Blood pressure measuring device and method

What is claimed is:

1. A device for measuring blood pressure of a living body having a pulse beat with a rhythm and producing a pulse wave propagating with a pulse wave velocity, comprising:

sensor means for generating sensor data when the sensor means is attached to the living body; and

electronic circuit means for determining the blood pressure of the living body from the sensor data, the electronic circuit means including

first means, responsive to the sensor data, for determining a measurement value which is a measure for a first variable that can assume a plurality of first variable values, the first variable changing over time in the rhythm of the pulse beat and being correlated with at least one of the blood pressure and a change in the blood pressure,

second means, responsive to the sensor data, for determining another measurement value which is a measure for a second variable that can assume a plurality of second variable values, the second variable being correlated with at least one of the pulse wave velocity and a change in the pulse wave velocity,

third means for receiving calibration data during a calibration procedure and for storing at least one constant determined by the calibration data,

fourth means for determining a function value on the basis of the measurement value for the first variable and the measurement value for the second variable; and

fifth means for using the function value and said at least one constant to determine a value for the blood pressure.

2. A device according to claim 1, wherein the first variable is selected from the group consisting of the momentary flow velocity of blood through at least one artery in a measuring region, a change in the flow velocity of blood through at least one artery in the measuring region, the blood flow quantity through at least one artery in the metering region, the volume of the blood in at least one artery in the measuring region, a cross-sectional dimension of at least one artery in the measuring region, and the cross section area of at least one artery in the measuring region, as they occur in synchronism with the pulse beat.

3. A device according to claim 1, wherein the sensor means comprises means for sending waves into a measuring region of the body including at least one arterial blood vessel and for receiving waves scattered by blood in the at least one arterial blood vessel, wherein the first variable is one of the flow velocity of blood through the at least one arterial blood vessel in the measuring region and the flow quantity of blood through the at least one arterial blood vessel in the measuring region, and wherein the first means comprises means for determining from the scattered waves a measurement value for one of the flow velocity and flow quantity of blood flowing through the at least one arterial blood vessel in the measuring region.

4. A device according to claim 1, wherein the sensor means comprises means for sending lightwaves into a measuring region of the body and for converting scattered-back lightwaves into at least one electrical signal.

5. A device according to claim 4, wherein the means for sensing lightwaves comprises at least one light source which generates lightwaves whose wavelength is at least 700 nm and at most 1200 nm.

6. A device according to claim 1, wherein the sensor means comprises at least one ultrasound transducer which sends ultrasonic waves into at least one measuring region of the body and which converts scattered-back ultrasonic waves into at least one electrical signal.

7. A device according to claim 1, wherein the sensor means comprises electrodes, wherein the first variable is selected from the group consisting of the volume of blood in at least one artery in a measuring region, the blood flow quantity through at least one artery in the measuring region, the cross-sectional area of at least one artery in the measuring region, and the inner diameter of at least one artery in the measuring region, and wherein the first means comprises means for determining one of the electrical impedance, admittance, change in the impedance over time, and change in the admittance over time in the measuring region and for forming therefrom, as the measurement value for the first variable, a value for one of the volume of blood in at least one artery in the measuring region, the blood flow quantity through at least one artery in the measuring region, the cross-sectional area of at least one artery in the measurement region, and the inner diameter of at least one artery in the measuring region.

8. A device according to claim 1, wherein the sensor means comprises at least one ultrasound transducer for sending ultrasonic waves into at least one measuring region of the body and which receives reflected ultrasonic waves from at least one wall section of an artery, wherein the first variable is selected from the group consisting of the diameter of the artery, a change in the diameter of the artery, the cross-sectional area of the artery, and a change in the cross-sectional area of the artery, and wherein the first means comprises means for determining, as the measurement value of the first variable, a value for one of the diameter of the artery, the cross-sectional area of the artery, a change in the diameter of the artery, and a change in the cross-sectional area of the artery.

9. A device according to claim 1, wherein the sensor means comprises two sensors for determining, in two measuring regions which are spaced from one another along an artery, changes over time which occur periodically in the rhythm of the pulse beat in the first variable, wherein the second variable is the pulse wave velocity, and wherein the second means comprises means for determining, from a time shift between the periodic time changes in said first variable as determined by the two sensors, a value for the pulse wave velocity as the measurement value of the second variable.

