JP2014057688A - Pulmonary function testing method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a testing method and apparatus which enable a clinical pulmonary function test based on a respiratory tract cross section for testing a pulmonary function by using sounds.SOLUTION: In a pulmonary function testing method, forced oscillation is applied to a pulmonary airway, pressure fluctuation inside the pulmonary airway or a tube connected to the pulmonary airway is detected, a cross section of an upper respiratory tract is estimated on the basis of this pressure signal, and a pulmonary function is tested on the basis of information on the estimated cross section. Alternatively, the contribution of the upper respiratory tract is removed from respiratory impedance on the basis of the information on the upper respiratory tract cross section, and peripheral airway impedance expected from a peripheral side end position of the upper respiratory tract to the pulmonary airway is estimated.

Description

  The present invention relates to a technique for examining lung function using sound. Used as a clinical pulmonary function test method in the medical and health fields.

  In clinical lung function tests, there is a body plethysmograph method as a method for measuring lung volume and airway resistance. In recent years, forced vibration has been applied to the pulmonary airway. At this time, pressure fluctuations that occur near the lips in the pulmonary airway and fluctuations in the airflow flowing into the pulmonary airway are detected, and the respiratory impedance, which is the ratio of these two signals, is detected. (Forced Oscillation Technique = FOT method) is used.

DuBois AB, Botelho SY, Comroe JH Jr. “A new method for measuringairway resistance in man using a body plethysmograph: values in normal subjectsand in patients with respiratory disease,” J Clin Invest, 35, 327-335, 1956 N.B.Pride, “Forced oscillation techniques for measuring mechanical properties of the respiratory system,” Thorax, 47,317-320, 1992 E. Oostveen et al., “The forced oscillation technique in clinicalpractice: methodology, recommendations and future developments,” European Respiratory Journal, 22, 1026-1041, 2003 H.J.Smith et al., “Forced oscillation technique and impulseoscillometry,” European Respiratory Society Monograph, 31 (Lung FunctionTesting), Ch. 5, 72-105, 2005 Hirohisa Tsuji, Masatoshi Huang, “Respiratory Function Test”, Respiration and Circulation, Vol.57, No.4, 385-393, 2009 J.L.Flanagan, “SpeechAnalysis, Synthesis and Perception,” 2nd. Expanded ed., Springer-Verlag, 1983 M.R.Schroeder, “Computer Speech,” 2nd.ed., Springer-Verlag, 2004 M.M.Sondhi, B. Gopinath, “Determination of Vocal-Tract Shape from Impulse Response at the Lips,” Jounal of Acoustical Society of America, 49 (6-2), 1867-1873, 1971 J.D.Markel and A.H.Gray: Linear Predictionof Speech, Springer-Verlag, 1976

JP 62-161346 A JP-A-3-39140 Special table 2008-541957 JP 2010-264235 A

  The body plethysmography method is a large-scale examination using a container called a body box in which a subject enters, and also requires a special action of panting. In addition, the measurement principle has been established on the assumption that the gas in the lung airway changes isothermally, and this assumption does not hold during punting, so it can be said that the measurement result has a strict quantitative basis. Absent.

  What is measured by the FOT method is the input impedance of the pulmonary airway from the lips to the alveoli, through the trachea and from the lip position. The measured respiratory impedance includes both the contribution of the upper airway (central airway) close to the lips and the contribution of the peripheral airway close to the alveoli. However, what is important from the viewpoint of clinical lung function tests is usually the impedance of the peripheral airway. For example, if the cheeks or tongue vibrate with the application of forced vibration, the respiratory impedance is affected, but this effect is a cause of “upper airway artifacts” and hinders correct lung function diagnosis. In order to eliminate this effect, attempts have been made to apply forced vibration by putting the entire head of the subject into a container, but there is a problem that the examination becomes large and cumbersome, and the burden on the subject increases. In addition to the above vibration, the airway condition under examination, such as tongue height, cheek bulge, throat tension, glottal opening, and individual and age differences in the upper airway shape are also affected by the upper airway. There is a problem in that it affects impedance and hinders lung function tests using respiratory impedance.

