WO2002024070A1

WO2002024070A1 - Device for rapidly determining the diffusion capacity of a lung

Info

Publication number: WO2002024070A1
Application number: PCT/DE2000/003281
Authority: WO
Inventors: Peter Ganshorn
Original assignee: Peter Ganshorn
Priority date: 2000-09-20
Filing date: 2000-09-20
Publication date: 2002-03-28
Also published as: DE10085180D2

Abstract

The invention relates to a device for determining the diffusion capacity of a lung and distribution defects of the lung. The concentrations of carbon monoxide CO and helium He contained in the inspired and expired air are measured, the concentration of He being determined by measuring the echo time of the ultrasonic pulses between two ultrasonic transmitters/receivers, especially piezoelectric transmitters/receivers. An ultrasonic pulse is radiated from a transmitter (1) and at the same time, a period that is slightly shorter than the echo time in a static medium begins. At the end of this period, the discharging of a capacitor to which a voltage is applied, with constant current intensity is begun. The discharging process is terminated when the ultrasonic pulse is registered in the receiver (2), the voltage that is still present at the capacitor is measured and the resulting duration of discharging is determined. The echo time is determined by adding the period and the duration of discharging, the echo time measurement is repeated in the reverse direction and the flow speed and/or the molar mass is/are determined from the different echo times.

Description

Device for the rapid determination of the diffusion capacity of a lung

The invention relates to a device for determining the diffusion capacity and distribution disorders of the lungs, in which the concentrations of carbon monoxide contained in the inhaled / exhaled air

CO and helium He can be measured.

One of the important criteria for determining the performance and health of the lungs is their diffusion capacity, i.e. their ability and effectiveness in gas exchange, i.e. H. when submitting the

Oxygen to the tissue or the circulating blood or the absorption of carbon dioxide from the tissue into the lungs. It is determined and depends on the one hand on the given physiological conditions, such as the lung volume, the diffusion distance in the gas phase, the thickness and area of the alveolocapillary membrane and the blood volume in the capillaries, and on the other hand on the functional properties, such as ventilation, perfusion , Distribution disorders, diffusion properties of the separating membrane and the reaction rate of 0 ₂ and the CO with the hemoglobin. The sum of all of the above factors determines the diffusion capacity. In principle, there is the possibility of using 0 ₂ and CO gases, since they both have the properties in common after the diffusion from the alveolus into the capillary or in the erythrocytes to form a chemical bond with hemoglobin immediately. On the one hand, the measurement based on 0 ₂ corresponds to a value of

Diffusion capacity that better corresponds to the physiological conditions. However, as will be explained in more detail below, the measurement of the diffusion capacity based on the CO forms the advantage of the much simpler methodology. According to relevant basic Considerations are the diffusion capacities measured with oxygen 0 ₂ not identical in value, but proportional to the diffusion capacity of the carbon monoxide CO. The advantage of using CO is that, in contrast to 0 _2, a significantly lower pressure is sufficient to achieve full saturation of the hemoglobin.

In addition, the CO is almost completely bound to the hemoglobin, so that the partial pressure of the CO in the lung capillary is so low that it can be neglected. The advantage is that one of the most difficult measurement variables when determining the diffusion capacity, namely the mean capillary gas partial pressure, becomes 0. The carbon monoxide CO then has the diffusion capacity from the quotient of the amount of gas CO that is absorbed per minute to the average alveolar gas partial pressure, the latter being determined directly from the alveolar air.

For routine diagnostics, two methods for determining the CO diffusion capacity, namely the single-breath method and the steady-state method, have become established. The former can be carried out quickly and is therefore particularly suitable for screening examinations. The prerequisite is that the patient holds his breath for 10 seconds, for example. During this period, part of the inhaled amount of CO diffuses from the alveolar space into the blood. The subject is offered an air mixture that contains about 21% oxygen 0 _2, about 0.3% CO and also 2 - 12% helium. Assuming that helium and carbon monoxide dilute in the alveolar space in the same way, but helium does not diffuse, the difference between expired and inspired heli the original CO concentration in the alveoli CCOA, so:

When calculating, it must be taken into account that the alveolar CO concentration does not drop linearly, but in the form of an e-function. The following variables must be known to determine them:

1. The intrapulmonary gas volume V (= functional residual volume

+ Inspiration volume) and

2. the CO and helium concentration of the inspiratory air and the expired alveolar air.

