determined to be in a calibration state (box  256 ), the system is updated (box  259 ) periodically, such as every 20 milliseconds for example. This means all sensor intermediate data is updated. Once calibration of all mentioned sensors is complete, the device  50  automatically switches to the RECORD state. 
     Referring to  FIG. 31B , the differential pressure sensor is first polled (box  261 ) by the device&#39;s software to determine the status thereof. The environmental sensor is next polled by the device&#39;s software for absolute pressure, temperature and relative humidity (box  262 ). The oxygen sensor temperature-compensated analog output is next polled by the device&#39;s software, as indicated by box  264 . The device&#39;s processor determines and stores ambient pressure data from the absolute pressure signal (box  266 ). The device&#39;s processor next determines and stores the environmentally-normalized oxygen concentration value (box  268 ). The environmental sensor  180  and differential pressure sensor  176  seen in  FIG. 9  are thus calibrated to their ambient measurements, as shown by box  270  in  FIG. 31A . This is done to effectively track sensor signal drift over time due to change in environment. 
     For the calibration state, a pre-workout calibration method is needed to sample ambient oxygen concentration in order to create a linear oxygen concentration conversion scale for the workout. Calibration must be performed prior to each workout. In order to obtain a passive oxygen concentration measurement, there is further provided a method of calibrating the device to obtain an ambient oxygen sensor value. The method includes normalizing the oxygen sensor signal with ambient pressure, temperature, and relative humidity to inhibit drift caused by changes in environment, such as changes in elevation, as shown by box of numeral  272  in  FIG. 31A . The method includes purging the venturi tube  64  by having a user take two slow, large-volume inhales of air through the device successively without exhaling through the device. In other embodiments, this could be three breaths or more. The method further includes measuring and storing via a processor the ambient oxygen sensor value thereafter. With this data point a linear scale is realized to measure any oxygen sensor output in percent concentration. 
     Referring to  FIG. 31A , one can thereafter begin recording data (box  258 ). The oxygen sensor has a response delay of T90=1 second according to one example. 
     
       
         
           
             V 
             = 
             
               
                 
                   V 
                   0 
                 
                 ⁢ 
                 e 
               
               - 
               
                 RC 
                 t 
               
             
           
         
       
     
     where: V is extrapolated O 2 %;
         V 0  is the change in O 2  from a breath segment from start to end;   e is the natural log constant;   t is the time delta between O 2  delta start to end; and   RC is an experimentally determined correction constant.
 
Using the above formula, for each inhale and exhale breath segment, the microprocessor extrapolates at what value the oxygen sensor would settle were it given the time to do so prior to the upcoming breath segment. This extrapolated value is the oxygen concentration of the given breath segment (FeO2 for exhale and FiO2 for inhale).
       

     The oxygen sensor measures inspired and expired oxygen concentrations (FiO2 &amp; FeO2) breath-by-breath. Using the passive oxygen concentration measurement and the bidirectional flow measurement processes to acquire intermediate data, compute oxygen consumption using this formula: VO2=Ve*(AmbientO2−FeO2)/100, where VO2 (mL/min) is oxygen consumption, AmbientO2(%) is the ambient oxygen concentration of the environment, and FeO2(%) is the oxygen concentration of the user&#39;s expired breath. One divides by 100 to convert the 0-21% oxygen delta into a 0.0-1.0 coefficient. 
     The device  50  measures both inhale and exhale flow and oxygen concentrations, but only considers exhale-phase metrics to produce final values for the breath. This is due to the asymmetrical shape of the venturi tube which causes exhale metrics to be much more accurate and repeatable. Less venturi turbulence on the exhale means greater flow through the oxygen sensor. Inhale flow measurement for the device  50  is only used to check for mask leaks. Inhale flow is used in comparison with that of exhale to detect mask leaks. 
     The device as herein described is compact and requires low power, with a 30 mA current draw according to one example. The device  50  as herein described uses passive sampling of metrics. This as a result may reduce power requirements. The device  50  so configured may also thus inhibit external vibration by eliminating the need for a sampling pump and mixing chamber. Such a sampling system may decrease the total size of the device and also increase oxygen sensor response time. 
