JPH064093B2 - Ultrafiltration amount and dialysate concentration measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an ultrafiltration amount and a dialysate capable of measuring the ultrafiltration amount and the concentration of the dialysate using ultrasonic waves during hemodialysis. The present invention relates to a concentration measuring device.

[Conventional technology]

In hemodialysis in recent years, as the performance of hemodialyzers has improved, it is necessary to automatically control the amount of ultrafiltration, that is, the amount of water removed from blood, and a measurement technique for that purpose is essential. ing. However, since the amount of ultrafiltration that increases to the discharge side is a small amount of less than several percent of 500 ml for the dialysate flowing in at 500 ml per minute, the measurement accuracy is 500 ml.
However, it must be 0.1% or less.

Conventionally, the following three methods have been mainly put into practical use as methods for measuring the amount of ultrafiltration, but each has its drawbacks.

One is to prepare two sets of constant volume chambers separated by a moving partition, and move the switching valve so that the inflow rate and outflow rate to the hemodialyzer are the same, and ultrafiltration is separate. It is a method of forcibly carrying out by means of. Although this method has high accuracy, the system is complicated and requires many expensive parts. In addition, the operation of the switching valve is frequent and is easily consumed, and the accuracy is greatly reduced due to the consumption of the switching valve, but it is difficult to know the deterioration of the accuracy.

The second method is to temporarily close the inflow circuit and the outflow circuit of the hemodialyzer, measure the transmembrane pressure and the ultrafiltration amount,
From that relationship, it is a method of estimating and calculating the amount of ultrafiltration for most of the time when it is not closed from the transmembrane pressure. Although this method can measure the amount of ultrafiltration with a simple configuration, it has a drawback in that the accuracy decreases when a high-performance hemodialyzer or a special hemodialyzer is used. In addition, the condition at the time of closing and the condition at the time of calculation are different from each other, and the condition also changes with time, so the reliability of the measured value is low.

The third method is a method in which the inflow amount and the outflow amount into the hemodialyzer are directly measured by a flow meter and the ultrafiltration amount is obtained from the difference in the flow rates. Although this method is basic, it is difficult to obtain a flow meter with an accuracy that can be used, and since the outflow side is heavily soiled and cannot maintain its accuracy for a long period of time, there are few practical applications. There is also an example of switching and using a flow meter with poor accuracy (Japanese Patent Publication No. 59-10227), but since the inflow circuit and the outflow circuit are shared, there is a problem in terms of contamination and disinfection.

On the other hand, as a method of knowing the concentration of the dialysate, it is common to electrically measure the electrical conductivity of the dialysate using a metal or carbon electrode. However, in recent years, a bicarbonate-based dialysate, which has little adverse effect on patients, is often used, and when the dialysate loses its tissue balance for some reason,
There is a drawback that carbonate, which is an electrically insulating material, is deposited on the electrode surface. This means that the concentration control of the dialysate may not be successful, but the concentration abnormality may not be alarmed. Such abnormal concentrations of dialysate are extremely dangerous to the patient.

[Problems to be Solved by the Invention]

Conventional ultrafiltration amount measuring method and dialysate concentration measuring method,
Each of them has the above-mentioned drawbacks and is not suitable for practical use.

The present invention has been made to eliminate those drawbacks. That is, the present invention can measure the inflow rate and outflow rate of the dialysate directly and continuously know the ultrafiltration rate with a simple configuration without expensive parts and consumable parts, and various conditions can be obtained. An object of the present invention is to provide an ultrafiltration amount measuring device in which the measurement accuracy does not deteriorate even under the conditions.

Another object of the present invention is to provide a dialysate concentration measuring device which has the same structure as the ultrafiltration amount measuring device and is not affected by the precipitation of carbonate and can be used safely. Is.