Then the diffusion capacity can be calculated as follows:

D _LCO = intrapulmonary gas volume * 60 / test duration in

Sec. * RAtmosphere ⁼ In (CcOA beginning / C-cOA end) = 0.0084 * V * In (C _H eA * C _C oι / (CcoA * C _H ei))

(See publications such as "Die Lungenfunktion" by Ulmer, Reichert, Nolte, Islam, Georg Thiemer Verlag, 4th edition, pages 146, 147).

A determination of the concentration of the carbon monoxide CO is therefore required for the measurement, which is usually done by means of infrared absorption or in some cases with the help of chemical cells; that of helium with the help of thermal conductivity or in apparatus complex cases with the help of gas chromatographs. However, the measurement of the helium concentration with the aid of the thermal conductivity is comparatively slow, so that an average value is obtained over the individual exhalation process. It would be crucial, however, to use a rapidly displaying analyzer for the helium in order to be able to recognize further and more precise values and in particular distribution disorders within the lungs. For the medical professional, there are significant information about whether the ventilation of the lungs is even or uneven, i.e. whether individual areas are better ventilated and others less or not at all. With a slow analysis, one obtains an averaging that does not allow any information about distribution problems.

The object of the present invention is therefore to provide an analyzer which permits rapid and continuous analysis of the helium concentration.

This invention is achieved in that an ultrasound pulse is emitted by a transmitter, and at the same time the lapse of a period that is slightly shorter than the running time in the stationary medium begins after the end of the period the discharge of a capacitor to which one Voltage is applied, begins with a constant current, the discharge is ended with the registration of the ultrasound pulse in the receiver, the voltage still applied to the capacitor is measured and the discharge duration is determined therefrom

Running time from time span and discharge time is added, the running time measurement is repeated in the opposite direction, the flow rate and / or the molar mass is determined from the different running times. It must be assumed that when determining the diffusion capacity of the lungs, the proportion of carbon monoxide continues to be produced in the known manner, namely by infrared absorption or with the help of chemical cells, which have the advantage of being cheaper, but the disadvantage of much slower analyzes. The decisive factor for the invention is the use of ultrasound as a fast analyzer for determining the helium concentration. The molar mass of the helium portion to be measured in the exhaled air is determined continuously in discrete steps, from which the density or concentration of the helium can be determined by conversion, ie taking into account the temperature of the air pressure. The rapid measurement of the helium allows numerous closely spaced measurement points to be recorded during a single exhalation process that describe a curve. The slow measurement of the state of the

Technology, on the other hand, only gives the average over a single exhalation process. The course of the curve allows conclusions to be drawn about the ventilation of the individual areas of the lungs. With the method of mass spectrography, there is another fast analysis method available, but due to the considerable expenditure on equipment, it is not very manageable in practice and is therefore not recommended. The CO concentration can and should continue to be measured as an average, so that a slow analyzer can be used without any problems. In the case of distribution disturbances, a correction factor can be determined from their degree, with which the CO value can be corrected.

In the ultrasonic transit time method, an ultrasonic pulse is transmitted essentially in the direction of movement through the medium, the transit time of which on the defined path between the transmitter and the receiver measured and the process repeated immediately afterwards in the opposite direction. The speed of propagation of the impulse is increased or decreased by the flow of the medium and the molecular weights and the density or concentration derived from them can be determined from the different values. With the usual geometric conditions and a change in the composition of the exhaled air in the order of 5 percent by volume, the runtime changes in the order of 1 microsecond. A measurement in the nanosecond range is therefore required to adequately resolve this time interval by dividing it by at least 1000 steps. The clocked counters used to count the time between transmission and reception of the signal work with frequencies in the GHz range. But since the entire runtime is counted, a relative error of z. For example, only 1% already have falsifications which are in the order of magnitude of the changes in the term. A more precise time resolution, ie an even faster counter is not possible, so that the invention has followed the following path:

