Patent Publication Number: US-2011060237-A1

Title: Respiration impedance measuring device and method, and respiration impedance display method

Description:
TECHNICAL FIELD 
     The present invention relates to a respiratory impedance measuring apparatus and method that are capable of continuously measuring a respiratory impedance of a human being, etc., and to a respiratory impedance display method. 
     BACKGROUND ART 
     Conventionally, an apparatus of this kind is known that includes a sine-wave pressurizing apparatus to apply as a load a sine-wave air vibration pressure to a respiratory system, an air current velocity detector to detect an air current velocity of the respiratory system, an air pressure detector to detect an air pressure of the respiratory system, and a resistance computing unit that calculates breathing resistance from the air current velocity and the air pressure detected by the air current velocity detector and the air pressure detector. 
     The conventional apparatus: further includes a reference signal converter to convert a signal of the sine-wave air vibration pressure that is applied by the sine-wave pressurizing apparatus into a reference signal and a vector computing device that processes a signal of the air current velocity using the reference signal of the sine-wave air vibration pressure from the reference signal converter and that, thereby, takes out only a component at the same frequency as that of the reference signal; and is adapted to calculate the breathing resistance using the resistance computing unit from the signal of the air current velocity obtained by the vector computing device and the signal of the air pressure detected by the air pressure detector. 
     As above, this apparatus is adapted to measure the breathing resistance using the resistance computing unit from the signal of the air current velocity obtained by the vector computing device and the signal of the air pressure detected by the air pressure detector and, therefore, noises may be removed even when the amount of ventilation of the breathing is a little and the number of ventilating sessions is large. Therefore the apparatus has an advantage that the apparatus may execute high precision measurement of breathing resistance (see Patent Document 1). 
     However, the removal of the noises is not sufficient even by the conventional apparatus and realization of a higher-performance respiratory impedance measuring apparatus is demanded. 
     Patent Literature 1: Japanese Patent Application the KOKAI Publication No. H03-039140. 
     DISCLOSURE OF THE INVENTION 
     Problems to Be Solved by the Invention 
     The present invention was conceived in view of the current circumstances in respiratory impedance measurement and an object thereof is to provide a respiratory impedance measuring apparatus and method that are capable of continuously measuring impedance for a plurality of frequencies at one time. Another object thereof is to provide a respiratory impedance measuring apparatus and method that are capable of removing noises and measuring respiratory impedance with extremely high precision, and a respiratory impedance display method. 
     Means for Solving the Problems 
     The respiratory impedance measuring apparatus according to the present invention characteristically includes: a pressurizing means to apply an air vibration pressure to the inside of an oral cavity, a control means that causes the air vibration pressure to be generated, by an oscillation wave that is a signal to drive this pressurizing means and that is a signal obtained by frequency-culling executed such that the signal has only the frequency components that are left after the culling is executed from a plurality of different frequencies; a pressure detecting means that detects the pressure of the inside of an oral cavity; a flow detecting means that detects a flow generated by breathing; a Fourier transforming means that obtains signals obtained by the pressure detecting means and the flow detecting means under the pressurized condition provided by the pressurizing means, that Fourier-transforms the signals obtained, and that obtains a spectrum; an extracting means that obtains a breathing high frequency component based on a spectrum that corresponds to the frequency component culled from the result of the transformation by the Fourier transforming means, and that takes out an oscillation wave component by subtracting the breathing high frequency component from a spectrum that corresponds to a frequency component left by the culling; and a computing means that divides a pressure component by a flow component for each frequency for the result of the extraction by the extracting means. 
     The respiratory impedance measuring apparatus according to the present invention is characterized in that the control means causes the air vibration pressure to be generated, by the oscillation wave having only n/T (n: an integer, T: a real number) frequency components, by giving a pulse wave having the cycle T as the frequency culling. Such frequency-culling is referred to as &lt;frequency-culling 1&gt;. In &lt;frequency-culling 1&gt;, when T is determined, a plurality of frequency components are obtained that are left by culling the frequency components other than n/T (n: an integer) frequency components. 