     The device as herein described provides a mixing chamber that is relatively small. The passive sampling system of the device may thus provide significantly improved oxygen sensor reaction time due to the reduced dead space between the main air stream and sensor. 
     Coupled with a differential pressure sensor that measures bidirectional flow, this compact, portable device  50  as herein described may thus produce at least the following ventilatory and oxygenation metrics:
         a. tidal volume, namely, the volume of air that is moved per breath (“TV”);   b. respiratory frequency in breaths per minute (“RF”);   c. minute ventilation, namely, the amount of air moved in and out of the lungs in litres per minute (“VE”);   d. the fraction of expired air that is oxygen (“FEO2”);   e. the fraction of inspired air that is oxygen (“FIO2”);   f. volume of oxygen consumed (“VO 2 ”)=O2 volume inspired−O2 volume expired in mL/min; and   g. maximum oxygen consumption (“VO 2MAX ”).       

     The asymmetrical, ovular shape of the venturi tube  64  may increase accuracy of exhale metrics, while decreasing the accuracy of inhale metrics. The device  50  as herein described includes an asymmetrical venturi that drastically reduces turbulence in the exhale phase while increasing turbulence in the inhale phase. Less turbulence means greater flow through the respiratory flow channel, resulting in an oxygen sensor that is better purged with expired air during regular breathing. Referring to  FIG. 10 , the greater length between proximal ports  108  and  110  and constriction ports  112  and  114  of the venturi tube  64  may allow for a slower change in inner diameter, thereby creating air flow having less turbulence. Air turbulence along a concave wall may be proportional to its angle. The ports  108  and  110  are thus located on the flattest side of the ellipse cross-section. 
     Venturi tube  64  of the embodiment shown in  FIGS. 1 to 31C  is shaped to perform measurements and acquire data during sub-maximal exercise testing, such as when a user is hiking, for example. 
     Referring to  FIG. 31A , in the recording state (box  258 ), after an update (box  259 ) of the device data has occurred, the data is next processed (box  273 ). Referring to  FIG. 31C , a flow chart of the processing of data is shown. The device  50 . 1  determines breath state (box  274 ) by evaluating differential pressure data. The device may also use environmental data to this end. The processor may determine based on this data that there is a no breath (box  276 ), an inhale breath state (box  278 ), or an exhale breath state (box  279 ). 
     Where the processor determines that there is an inhale breath state, sensor data is used to determine flow volume since the previous loop execution (box  280 ). Put another away, the processor determines the volume of air that has passed through the venturi tube since the previous loop execution using the differential pressure waveform or absolute pressure waveform from the environmental sensor. The processor thereafter determines the sum of the flow volume of the inhale breath since the beginning of the breath segment (box  282 ). The processor next determines if the breath state has just been switched from an exhale breath state (box  284 ) using differential pressure data. If so, the processor then determines the final metrics for the entire previous exhale breath segment ( 286 ). Thereafter, the flow chart returns to being the loop (box  260 ) once more as seen in  FIG. 31A . Alternatively, if the processor determines that there has not been a recent switch in breath state, such calculations are omitted and here too the flow chart returns (box  287 ) to the begin loop state (box  26 ) of  FIG. 31A . 
     If the processor determines that there is an exhale state (box  279 ), sensor data is used to determine flow volume since the previous loop execution (box  288 )) using the differential pressure waveform or absolute pressure waveform from the environmental sensor. Put another away, the processor determines the volume of air that has passed through the venturi tube since the previous loop execution. The processor thereafter determines the sum of the flow volume of the exhale breath since the beginning of the breath segment (box  290 ). The processor next determines if the breath state has just been switched from an inhale breath state (box  292 ) using differential pressure data. If so, the processor then determines both the final metrics for the entire previous inhale breath segment and the final metrics for the entire previous breath ( 294 ). Thereafter, the flow chart returns (box  287 ) to being the loop (box  260 ) once more as seen in  FIG. 31A . Alternatively, if the processor determines that there has not been a recent switch in breath state, such calculations are omitted and here too the flow chart returns to the begin loop state (box  26 ) of  FIG. 31A . 
