JPH0131897B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a breath measuring device that measures the flow rate of breath to be measured using a resistance wire heated by an electric current.

Measurement of the flow rate per unit time of exhalation and inspiration is as follows:
It is widely needed in the fields of diagnosis of lung diseases in subjects, clinical examination of the degree of recovery from impaired respiratory function, and also in the fields of environmental medicine, industrial medicine, and sports medicine.

The exhaled breath to be measured is heated by a heat pulse on the upstream side of the flow tube of the exhaled breath to be measured, and the heated exhaled breath to be measured is detected by a temperature sensing element on the downstream side of the flow tube separated by a predetermined distance from the heating position, The flow rate of the exhaled breath to be measured is measured by measuring the time from the time of heating to the time of detection, and the flow rate of the exhaled breath to be measured is measured based on the measured time. Hereinafter, exhalation as used in this specification refers to the state of fluid including exhalation and inspiration caused by breathing.

In this case, the flow rate of exhalation to be measured is Lml/sec,
When the cross-sectional area of the flow tube for measurement is Scm ² , the average flow velocity v of exhaled breath to be measured is given by the following equation.

v=L/S (cm/sec) (1) The distance between the heating section for exhaled air to be measured, which is provided on the upstream side of the flow tube, and the temperature sensing section, which is provided on the downstream side of the flow tube, is d (cm). If T is the time required from the heating of the exhaled breath to be measured in the heating section to the detection of the heated exhaled breath to be measured in the temperature sensing section, then the following equation holds true.

T=1/LS・d(sec) (2) In this case, a W wire with a diameter D and a length l is used as the heating element of the heating part, and the density of the W wire is P (g/cm ³ ), and its thermal conductivity is When the rate is Cp, the (cal/g〓) resistance value is R, the applied voltage is V, and the energization time is t, the amount of heat ΔT given to the breath to be measured is given by the following equation.

△T=V ₂ /R・t・1/4.2×πD ² /4l・P・Cp(
3) As is clear from equation (2), as the flow rate L of exhalation to be measured increases, the time T decreases in inverse proportion to this. Therefore, especially in a measurement system where the flow rate of the fluid to be measured changes significantly, it is difficult to set the heating time period of the fluid to be measured in the heating section. In other words, if this heating time period is set too long, it will not be possible to perform correct heating for the exhaled breath to be measured, whose flow rate changes rapidly and over a wide range over time, making it impossible to perform measurements that accurately follow changes in the exhaled air flow rate. become unable. On the other hand, if the heating time period is made too short, the exhaled air detected on the downstream side of the flow tube for each unit time will be affected by the heating in the next time period, and the effect of the previous temperature sensing of the temperature sensing element will be affected. Since the next detection will be performed with the residual remaining, the detection will be inaccurate.

This invention solves the above-mentioned difficulties in conventional devices, and makes it possible to heat exhaled air, whose flow rate changes rapidly and significantly over time, with high precision and efficiency. An object of the present invention is to provide an exhalation measuring device that can constantly measure the flow rate with high accuracy in response to sudden and large changes.

According to this invention, a heating means for instantaneously heating the exhaled air to be measured is provided in the flow tube into which the exhaled air to be measured flows, and a temperature sensor is placed at a position through which the exhaled air heated by the heating means passes. A driving means is driven by the output of the temperature sensing element to heat the heating means, and the flow rate of the exhaled breath to be measured is measured based on the driving cycle of the heating means.

In the present invention, in this type of respiration measurement device, when the detection means provided in the flow tube detects that there is no breath to be measured in the flow tube, the heating means is activated by the preheating means during the detection period. is driven to perform preheating, and respiration measurement is always performed with high precision even for exhaled air, where the flow rate changes rapidly over time and the flow rate changes significantly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The respiration measurement device of the present invention will be described in detail below based on embodiments thereof with reference to the drawings.

FIG. 1 is a diagram showing the configuration of the present invention, in which a flow tube 11
The exhaled breath F to be measured from the subject is introduced from a mouthpiece (not shown) in the flow tube 11, and on the upstream side of the flow tube 11, a turbulent flow is created on the inner peripheral surface of the flow tube 11 at right angles to the flow direction of the exhaled breath F to be measured. A generator 12 is provided. The turbulent flow generator 12 has a structure in which a mesh-like body is formed of metal wire on a plane perpendicular to the flow of the exhaled breath F to be measured, for example.

