Abstract:
A method and apparatus to assess cardiac function in a subject involves supporting a probe in the trachea for transmitting movement of the trachea in response to heart function. The transmitted movement is detected by a sensor which generates a waveform signal. The waveform signal is displayed and assessed to determine cardiac function. By directly engaging the trachea, the apparatus and method of the present invention are sensitive to very small accelerations, velocities or displacements of the trachea to permit accurate measurement of cardiac function.

Description:
FIELD OF THE INVENTION 
     This invention relates to an apparatus and method to assess cardiac function in a subject. 
     BACKGROUND OF THE INVENTION 
     Non-invasive methods of determining cardiac functioning include the following: 
     a) Mechanical methods that include pulse recording of the jugular, carotid artery or apexcardiogram. This group also includes sound recordings, for example, use of the stethoscope and phonocardiographic techniques. 
     b) Electrical techniques which are best exemplified by the electrocardiogram (ECG). 
     c) Relatively more recent techniques include imaging techniques, for example echocardiography, nuclear cardiography, radiographic techniques and magnetic resonance imaging (MRI). 
     All of the above the mechanical methods, which rely on vibration and sound recording, involve measuring the movements of the body resulting from cardiac activity. This means that the mass of the body is part of the recording means. This is not desirable. Chest movements, for example, are dependent upon chest shape, and sound recording is dependent upon the amount of fat and the condition of the lung tissue for its amplitude. An accurate trace pattern is difficult to achieve and these techniques are therefore of limited diagnostic value. 
     Electrical methods measure only the electrical field generated by the heart. This cannot provide a direct measure of the cardiac forces generated by the heart and therefore these methods are incapable of evaluating the heart&#39;s function as a pump. 
     Imaging techniques have limited ability to evaluate the force of the heart&#39;s contraction. 
     Thus none of the above methods is capable of measuring the force of the heart&#39;s contraction. As a result the evaluation of the condition of the myocardium is not possible. Heart attack risk cannot be determined by any known non-invasive method. A patient may be diagnosed as normal and yet die of a heart attack shortly after the diagnosis. 
     Relevant literature includes the following text books: Clinical Phonocardiography and External Pulse recording by Morton E. Tavel, 1978 Yearbook, Medical Publishing Inc.; Non-Invasive Diagnostic Techniques in Cardiology by Alberto Benchimol, 1977, The Williams and Wilkins Co.; and Cardiovascular Dynamics by Robert F. Rushmer, 1961, W.B. Saunders Company. 
     Rushmer first postulated that acceleration and deceleration of the various structures of the heart and blood explain heart sounds as well as their modifications with changing dynamic conditions. As acceleration is a function of force, the aortic blood acceleration is a manifestation of the force that sets the cardiac structures in motion. Other forces originate from the pressure gradient between the aorta and the left ventricle, which acts over the closed semilunar valve. The valve behaves like a circular, stretched membrane in which the thin, flexible leaflets can be stretched in all directions by the differential aorta—ventricular pressure. The energy of the rapid ejection phase of the left ventricle expands the aorta and the stored energy is in direct relationship to its wall elasticity. Measurement of the amplitude of the wave created after the maximum ejection rate, is a measure of the elasticity of the wall of the aorta. The elasticity of the aortic valve can also be measured by measuring the amplitude of the wave created after the valve is closed. The most sensitive indicators of performance are the rates of change of momentum as indicated by changes in velocity of the blood and heart mass. This acceleration is directly indicative of myocardial contractility which is one of the most difficult parameters to measure. In 1964 Rushmer established a direct relationship between the initial ventricular impulse and the peak flow acceleration during the systolic ejection—see Circulation—Volume 29: 268-283 1964. 
     Commonly owned U.S. Pat. No. 5,865,759 discloses a method and apparatus for measuring cardiac function using an external sensor positioned against the thyroid cartilage in the neck. The subject matter of U.S. Pat. No. 5,865,759 is incorporated herein by reference. The sensor detects the response of the thyroid cartilage to heart function and generates a signal that is fed to a signal processing unit to generate a waveform signal characteristic of heart function for assessment by a user. The apparatus and method of U.S. Pat. No. 5,865,759 provide reliable, accurate and inexpensive assessment of cardiac function. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved apparatus and method for assessment of cardiac activity by directly measuring the movement of the trachea. The apparatus and method rely on introduction of a sensing apparatus into the throat of the user to engage with the trachea. This arrangement is sensitive to very small movement forces and permits accurate measurement of cardiac function with even finer details. 