The actual time measurement only begins shortly before the presumed arrival of the ultrasonic pulse in the receiver, and the charge stored in a capacitor is used for the time measurement. As stated above, the runtime is subject to only minor changes, so that the actual measurement only has to be started shortly before the end of the known runtime in the still medium. It can be determined with a blind test, ie without flow, and then a slightly shorter period of time, e.g. B. 148 instead of 150 microseconds, can be set as a so-called dead time, after which the discharge of a capacitor is started. It is charged with a known amount of charge by the application of a voltage. It is that Specialist possible to discharge it with a constant current, so that the charge stored in the capacitor and thus the electrical voltage decreases continuously. The discharge process is then ended when the pulse is registered in the receiver. The voltage applied to the capacitor is converted into the discharge time of the capacitor, using the formula t = (C x U): I, with the capacitor capacitance C, the electrical voltage U and the constant discharge current I. It becomes dead time added and get the total duration of the ultrasonic pulse from the transmitter to the receiver. After the process was repeated immediately afterwards in the opposite direction, ie the previous receiver acts as a transmitter and vice versa, the transit times of the ultrasound pulse are measured with the direction of movement and against the direction of movement and the molar mass of the medium can be calculated using the known formulas. The measures necessary for this, ie the coupling of a

Receiver to a capacitor, as well as the determination of the discharge time and the addition to the dead time and the calculation of the desired measurement results can be carried out automatically by electronic circuits, as is known to the trained expert.

The advantage of the invention is that the measurement of electrical quantities, such as the voltage applied to the capacitor in mV, can be carried out with inexpensive measuring devices and small measurement errors. Furthermore, the analog output signals with known electrical circuits, e.g. B. operational amplifiers, are processed further, so that the evaluation of the measurement results, ie the summation and difference formation of the transit times, can be implemented in a simple manner. In addition, there is a reduction in the absolute size of the relative due to the short time period in which measurements are taken Measurement error that occurs with each measurement, since an error of 1% in one microsecond falsifies the result less than with the measurement methods mentioned above. This proposed ultrasound measurement method allows a precise and at the same time quick determination of the density or concentration of the helium component and thus allows the implementation of devices which, in contrast to mass spectrometers, permit rapid helium analysis with little outlay on equipment, and thus the better assessment of the diffusion capacity and the determination distribution disorders of the lungs. The proposed device not only gives the diagnostician much more precise, but also additional values for assessing lung function.

Advantageous embodiments of the method and an apparatus for performing the method are the subject of subclaims.

In order to adapt the method to the most varied of circumstances, an advantageous embodiment consists in changing the time period and / or the voltage applied to the capacitor and / or the discharge current. With a change in the applied to the capacitor

The voltage and the discharge current are adapted to the required measuring range. If, for example, the capacitor voltage is increased, a longer period of time can be measured with a constant discharge current, as is necessary in the case of a fast flow and a large change in the transit time associated therewith. It is also possible to increase the discharge current at the same time, so that the decrease z. B. always the same period of time is assigned to an mV of capacitor voltage in order to obtain a consistently high resolution of the respective measuring range. A simplification of the method is to determine the transit time of a pulse in the quiescent medium and to set the voltage and / or the discharge current applied to the capacitor such that the voltage 0V, which is reached after a certain discharge duration, is assigned to the transit time in the quiescent medium is, that the zero crossing of the capacitor voltage, when a positive voltage has been applied, corresponds to the point in time at which a pulse in the stationary medium would be registered in the receiver. The measuring range, ie the voltage and the discharge current, is the respective medium

Helium adjusted with its flow rate. The advantage is that with a linear approach, as explained below, the small changes in the running time, or the measured applied voltage after the end of discharge, directly into the change in the flow rate or the change using known circuits

Molar mass can be converted, whereby the running times differ from the time in the still medium by the same small value.