       FIGS. 32 to 36  show a venturi tube  64 . 1  for a device  50 . 1  for measuring a user&#39;s oxygen-consumption according to a second aspect. Like parts have like numbers and functions as the tube  64  and device  50  shown in  FIGS. 1 to 31C  with the addition of decimal extension “.1”. The device  50 . 1  and venturi tube  64 . 1  are the same as described for tube  64  and device  50  with the following exceptions. 
     As seen in  FIG. 33 , constriction  102 . 1  of venturi tube  64 . 1  is oval-shaped in cross-section. The width C W.1  of the constriction is substantially the same as width C W  of constriction  102  for tube  64  seen in  FIG. 5 . The height C H.1  of the constriction  102 . 1  of the venturi tube is longer than its width C W1  and longer than that of height C H  of the constriction  102  of tube  64  seen in  FIG. 5 . The cross-sectional area of constriction  102 . 1  is larger than that of constriction  102  for tube  64  seen in  FIG. 5 . Tube  64 . 1  shown in  FIGS. 32 to 35  is shaped to perform measurements and acquire data during maximal tests or high-intensity exercise while running or biking. Tube  64 . 1  is thus shaped for high flow rates. 
       FIGS. 36 to 39  show a venturi tube  64 . 2  for a device  50 . 2  for measuring a user&#39;s oxygen-consumption according to a third aspect. Like parts have like numbers and functions as the tube  64  and device  50  shown in  FIGS. 1 to 31C  with the addition of decimal extension “.2”. The device  50 . 2  and venturi tube  64 . 2  are the same as described for tube  64  and device  50  with the following exceptions. 
     As seen in  FIG. 37 , constriction  102 . 2  of venturi tube  64 . 2  is oval-shaped in cross-section. The width C W.2  of the constriction is substantially the same as width C W  of constriction  102  for tube  64  seen in  FIG. 5  and substantially the same as width C W.1  of constriction  102 . 1  for tube  64 . 1  seen in  FIG. 33 . The height C H.2  of the constriction  102 . 2  of the venturi tube is shorter than its width C W2  and shorter than that of height C H  of the constriction  102  of tube  64  seen in  FIG. 5 . 
     The cross-sectional area of constriction  102 . 2  is smaller than that of constriction  102  for tube  64  seen in  FIG. 5  and smaller than that of constriction  102 . 1  of tube  64 . 1  seen in  FIGS. 33 to 36 . Tube  64 . 2  of the embodiment shown in  FIGS. 36 to 39  is shaped to perform measurements and acquire data when the user is resting or walking. Tube  64 . 2  is thus shaped for low flow rates. 
     The sensor assembly  120  and tubes  64 ,  64 . 1  and  64 . 2  as herein described may thus be part of a kit comprising the assembly and venturi tubes of varied shapes. The device so configured may thus be customizable to desired test conditions and criteria. This is advantageous because it allows for tubes having different flow ranges for each size. The replaceability of the venturi tube, while keeping the rest of the device the same as before, may function to reduce overall costs and improve the versatility of the device. 
       FIG. 40  shows a schematic diagram of a device  50 . 3  for measuring a user&#39;s oxygen-consumption according to a fourth aspect. Like parts have like numbers and functions as the tube  64  and device  50  shown in  FIGS. 1 to 31C  with the addition of decimal extension “.3”. The device  50 . 3  is the same as described for device  50  with the following exceptions. 
     In this embodiment, a second environmental sensor  244  for oxygen correction is employed right at the oxygen sensor  232 . 2  in order to achieve an improved environmental correction. The sensor is interposed between and in communication with dessicant tube  228 . 3  and oxygen sensor port  234 . 3  of oxygen sensor  232 . 3 . 