  Because of these problems, the measurement results of the lung function test are used as a diagnostic guideline, neglecting the exact quantitative basis. For example, in the measurement of airway resistance by the FOT method, of the respiratory impedance measured at the lip, the resistance at the low frequency (5 Hz) (the real part of the respiratory impedance) is the total airway resistance, and the resistance at the high frequency (20 Hz) is the central airway resistance. Assuming that the latter is subtracted from the former, the estimated value of peripheral airway resistance is estimated (Non-patent Document 5). However, since this estimation method is not based on a clear quantitative basis, it is only a convenient measure and discards the information provided by the impedance as a function of frequency.

  In order to solve the above-described problems, in the present invention, forced vibration is applied to the lung airway, pressure fluctuation in the lung airway or a tube connected to the lung airway is detected, and the upper airway is detected based on the pressure fluctuation signal. The cross-sectional area is estimated, and lung function is examined based on the estimated cross-sectional area information.

  In the invention described in claim 2, forced vibration is applied to the lung airway from the lips, pressure fluctuations generated in the vicinity of the lips are detected at this time, traveling waves propagating from the lip side toward the peripheral side, and from the peripheral side The reflected waves propagating toward the lips are separated, and the cross-sectional area of each position in the lung airway and the estimation of the reflections that occur are sequentially advanced toward the distal side using information on the time required to propagate the sound waves. The cross-sectional area up to a desired position in the lung airway is estimated, and a lung function test is performed based on the estimated cross-sectional area.

  According to the third aspect of the invention, based on the estimated cross-sectional area of the upper airway, the impedance of the peripheral side of the pulmonary airway is estimated from the peripheral end position of the upper airway, excluding the contribution of the upper airway to the respiratory impedance. To do.

  In the invention according to claim 4, a voice signal emitted by the subject is detected in the vicinity of the lips, and an upper airway cross-sectional area from the vicinity of the lips to the glottis is sequentially estimated along the airway axis based on the detected voice signal. Based on this information, a lung function test is performed.

  The present invention enables a clinical lung function test based on the cross-sectional area of the airway. Further, according to the present invention, it is possible to measure the peripheral lung airway impedance by removing the contribution of the upper airway from the respiratory impedance, so that the clinical lung function test can be performed without being affected by the upper airway artifact or the shape of the upper airway. Can be done more accurately.

(First Example)
Hereinafter, embodiments of the present invention will be described based on examples. FIG. 1 shows a first embodiment of the present invention. In the figure, 1 is a speaker box for applying a forced vibration to the lung airway of the subject 5. Reference numeral 2 denotes a tube for applying forced vibration to the lung airway, the left end is connected to the speaker box 1 and the right end is connected to the lip of the subject 5 via a mouthpiece (not shown). 21 is an opening for exhalation and inhalation of the subject. Reference numerals 3 and 3 ′ denote microphones attached to the tube 2 and detect pressure fluctuations in the tube 2. A signal processing device 4 outputs a forced vibration signal to the speaker box 1 and takes in signals from the microphones 3 and 3 ′ and the flow rate sensor 6 to perform signal processing. The actual condition of the signal processing device 4 is a digital computer including an A / D converter and a D / A converter, and a function for performing a lung function test based on the signal processing result is also installed. The vibration generated in the speaker box 1 is applied to the lung airway of the subject 5 via the tube 2. 51 represents the upper airway close to the lips, 52 represents the peripheral airway including the alveoli, 53 represents the glottis, and 54 represents the thorax. The respiratory impedance measured at the position of the microphone is an impedance in which the mechanical impedances of the upper airway 51, the peripheral airway 52, and the thorax 54 are connected. 6 is a flow sensor for measuring the respiratory flow rate.