     The respiratory impedance measuring apparatus according to the present invention is characterized in that the control means combines a plurality of sine waves at different frequencies, thereby, obtains an oscillation wave frequency-culled, and causes the air vibration pressure by the oscillation wave to be generated. Such frequency-culling is referred to as &lt;frequency-culling 2&gt;. In &lt;frequency-culling 2&gt;, the signal is also enabled to have only a plurality of integer-frequency components left by culling desired integers from consecutive integers and, therefore, the signal may include a plurality of integer-frequency components left by culling odd-number frequency components. 
     The respiratory impedance measuring apparatus according to the present invention is characterized in that the control means includes a signal input means that supplies an input signal to the pressurizing means such that an oscillation wave having a desired pressure waveform is an output signal, based on reverse computation using the input signal and the output signal of the pressurizing means and a transfer function of the pressurizing means. 
     The respiratory impedance measuring apparatus according to the present invention is characterized in that the signal input means supplies to the pressurizing means as an input signal a signal obtained by adding a specific value to each of frequency components of the signal obtained by the reverse computing, or by reverse computing the signal formed by adding an impulse to an onset portion of the output signal. 
     The respiratory impedance measurement method according to the present invention characteristically includes: a pressurizing step to apply an air vibration pressure to the inside of an oral cavity; a control step of causing the air vibration pressure to be generated, by an oscillation wave that is a signal to control this pressurizing step and that is a signal obtained by frequency-culling executed such that this signal has only the frequency component that is left after the culling is executed from a plurality of different frequencies; a pressure detecting step of detecting the pressure of the inside of the oral cavity; a flow detecting step of detecting the flow generated by breathing; a Fourier-transforming step of obtaining signals obtained at the pressure detecting step and the flow detecting step under the pressurized condition provided at the pressurizing step, Fourier-transforming the signals obtained, and, thereby, obtaining a spectrum; an extracting step of obtaining a breathing high frequency component based on a spectrum that corresponds to the frequency components culled from the result of the transformation at the Fourier transforming step, and taking out an oscillation wave component by subtracting the breathing high frequency component from a spectrum that corresponds to frequency components left by the culling; and a computing step of dividing a pressure component by a flow component for each of frequencies for the result of the extraction at the extracting step, and the method is characterized in that each of the steps is executed by processing and control of a computer. 
     The respiratory impedance measurement method according to the present invention is characterized in that, at the control step, the air vibration pressure is caused to be generated, by an oscillation wave having only n/T (n: an integer, T: a real number) frequency components by supplying a pulse wave having a cycle T as the frequency-culling. Such frequency-culling is &lt;frequency-culling 1&gt;. 
     The respiratory impedance measurement method according to the present invention is characterized in that, at the control step, the air vibration pressure is caused to be generated, by an oscillation wave by obtaining the oscillation wave frequency-culled, that is obtained by combining a plurality of sine waves at a plurality of different frequencies. Such frequency-culling is &lt;frequency-culling 2&gt;. 
     The respiratory impedance measurement method according to the present invention is characterized in that the control step includes a signal input step of supplying an input signal at the pressurizing step such that an oscillation wave having a desired pressure waveform is an output signal, based on reverse computation using the input signal and the output signal at the pressurizing step and a transfer function at the pressurizing step. 
     The respiratory impedance measurement method according to the present invention is characterized in that, at the signal input step, a signal is supplied at the pressurizing step, that is obtained by adding a specific value to each of frequency components of the signal obtained by the reverse computing, or by reverse computing the signal formed by adding an impulse to an onset portion of the output signal. 