     Environmental sensor  180 . 3  is used for flow correction in this embodiment. The sensor is interposed between and in communication with constriction sample port  112 . 3  and pressure sensor inlet  170 . 3  of differential pressure sensor  176 . 3 . 
       FIGS. 41 to 46  show a device  50 . 4  for measuring a user&#39;s oxygen-consumption according to a fifth aspect. Like parts have like numbers and functions as the tube  64  and device  50  shown in  FIGS. 1 to 31C  with the addition of decimal extension “.4”. The device  50 . 4  is the same as described for device  50  with the following exceptions. 
     As seen in  FIG. 41 , the sensor assembly  120 . 4  is generally a hollow rectangular prism in shape in this example. The top  52 . 4 , bottom  54 . 4  and sides  60 . 4  and  62 . 4  of the device are rectangular, with the top and bottom being wider than said sides in this example. As seen in  FIG. 42 , the sensor assembly  120 . 4  includes a mouth piece  300  located at the rear  56 . 4  of the device  50 . 4 . The mouth piece includes a pair of spaced-apart flanged side members  302  and  304  which align with sides  60 . 4  and  62 . 4 , respectively, of the device. The proximal end  66 . 4  of the venturi tube  64 . 4  is centrally located between and partially enclosed by the side members of the mouth piece  300  in this example. As seen in  FIG. 45 , annular groove  74 . 4  is formed in this example via flange  68 . 4  of the venturi tube  64 . 4  and an outer end  306  of the circuit board cover  144 . 4 . The groove couples with corresponding flanges of the face mask  76 . 4  in a substantially similar manner as described in  FIG. 11  for device  50 . 
     Referring to  FIG. 42 , the device  50 . 4  with its mouth piece is shaped to also enable a patient to operate the device by wrapping their lips about the proximal end of the venturi tube. The side members  302  and  304  are shaped for alignment with the mask. 
     As seen in  FIG. 41 , the sensor assembly  120 . 4  comprises a single, integrated curved outer wall  138 . 4  in this example. The front walls  130 . 4  and  131 . 4  of the sensor assembly are likewise integrally formed and comprising a unitary whole. As seen in  FIG. 45 , the circuit board cover  144 . 4 , oxygen sensor cover  145 . 4  and mouth piece  300  are integrally coupled together and form a unitary whole in this example. 
     As seen in  FIG. 46 , the oxygen sensor  232 . 4  of device  50 . 4  includes a first oxygen port  234 . 4  connected to and in fluid communication with the proximal end  66 . 4  of the venturi tube  64 . 4  via proximal sample port  110 . 4  in this example. The second oxygen port  236 . 4  of the oxygen sensor is connected to and in fluid communication with the ambient air/atmosphere  308  via conduit  222 . 4  and open air port  310 . The oxygen sensor  232 . 4  of device  50 . 4  is thus in communication with ambient air in this embodiment. Device  50 . 4  so configured may allow for better purging of the oxygen sensor  232 . 4 . As seen in  FIG. 41 , the open air port extends through the outer wall  138 . 4  of sensor assembly  120 . 4  and is adjacent to the top  52 . 4 , side  60 . 4  and front  58 . 4  of the device  50 . 4  in this example. 
     Referring to  FIG. 46 , the differential pressure sensor  176 . 4  of the device includes a first pressure sensor inlet  170 . 4  connected to and in fluid communication with the proximal end  66 . 4  of the venturi tube  64 . 4  via proximal sample port  108 . 4  in this example. The other pressure sensor inlet  168 . 4  is connected to and in fluid communication with the ambient air/atmosphere  308  via conduit  172 . 4  and open air port  312 , which may be the same as open air port  310 . The pressure sensor  176 . 4  of device  50 . 4  is thus in communication with ambient air in this embodiment. Device  50 . 4  so configured may result in a more reliable differential pressure reading, thereby resulting in more accurate flow measurement. 