10. A device according to claim 1, wherein the second variable is the pulse wave velocity, and wherein the second means comprises means for identifying a primary extreme occurring during a pulse period and corresponding to the systolic blood pressure as well as an additional extreme caused by interference between a pulse wave moving away from the heart and a reflected pulse wave and to determine a time or phase shift between the two extremes and to form therefrom a value constituting a measure for the pulse wave velocity as the measurement value for the second variable.

11. A device according to claim 1, wherein the sensor means is disposed at a measuring location that is remote from the cardiac muscle of the living body, wherein a graph of the first variable as a function of time has a predetermined feature occurring during each pulse period, further comprising additional sensor means for determining an electrical current associated with the cardiac muscle, the electrical current associated with the cardiac muscle changing over time and having a predetermined feature occurring during each pulse period in the change over time, and wherein the second means is responsive to the electrical current associated with the cardiac muscle and comprises means for determining the measurement value for the second variable on the basis of a time shaft between the occurrence of the predetermined feature occurring during each pulse period in the change over time of the electrical current associated with the cardiac muscle and the predetermined feature occurring during each pulse period in the graph of the variable as a function of time.

12. A device according to claim 1, wherein the first means comprises means for determining a measurement value for the first variable repeatedly for the same living body, wherein the second means comprises means for determining a measurement value for the second variable repeatedly for the same living body, wherein the fourth means comprises means for determining function values repeatedly, and wherein the fifth means comprises means for repeatedly using the function values and said at least one constant to repeatedly determine at least one of the systolic and diastolic blood pressure of the same living body.

13. A device according to claim 12, wherein the means for repeatedly using function values and said at least one constant to repeatedly determine at least one of the systolic and diastolic blood pressure of the body comprises means for determining at least one of the systolic and diastolic blood pressure at each heart beat of the body.

14. A device according to claim 1, wherein the calibration procedure is conducted on the same living body and the calibration data comprises at least one calibration blood pressure value measured during the calibration procedure, and wherein the third means further comprises means for determining the at least one constant from the at least one calibration blood pressure value.

15. A device according to claim 1, wherein the calibration procedure is conducted on the same living body, wherein the third means comprises means for storing two constants determined by the calibration data, and wherein the fifth means comprises means for multiplying one of the constants by the function value to determine a product and for adding the other constant to the product to determine the value for the blood pressure.

16. A device according to claim 1, wherein the fourth means comprises means for storing a table that associates a function value to every pair of a first variable value and a second variable value, and means for reading from the table, for each pair of a first variable value and a second variable value, an associated function value.

17. A device for measuring blood pressure of a living body having a pulse beat with a rhythm and producing a pulse wave propagating with a pulse wave velocity, comprising:

sensor means for generating sensor data when the sensor means is attached to the living body; and

electronic circuit means for determining the blood pressure of the living body from the sensor data, the electronic circuit means including

first means, responsive to the sensor data, for determining a measurement value which is a measure for a first variable that can assume a plurality of first variable values, the first variable changing over time in the rhythm of the pulse beat and being correlated with at least one of the blood pressure and a change in the blood pressure,

second means, responsive to the sensor data, for determining another measurement value which is a measure for a second variable that can assume a plurality of second variable values, the second variable being correlated with at least one of the pulse wave velocity and a change in the pulse wave velocity,

third means for receiving calibration data during a calibration procedure and for storing at least one constant determined by the calibration data,

fourth means for storing a table which associates table values with variable values, including at least the second variable values,

fifth means for selecting one of the table values on the basis of the measurement value for the second variable to provide a selected table value,

sixth means for multiplying the selected table value by one of the measurement value for the first variable, a table value associated by the table with the measurement value for the first variable, and a value computed from the measurement value for the first variable by a predetermined equation to provide a product value, and

seventh means for using the product value and said at least one constant to determine a value for the blood pressure.

18. A device according to claim 17, wherein the first means comprises means for determining a measurement value for the first variable repeatedly for the same living body, wherein the second means comprises means for determining a measurement value for the second variable repeatedly for the same living body, wherein the fifth means comprises means for providing selected table values repeatedly, wherein the sixth means comprises means for providing product values repeatedly, and wherein the seventh means comprises means for repeatedly determining a value for at least one of the systolic and diastolic blood pressure for the same living body.

19. A device according to claim 17, wherein the calibration procedure is conducted on the same living body and the calibration data comprises at least one calibration blood pressure value measured during the calibration procedure, and wherein the third means further comprises means for determining the at least one constant from the at least one calibration blood pressure value.