     The respiratory impedance display method according to the present invention is characterized in that, in a respiratory impedance display method of executing display on a displaying apparatus based on the respiratory impedance measured by the respiratory impedance measuring apparatus: the display is executed by three-dimensionally taking values based on an impedance axis, a frequency axis, and a time axis; an image is created by including respiratory impedance obtained by executing an interpolation process for the culled frequencies, in the display to execute the display by three-dimensionally taking values; and, thereby, the display is executed. 
     The respiratory impedance display method according to the present invention is characterized in that the display is executed by creating the image with the length in the direction of the time axis, that is taken to be a length enough to repeat therein at least two sets of exhalation and inhalation. 
     The respiratory impedance display method according to the present invention is characterized in that the display is executed by creating an image that expresses magnitude of an impedance value using variation in color or variation in gradation. 
     EFFECTS OF THE INVENTION  
     According to the present invention: an air vibration pressure by an oscillation wave that is frequency-culled is applied to the inside of an oral cavity; the pressure of the inside of the oral cavity is detected; the flow of breathing is detected; a spectrum is obtained by Fourier-transforming these signals obtained; a breathing high frequency component that contributes as a noise is obtained using a spectrum that corresponds to frequency components culled from the result of the Fourier transformation; the breathing high frequency component is subtracted from a spectrum that corresponds to the frequency components left by the culling; thereby, an oscillation wave component is extracted; computing is executed of dividing a pressure component by a flow component for each of frequencies for the result of this extraction; and, thereby, respiratory impedance is obtained. Therefore, the respiratory impedance may be obtained using the oscillation wave component from which the breathing high frequency component is securely removed and, therefore, impedance measurement with extremely high precision may be enabled. 
     According to the present invention: the air vibration pressure by the oscillation wave having only the n/T (n: an integer, T: a real number)frequency components is caused to be generated by supplying the pulse having the cycle T; therefore, the breathing high frequency component is obtained using the spectrum that corresponds to the frequency components culled; and the breathing high frequency component is subtracted from the spectrum that corresponds to the frequency components left by the culling. Therefore, the breathing high frequency component may securely be removed and the respiratory impedance measurement with extremely high precision is enabled. 
     According to the present invention, the plurality of sine waves at the plurality of different frequencies are combined and, thereby, the air vibration pressure by the oscillation wave that is frequency-component-culled is caused to be generated. Therefore, only the breathing high frequency component is included by the spectrum that corresponds to the frequency components culled and, therefore, the breathing high frequency component may securely be removed and the respiratory impedance measurement with extremely high precision is enabled. 
     According to the present invention, an input signal is supplied to a pressurizing executing portion such that the oscillation wave having a desired pressure waveform is the output signal based on the reverse computation using the input signal and the output signal for the pressurizing and a transfer function of the pressurizing executing portion. Therefore, the measurement may be executed using the oscillation wave having the desired pressure waveform and respiratory impedance measurement with extremely high precision is enabled. 
     According to the present invention, the input signal is the signal obtained by adding a specific value to each of the frequency components of the signal obtained by the reverse computing, or by reverse computing the signal formed by adding an impulse to the onset portion of the output signal. Therefore, the signal waveform of the result of the reverse computing may be stabilized and, thereby, the measurement using the oscillation wave having a desired waveform may be executed and the respiratory impedance measurement with extremely high precision is enabled. 
     According to the respiratory impedance display method according to the present invention, in the respiratory impedance display method of executing display on a displaying apparatus based on the respiratory impedance measured by the respiratory impedance measuring apparatus: the display is executed three-dimensionally taking values based on the impedance axis, the frequency axis, and the time axis; an image is created by including the respiratory impedance obtained by executing an interpolation process for the culled frequencies, in the display to execute display three-dimensionally taking values; and, thereby, the display is executed. Therefore, the result of the interpolation process is also displayed as an image. Therefore, variation of the impedance value may minutely and smoothly be displayed and grasp of the impedance for the whole frequencies may properly be executed. 
     According to the respiratory impedance display method according to the present invention, the display is executed by creating the image with the length in the direction of the time axis that is a length long enough to repeat therein at least two sets of exhalation and inhalation. Therefore, not an observation of a sudden variation but an observation having a specific span is enabled and, thereby, proper observations may be secured. 