     As seen in  FIGS. 44 and 45 , the second tapered portion  106 . 4  of the venturi tube  64 . 4  has a flared section  103 . The flared section extends from the distal end  84 . 4  of the venturi tube towards the proximal end  66 . 4  of the tube. As seen in  FIG. 41 , the flared section  103  of the second tapered portion  106 . 4  of the tube is generally annular. 
     Still referring to  FIG. 41 , the constriction  102 . 4  of venturi tube  64 . 4  is generally rectangular in cross-section in this example, with rounded corners as seen by corners  109  in  FIG. 43 . Referring back to  FIG. 41 , the second tapered portion  106 . 4  of the venturi tube  64 . 4  is thus generally rectangular in lateral cross-section at least in part, in a region inwardly positioned from flared section  103  in this example. However, this is not strictly required. 
     Referring to  FIGS. 44 and 45 , the first tapered portion  104 . 4  of the venturi tube  64 . 4  is also generally rectangular in lateral cross-section at least in part in this embodiment. However, here too this is not strictly required. 
       FIG. 47  shows a device  50 . 5  for measuring a user&#39;s oxygen-consumption according to a sixth aspect. Like parts have like numbers and functions as device  50 . 4  shown in  FIGS. 41 to 47  with decimal extension “.5” replacing decimal extension “.4” and being added for like parts not previously having decimal numbers. The device  50 . 5  is the same as described for device  50 . 4  with the following exceptions. 
     Device  50 . 5  further includes an electromechanically operated valve, in this example a solenoid valve  314 . The solenoid valve is an off-the-shelf component, in this example an 8 mm latching Series LX™ solenoid valve which may be purchased at Parker Hannifin Corp, having an address of Milton Parker Canada Division, 160 Chisholm Drive, Milton, Ontario, Canada. However, this is not strictly required and other types of electromechanically operated valve and/or solenoid valves may be used in other embodiments. 
     A first port  316  of the valve is connected to and in fluid communication with proximal sample port  110 . 5  in this example via conduit  318 . A second port  320  of the valve  314  is connected to and in fluid communication with port  181 . 5  of the environmental sensor  180 . 5 . The second portion of the valve is also connected to and in fluid communication with oxygen sensor port  234 . 5  of oxygen sensor  232 . 5 . The valve  314  is in communication with and interposed between the oxygen sensor  232 . 5  and the first tapered portion  104 . 5  of the venturi tube  56 . 5 . The environmental sensor  180 . 5  is in communication with the solenoid valve and the oxygen sensor  232 . 5 . 
     The valve  314  has a closed position in which fluid communication between the oxygen sensor  232 . 5  and the proximal sample port  110 . 5  is inhibited. Fluid communication between the environmental sensor  180 . 5  and the proximal sample port is also inhibited when the valve is closed. 
     The valve  314  is configured to be selectively actuated to open. The valve when opened promotes fluid communication between the oxygen sensor  232 . 5  and the proximal sample port  110 . 5 . The valve  314  also enables fluid communication between the environmental sensor  180 . 5  and the proximal sample port when the valve is open. 
     The solenoid valve positioned between the oxygen sensor  232 . 5  and proximal end  66 . 5  of the venturi tube  56 . 5  allows device  50 . 5  to control when the oxygen sensor  232 . 5  is purged with new gas. This allows the device to run in three modes: a calibration mode, a regular operation mode, and a humid operation mode. 
     Device  50 . 5  may comprise a different method of calibrating to obtain an ambient oxygen concentration level. The method includes normalizing the oxygen sensor signal with ambient pressure, temperature and relative humidity to inhibit drift caused by changes in elevation and environment. The method includes actuating the solenoid valve  314  to open only during a user inhale-phase in which the user inhales air through the device  50 . 5  with the air passing from the second tapered portion  106 . 5  thereof to the first tapered portion  104 . 5  thereof. The oxygen sensor  232 . 5  is in communication with ambient air, as shown by arrow of numeral  239 , and determines the ambient oxygen concentration level thereby. 