20. A device according to claim 17, wherein the calibration procedure is conducted on the same living body and the third means comprises means for storing two constants determined by the calibration data, and wherein the seventh means comprises means for multiplying the product value by one of the constants to obtain a resulting value and for adding the resulting value to the other constant.

21. A device for measuring blood pressure of a living body having a pulse beat with a rhythm and producing a pulse wave propagating with a pulse wave velocity, comprising:

sensor means for generating sensor data when the sensor means is attached to the living body; and

electronic circuit means for determining the blood pressure of the living body from the sensor data, the electronic circuit means including

first means, responsive to the sensor data, for determining a measurement value which is a measure for a first variable that changes over time in the rhythm of the pulse beat and is correlated with at least one of the blood pressure and a change in the blood pressure,

second means, responsive to the sensor data, for determining another measurement value which is a measure for a second variable that is correlated with at least one of the pulse wave velocity and a change in the pulse wave velocity,

third means for receiving calibration data during a calibration procedure and for storing at least one constant determined by the calibration data, and

fourth means for computing a blood pressure value using an equation expressing the blood pressure explicitly in dependence on the measurement value for the first variable, the measurement value for the second variable, and the at least one constant.

22. A device according to claim 21, wherein the calibration procedure is conducted on the same living body and the third means comprises means for storing two constants determined by the calibration data, and wherein the fourth means comprises means for computing a first function value from the measurement value for the first variable, means for computing a second function value from the measurement value for the second variable, means for multiplying one of the constants by the first function value and by the second function value to provide a product, and means for adding the other constant by the product.

23. A method of determining the blood pressure of a living body using a device which includes sensor means for generating sensor data and electronic circuit means for determining the blood pressure of the living body from the sensor data, the living body having a pulse beat with a rhythm and producing a pulse wave propagating with a pulse wave velocity, said method comprising the steps of:

(a) disposing the sensor means on the body at at least one measuring region that includes at least one arterial blood vessel;

(b) using the electronic circuit means to repeatedly determine, in response to the sensor data, a measurement value which is a measure for a first variable that can assume a plurality of first variable values, the first variable periodically changing over time in the rhythm of the pulse beat;

(c) using the electronic circuit means to repeatedly determine, in response to the sensor data, another measurement value which is a measure for a second variable that can assume a plurality of second variable values, the second variable being the pulse wave velocity;

(d) measuring the blood pressure of the body during a calibration procedure;

(e) storing, in the electronic circuit means, at least one constant determined by the calibration procedure;

(f) using the electronic circuit means to repeatedly determine a function value on the basis of the repeatedly-determined measurement value for the first variable and the repeatedly-determined measurement value for the second variable; and

(g) using the repeatedly-determined function value and the at least one constant in the electronic circuit means to provide blood pressure values.

24. A method according to claim 23, wherein a table containing a plurality of function values is stored in the electronic circuit means, the table associating each function value with a first variable value and a second variable value, and wherein step (f) comprises selecting one of the function values contained in the table on the basis of the measurement value for the first variable and the measurement value for the second variable.

25. A method according to claim 23, wherein step (d) comprises the steps of temporarily fastening a cuff defining a cavity to the body inflating and deflating the cuff; measuring the pressure in the cavity; determining the at least one calibration value; and removing the cuff.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

The invention relates to a device and a method for measuring blood pressure.

The device and the method serve to measure blood pressure, namely to measure blood pressure in a non-invasive manner. The term "non-invasive" here means that the measurement is performed without an instrument being introduced into a blood vessel and is thus effected with sensor means which are disposed completely outside of the living human, or possibly animal body whose blood pressure is being measured.