     Accordingly, the present invention provides apparatus to assess cardiac function in a subject comprising: 
     a probe insertable and supportable in the trachea to transmit movement of the trachea in response to cardiac function through the probe; 
     a sensor to detect the transmitted movement of the trachea and generate a signal indicative of the movement of the trachea; and 
     a signal processing unit to receive the signal from the sensor and generate a waveform signal characteristic of the cardiac function. 
     The probe can be a hollow tube having an internal passage to deliver air to the subject and whereby movement of the hollow tube serves to transmit the movement of the trachea. 
     Alternatively, the apparatus can employ an endotracheal tube for housing the probe in which case the probe comprises a tubular member having an inner end adapted to protrude from the endotracheal tube and engage against the carina region at which the trachea bifurcates into the lungs. 
     The present invention also provides apparatus to assess cardiac function in a subject comprising: 
     a tube insertable into the mouth of a subject such that a first end extends into the trachea and a second end protrudes from the mouth; 
     a flexible support extendable from the tube to engage the trachea and suspend the tube within the trachea for movement of the tube along the longitudinal axis of the tube; 
     a rigid anchor extendable from the tube to engage the trachea and transmit movement of the trachea due to cardiac function to the tube; 
     a sensor to sense the movement of the tube and generate a signal indicative of the movement of the trachea; and 
     a signal processing unit to receive the signal from the sensor and generate a waveform signal characteristic of the cardiac function. 
     In a still further aspect, the present invention provides a method of assessing cardiac function in a subject comprising: 
     supporting a probe in the trachea to transmit movement of the trachea in response to cardiac function; 
     sensing the movement transmitted by the probe; 
     generating and displaying a waveform signal based on movement transmitted by the probe; and 
     assessing the waveform signal to determine cardiac function. 
     The apparatus and method of the present invention are intended to be used primarily with human patients, however, the subject matter also finds application with animal subjects. The apparatus and method can be used with a conscious subject or when the subject is anaesthetised, for example, during surgery. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Aspects of the present invention are illustrated, merely by way of example, in the accompanying drawings. 
     FIG. 1 is a schematic view of a first embodiment of the apparatus of the present invention which relies on movement of a tube within the trachea to transmit movement of the trachea due to cardiac function; 
     FIG. 1 a  is a detail view showing the manner of attachment of the sensor to the tube of FIG. 1; 
     FIG. 2 a  is a detail view of the anchor for coupling the tube to the trachea in the folded position; 
     FIG. 2 b  is a detail view of the anchor in the expanded position; 
     FIG. 3 is a detail view of the retaining strap for holding the tube of the first embodiment in place; 
     FIG. 4 shows a second embodiment of the apparatus of the present which relies on a probe inserted through an endotracheal tube to measure the movement of the carina region of the trachea; 
     FIG. 5 is a detail section view through the mounting assembly that supports one end of the probe of the second embodiment via a movable carriage; 
     FIG. 5 a  is a detail view of an alternative sensor that can be used in apparatus of the second embodiment; 
     FIG. 5 b  is a detail view taken along line  5 — 5  in FIG. 5 showing the wheel arrangement that permits movement of the carriage; 
     FIG. 6 shows an endotracheal tube used with the probe of the second embodiment; 
     FIGS. 7 a  and  7   b  show the probe with an inner end having locating fingers in a collapsed position to facilitate insertion through the endotracheal tube and an extended position to locate the inner end on the carina region; 
     FIG. 8 shows the probe and mounting assembly of the second embodiment prior to insertion into the endotracheal tube of FIG. 6; and 
     FIG. 9 is a schematic view of the display unit used with the apparatus of the present invention to show typical cardiac events and inputs from the sensors. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The apparatus and method of the present invention are directed to a new system for assessing cardiac function in a subject. Essentially, the apparatus of the present invention comprises a probe  4  insertable and supportable in the trachea of a subject to transmit movement of the trachea due to cardiac function. The transmitted movement of the trachea is detected by a sensor which generates a signal indicative of the trachea movement. This signal is passed to a signal processing unit which generates a waveform signal characteristic of the cardiac function. Details of the processing of the signal are disclosed in commonly owned U.S. Pat. No. 5,865,759 which also discloses externally monitoring the movement of the thyroid cartilage in order to monitor heart function. The present invention is directed to a n improved system which relies on internal monitoring of the movement of the trachea to provide an even more accurate picture of the heart function. The trachea is the passage reinforced by rings of cartilage through which air reaches the bronchial tubes from the larynx. 