The exhaled air F to be measured introduced into the flow tube 11 is generally a laminar flow and has a certain velocity distribution in a plane perpendicular to the flow. The introduced laminar flow of breath F to be measured becomes turbulent due to the turbulent flow generator, and has a uniform average velocity in a plane perpendicular to the flow.

A heating element 13 is placed in the flow tube 11 on the downstream side of the turbulence generator 12 in the diametrical direction of the flow tube 11 . The heating element 13 is formed of a W wire having a diameter of 5 μm, for example, and a heat pulse for heating the exhaled breath to be measured is applied from this heating element 13 to the exhaled breath to be measured.
That is, a heating circuit section 14 is provided, and in this heating circuit section 14, a heating pulse S _H of a predetermined pulse width generated from a heating pulse width setting circuit 10 is applied to a heating circuit 18 consisting of a constant temperature resistance wire heater. ,
The heating circuit 18 is excited by this heating pulse S _H , the heating element 13 connected to the excited heating circuit 18 generates heat, and the breath to be measured is heated by this heating pulse.

A temperature sensing circuit section 15 is provided downstream of the heat generating circuit section 14 including the heating element 13 with respect to the flow tube 11 .
The temperature sensing circuit section 15 is provided with a temperature sensing element 19, a temperature sensing circuit 20 is connected between the output terminals of this temperature sensing element 19, and an amplification shaping circuit 21 is connected to the output terminal of this temperature sensing circuit 20. A filter 9 is connected to the output end of this amplification and shaping circuit 21. A comparison circuit (not shown) is connected to the output stage of the amplification and shaping circuit 21, and the detection pulse S _S is compared with the reference signal from the reference signal setter given to this comparison circuit, and if this exceeds the reference value, , Schmitt circuit 7
An actuation signal S _D is emitted from. That is, the pulse corresponding to the heated breath to be measured detected by the temperature sensing element 19 is amplified and shaped, the DC component is blocked by the filter 9, and the output signal of the filter 9 is sent to the Schmitt circuit 7 via the minimum hold circuit 8. and an actuation signal S _D is obtained from the output of the Schmitt circuit 7. The time setting circuit 16 is driven by this operating signal S _D , and after a predetermined time, the time setting signal _ST is generated from the time setting circuit 16.

When measuring exhaled air, the amount of heat given to exhaled air by the human body that emits the exhaled air differs for each subject, so it is necessary to make corrections for this. For this reason, in the embodiment shown in FIG.
-2, each of which is arranged with its position shifted from the other. When measuring exhaled breath,
Since the second temperature sensing element 19-2, which is arranged offset from the first temperature sensing element 19-1, separates and detects the amount of heat given by the human body to exhaled air, the temperature sensing circuit 20 It is possible to perform measurements that remove the influence of the amount of heat given to the fluid by the human body.

In the measurement state in which exhaled air flows into the flow tube 11, the heating pulse S _H is output from the heating pulse width setting circuit 10.
is emitted, and when the heating element 13 connected to the heating circuit 18 is heated by this heating pulse S _H , the fluid to be measured flowing through the heating element 13 is heated at the time of heating.

When this heated fluid to be measured passes through the temperature sensing element 19, the temperature sensing element 19 is heated and its resistance value increases. As shown in FIG. 2, a bridge 34 having one side of this temperature sensing element 19 is constructed,
An amplifier 35 is connected between the detection terminals of the bridge 34. When a temperature change occurs in the fluid to be measured and the bridge 34 becomes unbalanced, the amplifier 35 generates a detection signal S _C.

This detection signal Sc is connected to the resistor 37 and capacitor 38.
The integrator circuit 36
The output of Sc is applied to a capacitor 39, and the DC component in the detection signal Sc is blocked. The detection signal Sc with the DC component blocked is amplified and shaped by amplifiers 40 and 41, and a shaped detection pulse S _S is obtained at the output end of the amplifier 41. This detection pulse S _C is applied to the non-inverting input terminal of the comparison amplifier 42 of the temperature sensing circuit section 15 .

On the other hand, the output terminal of the amplifier 41 is connected to the comparator amplifier 4
3, and is connected to the non-inverting input terminal of the comparison amplifier 43.
The cathode side of the diode 44 is connected to the output terminal of the diode 44 . The anode side of the diode 44 is connected to the capacitor 4
5, and the other end of this capacitor 45 is grounded. The anode side of the diode 44 is connected to the non-inverting terminal of the comparison amplifier 46, and the non-inverting terminals of the comparison amplifiers 43 and 46 are connected to each other. The output terminal of comparison amplifier 46 is connected to the variable terminal of variable resistor 49 via resistors 47 and 48. The connection point between resistors 47 and 48 is connected to the inverting input terminal of comparator amplifier 42.