At present, blood pressure is mostly measured by methods based on the Riva-Rocci method. Prior art devices provided for such blood pressure measurements include a deformable cuff. This cuff defines a cavity which is connected with a compressed gas source, usually formed by a pump that pumps air, an outlet and a pressure measuring device. Means are further provided to be able to associate two values of this pressure when there is a change in the pressure existing in the cuff--namely upon deflation of the cuff--with the systolic and the diastolic pressure. The association with the systolic and the diastolic pressure can here be made either on the basis of Korotkoff sounds generated when the blood flows through an artery or according to the oscillometric variant of the method. In more recent prior art sphygmomanometers, the pressure measuring devices include a measuring transducer that is connected with the cavity in the cuff for converting the pressure into an electrical value, electronic circuit means and a display member for the analog or digital display of the systolic and diastolic blood pressure. Devices for determining the systolic and diastolic blood pressure on the basis of the Korotkoff sounds additionally include either a stethoscope or a microphone. Reference is here made, for example, to German Laid-Open Patent Application 3,014,199 and the corresponding U.S. Pat. No. 4,459,991. The pulsating flow of the blood is able to excite vibrations in the gas present in the cuff, normally air. In the devices provided for oscillometric measurements, the pressure measuring transducer and the electronic circuit means are configured to detect the fluctuations of the pressure in the cuff connected with the above-mentioned vibrations.

For a measurement according to the Riva-Rocci method, the cuff is fastened to a body segment--for example an upper arm or a finger--and is pumped up until the pressure of the air present in its cavity is sufficient to constrict the artery in the enclosed member. Then the cuff is slowly deflated. In the variant involving the detection of the Korotkoff sounds by means of a stethoscope or microphone, two values are detected and identified for the pressure in the cuff cavity during deflation of the cuff as the systolic blood pressure and the diastolic blood pressure, respectively. The pressure existing in the cuff during the first occurrence of Korotkoff sounds is associated with the systolic blood pressure. The diastolic pressure is recognized by the fact that the actual Korotkoff sounds disappear, with the sounds generated by the flowing blood becoming lower and less distinct or disappearing altogether. In the oscillometric variant of the method, the pressures of the air contained in the cuff and corresponding to the systolic and diastolic blood pressures are determined in that the fluctuations in the cuff pressure caused by the pulsating flow of the blood begin to appear or disappear again.

For seriously ill or critical accident victims and/or patients just coming out of surgery and in other cases it may be necessary or at least desirable to measure the blood pressure of the respective patient over a certain period of time--for example over several hours or days--permanently and as continuously as possible. In practice, devices are known for this purpose which operate according to the Riva-Rocci method and in which the cuff can be inflated and deflated automatically in cycles during operation, with the systolic and diastolic blood pressure each being measured during the deflation. However, periodic pumping up and subsequent deflating of the cuff and the interruption of blood circulation connected therewith in the limb around which the cuff is placed is unpleasant for the patient being examined and may even be damaging to his health. Since an inflation/deflation cycle usually requires at least about one minute and, moreover, short pauses should be introduced between successive measurements to keep annoyance to the patient being examined at a minimum, the Riva-Rocci method does not really permit truly continuous blood pressure measurements.

The publication entitled "Possible Determinants of Pulse-Wave Velocity In Vivo" by Masahiko Okada, in IEEE Transactions on Biomedical Engineering, Volume 35, No. 5, May 1988, pages 357-361, discloses a photoplethysmographic method for measuring pulse wave velocity that will be discussed in greater detail below. The measurement is made at the finger or toe tips with the use of light at a wavelength of 300 nm to 500 nm. This publication describes the correlation of the pulse wave velocity with various other parameters and variables, one of which is the blood pressure. According to this publication, a certain correlation was found to exist between the pulse wave velocity and the systolic and diastolic blood pressure. Such a relatively slight correlation, however, does not permit a determination of the blood pressure. Since the pulse wave velocity does not change periodically, it would also not be possible, in particular, to determine the systolic and the diastolic blood pressure from the pulse wave velocity. Moreover, the walls of the large arteries and the tissue portions usually covering them toward the exterior are practically impermeable to light of a wavelength of 300 nm to 500 nm. The method disclosed in the publication by M. Okada is therefore suitable only for measurements at thin-walled blood vessels near the surface, which are correspondingly small and is not suitable for measurements at large, correspondingly thick-walled blood vessels that may possibly be relatively far removed from the surface of the body part being examined.