     FIGS. 1-3 b  illustrate a first embodiment of the apparatus of the present invention in which the probe is a hollow tube  4  insertable through the mouth and throat of a user into the trachea and supportable therein. Movement of the tube itself serves to transmit the movement of the trachea. 
     Referring to FIG. 1, hollow tube  4  has a structure similar to a conventional intubation device in that there is a hollow interior  6  that extends between an outer end  8  and an inner end  10  formed with a structure known as a Murphy Eye which ensures that the inner end does not become blocked. Tube  4  is insertable into the mouth of a subject such that inner end  10  extends into the trachea and outer end  8  protrudes from the mouth. Outer end  8  includes an attachment for ready connection to a ventilator unit (not shown) which can deliver air through tube interior  6  to inner end  10  and the trachea to allow a subject to breathe while the tube is in place. 
     A flexible support in the form of inflatable cuffs  14  and  16  are extendable from the tube to engage the anatomy of the subject and suspend tube  4  within the trachea for longitudinal movement. Lower cuff  14  is positioned to engage with the trachea. Upper cuff  16  is positioned within the mouth of the subject to prevent opposition to tube motion by mouth structures such as the teeth or tongue Cuffs  14  and  16  are shown in their inflated state in FIG. 1 extending radially outwardly from tube  4 . As with a conventional intubation device, the side walls of tube  4  include sealed embedded air passages to permit inflation and deflation of cuffs  14  and  16 . A separate syringe  18  or  20  is connected via line  18 ′ or  20 ′, respectively, to embedded air passages for independent control of each cuff. Syringes  18  and  20  include a check valve  19  to ensure that the cuffs remain inflated. Cuffs  14  and  16  are formed from soft, pliable plastic and dimensioned to be inflatable to a diameter that securely engages with the walls of the trachea or the mouth of the subject to reliably suspend tube  4  in place within the trachea. Two spaced cuffs  14  and  16  are shown supporting each end of tube in FIG. 1, however, it will be readily apparent to a person skilled in the art that additional cuffs may used intermediate the ends of the tube. 
     Cuffs  14  and  16  are sealably mounted to the external surface of tube  4  by annular end walls  22  that extend generally radially from the external surface. Transverse flexing of end walls  22  permits longitudinal movement of tube  4  in the direction indicated by arrow  24  within the trachea. On deflation, cuffs  14  and  16  collapse against external surface of tube  4  to permit ready insertion or removal of tube  4  from the trachea and mouth of the subject. 
     In order to ensure that tube  4  moves with the trachea in response to cardiac function, tube  4  also includes a rigid anchor in the form of at least two hinged flanges  30  that are extendable radially outwardly from the external surface of tube  4  to engage the trachea. Each flange  30  is pivotally connected via a hinge joint to collar  32  which encircles tube  4 . Preferably, an inflatable bladder  34  is provided inside flanges  30  between the flanges and tube  4 . Bladder  34  acts to pivot the flanges between a folded position against the tube and a radially expanded position extending between the tube and the trachea. FIG.  1  and FIG. 2 a  show flanges  30  in the folded position in which the flanges lie substantially flat against the side of tube  4 . FIG. 2 b  shows the flanges in the radially expanded position due to inflation of bladder  34 . When in the expanded position, flanges  30 , which are preferably formed from a rigid plastic, engage against the walls of the trachea to anchor tube  4  to the trachea such that tube  4  moves with the trachea. Tube  4  is supported by cuffs  14  and  16  within the trachea for longitudinal movement so that any movement of the trachea due to beating of the heart is transmitted by flanges  30  to tube  4 . Inflation of cuff  34  is controlled manually by syringe  36  via line  36 ′ (FIG.  1 ). A check valve  19  is also provided. Alternatively, a small air pump  38  can be programmed under computer control to vary pressure in bladder  34  so that the pressure is increased to a predetermined value for a period and reduced to a different pressure for another period. Operating in this manner prevents tissue necrosis in the trachea due to pressure of rigid flanges  30  against the trachea for extended periods. 