     According to one example, the solenoid valve  314  is only open during user inhale-phase for three consecutive breaths, allowing the oxygen cell to settle at exactly the ambient oxygen concentration level. After the end of the third breath, the device&#39;s processor determines whether a signal from the oxygen sensor is stable based on a pre-set threshold. If so, the processor uses this information as a baseline for measurement by assuming whatever value measured is an ambient oxygen level concentration. Thereafter, the device records pressure, temperature, and relative humidity information for said baseline via the environmental sensor. The processor uses one or more oxygen sensor compensation algorithms which take into account relative change in trend from the baseline. 
     This ambient concentration level, combined with the absolute pressure, temperature, and humidity measurements determined by the environmental sensor  180 . 5 , are used to calibrate the oxygen sensor for the current recording. This is similar to the calibration method for the device  50  of  FIGS. 1 to 31C , but instead of the user having to take four consecutive inhales, the solenoid valve  314  calibrates during regular, bidirectional user breathing. The unit may decide to recalibrate mid-way through a recording, should the elevation change by more than 100 meters, or the temperature change more than 5 degrees Celsius, for example. 
     The device  50 . 5  further includes a method of operation to obtain an oxygen concentration of the user&#39;s expired breath. The method includes actuating the solenoid valve  314  to open only during a user exhale-phase in which the user exhales air through the device with the air passing from the first tapered portion thereof  104 . 5  to the second tapered portion  106 . 5  thereof. The oxygen sensor  236 . 5  is in communication with the air passing through conduit  222 . 4  from proximal sample port  110 . 4  to open air port  310 , as shown by arrow of numeral  241 , and determines the oxygen concentration of the user&#39;s expired breath thereby. 
     The device  50 . 5  alternates between exhale-only sampling, and inhale-only sampling. During exhale-only sampling, the solenoid valve  314  is only open when the pressure sensor  176 . 5  determines that an exhale is occurring. The device  50 . 5  alternates between exhale-only sampling and inhale-sampling for three consecutive breaths before taking a stable expired oxygen concentration (FeO2) measurement and switching to inhale-only sampling. Sampling three consecutive exhales, instead of one-exhale one-inhale, may allow for a more accurate FeO2 reading, resulting in more accurate measurement of conventional oxygen consumption (VO2). During inhale-only sampling, the solenoid valve  314  is only open when the pressure sensor  176 . 5  determines that an inhale is occurring. This inhale phase serves to desiccate the gas sample line with dry ambient air to ensure that the oxygen sensor  232 . 5  does not get too humid or flooded with water accidentally. 
     In humid operation mode, if the environmental sensor humidity reading exceeds some level—for example 80% relative humidity—then the device will perform a modified regular operation. Instead of three exhales followed by three inhales, the device will monitor/measure three exhales followed by six inhales, until the environmental sensor humidity reading has decreased to a safe level (70% relative humidity). If the relative humidity exceeds 90%, the device  50 . 5  will enter inhale-only purge mode, until the relative humidity has decreased below 80%. 
       FIG. 48  shows a device  50 . 6  for measuring a user&#39;s oxygen-consumption according to a seventh aspect. Like parts have like numbers and functions as device  50 . 5  shown in  FIG. 47  with decimal extension “.6” replacing decimal extension “.5” and being added for like parts not previously having decimal numbers. The device  50 . 6  is the same as described for device  50 . 5  with the following exceptions. 
     The device includes a desiccant tube  228 . 6  positioned along conduit  318 . 6 . The device  50 . 6  further includes a drying agent  231 . 6  adjacent to and surrounding the desiccant tube  228 . 6 . The drying agents is in the form of silicate gel beads in this example. However, this is not strictly required and other drying agents may be used in other embodiments. 
     The desiccant tube  228 . 6  is between and in communication with the environmental sensor  180 . 6  and the proximal end  66 . 6  of the venturi tube  64 . 6  via proximal sample port  110 . 6 . The desiccant tube  228 . 6  is also between and in communication with the oxygen sensor  232 . 6  and the proximal sample port. 
