Abstract:
A system, flow meter, and method for measuring gas flow information, such as respiratory information. In an exemplary embodiment, the flow meter may include a cylindrical body that allows the respiratory gas to flow through and at least one hot wire disposed within the cylindrical body. Further, the flow meter may include a bridge circuit that includes the at least one hot wire as a resistive element and an extraction circuit that extracts a signal from the bridge circuit indicating the respiratory volume. A first filter and second filter may be disposed at an output side of the extraction circuit, and a detection circuit may be included that detects the respiratory flow rate from the output signal of the first filter and detects sound, such as snoring from the output signal of the second filter.

Description:
[0001]    This application claims priority to Japanese Patent Application No. 2008-311290 filed on Dec. 5, 2008 in the Japan Patent Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The disclosure relates generally to flow meters, and more particularly to a gas flow system, flow meter, sound detector, and method for measuring gas flow rate and sound, such as respiratory flow rate and snoring, using at least one hot-wire-type sensor. 
         [0004]    2. Description of the Related Art 
         [0005]    In recent years, respiratory flow rate and snoring have become basic parameters needed for diagnosing sleep apnea syndrome (hereinafter referred to as “SAS”). The widely used traditional method is to attach a sensor near the throat to detect the snoring as audio signals or as vibrating signals. This method requires a totally separate sensor aside from the sensor for respiratory flow rate, and causes the problem of creating annoying and uncomfortable feelings for the patient from attaching the sensor. 
         [0006]    In the related art, there is also a method of utilizing a piezoelectric element that detects respiration and snoring from a living body as noted in Japanese Published Unexamined Patent Application No. 2006-212271. However, in this method, the output generated from the respiratory flow rate will vary depending on the attachment condition of the piezoelectric element, the shape of the mouth, or the size of opening of the mouth, etc. In addition, this method can only qualitatively measure the inhalation and exhalation flow rates because the piezoelectric element is exposed to the ambient air, and cannot measure quantitatively the respiratory flow rate. 
         [0007]    For the method described above, the device to detect the snoring is used for the purpose of controlling the respiratory flow rate. In this device, the pressure sensor is used to monitor and detect the airway pressure. The detected pressure signal is filtered, and then only those frequencies contained within the specified frequency bandwidth are obtained as the filtered pressure signal. This filtered pressure signal is compared against the threshold value. The vibration of the filtered pressure signal around the threshold is detected as the first vibration, and the standard period of the first vibration is determined. 
         [0008]    Furthermore, when there is a second vibration continuing within the filtered pressure signal and when this second vibration exceeds the threshold, the second vibration is detected and the period of the second vibration is determined. This second period is compared against the standard period in order to determine whether the second period is consistent with the standard period. If it is consistent, then the second vibration is determined as the snoring as noted in Japanese Patent Application Publication No. 2005-505329. 
         [0009]    However, in this device, the processing is very complex as described above, and the snoring cannot be detected simply by looking at the waveform. In addition, since the respiratory signal is measured from the airway pressure, if this device is applied to a patient with a low respiratory volume, such as an infant, sufficient pressure or the vibration cannot be obtained because of weak respiration, and the snoring cannot always be captured precisely. 
         [0010]    The present invention overcomes the aforementioned and other problems of the related art, and provides, as one aspect, a flow meter, such as a respiratory air information sensor that can appropriately detect the respiratory flow rate and snoring simultaneously. 
       SUMMARY OF THE INVENTION 
       [0011]    A first aspect of the disclosure provides a flow meter, such as a respiratory information sensor for measuring respiratory flow rate. The flow meter may comprise a body structured to allow gas to flow through; at least one hot wire installed within the body; a bridge circuit including at least one hot wire as a resistive element; an extraction circuit structured to extract one or more signals from the bridge circuit, and a detection circuit structured to detect a sound such as snoring from one or more outputs of the extraction circuit. 
         [0012]    According to the first aspect of the invention, the flow meter may further comprise one or more filters disposed at an output side of the extraction circuit and operable to process the one or more outputs of the extraction circuit and provide the processed outputs as output signals to the detection circuit. 
         [0013]    Further, a first of the one or more filters may be a low-pass filter and a second of the one or more filters may be one of a high-pass filter and a band-pass filter. 
         [0014]    A second aspect of the disclosure provides a method for measuring gas flow. The method may comprise increasing a temperature of a hot wire installed within a body above ambient; flowing gas, such as respiratory gas through the body; and detecting a change in current flowing through the hot wire and corresponding gas flow rate and sound. 
         [0015]    Further, the method may comprise determining a respiratory volume from the gas flow rate and/or detecting a direction of flow of the gas. 
