Regional flow catheter

Surgery – Diagnostic testing – Cardiovascular

Reexamination Certificate

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C600S505000, C600S506000

Reexamination Certificate

active

06332870

ABSTRACT:

BODY OF THE INVENTION
The present invention relates to the use of at least two electrode pairs in the generation if a difference signal that corresponds to the flow through a vein upstream and downstream of the connection of a venous duct to said vein.
In the present invention no protection is requested for operations which fall within the scope of Article 52, paragraph 4 of the European Patent Convention or comparable provisions under national law.
No measurement methods for determining the distribution of the blood flow in a person or an animal over the organs and the limbs are disclosed in the prior art. However, it is clear that more information on the blood distribution and in particular information on regional flow distribution would be an enormous asset in determining the condition of a person and for making a diagnosis. The serious pathophysiological abnormalities with which physicians are confronted nowadays and the widespread use of very powerful drugs which have an effect on the circulation underline the need which exists for more information on the cardiovascular system.
Only recently it became generally known that the cardiac output is to a significant extent determined by changes which occur in the distribution of the blood flow and that the output is not determined solely by the factors which determine the functioning of the heart. These factors are, inter alia, the preload, the afterload, contractility and the heart rate. Quantitative information on the regional blood flow is therefore of great importance in order to make headway in respect of diagnosis, evaluation of the functional status of the cardiovascular system and the treatment thereof in the case of seriously ill patients. The problem of the interpretation of haemodynamic measured data is further complicated by the fact that the cardiovascular system is a closed circuit, with all variables influencing one another. That is why an evaluation of the cardiovascular system without taking account of information on the blood flow distribution is a risky undertaking which can lead to misleading conclusions and thus can be harmful to the patient.
To summarise, it can be stated that the evaluation of the haemodynamic status of a seriously ill patient cannot be based solely on parameters which determine the performance of the heart because other factors, such as, for example, the blood flow distribution, are of crucial importance for the functioning of the circulation system.
SUMMARY OF THE INVENTION
The aim of the present invention is to provide a method and an apparatus for determining the regional blood flow from and to the various organs and limbs in a person or in a mammal.
In a first aspect, the present invention therefore relates to the use of at least two electrode pairs in the generation of a difference signal that corresponds to the flow through a vein upstream and downstream of the connection of a venous duct to said vein,
wherein
a first signal is generated that corresponds to the resistance over the first electrode pair, located upstream of the connection of the venous duct to the vem;
a second signal is generated that corresponds to the resistance over the second electrode pair, located downstream of the connection of the venous duct to the vein; and then
the difference signal between the first and the second signal is determined.
The difference signal that is obtained in this way can, if desired, be converted with the aid of analogue or digital means into a regional blood flow. The advantage of such an application is that the contribution of the various venous ducts to the blood flow in a main vessel can be determined in any desired outflow region of a patient. In this way the regional blood flow can be determined in situ. As a result of also using electrode pairs, no point measurements are made in the blood vessel but the blood flow is determined over a segment of a vein. The result of such a segmental measurement is much more accurate than that of a point measurement which, for example, would be carried out using a thermometer.
The generation of the difference signal is further facilitated if the electrodes are placed on a catheter.
In a second aspect, the present invention relates to a catheter for the generation of a difference signal that corresponds to the flow through a vein upstream and downstream of a connection of a venous duct to said vein. The catheter according to the present invention comprises an essentially tubular catheter element, provided close to the end thereof with a number of measurement electrodes, which are connected by means of leads to a connection element for connecting the measurement electrodes to a power source and/or a monitor. The catheter according to the present invention is characterised in that the measurement electrodes are mounted on the catheter element such that the measurement electrodes of a catheter element inserted in a main vein are located downstream with respect to the respective connections of the venous ducts to the main vein.
In a particular embodiment the distance between the measurement electrodes and the end of the catheter element essentially corresponds to the distance spanned by the venae cavae, from the opening into the right atrium to the respective connections of the venous ducts to the venae cavae. The advantage of such a regional flow catheter is that it is possible to measure the regional blood flow and thus the distribution of the blood over the intestines and the liver, the kidneys, the legs and the arms and the head. A measurement of this type provides a physician with an accurate picture of the condition of the cardiovascular system of a person. Moreover, the regional blood flow measurement offers the possibility of intervention at an early stage when changes occur in the blood circulation. Long before changes in the systemic blood pressure and the cardiac output can be recorded, compensation mechanisms are active in the event of threatening decompensation of the cardiovascular system, the blood flow being fed to the most vital organs. A very early detection of a possible circulatory dysfunction is possible by measuring the regional blood flow.
In another embodiment of the catheter according to the present invention for use in the vena cava inferior the measurement electrodes are mounted on the catheter element 140-220 mm, preferably 175 mm, away from the end of the catheter element. With this embodiment it is advantageous that five first measurement electrodes with a mutual spacing of 4-8 mm, preferably 5 mm, are mounted on the catheter element, one of said first measurement electrodes being positioned 4-8 mm, preferably 5 mm, away from the end of the catheter element. The catheter according to the present invention for use in the vena cava inferior is further improved in that six second measurement electrodes with a mutual spacing of 20-30 mm, preferably 25 mm, are mounted on the catheter element, the distance between that first measurement electrode which is positioned furthest from the end and that second measurement electrode positioned closest to the end being 20-30 mm, preferably 25 mm. The advantage of these measures is that on introducing the catheter into the vena cava inferior as far as the right atrium, the measurement electrodes are downstream with respect to the connections of the venous ducts to the vena cava inferior. Consequently, the blood supply from said venous ducts can be determined using said measurement electrodes.
Yet a further embodiment of the catheter according to the present invention for use in the vena cava superior is characterised in that the measurement electrodes are positioned 200-400 mm away from the end of the catheter element, the mutual spacing being 10-20 mm. The advantage of this is that on introducing the catheter into the vena cava superior as far as the right atrium, the measurement electrodes are located downstream with respect to the connections of the venous ducts to the vena cava superior. As a result of this measure, the blood supply from said venous ducts towards the heart can cons

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