1993-11-05
1995-04-18
Manuel, George
Surgery
Truss
Pad
7386125, A61B 800
Patent
active
054069483
DESCRIPTION:
BRIEF SUMMARY
This invention concerns flowmeters and more particularly flowmeters of Doppler ultrasound form.
Flowmeters of this last form are routinely used in medical practice for the purposes of blood flow measurement. These meters are usually designed for transcutaneous application, but some have been developed for catheterised application into a blood vessel of interest. However, such meters are often limited to the provision of measures only of blood velocity, and commonly so in the case of catheter flowmeters, whereas the medical community frequently has an interest in knowing the blood volume flow rate in the relevant vessel. This interest extends particularly to the case in which the vessel is the aorta because the rate is then an effectively direct indication of cardiac power output. In any event, although blood velocity may be measured without undue difficulty and blood volume flow rate is provided simply as the product of velocity and vessel cross-sectional area, an indication of the area in question is not readily attained. Indeed in the case of the interest in cardiac output, area is often estimated for a given patient by way of a quite separate imaging procedure.
An object of the present invention is to improve this situation and to this end there is provided a method for measuring the cross-sectional area of a conduit through which fluid is flowing, which method comprises projecting a diverging ultrasound beam along the conduit and detecting the resulting Doppler signals from a plurality of successive ranges including one where the beam has diverged at least to the boundary of the conduit, producing for said ranges respective representations of the power of the associated Doppler signals and providing a representation of the cross-sectional area of the conduit by comparison of said power representations with stored predetermined data.
Clearly the conduit can be a blood vessel and, more particularly, the aorta and, in this particular case, the beam is conveniently directed transcutaneously by way of the suprasternal notch to pass longitudinally down the ascending aorta.
In a preferred form, the presently proposed method also entails determination of a measurement of the fluid flow velocity in the conduit by way of the Doppler signals, and preferably by reference to such signals at a range from the beam origin at least that of said one range.
The invention also provides, in another aspect from the presently proposed method, apparatus for carrying out such a method.
In order to clarify the invention as so far expressed, the same will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 schematically illustrates one form of the invention;
FIG. 2 graphically illustrates in an idealised manner the operational basis for the invention;
FIG. 3 diagrammatically illustrates a form of a detail of the invention; and
FIG. 4 illustrates an alternative form of a detail of the invention.
In FIG. 1 the invention is illustrated for use relative to a patient's body denoted in part at 10, with the aorta, heart, sternum and suprasternal notch indicated respectively at 11-14 within the body.
Apparatus according to the invention in FIG. 1 comprises an ultrasound transducer 20 operable in a transmission mode in response to an oscillator 21 to project a divergent beam 22 into the body 10. When the transducer is suitably located, the beam passes through the body tissue above the suprasternal notch and then longitudinally down the ascending aorta until the beam divergence is such that, at one range along the beam path, all of the blood flow through the aorta is isonated. Thereafter the beam diverges increasingly into the body tissue around the aorta.
This transmission operation is conducted in a pulsed manner under the control of an output from a pulse generator 23 which opens and closes switch 24 between the oscillator and transducer.
The transducer is also operable between transmission pulses in a receiver mode to detect returning signals which return along the beam path. The resultan
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D. H. Evans et al "Physics, Instrumentation and Clinical Application" Doppler Ultrasound, Feb. 1989, pp. 100-102.
British Technology Group Ltd.
Manuel George
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