     Solenoid valve  314 . 6  is between oxygen sensor port  236 . 6  and open air port  310 . 6  in this embodiment. The solenoid valve is thus between and in communication with the oxygen sensor  232 . 6  and ambient air. The solenoid valve  314 . 6  is also between and in communication with the environmental sensor  180 . 6  and ambient air. 
     The solenoid valve so positioned and when closed, inhibits ambient air from passively diffusing into the oxygen sensor  232 . 6 , whereas the conduits  222 . 6 ,  224 . 6  and  318 . 6  are sufficient long that that air from the venturi tube  64 . 6  does not have the same effect on the oxygen sensor in this embodiment. 
     It will be appreciated that many variations are possible within the scope of the invention described herein. For example, various screws are shown and described to hold the various parts of the device  50  together in the embodiments herein described; however, this is not strictly required. 
     In an alternative embodiment, the user may directly operate the device without a mask, for example. 
     Additional Description 
     Examples of devices for measuring a user&#39;s oxygen-consumption have been described. The following clauses are offered as further description.
     (1) A device for measuring a user&#39;s oxygen-consumption, the device comprising: a venturi tube including a first tapered portion, a second tapered portion that is more tapered compared to the first tapered portion, and a constriction between said portions thereof; a pressure sensor in communication with the first tapered portion of the venturi tube; and an oxygen sensor in communication with the first tapered portion of the venturi tube.   (2) The device of clause 1, wherein the oxygen sensor is a passive sensor.   (3) The device of any preceding clause, wherein the pressure sensor is a differential pressure sensor.   (4) The device of any preceding clause, wherein the pressure sensor is in communication with the constriction.   (5) The device of any preceding clause, wherein the oxygen sensor is in communication with the constriction.   (6) The device of any one of clauses 1 to 3, wherein the pressure sensor is in communication with ambient air.   (7) The device of any one of clauses 1 to 3, wherein the oxygen sensor is in communication with said ambient air.   (8) The device of any preceding clause, wherein the venturi tube has a proximal end through which exhalations enter into the device and a distal end through which inhalations enter into the device.   (9) The device of any preceding clause, wherein the first tapered portion of the venturi tube is substantially oval-shaped in lateral cross-section.   (10) The device of any preceding clause, wherein the second tapered portion of the venturi tube is substantially circular in lateral cross-section.   (11) The device of any one of clauses 1 to 6, wherein the venturi tube has a laterally-extending, cross-sectional first plane and a laterally-extending, cross-sectional second plane which extends perpendicular to the first plane, and wherein the first tapered portion of the venturi tube tapers in a direction extending along the first plane and has a substantially constant diameter at least in part in a direction extending along the second plane.   (12) The device of any one of clauses 1 to 6, wherein the venturi tube has a proximal end through which exhalations enter into the device, the first tapered portion being adjacent to said proximal end of the venturi tube, wherein the venturi tube has a laterally-extending, cross-sectional first plane along which the first tapered portion of the venturi tube tapers and wherein the venturi tube has a laterally-extending, cross-sectional second plane which extends perpendicular to the first plane, the first tapered portion of the venturi tube in a direction extending along the second plane being flared adjacent to the proximal end of the venturi tube and having a substantially constant diameter as the first tapered portion of the venturi tube extends to the constriction.   (13) The device any one of clauses 4 to 5, further including a first pair and a second pair of conducts, wherein the pressure sensor is in communication with the constriction and the proximal end of the venturi tube via the first pair of conduits and wherein the oxygen sensor is in communication with the constriction and the proximal end of the venturi tube via the second pair of conduits.   (14) The device of any preceding clause, wherein the first tapered portion of the venturi tube is substantially oval-shaped in lateral cross-section and wherein the venturi tube includes sample ports located in regions of the first tapered portion of the venturi tube that are flattest.   (15) The device of any preceding clause, further including a processor that receives input from the pressure sensor to determine measure the instantaneous flow rate through the device, the processor also receiving input from the oxygen sensor to determine change in oxygen concentration between inhalations and exhalations of air through the device, volume measurement being determined thereby.   (16) A device for measuring a user&#39;s oxygen-consumption, the device comprising: a venturi tube having a constriction and being shaped to promote laminar flow through an exhale-receiving portion thereof; a pressure sensor in communication with the constriction and the exhale-receiving portion of the venturi tube; a first desiccant tube in communication with the constriction and a second desiccant tube in communication the exhale-receiving portion of the venturi tube; and an oxygen sensor between and in communication with said desiccants tubes.   (17) A method of calibrating the device of clause 12 to obtain an ambient oxygen sensor value or environmental value, the oxygen sensor emitting an oxygen sensor signal, and the method comprising: normalizing the oxygen sensor signal with ambient pressure, temperature and relative humidity to inhibit drift caused by changes in elevation and environment; purging the venturi tube by having a user take two or more consecutive, deep inhales of air through the device without exhaling through the device; measuring and storing via a processor the ambient oxygen sensor value or environmental value thereafter.   (18) The device of any one of clauses 1 to 15, further including an electromechanically operated valve in communication with and interposed between the oxygen sensor and the first tapered portion of the venturi tube.   (19) The device of clause 18 wherein the valve is a solenoid valve.   (20) A device for measuring a user&#39;s oxygen-consumption, the device comprising: a replaceable venturi tube having a proximal end connectable to a breath-receiving member and a distal end through which air enters during inhalation; and a sensor assembly comprising two parts hingedly connected together and between which the venturi tube is selectively received.   (21) The device of clause 20 wherein each of the parts is arc-shaped in cross-section.   (22) The device of any one of clauses 20 to 21, wherein the parts of the sensor assembly hingedly connect together at first ends thereof and include a latch mechanism at second ends thereof for selectively coupling together.   (23) The device of any one of clauses 20 to 22, wherein the ends of the venturi tube are outwardly extending flanges and wherein the venturi tube includes an annular outer surface extending between the flanges and about which the sensor assembly selectively extends, the outer surface of the venturi tube being oval-shaped in cross-section.   (24) The device of any one of clauses 20 to 23, wherein the sensor assembly is moveable from an open position in which the parts thereof angled outwards from each other, to a closed position, the parts of the sensor assembly when in the closed position forming an aperture through the venturi tube is received.   (25) The device of any one of clauses 20 to 24, wherein the aperture is oval-shaped in cross-section.   (26) A kit comprising the device of any one of clauses 20 to 25, and further including additional venturi tubes of varied shapes, the kit thus being customizable to desired test conditions and criteria.   (27) In combination, a breath-receiving member and the device of any one of clauses 20 to 25, the breath-receiving member being a facemask.   (28) A kit for measuring a user&#39;s oxygen-consumption, the kit comprising: a plurality of replaceable venturi tubes of different shapes, each having a proximal end connectable to a breath-receiving member and a distal end through which air enters during inhalation; and a sensor assembly comprising two parts hingedly connected together and between which a respective one of the venturi tubes is selectively received.   (29) The kit of clause 28, wherein first and second ones of the venturi tubes have constrictions that are oval-shaped in cross-section, the constriction of the first one of the venturi tubes being larger in cross-section relative to the constriction of the second one of the venturi tubes, and wherein a third one of the venturi tubes has a constriction that is circular in cross-section, the third one of the venturi tubes has a cross-sectional area that is smaller than that of the first one of the venturi tubes and larger than that of the third one of the venturi tubes.   (30) The kit of any one of clauses 28 and 29, wherein each of the venturi tubes includes a first tapered portion, a second tapered portion and a constriction in communication with and between said tapered portions, each of the constrictions have a width and a height, the widths of the constrictions being substantially the same, the constriction of a high-intensity exercise type one of the venturi tubes being longer than that of the other ones of the venturi tubes, and the constriction of a resting/walking type one of the venturi tubes being shorter than the rest of the venturi tubes.   

     It will further be understood by someone skilled in the art that many of the details provided above are by way of example only and are not intended to limit the scope of the invention which is to be determined with reference to at least the following claims.