         [0016]    A third aspect of the disclosure provides a system for measuring gas flow. The system may comprise a body structured to allow gas to flow through; at least one hot wire installed within the body; a bridge circuit including the at least one hot wire as a resistive element; an extraction circuit structured to extract one or more signals from the bridge circuit, a detection circuit structured to detect a sound from one or more outputs of the extraction circuit; a processor; and a memory, wherein the processor is structured to determine an amplitude of the sound in the gas flow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure, in which: 
           [0018]      FIG. 1  is a block diagram showing the configuration of an exemplary embodiment of a flow meter, such as a respiratory information sensor according to the present invention; 
           [0019]      FIG. 2  is a diagram showing an exemplary embodiment of a bridge circuit used in a flow meter according to the present invention; 
           [0020]      FIG. 3  is a diagram showing another exemplary embodiment of a bridge circuit used for differentiating the gas flow direction according to the present invention; and 
           [0021]      FIG. 4  is a diagram showing waveforms of a respiratory volume and snoring that are displayed by an exemplary embodiment of the flow meter according to the present invention. 
       
    
    
       [0022]    It is noted that the drawings of the disclosure are not to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The present invention will now be described more fully with reference to the accompanying drawings. A flow meter, such as a respiratory information sensor according to an exemplary embodiment of the invention is shown in  FIG. 1 . This embodiment of the respiratory information sensor utilizes the sensor section  10  that is configured such that the opening  21  at one end of the cylindrical body  20  is connected to the mask  11 . The mask  11  covers the mouth and nose of the patient and is configured to have all of the inhaled and exhaled gas flowing through the cylindrical body  20 . 
         [0024]      FIG. 1(   a ) shows an overall configuration of the respiratory information sensor and  FIG. 1(   b ) shows an enlarged diagram of the inside of the cylindrical body  20 . In the inside of the cylindrical body  20  where the respiratory flows through, three hot wires  22 A,  22 B and  22 C are placed and aligned adjacently in the longitudinal direction of the cylindrical body  20 . Of course, longitudinal placement of the hot wires does not preclude other configurations, such as placing the hot wires in a transverse direction, and the body may also take on some other shape than cylindrical. The hot wires  22 A,  22 B and  22 C may comprise, for example, platinum and tungsten. The elements of these materials generate heat and change their resistance values when electricity is applied. In the embodiment, the hot wire  22 A is positioned closest to the mask  11 , the hot wire  22 B is positioned farthest away from the mask  11 , and the hot wire  22 C is positioned between the hot wires  22 A and  22 B, although other placements of the wires or use of less or more hot wires is not prohibited. The lead wires  23 A and  24 A attached to the ends of the hot wire  22 A, the lead wires  25 B and  26 B attached to ends of the hot wire  22 B, and the lead wires  27 C and  28 C attached to the ends of the hot wire  22 C are all connected to the extraction circuit  30 . 
         [0025]    The extraction circuit  30  may contain the bridge circuit  31  as shown in  FIG. 2 , and the bridge circuit  31  may have the hot wire  22 C as one of the resistive elements. From this bridge circuit  31 , the signal indicating the flow rate of the inhaled or exhaled gas is obtained as the resistance of the hot wire  22 C varies responding to the inhaled or exhaled gas flowing upon it. The extraction circuit  30  of this embodiment additionally may have the bridge circuit  32  as shown in  FIG. 3  to detect the direction of the flow differentiating between inhalation or exhalation. 
         [0026]    The bridge circuit  31  shown in  FIG. 2  may be known as a hot wire constant temperature circuit. The resistor R shown in the bridge circuit  31  represents the resistance of the hot wire  22 C, and other resistors r 1  through r 3  are fixed value resistors. The feedback current from the output of the operational amplifier  33  is fed to the junction of the resistors r 1  and r 3 . The junction of the resistors R and r 2  is connected to the ground, and thus, the current flows through the bridge. The resistive values of the fixed resistors are set so that the bridge  31  attains the equilibrium state when the resistance of R is heated to a certain temperature, 400 degrees C. for example, under a current application. 
         [0027]    The junction of the resistors r 1  and r 2  may be connected to the non-inverting input terminal of the operational amplifier  33 . The junction of the resistors r 3  and R may be connected to the inverting input terminal of the operational amplifier  33 . When the bridge circuit  31  becomes unbalanced, the difference at the inputs may be amplified to obtain the output signal Eo. The current from the output signal Eo may be fed back to the bridge circuit  31 , and the current may continue to increase until the bridge  31  attains the equilibrium state. In the pre-measurement state of the cylindrical body  20 , the output of the operational amplifier  33  may continue to increase and the current to the bridge circuit  31  may also continue to increase until the resistor R is heated and increases its resistance value to the set point, 400 degrees C. for example, and the bridge  31  attains the equilibrium state. 
         [0028]    Once the extraction circuit  30  attains the measurement state, and if the respiration flows within the cylindrical body  20 , the resistor R of the hot wire  22 C may be cooled and the resistance value of the resistor R will change and the bridge circuit  31  will be unbalanced. The differential voltage created by the unbalanced bridge circuit  31  will be amplified to produce the greater output voltage that is in turn fed back to increase the current to the bridge circuit  31  until the bridge circuit  31  attains the equilibrium state again. Since the resistor R may be cooled in proportion to the respiratory flow rate, the output signal Eo of the operational amplifier  33  can be converted to the respiratory flow rate by computation considering the inner diameter of the cylindrical body  20 . 