[Means for Solving the Problems]

The present invention provides a measuring tube having ultrasonic transducers arranged on the upper and lower sides, and an intermediate wall of the measuring tube is provided with a partition wall that transmits ultrasonic waves but does not pass dialysate. And an inflow quantity measuring section and an outflow quantity measuring section having the same flow path cross section, and an inflow path or an outflow path is provided at the ultrasonic transducer installation side end of each measurement section, and the partition wall installation side end is provided. An outflow passage or an inflow passage in each of the parts, so that the distance between the inflow passage and the outflow passage in the inflow amount measuring unit and the distance between the inflow passage and the outflow passage in the outflow amount measuring unit are equal, The outflow passage of the inflow amount measuring unit is connected to the inflow circuit of the hemodialyzer, the outflow circuit of the hemodialyzer is connected to the inflow passage of the outflow amount measuring unit, and the inflow amount measuring unit and the outflow amount measuring unit An ultra limit set with and so that the flow direction is reversed. Overdose and dialysate concentration measuring apparatus has solved the above problems with a.

[Action]

The difference between the time required for the ultrasonic wave to reach the other transducer from one transducer and the time to reach the one transducer from the other transducer, and the distance between the transducers. The flow velocity increased by ultrafiltration can be calculated from the correlation between the flow velocity increased by the amount of ultrafiltration in the outflow amount measurement unit and the propagation velocity of ultrasonic waves when the inflow liquid is stationary. The ultrafiltration amount can be known from the numerical value and the cross-sectional area of the flow rate measuring unit.

The dialysate concentration can be calculated from the correlation between the ultrasonic wave propagation velocity, the liquid temperature, and the liquid concentration.

〔Example〕

 The present invention will be described in more detail below.

When the flow rate of dialysate is measured with an ultrasonic flow meter, the propagation speed of ultrasonic waves changes depending on the temperature and concentration of the solution and is affected.
This change amount is several thousand times larger than the target ultrafiltration amount. Therefore, in the present invention, the inflow rate and the outflow rate of the dialysate are canceled without being affected by the liquid temperature and the concentration, and only the ultrafiltration amount can be measured.

First, the flow rate measurement method using ultrasonic waves will be described with reference to FIG. 1. The liquid to be measured passes through the flow rate measurement unit 3 from the inflow circuit 1 at a flow velocity v ₆ and exits from the outflow circuit 2. At this time, when ultrasonic waves are emitted from the ultrasonic transducer 4, the propagation velocity V ₇ in the flow rate measuring unit 3 is obtained by the equation (1), where V is the velocity at which the ultrasonic waves propagate in the stationary liquid.

V ₇ = V + v ₆ (1) From the equation (1), the time T ₄ → ₅ for the ultrasonic wave to propagate from the transducer 4 to the transducer 5 is given by the equation (2) when the distance of the flow rate measuring unit is l _3. Become.

Similarly, the time T ₅ → ₄ for the ultrasonic wave to propagate from the oscillator 5 to the oscillator 4 is given by the equation (3).

When the time difference ΔT between T ₅ → ₄ and T ₄ → ₅ is calculated from the equations (2) and (3), the equation (4) is obtained.

If ΔT is measured from the equation (4), l ₃ and V are known, so that the flow velocity v _{6 of} the liquid is known. Further, the flow rate of the liquid can also be known from the cross section of the measuring portion and v ₆ .