     According to the respiratory impedance display method according to the present invention, the display is executed by creating the image that expresses magnitude of an impedance value using variation in color or variation in gradation. Therefore, to obviously distinguish the magnitudes of impedance values is easily enabled and it is expected that the method is very useful for various researches and inspections that use the respiratory impedance. 
     BEST MODES FOR CARRYING OUT THE INVENTION 
     Embodiments of a respiratory impedance measuring apparatus and method according to the present invention will be described with reference to the accompanying drawings.  FIG. 1  is a diagram of the configuration of the embodiment of the respiratory impedance measuring apparatus according to the present invention. The respiratory impedance measuring apparatus includes as its main components: a tube  11  whose tip is attached to an oral cavity of a human and through which a breathing flow flows; a pressure sensor  12  that is attached to the tube  11  and that makes up a pressure detecting means to detect the pressure in the oral cavity; a flow sensor  13  that makes up a flow detecting means of detecting the flow of breathing at the same position as that of the pressure sensor  12 ; a loudspeaker  21  that makes up a pressurizing means to apply an air vibration pressure to the inside of the oral cavity; and a computer  30 . 
     An output signal of the pressure sensor  12  is amplified by an amplifier  14 , is digitized by an A/D converter  15 , and is taken in by the computer  30 . An output signal of the flow sensor  13  is amplified by an amplifier  16 , is digitized by an A/D converter  17 , and is taken in by the computer  30 . 
     The computer  30  includes a control means  31 , a Fourier transforming means  32 , an extracting means  33 , and a computing means  34 . The control means  31  includes a signal input means  35 . The control means  31  outputs a signal driving the loudspeaker  21  that is the pressurizing means and causes the air vibration pressure by an oscillation wave having only odd-number frequency components or even-number frequency components, to be generated. An output of the control means  31  is converted into an analog signal by a D/A converter  22  and is sent to a driver  23 . The driver  23  drives the loudspeaker  21  and, thereby, the air vibration pressure is applied to the inside of the oral cavity. 
     In the above, the control means  31  causes the air vibration pressure by the oscillation wave having n/T (n: an integer, T: a real number) frequency components, to be generated by giving a pulse wave having the cycle of T second (&lt;frequency-culling 1&gt;). Though various waveforms may be considered as the pulse wave, for example, as depicted in  FIG. 2(   a ), a triangular pulse has the temporal width of about 25 ms at the base level. When this triangular pulse is output with the cycle T that is, for example, T=0.5 second, a triangular pulse wave having a spectrum of 2, 4, 6, 8 Hz, . . . may be given ( FIG. 2(   b )). When the triangular pulse is output with the cycle T that is, for example, T=0.333 second, a triangular pulse wave having a spectrum of 3, 6, 9, 12 Hz, . . . may be given. 
     As depicted in  FIG. 3 , a Hanning pulse as another example has the temporal width of about 25 ms at the base level. A pulse wave using this pulse is created and output similarly to the case of the triangular pulse wave. 
     The control means  31  causes the air vibration pressure by an oscillation wave having only desired real-number frequency components, to be generated by giving a wave obtained by combining a plurality of sine waves at a plurality of different frequencies (&lt;frequency-culling 2&gt;). In this case, a signal depicted in  FIG. 4  that is a noise wave is output. In this case, a noise wave having only even-number frequency components is obtained by combining sine waves having even-number frequencies such as, for example, 2, 4, 6, . . . , 34 Hz. A noise wave having only odd-number frequency components is obtained by combining sine waves having odd-number frequencies such as, for example, 1, 3, 5, . . . , 33 Hz. A noise is realized by randomizing the phase of each the sine waves. 
     The signal input means  35  included in the control means  31  supplies an input signal to the loudspeaker  21  such that an oscillation wave having a desired waveform is an output signal, based on reverse computing using an input signal and an output signal of the loudspeaker  21 , and a transfer function of the loudspeaker  21 . 