FIG. 2 is a schematic diagram of a lung airway (part) in which a lung airway whose cross-sectional area continuously changes is represented by a chain of short tubes having a constant cross-sectional area. Each short tube (section) is numbered 0, 1, 2,..., M-1, m, m + 1,. A section of the end of the upper airway and the M segment, the right end of the M intervals, that considered to be terminated at this from the peripheral side of the lung airways acoustic impedance Z _P, to model the entire lung airways it can. Since the diameter of each section is usually sufficiently smaller than the wavelength of forced vibration applied by the speaker box 1, the sound wave propagating in the section can be assumed to be a plane wave.

FIG. 3 is a diagram showing the propagation of sound waves in the m-th section. S _m represents the sectional area of the section, p _m ⁺ represents the sound pressure of the traveling wave traveling toward the distal side within the section, and p _m ⁻ represents the sound pressure of the reflected wave traveling toward the central side within the section. The traveling wave p _m ⁺ in the section m is partially reflected at the boundary with the section (m + 1). On the other hand, a part of the reflected wave p _{m + 1} ⁻ that has traveled in the section (m + 1) toward the central side passes through the section boundary. The reflected wave p _m ⁻ is obtained by superimposing these reflected wave and transmitted wave. The traveling wave p _{m + 1} ⁺ in the section (m + 1) is a superposition of a part of p _m ⁺ that has passed through the section boundary and a part of p _{m + 1} ⁻ that has been reflected at the section boundary. is there. Note that the length of each section is l, the position in each section is indicated by coordinates x _m , and the sound pressure at time t and position x _m is written as p _m ⁺ (x _m , t). However, if there is no possibility of confusion, the subscript m is omitted and the position is represented by x.

  Since the sound pressure and the volume velocity are continuous at the section boundary, the following relationship is established between the values of each sound pressure at time t.

Where μ _m represents the reflection coefficient,

It is. The above relationship can be expressed as a signal flow diagram as shown in FIG. Here, τ is a time required for the sound wave to propagate through the section length l, and r _m ^(l) (t) is an impulse response representing a waveform change when the sound wave travels within the section m by the distance l. . The relationship of equation (1) is

It is expressed. Where k _m is the wave number in the m-th section, ω is the angular frequency, c ₀ is the speed of sound (approximated to be constant regardless of the section area), and P is the Fourier transform of the sound pressure p. In addition, the Fourier transform of r _m ^(l) (t) is e ^{−αm l} . When this relationship is transformed into a recurrence form of sound pressure

It becomes. If the propagation characteristic e ^{-j km l} and the reflection coefficient μ _{m in} the section m are known from the equation (4), the traveling wave and the reflected wave in the section m + 1 can be obtained from the traveling wave and the reflected wave in the section m. I understand. (4) When recursively using

If k _m and μ _m are known for all m from 0 to M, the traveling wave P _{M + 1} ⁺ and the reflected wave P _{M + 1} ^{− at} the position of the upper airway end also progress in the lip position. It can be seen that the wave P ₀ ⁺ and the reflected wave P ₀ ⁻ can be calculated sequentially. The traveling wave P ₀ ⁺ and the reflected wave P ₀ ^{− at the} lip position can be obtained based on the sound pressure detected by the microphones 3 and 3 ′ using a traveling wave / reflected wave separation method known in the acoustic measurement field. . In this embodiment, two microphones are used. However, a traveling wave and a reflected wave at the lip position may be obtained using one microphone and particle velocity detection means. As the particle velocity detection means, a particle velocity detection device used for sound intensity measurement, a pneumotachograph used in the conventional FOT method, or the like can be used.

Next, a method for sequentially determining the k _m and mu _m. When e ^{-j km l} is applied to both sides of the second equation in equation (4) and expressed in the time domain,

It becomes. Here, r _m ^(2l) (t) is an impulse response representing a waveform change when the sound wave reciprocates within the section m, and can be written as e ^{−2αml in the} frequency domain. By the way, if the time to start applying the forced vibration is t = 0, it takes mτ time for the sound wave to reach the section m.