Several general characteristics relating to blood circulation will now be discussed. The circulatory system includes arterial blood vessels -(that is, arteries),-venous blood vessels, and capillaries that interconnect the two types of vessels. The smallest arterial blood vessels or arteries, that are connected directly with the capillaries, are called arterioles. The arterial blood vessels have elastically deformable walls and are at least in part provided with muscle fibers and/or enclosed by such muscle fibers. These muscle fibers are able to compress the arteries and particularly the arterioles to different degrees and thus influence their elasticity, the flow resistance and the distribution of blood to the various blood vessels. The heart pumps the blood in a pulsating manner--that is, in surges--through the blood vessels. The blood flows through the blood vessels at a flow velocity v that is a function of locus as well as time. If, for the sake of simplification, it is initially assumed that the blood vessels have rigid walls, changes in pressure in the blood propagate at the speed of sound cs, whose second power or square is defined by the following formula:

c.sub.s.sup.2 =k/.rho. (1)

where .rho. is the density of the blood and K the modulus of compression, which is also called the volume elasticity modulus and is equal to the reciprocal of compressibility, usually identified as .kappa..

In reality, however, the arterial blood vessels do not have rigid walls but--as already mentioned--elastically deformable walls. During each blood surge caused by one cardiac cycle and the pulse-like pressure increase connected therewith, the arterial blood vessels are distended. These distensions propagate along the arterial blood vessels. The velocity at which the change in pressure caused by a cardiac cycle or blood surge propagates along an arterial blood vessel under the influence of its wall elasticity, is the already mentioned pulse wave velocity c.sub.pw. According to the book by Ludwig Prandtl, entitled "Furer durch die Stromungs-lehre" [Fluid Mechanics Guide], published by Verlag Friedr. Vieweg & Sohn, Braunschweig, 1965, the second power or square of the propagation velocity of pressure changes in tubes having elastically distensible walls, and thus at least approximately also the second power or square of the pulse wave velocity, neglecting flexural vibrations, is given by the following equation: ##EQU1## where E is the modulus of elasticity of the blood vessel wall, s is the thickness of the blood vessel wall and d is the interior diameter of the blood vessel.

According to the above-cited publication by M. Okada, the square of the pulse wave velocity is given by the following equation: ##EQU2##

By inserting c.sub.s in Equation (2), it can be demonstrated that Equation (3) is derived from Equation (2) if, for the sake of simplicity, the second product in the parenthetical expression in Equation (2) is omitted.

The flow velocity of the blood is--as already mentioned--a function of locus as well as time. Its maximum value in an arterial blood vessel and particularly in a large artery of a grown human being is at most about 0.5 m/s and normally a little less. According to Equations (2) and (3), the pulse wave velocity is dependent upon the ratio of the wall thickness to the diameter of the arteries. Since this ratio increases from the heart toward the capillaries and since the pulse wave velocity additionally is a function of the modulus of elasticity and of the tension in the muscle fibers belonging to the respective blood vessel, the pulse wave velocity changes along the arterial blood vessels and is also dependent upon the state of the human beings or animals examined. In the arteries, the pulse wave velocity is typically about 4 m/s to 5 m/s. The speed of sound in water, which is known to be the major component of blood, lies in an order of magnitude of 1500 m/s. The pulse wave velocity c.sub.pw is thus significantly greater, namely at least or approximately 10 times greater, than the flow velocity v, and the speed of sound c.sub.s, in turn, is very much greater than the pulse wave velocity.

The blood pressure developing in a certain blood vessel depends on the pumping output of the heart, on the flow resistance of the blood vessel, on the momentary quantity flowing through, on the elasticity of the blood vessel wall and on the viscosity of the blood.

SUMMARY OF THE INVENTION

The object of the invention is to provide a device and a method for non-invasively measuring blood pressure, with the device and method avoiding the drawbacks of the prior art devices and methods discussed above. More particularly, the object of the invention is to make it possible to monitor the blood pressure of a human being or possibly an animal essentially continuously without having to alternatingly inflate and deflate a cuff, while nevertheless attaining good measuring accuracy.

It has been found that the blood pressure can be determined relatively accurately by obtaining two different value, a first one of the volume being a variable that changes continuously in at least one measuring region periodically over time in the rhythm of the pulse beat and/or its change as a function of the pulse, while the other or, second value is a value which provides a measure for the pulse wave velocity and/or its change. By using at least one calibration value determined according to the above-described Riva-Rocci method and linking the two values together, it is possible to form at least one value which is a measure for a characteristic blood pressure value and/or its change, with it being possible to measure and display, for example, at least the systolic pressure and, for example, also the diastolic and/or the average blood pressure.

The device includes sensor means which comprise, for example, at least one sensor that is releasably fastened to a body part, with it being possible to employ two identical or two different sensors. At least the sensor or each sensor serving to measure the first, periodically changing value is preferably attached to an arm or possibly a leg. The device preferably further includes a display and monitoring unit constituted by one or several such devices and including at least part of the electronic circuit means of the device.