The anode side of the diode 44 is connected to the cathode side of the diode 50, and the anode side of this diode 50 is connected to the output terminal of the switch element 51. An inverting circuit 52 is connected to the output terminal of the comparison amplifier 42.

Detection pulse obtained at the output terminal of the comparator amplifier 41
When S _S has a peak value smaller than a predetermined value, the output signal of the comparator amplifier 43 is smaller than the predetermined value, and the diode 44 is in a conductive state. When the diode 44 is conductive, the charge in the capacitor 45 is discharged, a negative voltage appears at the output of the comparison amplifier 46, and no activation signal S _D is generated at the output of the inversion circuit 52.

However, when the peak value of the detection pulse S _C exceeds a predetermined set value, the diode 44 becomes cut off,
A predetermined reference voltage is set at the inverting terminal of the comparison amplifier 42, and an actuation signal S _D is generated at the output terminal of the inverting circuit 52. When a reset signal is applied to the excitation terminal _t1 of the switch element 51, a positive pulse is applied to the capacitor 45 and a reset operation can be performed.

The actuation signal S _D is applied to an input terminal of a NOR circuit 60, and the output terminal of the NOR circuit 60 is connected to one input terminal of a NOR circuit 61, as shown in FIG. An output terminal of NOR circuit 61 is connected to another input terminal of NOR circuit 60. NOR circuit 6
1 output terminal is connected to one input terminal of the NOR circuit 62. The output terminal of the NOR circuit 62 is NOR
connected to one input terminal of the circuit 63;
An output terminal of NOR circuit 63 is connected to another input terminal of NOR circuit 62. The output terminal of a NAND circuit 64 is connected to the other input terminal of the NOR circuit 63, and one end of a capacitor 65 is connected to one input terminal of this NAND circuit 64.
The other end of 5 is grounded.

A predetermined power supply is applied via a resistor 66 to a terminal of the NAND circuit 64 to which a capacitor 65 is connected. A start switch 67 is connected between the two plates of the capacitor 65. NOR circuit 62
An input terminal of an inverting circuit 68 is connected to the output terminal of the inverting circuit 68 , and an output terminal of the inverting circuit 68 is connected to one input terminal of a NAND circuit 69 . The other input terminal of the NAND circuit 69 has a 20KHz output from the oscillator 25.
A reference signal is given. An output terminal of the inverting circuit 68 is connected to one input terminal of a NAND circuit 71 via another inverting circuit 70. this
The other input terminal of the NAND circuit 71 is connected to the oscillator 25.
A 20KHz reference signal is given from

The respective output terminals of the NAND circuits 69 and 71 are connected to the respective input terminals of the NOR circuit 72. The output terminal of this NOR circuit 72 is connected to up/down counters 73 and 74 connected in series.
and 75 clock terminals, respectively.
Further, the output terminal of the inverting circuit 68 is connected to the control terminal tc of each of the counters 73, 74, and 75. Up-down counters 73, 74 and 7
The output terminals of the gate circuits 10-G are connected to each reset terminal _tR of the gate circuit 10-G.

Each output terminal t ₀₁ of the counters 73, 74 and 75,
The terminal where t ₀₂ , t ₀₃ and each control terminal are grouped together is
They are respectively connected to input terminals of the NOR circuit 76.
The output terminal of this NOR circuit 76 is connected to one of the input terminals of the NAND circuit 64 via a NOR circuit 77.

At the time of starting, the switch 67 is turned on,
At the same time, the output signal Sm of the switch circuit 6 is applied to the base of the transistor 30, and the heating pulse S _H is generated from the pulse width setting circuit 10. A pulse counter calculation circuit 3 is connected to the output end of the pulse width setting circuit 10, and a display 2 is connected to the output end of the pulse counter calculation circuit 3, so that the heating state of the fluid to be measured by the heating pulse S _H is calculated and displayed. It is structured like this. This heating pulse S _H passes through the gate circuit 10-G to the up-down counter 73,
74 and 75 are reset, and at the same time S _H is applied to the input terminal _T1 of the NOR circuit 61, the logic value of the signal at the output terminal of the NOR circuit 62 becomes "1".
Each counter 73, 74,
The logic value of the signal at the control terminal tc of the clock 75 is set to "0", and each counter 73, 74, 75 counts the 20 KHz signal of the oscillator 25 applied to the clock terminal _CK .