The condition is established. If this condition is taken into account in Eq. (8), the distance between the traveling wave and the reflected wave in interval m

The relationship holds. If μ _m-1 is known, S _m is known. The sound wave propagation characteristic r _m ^(2l) (t) in the section m (or its Fourier transform e ^{−2αm l} ) can be estimated based on the cross-sectional area S _m . Using this r _m ^(2l) (t) and p _m ⁺ , p _m ⁻ , μ _m can be estimated from equation (10), so that the cross-sectional area S _{m + 1 of} the (m + 1) -th section can be calculated. . As described _{above, k m, μ m, p} m + (P m +), p m - (P m -) and toward the peripheral side from the lip side, it is possible to continue to determine sequentially. As is clear from the above description, the airway whose cross-sectional area continuously changes is approximated by a chain of short tubes, and the cross-sectional area S _m of the section _m is an acoustic representation of the cross-sectional area of the section. It represents the averaged meaning. Also, the distal side of the bifurcation of the trachea (carina), k _m, mu _m represents an equivalent cross-sectional area as the propagation characteristics when regarded as one airway.

Based on the cross-sectional area S _m, propagation characteristics k _m in the interval (r m ^{_(l) (t))} for the method of estimating the has been studied in the fields of speech analysis (Non-Patent Document 5) In addition, data on the mechanical properties of the inner wall of the vocal tract (upper lung airway) are also accumulated. In this embodiment, the estimation of the propagation characteristic ^{_{k m (r m (l)}} (t)), is performed based on the well-known wall model speech analysis art.

  From the airway cross-sectional area estimated as described above, it is possible to examine whether there is a lesion such as central airway stenosis. Further, it is possible to determine whether or not an expiration airway stenosis has occurred by determining an expiration period and an inspiration period based on a signal from the flow sensor 6, and performing an airway cross-sectional area estimation and comparing in each period. It becomes possible.

In this embodiment, the forced vibration waveform is a waveform obtained by extending the pulse signal of FIG. 5 as shown in FIG. The waveform of FIG. 5 is created by sigmoidizing a Gaussian pulse with an error function. When using the signal of FIG. 5, in (10), p _m ⁺ and p _m ^- it can be determined mu _m by simply comparing the maximum value. The signal of FIG. 6 is obtained by adding a phase rotation proportional to the square of the frequency to each frequency component of the signal of FIG. 6 is output from the speaker box, and the signal detected by the microphone is subjected to a reverse operation to remove the phase rotation, so that the same measurement as when the pulse signal of FIG. 5 is transmitted from the speaker box is equivalently performed. it can. In the signal of FIG. 6, since each frequency component is dispersed on the time axis, the crest factor is greatly reduced, and a high S / N ratio can be secured.

(Second embodiment)
In the pulmonary function test apparatus of the second embodiment, the peripheral airway impedance when the peripheral side is viewed from the end of the upper airway is measured by removing the contribution of the upper airway from the respiratory impedance measured in the vicinity of the lips. The configuration of the apparatus and the forced vibration signal are exactly the same as in the first embodiment.

If sequential estimation is advanced to the upper airway end in the same procedure as in the first embodiment, the sound pressure signals P _{M + 1} ⁺ and P _{M +} at the upper airway exit are obtained as shown in Equation (5). ₁ ^- is found. The acoustic impedance Z _p of the upper air roadside unit, traveling wave P _{M + 1} ⁺ and the reflected wave P _{M + 1} ^- from

Can be calculated. This impedance is an input impedance when the peripheral airway is viewed from the end of the upper airway, and does not include the contribution of the upper airway. Therefore, it is possible to estimate peripheral airway resistance and peripheral airway reactance without being affected by upper airway artifacts and upper airway conditions.