The mentioned first value which changes over time in synchronism with the pulse beat and also in synchronism with the blood pressure--that is, in the same rhythm as the blood pressure--is correlated with the blood pressure by way of a physical linkage, but must be formed, of course, differently from the blood pressure and not directly by the blood pressure itself or by a change in the blood pressure. The sensor means and the electronic circuit means may be configured to determine and display in the form of an electrical signal as the first value, a value that is a measure for the momentary value of the flow velocity and/or its change in synchronism with the pulse beat and/or the flow quantity and/or the volume of the blood in a measuring region and/or a cross-sectional dimension and/or the area of the passage cross section of at least one arterial blood vessel. Since the blood vessels and particularly the arteries normally have an approximately circular cross section, the mentioned or determined cross-sectional dimension may be formed at least in approximation by the interior or exterior diameter or by an average diameter of the blood vessel. In this connection, it should also be noted that the variables mentioned for the first value are closely linked with one another. If the quantity of the flow is measured in volume units per unit time, the flow quantity is equal to the product of the average flow velocity averaged over the cross-sectional area times the area of the flow passage cross section of the blood vessel.

The device may, for example, be configured to detect the flow velocity and/or the flow quantity as the first value in that lightwaves--namely monochromatic coherent lightwaves--or ultrasonic waves are directed into a body part to be examined and lightwaves or ultrasonic waves, respectively, that are scattered by the blood or--more precisely--by the blood cells are detected. The light or ultrasonic radiation may here be pulsed. In these methods which are based on the scattering of light or ultrasound, components of the flow velocity or flow quantity that are directed at a right angle and/or parallel to the direction of incidence of the light or ultrasound can be detected as desired. Various types of such measuring methods based on the scattering of light or ultrasound are known. If light is employed, the measurements may be effected, for example, with the aid of photon correlation, light beating spectroscopy, speckle interferometry or the Doppler effect. In this connection, reference is made, for example, to the publication by E. R. Pike, entitled "Laser Doppler Anemometry, a Comparative Study of the Measurement of Motion by Light Scattering", in "The Engineering Uses of Coherent Optics", "Proceedings and Edited Discussion of a Conference Held at the University of Strathclyde, Glasgow," Apr. 8-11, 1975, Cambridge University Press, pages 431-457.

If ultrasound is employed, the measurements may be done in similar ways, namely, for example, with the aid of time domain correlation, an interference speckle pattern and/or a Fourier transformation or the Doppler effect. A few such measuring methods are described, for example, in the following articles published in "Proceedings zum IEEE Ultrasonics Symposium" [Proceedings of the IEEE Ultrasonics Symposium] 1990, Volume 3: M. R. Sturgill, R. H. Love, B. K. Herres, "An Improved Blood Velocity Estimator Optimized For Real-Time Ultrasound Flow Applications", pages 1467-1471; H. F. Routh, T. L. Pusateri, D. D. Waters, "Preliminary Study Into High Velocity Transverse Blood Flow Measurement", pages 1523-1526; and T. Tamura, R. S. C. Cobbold, K. W. Johnston, "Determination of 2-D Velocity Vectors Using Color Doppler Ultrasound", pages 1537-1540. Reference is also made to the publication by L. N. Bohs, G. E. Trahey, entitled "A novel Method For Angle Independent Ultrasonic Imaging of Blood Flow and Tissue Motion", in IEEE Transactions on Biomedical Engineering, Volume 38, No. 3, 1991, pages 280-286.

Regarding the various methods based on lightwaves or ultrasonic waves, it should also be noted that these methods are sometimes identified somewhat non-uniformly by the various authors and equipment manufacturers. For example, methods in which a flow velocity is measured that occurs at a right angle to the direction of the radiation are sometimes included in the Doppler effect methods although, strictly speaking and in the classical sense, the Doppler effect is understood to mean the generation of a frequency shift by a velocity component that is parallel to the direction of propagation of the waves in a wave radiation source.

If a determination of the flow velocity and/or flow quantity by means of light is provided, the device may include one or a plurality of light sources and one or a plurality of light receivers. The or each sensor may then include, for example, at least one optoelectronic transducer serving as a light source, for example a laser light emitting diode, and at least one optoelectronic transducer serving as a light receive