The heat pulse given to the fluid to be measured is detected by the detection object 19.
When the actuation signal S _D is detected by the inverting circuit 52 and the actuation signal S D is detected, the actuation signal S _D is sent to the NOR circuit 60.
is applied to the input terminal T _{2 of} . When the time comes, NOR
The theoretical value of the signal at the output terminal of the circuit 62 is "0", and the signal is sent to each counter 73, 7 via the inverting circuit 68.
When the logical value of the signal at the control terminal tc of the counters 4 and 75 becomes "1", each counter is controlled to perform a down-count operation, and the already counted value is down-counted by the signal applied to the clock terminal.

The count values that have already been counted are exhausted and the signals at the output terminals t ₀₁ , t ₀₂ , and t ₀₃ all have a logical value of “0”.
At this time, since the logic value of the signal at the control terminal tc has already become "0", this is detected by the NOR circuit 76, and the time setting signal S _T appears at the output terminal of the NOR circuit 76.

When there is no breath to be measured in the flow tube 11, the temperature sensing circuit section 15 does not generate the activation signal S _D , and therefore the coincidence circuit 26 does not supply the time setting signal S _T. Therefore, the presence or absence of the exhaled air to be measured in the flow tube 11 can be determined based on the presence or absence of this time setting signal _ST .

That is, the output terminal of the matching circuit 26 is connected to the input terminal of the timer 4, and the output terminal of the timer 4 is connected to the gate terminal of the switch circuit 6. The timer 4 is configured such that a desired period can be set, and the period corresponding to the maximum resistance flow rate of exhaled air in the flow tube 11, that is, the time required for exhaled air to pass between the heating element 13 and the temperature sensing element 19 at the lowest flow rate is set. has been done.

If the time setting signal _ST is not emitted from the matching circuit 26 during the time corresponding to the lowest cycle set by the timer 4, it is determined that there is no breath to be measured in the flow tube 11.

In this invention, during the period in which the detecting means detects that the breath to be measured does not exist, the preheating means is driven to operate the heating means to perform preheating.

That is, when the timer 4 is given the time setting signal S _T from the coincidence circuit 26 during the minimum cycle corresponding to the minimum flow rate set in advance, the timer 4 emits the gate signal Sg, and this gate signal Sg is sent to the switch circuit 6. is applied to the gate terminal of The switch circuit 6 to which the gate signal Sg is applied to the gate terminal is cut off, and the input of the output signal Sm from the switch circuit 6 to the heating pulse width setting circuit 10 is blocked.

In this state, the heating pulse width setting circuit 10 is driven by the time setting signal S _T supplied from the coincidence circuit 26, and the heating pulse S H having a predetermined pulse width is emitted from the pulse width setting circuit 10, and the heating pulse width setting circuit 10 is driven by the time setting signal S _T supplied from the matching circuit 26. 18
given to.

On the other hand, if the time setting signal S _T is not given from the coincidence circuit 26 during the minimum period corresponding to the minimum flow rate set in advance in the timer 4, the timer 4
does not emit gate signal Sg. In this state, the switch circuit 6 receives e.g.
Output signal driven by 10Hz pulse signal
Emit Sm. A preheating pulse S _H is generated from the pulse width setting circuit 10 in response to this output signal Sm.

In addition, during preheating, for example, as shown in FIG.
The configuration is such that the input of S _H to the up-down counter 24 is blocked. To summarize the above operation and explain it with reference to Fig. 6, the heating pulse S _H
occurs at time _t1 , S _H is sent from the gate circuit 10-G, the up-down counter 24 is reset, the up-down counter 24 starts counting up, and the exhaled breath to be measured is heated by the heating pulse S _H , The heated exhaled air passes through the temperature sensing circuit section 15 after a time corresponding to its flow rate, and at time t ₂
An output S _C is obtained from the temperature sensing circuit section 15, and an actuation signal S _D is obtained based on this, and the up-down counter 24 is placed in a down-counting state by the actuation signal S _D. When the count value of the up-down counter 24 reaches zero, a time setting signal _ST is generated at that time _t3 , which causes the heating pulse S _H to be generated again. At the same time, the timer 4 is reset, and its output Sg becomes high. Therefore, the output pulse (for example, 10 Hz) of the pulse generator 5 is not output from the switch circuit 6.