The propagation characteristic k _m (r _m ^(l) (t)) in the sequential estimation process may be estimated not based on the model (0034) but based on the sound pressure signal itself detected by the microphone. Is possible. First, as a forced vibration signals by using the equivalent pulse waveform consisting of a high frequency component, according to the procedure described in the first _{embodiment, k m, μ m, p} m + (P m +), p m - (P _m ^-) to estimate. In the high frequency region, the influence of the upper respiratory tract artifacts or interval within the attenuation is small, k _m, the estimation of mu _m can proceed accurately. Next, in order to estimate the propagation characteristics in the low frequency range, using a forced vibration signal including a low frequency component, under the condition that the known cross-sectional area distribution mu _m, based on formula (10) k _m ( the estimation of ^{_{r m (l) (t)}} ). That is, in this case, the impedance estimate consists of two steps, the first step to determine the k _m and mu _m by using a high frequency component, in the second step, determining in the first step the mu _m using a (cross-sectional area distribution), so that to estimate the propagation characteristics including up to a low frequency band ^{_{k m (r m (l)}} (t)). If the frequency component included in the forced vibration of the second step still lacks low-frequency resolution, the frequency characteristics are reduced by using a mechanical-acoustic model of the lung airway wall as a priori knowledge. Extrapolation to the band side is performed.

  In the second embodiment, the upper airway is typically set from the lips to the glottis. The number of sections into which the upper airway is divided is determined by conditions such as the examination purpose and the signal frequency band. By the way, as can be seen from the above description, it is desirable that the length of each section length l is set so that the total length of the upper airway is an integral multiple of l. The length of the upper airway can be roughly estimated from the subject's physique, etc., but the reflection from the glottis is used by transmitting a pulse signal from the speaker box to estimate the upper airway length. If it is measured acoustically, it can be estimated more accurately. Depending on the examination purpose, the upper airway from the lips to the glottis may be approximated by one section.

  In the first embodiment and the second embodiment, it is assumed that the subject breathes the outside air spontaneously through the opening 21 and applies the forced vibration superimposed using the speaker box. However, when measuring the respiratory impedance, the forced breathing device superimposes the oscillatory airflow on the DC respiratory flow and sends it to the lung airway of the subject, but the forced breathing is superimposed on the spontaneous breathing. And no different. That is, this method can be used in combination with a ventilator or the like, and the means for applying forced vibration is not limited to the speaker box. Further, since the duration of the signal in FIG. 6 is short, the respiratory impedance at various levels of the lung air volume can be measured using the signal of the respiratory flow sensor 6.

(Third embodiment)
The third embodiment of the present invention is an implementation suitable for the case where the subject's voluntary cooperation is obtained during the examination. The configuration of the equipment is the same as in the first embodiment. In the third embodiment, the subject is required to temporarily close the glottis while holding the mouthpiece in the first step of the examination. When the glottis are closed, the impedance of the glottis 53 is approximately infinite.

  In the first step of the examination, the cross-sectional area and propagation characteristics of the upper airway to the glottis are measured. As the method, the same method as in the first and second embodiments may be used. However, taking advantage of the condition that the glottis are closed, the following method can be used. That is, as a forced vibration signal, a pulse wave, a random wave, a swept sine wave, a sine wave whose frequency is changed stepwise, or the like is used, and a vocal tract cross-sectional area estimation method known in the speech analysis field (Non-Patent Documents 7 and 8). ) To determine the cross-sectional area and propagation characteristics of the upper airway to the glottis. Depending on the purpose of the examination, the upper airway is approximated in one section, a signal with a sufficient low-frequency component is used, the characteristics are measured over a sufficient measurement time, and the equivalent cross-sectional area and propagation characteristics are estimated. In some cases.