Next, the configuration of the present invention will be described with reference to FIG. The dialysate passes from the inflow circuit 14 through the inflow amount measuring unit 15 at a flow rate v ₁₅ , enters the hemodialyzer 11 through the hemodialyzer inlet 12, and removes waste and water from the blood in the dialyzer 11, that is, Ultrafiltration is performed, and the dialysate increased by that amount exits the hemodialyzer outlet 13, passes through the outflow amount measuring unit 16 from below at a flow velocity v ₁₆ , and exits from the discharge circuit 17. Inflow amount measuring unit 15 and outflow amount measuring unit
The partition 16 is divided into upper and lower parts by a partition wall 18 that transmits only ultrasonic waves and does not allow liquid to pass through, and is located on the ultrasonic wave passing axis with the partition wall 18 interposed therebetween.
As the material of the partition wall 18, in the sense that the loss of ultrasonic waves at the interface between the dialysate and the partition wall 18 is minimized, the characteristic acoustic impedance, that is, the product of the density of the material and the propagation velocity is close to that of the dialysate. Select. Specifically, medical silicone resin, urethane resin, or the like is adopted. Even a metal can be used as long as it has a low density and is thin like titanium foil. The inflow amount measuring unit 15 and the outflow amount measuring unit 16 make the flow passage cross sections of the measuring unit equal so that the flow velocity with respect to the flow rate is the same. Furthermore, the flow directions of the inflow and the outflow are made opposite, that is, they are selected in the reverse direction or the opposite direction with the partition wall 18 sandwiched therebetween, and the distances l ₁₅ and l ₁₆ of the measurement portions are made equal to each other, and the inflow amount and the outflow amount are ultrasonic waves. Try to cancel out the influence on the propagation speed. In the above configuration, if the difference in the propagation time of ultrasonic waves in both directions is measured, the inflow amount measuring unit 15
And the flow rate difference between the outflow amount measuring unit 16 and the flow rate difference of the measuring unit can be known. That is, the amount of ultrafiltration can be measured. Under the hemodialysis conditions in the above configuration, the range of change in the temperature and concentration of the liquid is small, and the influence can be ignored.

Next, a method for calculating the ultrafiltration amount in the above configuration will be specifically described. The ultrasonic wave is sent from the ultrasonic oscillator 19 and the ultrasonic wave propagation speed when the inflow liquid is stationary is V
When _s, the propagation speed of the ultrasonic inflow amount measuring section 15 V
_{In the case of 21} , the equation (5) is obtained by adding the liquid flow velocity v ₁₅ to V _s .

V ₂₁ = V _s + v ₁₅ (5) If the distance of the inflow amount measuring unit 15 is l ₁₅ , the propagation time T _F15 of the ultrasonic wave passing through the inflow amount measuring unit 15 is given by the formula (6).

In addition, the propagation velocity V of the ultrasonic wave in the outflow amount measuring unit 16
Reference _{numeral 23} denotes the difference between the above-mentioned V _s and the difference in the propagation velocity caused by the difference in the liquid temperature and the concentration of the outflow rate measurement unit 16 with respect to the inflow rate measurement unit 15.
Let ΔV _s be the propagation time T through the outflow amount measurement unit 16
_F16 becomes the formula (7) similarly to the formula (6).

When the time to pass through the partition wall 18 and T _F18, ultrasonic time T _F from the oscillator 19 to reach the transducer 20 is (8).

T _F = T _F15 + T _F18 + T _F16 (8) Conversely, the propagation time T _R16 in the outflow amount measuring unit 16 when the ultrasonic wave is propagated from the ultrasonic vibrator 20 to the vibrator 19
Becomes equation (9).

Similarly, the propagation time T _R15 in the inflow measurement unit 15 is (1
It becomes expression (0).

Time T when the ultrasonic wave reaches the vibrator 19 from the vibrator 20
_R becomes equation (11).

T _R = T _R16 + T _R18 + T _R15 (11) When the difference ΔT in ultrasonic wave propagation time is calculated from the above equations (8) and (11), T _F18 and T _R18 are equal, so cancel each other out, (12)
It becomes an expression.

ΔT = T _R −T _F = T _R16 + T _R15 − (T _F15 + T _F16 ) ... (12) If the flow rate increased in the outflow rate measurement unit 16 by the ultrafiltration amount is Δv, then v ₁₆ = v ₁₅ + Δv. ,this
Substituting them into equations (7) and (9) and further adding them. Substitute in (12).
Substituting equations (6) and (10) into equation (12) yields equation (13).

Since l ₁₅ and l ₁₆ are the same, if they are put together as l (14)
It becomes an expression.

In equation (14), ± ΔV _s , Δv, and v ₁₅ are smaller than V _s , so equation (15) is obtained if the term in the denominator is ignored.