In a simplification of the calculation of the speed of sound and / or the molar mass of the medium, it is assumed that a small change in the speed of sound is proportional to a small change in the transit time, or inversely proportional to the change in molar mass. This linearization is exemplified by the formula for calculating the speed of sound: it contains the term (ti - t ₂ ) / (t ₁ * t ₂ ), with the two different terms, each of which is a small amount d from the term t Distinguish ₀ in the resting medium. From this follows: ((t ₀ + d) - (t ₀ -d)) / (t ₀ ² - d ² ) = (2 * d) / to ² . Since second-order d ² is small, it is negligible, as an estimate of the order of magnitude shows: in the exemplary embodiment of the drawing, t ₀ is 150 microseconds and d is approximately one microsecond, so that there is a relative error of 0.005%. It follows that the small change in flow velocity is proportional to the small change in transit time d. Of course, this approximation only applies in a limited range that is to be determined for each medium and each flow velocity or molar mass, ie as long as the deviation from the actual value is smaller than the measurement error of the device. The advantage of linearization is that the voltages measured on the capacitor in mV can be converted directly into changes in flow velocity or molar mass, which can easily be carried out using known circuits.

One possible method of determining the molar mass is that it is carried out in the still medium. As a result, the transit times of the ultrasonic pulses that are sent through the medium in the opposite direction have the same amount. It is irrelevant according to the invention how the medium in the flow tube is brought into a state of rest, relative to the tube.

Further details, features and advantages of the invention can be found in the following description, in which an embodiment of the invention is explained in more detail with reference to drawings. They show a schematic diagram of the proposed analyzer in the form of a block diagram. The subject inhales the gas mixture containing carbon monoxide CO and helium He, which, because they are inspiratory concentrations, are referred to as FICO and FIHE. The gas volume is measured with a pneumotachograph. With the one-breath

The respiration, stopping time and discharge of the expiratory air are electronically controlled using appropriate valves. The device is equipped for the determination of the carbon monoxide concentration by infrared absorption called CO-URAS and the concentration of helium is measured by the He analyzer.

The measured gas concentrations of the inhaled air (inspiratory helium concentration (= FIHE) and inspiratory carbon monoxide concentrations (FICO) are determined with the respective expiratory gas concentrations and evaluated and output together with the gas volume recorded by the PT by a computer.

Analysis devices of this basic structure are known per se; however, they use helium analyzers, which are much slower and therefore less precise, in that they measure gas concentration via thermal conductivity or a much higher apparatus structure in the

Require the use of mass spectrographs, which also do not allow statements about distribution disorders.

Claims

1. Device for determining the diffusion capacity and of these disruption of the lung, in which the concentrations of carbon monoxide (CO) and helium (He) contained in the inhaled / exhaled air are measured, characterized in that the He concentration is determined by time of flight measurement of ultrasonic pulses between two ultrasonic transmitters / receivers, in particular piezoelectric transmitters / receivers, is determined in that

an ultrasound pulse is emitted by a transmitter (1) and at the same time the lapse of a time period that is slightly shorter than the running time in the stationary medium begins,

after the end of the period, the discharge of a capacitor to which a voltage is applied begins with a constant current,

- the discharge is ended when the ultrasound pulse is registered in the receiver (2),

the voltage still present at the capacitor is measured and the discharge duration is determined therefrom,

- the runtime is added up from the time span and discharge time,

- the transit time measurement is repeated in the opposite direction, - The flow rate and / or the molecular weight is determined from the different running times.

2. Device according to claim 1, characterized in that the time period and / or the voltage applied to the capacitor and / or the discharge current can be varied.

3. Device according to claim 1 or 2, characterized in that the

Runtime of the ultrasound pulse in the stationary medium is assigned to the voltage 0V applied to the capacitor.

4. Device according to one of the preceding claims, characterized in that the linear dependence on the small change in transit time is assumed for a small change in the molar mass of the medium.

5. Device according to one of the preceding claims, characterized in that the determination of the molecular weight is carried out in the still medium.