     When inserted into the trachea, tube  4  has a tendency to move outwardly and must be restrained from doing so. In the apparatus of the present invention, a retainer member  39  is preferably provided adjacent outer end  8  of tube  4  to prevent excess outward movement of tube  4 . FIG. 3 shows retainer  39  in the form of a strap and buckle connectable about the neck of the subject. The strap includes a circular opening  41  dimensioned to permit free movement of outer end  8  of tube  4  therethrough while preventing passage of cuff  16 . Therefore, abutting of cuff  16  against the strap serves to prevent excess outward movement of tube  4 . 
     Movement of tube  4  is detected by sensor  40  attached to the outer end  8  of tube  4 . As best shown in FIG. 1 a , sensor  40  can be clipped to the tube via arms  40   a  to permit convenient interchange of sensors. In all cases, sensor  40  is selected to generate a signal indicative of movement of the tube and thus the trachea. Sensor  40  is preferably an accelerometer which senses the acceleration or velocity of tube  4 . Alternatively, sensor  40  can be selected to measure displacement of tube  4 . The signal generated by sensor  40  is sent via data line  42  to a data acquisition unit  44 . The data acquisition unit includes a signal processing unit  45  to receive the signal from sensor  40  and generate a waveform signal characteristic of cardiac function. Signal processing unit  45  includes an amplifier to amplify the signal from the accelerometer and a digitizer to digitize the amplified signal. A signal analysis unit is then used to analyze the amplified signal and generate a waveform signal characteristic of cardiac function. The resulting waveform signal is displayed on a monitor  46  for ease of inspection. The data acquisition unit  44 , signal processing unit  45  and display unit  46  are preferably organized into a control unit  50 . Control unit  50  includes a computer with keyboard  55  running appropriate software to acquire, manipulate, store and display the data provided by sensor  40 . As shown in FIG. 9, control unit  50  can also include inputs for additional sensor data and electrocardiogram (ECG) readings for simultaneous display on monitor  46  for comparison purposes. 
     In use, tube  4  is lubricated and manipulated according to standard procedures of intubation to insert the tube through the mouth of the user into the trachea with cuffs  14  and  16  collapsed and flanges  30  in the folded position. Cuffs  14  and  16  are then inflated using syringes  18  and  20 . Cuff  16  is located in the mouth and cuff  14  seals the airway between the tube and trachea. Together the cuffs co-operate to suspend tube  4  within the trachea for free vibratory movement in response to movement of the trachea. Flanges  30  are moved to the expanded position to contact the trachea and lock the tube and trachea together so that tube  4  transmits any movement of the trachea due to the heart&#39;s motion. Movement of tube  4  is sensed by sensor  40  clipped to the outer end of the tube. Sensor  40  is used to generate a waveform signal based on movement of the tube which is used to determine cardiac function. By inserting a tube directly into the trachea and using the tube itself to detect movement of the trachea, more accurate and reliable data regarding cardiac function can be acquired than was previously possible. 
     FIGS. 4-8 illustrate a second embodiment of the present invention in which the probe for insertion into the trachea comprises a tubular member  8  which is inserted through an endotracheal tube  50  to directly engage and monitor the movement of the carina region  52  where the trachea  54  bifurcates into the bronchial tubes  56 . 
     Referring to FIGS. 4 and 5, the apparatus of the second embodiment includes a mounting structure comprising a box housing  60  that supports one end of tubular member  8  to manipulate and manoeuvre the tubular member for insertion into the trachea of a subject via the mouth. Housing  60  includes tubular port  61  from which tubular member  8  protrudes. Housing  60  also includes an encircling clamp  62  and ball joint coupling  63  for connecting the housing to mounting bracket  64 . Bracket  64  supports the entire apparatus and permits the apparatus to be oriented for ease of insertion of tubular member  8  into the trachea of a subject. 