     More specifically, describing using, for example, a triangular pulse, when the loudspeaker  21  is driven by inputting thereinto a triangular pulse as depicted in  FIG. 5(   a ), an output signal of the loudspeaker  21  becomes a signal having a local maximum point on each of the upper and the lower sides of the zero level as depicted in  FIG. 5(   b ). A model as depicted in  FIG. 5(   c ) is considered. Representing the transfer function of the loudspeaker  21  as “H(ω)”, the input signal thereof as “X(ω)”, and the output signal thereof as “Y(ω)”, the following holds and, therefore, x′ (t) is obtained by reverse computation and is used as a driving signal. 
         Y (ω)= X (ω) H (ω)   [Eq. 1]
 
     Representing an input as X′ (ω) with which X(ω) is obtained, 
     
       
         
           
             
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     Y(ω) obtained has no component that includes frequencies up to a high frequency and, therefore, x′(t) obtained from (Equation 1) is unstable. Therefore, as expressed in (Equation 2), a term obtained by adding a constant “A 0 ” to the denominator of X′(ω) is inversely Fourier-transformed and, thereby, x′(t) is obtained and is used as the driving signal. The signal x′(t) depicted in  FIG. 5(   e ) may also be obtained by reverse-computing a signal formed by adding an impulse to an onset portion as depicted in  FIG. 5(   d ) of an output signal of the loudspeaker  21  as depicted in  FIG. 5(   b ). 
     Though the case for the triangular pulse is described in the above, as to a Hanning pulse, a signal may also be obtained by the reverse computation and this signal may also drive the loudspeaker  21 . As to a sine wave, a signal may also be obtained by the reverse computation and a noise wave may also be obtained by this signal combining. 
     As to which one of the pulse wave, the noise wave, and the sine wave having a single frequency is used, an instruction may be given to the computer  30  using a keyboard, etc., not depicted and, in response to this, the control means  31  outputs a signal waveform selected thereby. 
     The Fourier transforming means  32 , the extracting means  33 , and the computing means  34  included in the computer  30  will be described. Under the pressurized condition in the oral cavity caused by a driving of the loudspeaker  21  as above, the Fourier transforming means  32  obtains signals using the pressure sensor  12  and the flow sensor  13 , Fourier-transforms these signals obtained, and obtains a spectrum. A CIC filter  36  is provided in the pre-stage of the Fourier transforming means  32  and separates a breathing signal and an oscillation component obtained by the pressure sensor  12  and the flow sensor  13  from each other. The Fourier transforming means  32  takes out a signal using a Hanning window before the processing when necessary. 
     The extracting means  33  obtains a breathing high frequency component using the spectrum that corresponds to the frequency components culled from the result of the transformation by the Fourier transforming means  32 , and takes out the oscillation wave component by subtracting the breathing high frequency component from the spectrum that corresponds to the frequency components left by the culling. Describing based on &lt;frequency-culling 1&gt;, as to the spectrum obtained by the Fourier transforming means  32 , the breathing high frequency component is obtained using the spectrum that corresponds to other frequencies excluding n/T (n: an integer) frequency components, and the oscillation wave component is taken out by subtracting the breathing high frequency component from the spectrum that corresponds to the frequency components left by the culling (n/T-frequency components). 
     Describing based on &lt;frequency-culling 2&gt;, as to the spectrum obtained by the Fourier transforming means  32 , the extracting means  33  obtains the breathing high frequency component using the spectrum that corresponds to the frequency components (odd-number frequency components or even-number frequency components) that are different from the frequency components (in this case, even-number frequency components or odd-number frequency components) given to the loudspeaker  21 , and takes out the oscillation wave component by subtracting the breathing high frequency component from the spectrum that corresponds to the frequency components given to the loudspeaker  21 . 