In this way, the period of the time setting signal _ST becomes shorter when the flow rate of the exhaled breath to be measured is high, and becomes longer when the flow rate is slow. When the flow rate of exhaled air to be measured slows down to a predetermined value or less, for example, when it becomes zero, the timer ₄ is reset by the time setting signal _ST at time t4, which occurred last in FIG. When the timer time elapses during that time, the output Sg of the timer ₄ becomes low level at that time t5, and the output of the pulse generator 5 is outputted as the output Sm of the switch circuit 6. Therefore, a preheating pulse S _H is generated for each signal _Sm , and as shown in _FIG . The up-down counter 24 is reset every time. Therefore, the up-down counter 24 starts measuring immediately when the exhaled air to be measured flows in.

In this embodiment, when exhaled breath is measured, a heating pulse is emitted from the heating element 13 to the exhaled breath to be measured, and the time required for the heated exhaled breath to be detected by the temperature sensing circuit section 15 is determined. The configuration is such that heating pulses based on the time setting signal S _T are sequentially emitted at twice the interval. The generation interval of this heating pulse is 2 times the time until detection as in the embodiment.
The value is not limited to double, but can be set to an optimal value depending on the measurement conditions of exhaled breath. Furthermore, if it is necessary to separate and completely measure expiration and inhalation of the subject's respiration, the heating element 13 is narrowed and two sets of temperature sensing elements 19 are installed on both sides, as shown in FIG. 1
9' may be provided. Since the circuit used in this case has the same structure and operation as that already explained in the embodiment shown in FIG. 1, a redundant explanation thereof will be omitted.

The flow rate of exhaled breath to be measured changes rapidly over time, especially at the beginning of the breath, and the flow rate variation range is also extremely wide. If the preheating means were not present, exhaled air would flow into the flow tube 11 through the mouthpiece from a state where no exhaled air to be measured existed in the flow tube 11, resulting in a rapid increase in the flow rate of the exhaled air to be measured. In this case, the heating element 1 for the exhaled breath to be measured
3 is not effectively heated, and the temperature sensing element 1
9 may not be performed accurately.

However, in the present invention, by providing the preheating means as explained in the embodiment, even the exhaled breath to be measured whose flow rate changes rapidly and over a wide range can be effectively heated. Highly sensitive and highly accurate flow rate measurement using the thermal element 19 can be achieved. This preheating means is indispensable especially when measuring exhaled air corresponding to forced vital capacity or maximum ventilation.

Figure 4 shows the relationship between the expiratory volume l obtained with the respiration measuring device of the present invention and the time from the time of heating to the time of detection, and shows that the linearity is extremely good over a wide range of flow rates. .

As explained in detail above, according to the present invention, when measuring the flow rate of exhaled air, the flow rate changes rapidly over time, such as exhaled air corresponding to forced vital capacity or maximum ventilation, and the amount of change varies over a wide range. It is possible to provide a respiration measuring device in which the exhaled breath to be measured is effectively heated even in exhaled breath measurement over a long period of time, and detection using a temperature sensing element can be performed with high sensitivity and accuracy.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the structure of an embodiment of the respiration measurement device of the present invention, FIGS. 2 and 3 are specific circuit diagrams showing the structure of the embodiment of the respiration measurement device of the invention, and FIG. 5 is a diagram showing the measurement characteristics obtained in an embodiment of the respiration measuring device of the present invention, FIG. 5 is a diagram showing the configuration of the main part of another embodiment of the respiration measuring device of the present invention, and FIG. 6 is a diagram showing the operation of the present invention. This is a time chart to explain. 4: Timer, 11: Flow tube, 13: Heating element, 1
4: Heat generation circuit section, 15: Temperature sensing circuit section, 16: Time setting circuit, 17: Heating pulse generation circuit section, 18:
Heating circuit, 19: Temperature sensing element, 26: Matching circuit.

Claims (1)

[Claims] 1. A heating means for instantaneously heating the breath to be measured in the flow tube, a temperature sensing element provided at a position where the breath to be measured heated by the heating means passes, and a detection output of the temperature sensing element to heat the heating means In the respiration measurement device that measures the flow rate of the exhaled breath to be measured based on the drive cycle of the heating means based on the detection output of the temperature sensing element, the detection output of the temperature sensing element is not detected for a predetermined period of time. Breathing characterized by having a detection means for detecting the breath and a preheating means for preheating the heating means during a period when the detection means detects that the breath to be measured is not in the flow tube. measuring device.