     FIG. 5 is a detail section view through housing  60 . Housing  60  includes a movable carriage  66  to receive the outer end  74  of tubular member  8 . Carriage  66  is movably supported by wheels  68  on rails  70  to permit adjustment of the position of tubular member  8  so that the member is biased against carina region  52  of the subject as will be explained in more detail below. To further support tubular member  8 , wheels  68  are preferably mounted to the tubular member in the region of tubular port  61  to engage rails  70  mounted to the inner walls of the port. FIG. 5 b  is a section view taken along line  5 — 5  of FIG. 5 showing details of a preferred arrangement in which each wheel  68  includes a central channel to engage rail  70 . 
     Tubular port  61  includes a window  61   a  to monitor the position of an indicator  100  fixedly mounted to tubular member  8 . Indicator  100  in window  61   a  allows a user to determine the position of tubular member  8  within housing  60 . 
     Referring to FIG. 6, there is shown an endotracheal tube  50  used with the apparatus of the present embodiment. Tube  50  includes an inflatable cuff  15  that is controlled by syringe  53  via line  53 ′ to retain tube  50  in the trachea of a subject. Tube  50  includes a main port  57  to receive end  72  of tubular member  8 . Tubular member  8  is fed through the interior of endotracheal tube  50  via port  57  to protrude from end  58  for positioning against the carina. Endotracheal tube  50  also includes an auxiliary port  59  connectable to a ventilator for providing air to the subject through the interior of tube  50 . As best shown in FIG. 4, port  57  of endotracheal tube  50  is releasably connectable to tubular port  61  of housing  60  to form a continuous passage to house tubular member  8  when inserted into the trachea of a subject. 
     As best shown in FIG. 5, the positioning of movable carriage  66  and thus the position of the tubular member in the trachea of the subject is preferably controlled by a spring biasing system. In the illustrated embodiment, the biasing system relies on spring loaded clamps  65  arranged in opposed pairs at each end of housing  60 . Each clamp  65  controls a line connected to movable carriage  66 . Fixed length lines  67  (preferably of nylon cord) extend from one side of carriage  66  while elastic lines  69  extend from the opposite side to exert a biasing force that tends to move the carriage and the attached tubular member  8  toward the subject. Lines  67  are connected to handle  73 . Each clamp  65  includes a control knob  71  that is normally biased inwardly to grip and hold the line extending through the clamp. Pulling the control knob releases the clamp to allow movement of the lines. In use, the clamps controlling lines  67  are released and handle  73  is pulled to move carriage  66  and tubular member  8  to a predetermined position as shown by indicator  100  in port window  61   a . Carriage  66  is moved against the return force exerted by stretching of elastic cords  69 . The clamps for lines  67  are then engaged to hold the lines in place. This procedure locks the movable carriage  66  into a parked position for initial insertion of the tubular member into the trachea of a subject via endotracheal tube  50 . After insertion of tubular member  8 , the clamps  65  controlling lines  67  are released with the result that tubular member  8  mounted to carriage  66  will be biased against the carina of the subject by the tension force in stretched elastic lines  69 . The clamps  65  controlling elastic lines  69  are provided to permit adjustment of the tension in the elastic lines. 
     As best shown in FIGS. 7 a  and  7   b , tubular member  8  comprises an inner end  72  adapted to protrude from the endotracheal tube  50  and engage against carina region  52 , and outer end  74  supported in movable carriage  66  of housing  60 . Tubular member  8  has substantially rigid side walls  76  defining a sealed interior filled with a fluid  78  communicating the inner and outer ends. Preferably, side walls  76  include a bendable region  80  formed with corrugations to accommodate curvature of the trachea. 
     Inner end  72  and outer end  74  of tubular member  8  include resilient surfaces  82  and  84 , respectively, that communicate via the fluid in sealed interior  78 . Movement of resilient surface  82  at inner end  72  due to movement of the carina region  52  is transmitted by fluid  78  to resilient surface  84  at outer end  74 . To assist in locating inner end  72  of tubular member  8  on the carina region, collapsible locating fingers  86  are provided. Fingers  86  are movable between a collapsed position shown in FIG. 7 a  and a extended position shown in FIG. 7 b . In the collapsed position, fingers  86  are aligned with the side walls of tubular member  8  to facilitate insertion through endotracheal tube  50  and the trachea. In the extended position, fingers  86  are positioned to engage the carina region to maintain resilient surface  82  on the carina region. 