     As to the result of the extraction by the extracting means  33 , the computing means  34  calculates respiratory impedance by dividing a pressure component by a flow component for each frequency. Representing the respiratory impedance as Z(ω), an oscillation wave component of the pressure in the oral cavity as P(ω), and an oscillation wave component of the flow as F(ω) and assuming that the respiratory impedance Z(ω) includes a resistance component R(ω) and a reactance component X(ω), the respiratory impedance Z(ω) is obtained using the following equations. 
     
       
         
           
             
               
                 
                   
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     The respiratory impedance Z(ω) obtained by the computing means  34  is converted into a display signal for a displaying unit  40  such as an LCD that is connected to the computer  30  and is output to the displaying unit  40  and, thereby, display is executed. 
     Operations by the respiratory impedance measuring apparatus configured as above will be described. In this example, the triangular pulse wave is selected and a measuring operation is started. The loudspeaker  21  is driven with the cycle of T second (for example, at intervals of 0.5 second) by the control means  31  and the signal input means  35  using the waveform obtained by the reverse computation. 
     At this time, both of the waveforms of the signals obtained by the pressure sensor  12  and the flow sensor  13  each are a waveform formed by superimposing the triangular pulse wave on the breathing signal as depicted in  FIG. 6(   a ). This waveform is passed through the CIC filter  36  and the separation of the breathing wave and the oscillation wave (the triangular pulse wave) from each other is executed.  FIG. 7  depicts the frequency property of the CIC filter  36 . The CIC filter  36  may execute the separation without any shift of the phase. However, the breathing signal includes a high frequency component (the same frequency band as that of the oscillation signal) and, therefore, the separation may not be completely executed. 
     After the separation by the CIC filter  36 , as depicted in  FIG. 6(   b ), as to the oscillation wave, a section of one second is taken out at the intermediate point between two triangular pulses and is used for signal processing. As depicted in  FIG. 8 , a section of T second is taken out and a process using a Hanning window is executed for each pulse and, thereby, pulses are taken out. 
     Following the process using the Hanning window, Fourier transformation by the Fourier transforming means  32  is executed and a spectrum is obtained. At this time, as to the spectrum obtained, for example, when a pulse is driven with the cycle of 0.5 second, as depicted in  FIG. 9 , the breathing signal spectrum is obtained that includes no oscillation wave component in its spectrum of odd-number frequencies of 1, 3, 5, . . . that correspond to the frequency components culled. The spectrum of even-number frequencies of 2, 4, 6, . . . that corresponds to the frequency components left by the culling includes the oscillation wave component and the breathing signal component. 
     As depicted in  FIG. 10 , the extracting means  33  subtracts a noise component that is estimated from the spectrum of the odd-number frequencies, from the spectrum of the even-number frequencies and, thereby, takes out the oscillation wave component. 
     The breathing high frequency signal that is equal to or higher than 3 Hz and that is conventionally considered not to be included in the breathing signal, is removed by the processing of the extracting means  33  and, therefore, high precision respiratory impedance measurement is enabled. The computing means  34  divides the pressure component by the flow component and, thereby, calculates the respiratory impedance as expressed by Equation (2) for each frequency for the result of the extraction by the extracting means  33 . A display signal of the respiratory impedance calculated is created and is output to the displaying unit  40  and, thereby, display is executed. 
     The respiratory impedance that is measured and displayed as above is depicted in  FIG. 11 .  FIG. 12  depicts the respiratory impedance obtained when the breathing high frequency the removal of the breathing high frequency signal is not executed. In each of  FIGS. 11 and 12 , the axis of abscissa is a frequency axis whose one section of graduation corresponds to 1 Hz and the axis of ordinate represents the impedance. An oblique axis is the time axis. A genuine resistance portion is displayed in the upper portion of the diagram and a reactance portion is displayed in the lower portion of the diagram. In this case, by consecutively giving the triangular pulses at intervals of 0.5 second, display of new impedance appears one after another and the display is updated. Thereby, continuous measurement of the impedance is executed. As apparently seen from  FIGS. 11 and 12 , it is understood that the noise is removed and high precision respiratory impedance measurement is enabled. As apparent from the subtracting process by the extracting means  33 , the component left by the subtraction is the even-number-frequency component of 2, 4, 6, . . . that corresponds to the frequency component left by the culling and, the odd-number-frequency component of 1, 3, 5, . . . that corresponds to the frequency component culled is not present. The computing means  34  executes an interpolating process and, thereby, respiratory impedance measurement is enabled for the component that is not present. 