         [0029]    The bridge circuit  32  shown in  FIG. 3  is for differentiating the flow direction. The hot wire  22 A (R 1  in  FIG. 3 ) and the hot wire  22 B (R 2  in  FIG. 3 ) used in the bridge circuit  32  may be the same type of hot wire as the hot wire  22 C. However, the applied voltage to the bridge may be set so that the temperature of the hot wires  22 A and  22 B hardly increases. The hot wires  22 A and  22 B may be used to perform the function of thermo-sensitive hot wires. 
         [0030]    As described earlier, inside the cylindrical body  20 , three hot wires  22 A,  22 B and  22 C may be placed and aligned adjacently in the longitudinal direction of the cylindrical body  20 . The temperature of the hot wire  22 C is maintained high and the inhaled or exhaled gas flowing upon it will be warmed up, and the hot wire (either  22 A or  22 B) situated at the downstream side of the hot wire  22 C will receive warm air. As a result, the resistance of the hot wire (either  22 A or  22 B) will increase, causing the bridge circuit  32  to become unbalanced, and the unbalanced voltage will be output. The output unbalanced voltage will move in the plus or minus direction as shown in  FIG. 4B  depending on the direction of the flow, and thus the direction can be identified. In other words, it is possible to detect whether inhaled or exhaled gas is flowing within the cylindrical body  20 . The output of the operational amplifier  34 , to which the bridge circuit  32  having the hot-wires  22 A and  22 B is connected, may be routed to the inhalation/exhalation differentiation circuit  43 , such as an inhale-exhale detector, via the output line  38 . Based on the detection result from the inhalation/exhalation differentiation circuit  43 , processing, such as filtering and zero-adjustment, is performed, and then the output may be routed to the detection circuit  45 . 
         [0031]    The output of the operational amplifier  33 , to which the bridge circuit  31  having the hot wire  22 C is connected, may be output via the output line  39  that branches out in two directions. One branch of the output line  39  may be routed to the low-pass filter  41  with a cutoff frequency of approximately 20 Hz and to the linearizer circuit  44  for the purpose of performing the linear approximation. The other branch of the output line  39  may be routed to the high-pass  42  with a cutoff frequency of approximately 20 Hz. Note that the high-pass filter  42  may be replaced by for example, a band-pass filter. It is noted that a frequency over 150 Hz may include sounds other than snoring, in which situation a band pass filter from 20 Hz to 150 Hz may be used in an exemplary embodiment. 
         [0032]      FIG. 4(   a ) shows an exemplary embodiment of the waveform of the respiratory flow rate after processing through the low-pass filter  41 , and  FIG. 4(   b ) shows an exemplary embodiment of the waveform related to the direction of the flow after processing by the inhalation/exhalation differentiation circuit  43 .  FIG. 4(   c ) shows an exemplary embodiment of the waveform related to the snoring after processing through the high-pass filter  42 . 
         [0033]    As evidenced by  FIG. 4(   c ), the signal that has passed through the high-pass filter  42  may have a waveform having higher vibration amplitude within a shorter duration over a period. This enables the observer to capture the occurrence of the snoring visually. 
         [0034]    The output signal from the low-pass filter  41  may be first linearly approximated by the linearizer circuit  44 , then routed to the detection circuit  45  where the signal may be identified as either in the inhalation phase or the exhalation phase based on the other signal from the inhalation/exhalation differentiation circuit  43  and converted to the respiration flow rate signal. In addition, the detection circuit  45  may integrate the respiration flow rate signal and compute the respiration volume signal. Then the respiration flow rate signal, the respiration volume signal, and the snoring signal may be sent to the vital information measurement device  50 , such as a vital sign monitor. The vital information measurement device  50  may be configured with instruments such as a computer that would receive the signals from the detection circuit  45  and perform the signal processing for generating waveform display images, etc. 
         [0035]    The vital information measurement device  50  may receive the signals from the detection circuit  45 , create the waveform images, and display them. 
         [0036]    In the earlier descriptions, a constant temperature hot wire bridge is utilized for the bridge circuit  31 . However, a constant current type of bridge for the bridge circuit  32  may be used, in which the resistor R 1  is configured by the hot wire  22 C, to detect the respiratory flow rate and sound, such as snoring. 
         [0037]    It is also acceptable in the extraction circuit  30  to configure the bridge circuit  31  and the bridge circuit  32  by using two bridge circuits  31 . 
         [0038]    When two bridge circuits  31  are used, the output voltage from the downstream bridge circuit  31  will be smaller than the output voltage from the upstream bridge circuit  31  even though the same flow rate is applied to both bridges. This is because less heat, thus less temperature, is taken away from the downstream resistor being influenced by the heat from the upstream hot wire. This difference in the output voltages may be used to detect the direction of the flow. For detecting the flow rate, the upstream bridge circuit is used. The respiratory information sensor will be configured such that the output signal Eo from the upstream bridge circuit  31  is fed through one of the low-pass filters to obtain the respiratory flow rate waveform images, and is fed through one of the high-pass filters to obtain the snoring waveform images. Other exemplary embodiments may be configured similarly to the configuration already described earlier. 
         [0039]    Note that the processing of information in the present invention may be performed by a processor that may include a computer-readable medium as known to those of ordinary skill in the art. 
         [0040]    While this invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.