In the second step of the test, the subject is instructed to open the glottis. In this state, forced impedance is applied to measure respiratory impedance. Using the characteristics of the upper airway estimated in the first step, the traveling wave and the reflected wave at the upper airway exit are estimated, and the peripheral impedance excluding the contribution of the upper airway is calculated based on Equation (11). The procedure is the same as that described in the first and second embodiments. Depending on the test object, the pulmonary airways, characteristics based on the circuit model of the outlet of known upper airway is terminated with an unknown distal airways impedance Z _p, by measuring the respiratory impedance from lip position, end In some cases, a method of estimating the impedance Z _p is used. Further, if necessary, the subject may be instructed to interrupt the breathing operation with the glottal open at various lung air volume levels.

(Fourth embodiment)
The fourth embodiment of the present invention is an implementation suitable for a case where the subject can speak during the examination. The equipment configuration of this embodiment is the same as that of the first embodiment. In the first step of the examination, the subject is required to utter while keeping the mouthpiece in the same state as the spontaneous breathing organ. The pressure fluctuation signal (voice signal) at this time is detected by the microphone 3.

Based on the detected speech signal, an upper airway (vocal tract) cross-sectional area is estimated by a well-known estimation method in the field of speech analysis, in this embodiment, an estimation method using a partial correlation function (PARCOR) (Non-Patent Document 9). Estimated sequentially along the airway axis. Once the vocal tract cross-sectional area function, that is, the distribution of the cross-sectional area S _m from the lip to the glottis, is obtained, the propagation characteristics of the upper airway to the glottis can also be estimated by the same method as in the first and second embodiments. it can.

In the second step, the subject is instructed to stop speaking and resume spontaneous breathing. Hereinafter, the peripheral airway impedance in which the peripheral side of the pulmonary airway is expected from the glottis can be estimated by the same procedure as the second step of the third embodiment.

It is a figure which shows the structure of the 1st Example of this invention. It is a schematic diagram of the lung airway expressed by a chain of short tubes. It is a figure explaining the acoustic propagation in each area of a lung airway. It is a figure which shows the flow of the signal in the area of a lung airway, and a boundary. It is an equivalent waveform of a signal used for forced vibration. It is an actual forced vibration waveform extended in time.

1 Speaker box
2 Test tube 21 Breathing opening 3,3 'microphone
4 signal processing equipment
5 Subjects 51 Upper airway 52 Peripheral airway 53 Glottis 54 Thorax
6 Respiratory flow sensor

Claims (5)

  In the method of inspecting lung function by applying forced vibration to the lung airway, pressure fluctuation in the lung airway or a tube connected to the lung airway is detected, and the cross-sectional area of the upper airway is estimated based on this pressure fluctuation signal. A lung function test method, wherein the lung function is tested based on the estimated cross-sectional area information.   Applying forced vibration from the lips to the lung airway, detecting pressure fluctuations that occur in the vicinity of the lips at this time, traveling waves propagating from the lip side to the peripheral side, and reflected waves propagating from the peripheral side to the lip side Using the information on the time required for propagation of sound waves, the cross-sectional area of each position in the lung airway and the estimation of the reflection that occurs are sequentially advanced toward the distal side until the desired position in the lung airway. The lung function test method according to claim 1, wherein a cross-sectional area of the lung function is estimated.   The impedance of the peripheral side of the pulmonary airway is estimated from the position of the peripheral end of the upper airway, excluding the contribution of the upper airway to the respiratory impedance based on the estimated cross-sectional area of the upper airway. The lung function testing method according to 1-2.   The voice signal emitted by the subject is detected in the vicinity of the lips, and the upper airway cross-sectional area from the vicinity of the lips to the glottis is sequentially estimated along the airway axis based on the detected voice signal. The lung function test method according to 1. A means for applying a forced vibration to the lung airway, a means for detecting pressure fluctuations in the lung airway, and a means for estimating a cross-sectional area of the upper airway, and using the method according to claims 1 to 4 A device characterized by performing a function test.

Images