By measuring ΔT from the above, the flow velocity Δv increased by the ultrafiltration can be found from the equation (15), and the ultrafiltration amount can be known from the cross-sectional area of the flow rate measuring section. This means that, under the condition that the operating temperature range is narrow like the dialysate, and the difference in the temperature and concentration of the inflow and outflow is small, the ultrafiltration volume is extremely small with respect to the total flow rate with a simple configuration. It shows that it can be measured with high accuracy. In addition, the measurement of the propagation time of ultrasonic waves,
Performed by the sing-around method or the PLL method, which is a method of measuring the propagation time of an ordinary ultrasonic wave, and based on the measured time difference, the abnormal data is removed and the offset is canceled by using a microcomputer using a microcomputer.
A more accurate ultrafiltration amount can be obtained.

Next, a method for measuring the dialysate concentration will be described. The propagation velocity of ultrasonic waves in an aqueous solution becomes higher as the concentration of the aqueous solution becomes higher. In other words, it is a well-known fact that the higher the concentration of the aqueous solution, the more easily the ultrasonic waves propagate. It is also known that there is a correlation between the propagation velocity of ultrasonic waves and the temperature, pressure and concentration of the aqueous solution.

By the way, the absolute value of the propagation velocity of ultrasonic waves in the above-described configuration and structure can be known by measuring the amount of ultrafiltration. Further, knowing the temperature of the dialysate is an indispensable item in dialysis, and since the device for dialysis always has a temperature measuring function, it is easy to know the temperature of the dialysate. The change in pressure is negligible in this case. From these data, the concentration of the dialysate can be calculated from the correlation between the ultrasonic wave propagation velocity, the liquid temperature, and the liquid concentration. Even when the operating temperature range is narrow like a dialysate, the relationship between the propagation velocity, temperature and concentration is non-linear, but the concentration can be easily calculated by using a microcomputer.

Therefore, a highly reliable dialysate concentration measuring device can be configured without adding any constitution to the ultrafiltration amount measuring device described above.

Furthermore, since this device is not affected by the precipitation of carbonates, there is no risk of malfunction, and it is highly safe. When used in combination with an ultrafiltration amount measuring device, a dialysate concentration measuring device can be obtained at extremely low cost. be able to.

〔The invention's effect〕

Since the present invention is as described above, it has a simple structure, is not affected by dirt and use conditions, has no moving parts and consumable parts,
A safe and highly reliable ultrafiltration measuring device can be supplied at low cost. In addition, there is an effect that a dialysate concentration measuring device having the same configuration as the ultrafiltration amount measuring device can be obtained without being affected by precipitation of carbonate, without fear of malfunction, and having high safety.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an ultrasonic flowmeter, and FIG. 2 is a schematic configuration diagram showing an embodiment of the present invention. Explanation of symbols 11 ... Hemodialyzer, 14 ... Inflow circuit 15 ... Inflow amount measurement unit, 16 ... Outflow amount measurement unit 17 ... Discharge circuit, 18 ... Separator 19, 20 ... Ultrasonic transducer

Claims (1)

[Claims] 1. A measurement tube provided with ultrasonic transducers on the upper and lower sides, and a partition wall which transmits ultrasonic waves but does not pass dialysate is provided in the middle of the measurement tubes so that ultrasonic waves pass through the measurement tube. The flow rate is divided into an inflow rate measuring section and an outflow rate measuring section having the same distance and flow path cross section, and an inflow path or an outflow path is provided at each end of the ultrasonic transducer installation side of each of the measurement sections, and the partition wall installation side. An outflow passage or an inflow passage is provided at each end so that the distance between the inflow passage and the outflow passage in the inflow amount measuring unit is equal to the distance between the inflow passage and the outflow passage in the outflow amount measuring unit. Connecting the outflow path of the inflow rate measuring unit to the inflow circuit of the hemodialyzer, connecting the outflow circuit of the hemodialyzer to the inflow path of the outflow rate measuring unit, and measuring the inflow rate measuring unit and the outflow rate The limit is set so that the flow direction is opposite to that of the part Filtration rate and dialysate concentration measuring device.