     The case where the noise wave is selected instead of the triangular pulse wave and the measuring operation is started (&lt;frequency-culling 2&gt;) will be described. The loudspeaker  21  is driven by the control means  31  and the signal input means  35  using the noise wave having only even-number-frequency component based on the waveform obtained by the combining. At this time, both of the waveforms of the signals obtained by the pressure sensor  12  and the flow sensor  13  each are a waveform formed by superimposing the noise wave on the breathing signal as depicted in  FIG. 13(   a ). These signals are passed through the CIC filter  36  and, thereby, the separation of the breathing wave and the oscillation wave (noise wave) from each other is executed ( FIG. 13(   b )). 
     After the separation by the CIC filter  36 , as depicted in  FIG. 14(   a ), as to the oscillation wave, a section of one second is taken out and is used for the signal processing. As depicted in  FIG. 14(   b ), Fourier transformation by the Fourier transforming means  32  is executed for the noise wave from which the section of one second is taken out and, thereby, the spectrum is obtained. 
     As to the spectrum obtained by the Fourier transformation, the loudspeaker  21  is driven by the noise wave having only the even-number-frequency component combined by the control means  31  and the signal input means  35 . Therefore, a breathing signal spectrum is obtained whose spectrum of the odd-number frequencies of 1, 3, 5, . . . that corresponds to the frequency components culled does not include the oscillation wave component. The spectrum of the even-number frequencies of 2, 4, 6, . . . that corresponds to the frequency components left by the culling includes the oscillation wave component and the breathing signal component. 
     The extracting means  33  executes subtraction of the odd-number-frequency spectrum from the even-number-frequency spectrum and, thereby, takes out the oscillation wave component. The processes after this are same as the processes executed when the triangular pulse wave is used ( FIGS. 9 and 10  and the computation using Equation (2)). A display signal of the respiratory impedance calculated is created and is output to the displaying unit  40 , and, thereby, display is executed. When the noise wave is used as above, the noise may also be removed and high precision respiratory impedance measurement is enabled. By continuously giving the noise wave, new impedance display appears one after another and, thereby, the display is updated. Thereby, continuous measurement of the impedance is executed. When the noise wave is used, display whose noise is removed is executed similarly to the case depicted in  FIG. 11  and the continuous measurement of the impedance is enabled. 
     In the embodiment of the present invention, the computing means  34  creates the image to execute the display on the displaying apparatus and executes the display and, thereby, a respiratory impedance display method is realized. As to the respiratory impedance calculated by the computing means  34 , the computing means  34 , for example: determines a coordinate such that each frequency value is taken from the side distant from a viewer to the side close thereto of the image; takes out a resistance component Rrs for each frequency; plots this in the direction of the height of the screen of the displaying apparatus; takes the measurement time in the rightward direction of the screen; creates a three-dimensional image as depicted in  FIG. 15 ; and displays the three-dimensional image on the displaying apparatus. This display is executed three-dimensionally taking values using the impedance axis, the frequency axis, and the time axis. 
     For creating the image, an image is created and is displayed that is formed by including the respiratory impedance obtained by executing the interpolation process for the frequencies culled, in the case where values are three-dimensionally taken. For example, when the odd-number frequencies are culled, two impedance values are already obtained that correspond to even-number frequencies that are adjacent to an odd number culled. Therefore, the average of these two impedance values is obtained and is used as an impedance value that corresponds to the frequency culled. In this manner, the result of the interpolation process is also converted into an image and is displayed as the image and, therefore, variation of the impedance value may minutely and smoothly be displayed and grasp of the impedance for the whole frequencies may properly be executed. 