     Fingers  86  are movable between the collapsed and extended positions by hydraulic pressure created by withdrawing fluid  78  from or injecting fluid  78  into the interior of tubular member  8 . The inner and outer ends of tubular member  8  are formed as collapsible bulbs  77  and  79  that include resilient surfaces  82  and  84 . A syringe  87  with check valve  19  communicates with the interior of tubular member  8  via line  87 ′ to withdraw or inject fluid to collapse or inflate the bulbs. At inner end  72 , bulb  77  acts to bias fingers  86  between the collapsed and extended positions. 
     As best shown in FIG. 5, resilient surface  84  of outer end  74  of tubular member  8  is positioned against sensor  90  which is mounted to carriage  66  by resilient lines  87 . Any movement of resilient surface  82  at inner end  72  of member  8  is transmitted by fluid  78  to resilient surface  84  for detection by sensor  90 . In FIG. 5, sensor  90  comprises an accelerometer to measure the acceleration and velocity of resilient surface  84  in response to movement of resilient surface  82  at the carina region. Alternatively, as shown in FIG. 5 a , sensor  90  can be a pressure transducer mounted directly to the end of tubular member  8  to replace bulb  84  and to detect pressure changes at the inner end  74 . 
     In the arrangement of the second embodiment, it is also possible to include an additional sensor  94  mounted to the rigid side walls of tubular member  8  to detect acoustic energy transmitted through the side walls of the tubular member by the beating heart. In this manner, the sounds associated with cardiac function can also be recorded. 
     The various sensors  90  and  94  of the second embodiment are connectable via data lines  90 ′ and  94 ′ to the data acquisition unit shown in FIG. 9 for analysis and display of the collected data relating to cardiac function. As best shown in FIGS. 4 and 8, housing  60  is provided with ports  96  to permit syringe line  87 ′ and data lines  90 ′ and  94 ′ to extend from the interior of housing  60  to the exterior. Syringe line  87 ′ connects to syringe  87  via check valve  19 . 
     Using the apparatus of the second embodiment involves lubricating endotracheal tube  50  with a water soluble gel and intubating the subject in a conventional manner. When cuff  51  is well within the trachea and within a few centimeters of the carina, the cuff is inflated by syringe  87 . Tubular member  8  is positioned within housing  60  using handle  73 . FIG. 8 shows the apparatus prior to insertion of tubular member  8  into endotracheal tube  50  with fingers  86  in the collapsed position. Tubular member  8  is inserted through endotracheal tube via port  55 . The inner end  72  of tubular member  8  is pushed forward until the end exits the endotracheal tube about 2 cm at which point the endotracheal tube  50  is connected to tubular port  61  of housing  60 . Fluid  78  is injected into tubular member  8  by syringe  87  via line  87 ′ resulting in fingers  86  separating. Clamps  65  controlling lines  67  are slowly released and movable carriage  66  is moved by the biasing force of elastic lines  69  to carry tubular member  8  into engagement with the carina region. Resilient surface  82  of tubular member  8  abuts the carina while fingers  86  contact the sides of the carina region to assure proper positioning. Global movement of the heart is transmitted by the carina to the resilient surface  82 . As the carina moves in response to the forces of the heart, resilient membrane  82  transmits its acceleration and deceleration through fluid  78  to resilient surface  84  at outer end  74 . Accelerometer  90  is elastically attached and outputs to the data acquisition unit. An additional accelerometer sensor  94  having a higher frequency response outputs the acoustic energy received through the rigid walls  76  of tubular member  8 . This sound energy is fed to the data acquisition system via data line  94 ′. 
     When using the apparatus or method of the present invention, certain body positions are preferable for optimal recording of cardiac functions as follows: 
     1) Head bent slightly towards the chest. This position frees the trachea for movement. 
     2) Diaphragm pushed upwards. This position forces the heart against the bronchus for better transmission. 
     3) Sitting Position with the feet placed up on a rail 4″ higher than chair. This position compresses the diaphragm. The head is preferably bent towards the chest to free the trachea for movement. 
     4) Supine Position 
     5) On back with cushion under head inflated bag around abdomen with knees up. 
     6) Decubitus Position—legs folded against abdomen. 
     Although the present invention has been described in some detail by way of example for purposes of clarity and understanding, it will be apparent that certain changes and modifications may be practised within the scope of the appended claims.