     The sampling time is 0.5 second and, as depicted in  FIG. 15(   b ), the image is created and displayed taking the length in the direction of the time axis that is a length long enough to repeat therein at least two sets of exhalation and inhalation. In the example of  FIG. 15 , the length is taken to be long enough to repeat therein three sets of exhalation and inhalation. 
     An image is also created and displayed that expresses the magnitude of the impedance value using variation in color or variation in gradation. In  FIG. 15 , an image is created and displayed being colored for the resistance value Rrs based on the color scale presented in the lower portion of  FIG. 15 . 
     Images obtained by the processes are displayed and, therefore, a subject only has to repeat inhaling and exhaling and images as depicted in  FIG. 15  may automatically and time-sequentially be created and displayed. Each of the images may visually be observed as an image that expresses the variation of the respiratory impedance using variation in color or variation in gradation, including the portions that correspond to the frequencies culled. 
     Therefore, as apparently seen from the variation of the respiratory impedance of a 66-year-old healthy person depicted in  FIG. 15(   a ) and the variation of the respiratory impedance of a 65-year-old COPD (chronic obstructive pulmonary disease) patient depicted in  FIG. 15(   b ), to visually and obviously distinguish a non-healthy person and a healthy person from each other is easily enabled and it is expected that the method is very useful for various researches and inspections that use respiratory impedance. “% FEV1” of  FIG. 15(   b ) is a value that indicates how many % of the forced vital capacity is exhaled in one second. Therefore, in this example, it is presented that 24.4% was able to be exhaled in one second. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram of the configuration of a respiratory impedance measuring apparatus according to an embodiment of the present invention. 
         FIG. 2  is a diagram of an example of a triangular pulse wave that is an oscillation wave used in the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
         FIG. 3  is a diagram of an example of a Hanning pulse wave that is an oscillation wave used in the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
         FIG. 4  is a diagram of an example of a noise wave that is an oscillation wave used in the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
         FIG. 5  is a diagram for explaining the process of creating, using reverse computation, the oscillation wave used in the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
         FIG. 6  is a diagram of a process of obtaining the respiratory impedance using the triangular pulse wave that is the oscillation wave by the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
         FIG. 7  is a diagram of the frequency property of a filter employed in the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
         FIG. 8  is a diagram of a process of obtaining the respiratory impedance using the triangular pulse wave that is the oscillation wave by the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
         FIG. 9  is a diagram of a process of obtaining the respiratory impedance using the triangular pulse wave that is the oscillation wave by the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
         FIG. 10  is a diagram of a process of obtaining the respiratory impedance using the triangular pulse wave that is the oscillation wave by the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
         FIG. 11  is a diagram of the respiratory impedance obtained by the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
         FIG. 12  is a diagram of respiratory impedance obtained by a respiratory impedance measuring apparatus that does not use the approach of the present invention. 
         FIG. 13  is a diagram of a process of obtaining the respiratory impedance using a noise wave that is the oscillation wave by the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
         FIG. 14  is a diagram of a process of obtaining the respiratory impedance using a noise wave that is the oscillation wave by the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
         FIG. 15  is a diagram of an example of respiratory impedance for each of a healthy person and a non-healthy person displayed using the respiratory impedance measuring apparatus according to the embodiment of the present invention. 
     
    
    
     EXPLANATIONS OF LETTERS OR NUMERALS  
     
         
           11  tube 
           12  pressure sensor 
           13  flow sensor 
           13  loudspeaker 
           30  computer 
           31  control means 
           32  Fourier transforming means 
           33  extracting means 
           34  computing means 
           35  signal input means 
           36  CIC filter 
           40  displaying unit