Surgery – Diagnostic testing – Physical characteristics of blood
Reexamination Certificate
2001-03-12
2004-03-23
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Physical characteristics of blood
C600S369000, C600S547000
Reexamination Certificate
active
06709390
ABSTRACT:
The invention relates to a method for determining properties of blood, such as the blood viscosity of a person.
Atherosclerosis is the most common disease in the western world and partly for this reason represents one of the greatest problems with which our health care services and our society in general are confronted. Since atherosclerosis is clearly related to age, the problems associated with atherosclerosis will only increase due to the increase in the ageing population in the western world. Atherosclerosis is a generalized disease which can manifest itself in the coronaries by means of acute heart death, myocardial infarction or disabling angina pectoris. Atherosclerosis in the head is responsible for the largest number of strokes. Not only does this cause mortality, but also a greater or lesser degree of permanent invalidity. Elsewhere in the blood vessels of the body atherosclerosis can be the cause of reduced blood circulation in the legs or in the kidneys. Thrombosis is found to play an essential part in the process of atherosclerosis and increasingly recognized recently is also the significant part which inflammatory processes can play in activating and perhaps sometimes also in causing atherosclerosis. Much atherosclerosis therapy therefore focuses on suppressing thrombosis. It has also been found that the presence of “markers” of inflammation (such as CRP and other active-phase-proteins) entails an increased chance of atherosclerotic complications. The present invention has for its object to provide a method which enables monitoring of thrombosis processes and/or the activity of atherosclerosis. The prevention of atherosclerotic complications can hereby be controlled better and the medicinal therapy (anti-thrombotic and anti-inflammatory) can be adapted thereto.
It is known that the risk of thrombosis and atherosclerotic complications increases with an increase in the viscosity of the blood. The taking of blood so as to determine the viscosity is however time-consuming and costly, particularly when this has to be determined over a longer time and regularly in order to monitor the risks for a patient. Furthermore, when blood is taken for examination in vitro, the viscosity and coagulation parameters of blood are influenced to a certain extent and do not therefore give an accurate representation of the properties of blood in vivo. They are also only random indications which can be influenced by many factors and thus provide only limited certainty that, if necessary, timely treatment can be undertaken as the risk increases.
The invention therefore has for its object to provide a method of the type specified in the preamble which at least reduces these drawbacks.
In the method according to the invention this object is achieved by generating in vivo for a determined time, by means of an electrical alternating current of a determined frequency, a measurement signal of the impedance of the blood between at least two points centrally in a blood volume, wherein the measurement signal is processed such that variations therein with a frequency in the order of magnitude of the heart frequency are substantially absent therefrom, and comparing the processed measurement signal with predetermined relations between impedance and the properties of the blood, such as the viscosity. A continuously determined impedance measurement signal varies with ambient parameters such as the flow speed. By eliminating the variations with a frequency in the order of magnitude of the heart frequency a reliable value is obtained for the actual blood properties such as the viscosity, and thus the risks for the patient.
An ECG signal is further measured in a cavity containing the blood volume and processing of the measurement signal occurs by only considering measurement values in the same phase as the ECG signal. The phase of the ECG signal corresponds to the maximal and/or minimal impedance. By measuring each time in the same phase of the heart rhythm, the conditions for the flow speed and the like are the same each time, so that the variations with the frequency of the heart rhythm are eliminated. The energy consumption is moreover low herein, so that the device can operate on batteries and can for instance be portable.
According to a further development of the invention a blood viscosity reducing agent is applied to the patient in a dosage such that the measured impedance is reduced to a predetermined value. Precise determining of the viscosity enables a good dosing of the agent.
The distance between the aforementioned two points centrally in the blood volume is a small fraction of the distance between the two points and the boundary of the blood volume. In this way, the measurement is influenced by surrounding tissue to a negligible extent at most.
A good measurement is obtained particularly when the aforementioned two points are located centrally in the right atrium of the heart of the patient is applied. The right-hand atrium is readily accessible for the measurement and comprises a suitably large volume of blood to enable a precise measurement.
The invention likewise relates to and provides a device for in vivo determining of determined blood properties, such as the blood viscosity of a person, comprising a catheter, which comprises at least two electrode systems close to a distal end and connecting lines extending from the electrode systems to the proximal end of the catheter, a measuring device which is connectable to the connecting lines and which is embodied such that it can generate a measurement signal of the impedance between the electrode systems, and a processing device which is embodied such that it processes the measurement signal such that variations therein with a frequency in the order of magnitude of the heart frequency are substantially absent therefrom.
According to a suitable embodiment the measuring unit of the device according to the invention is received in an implantable unit. After introduction into a patient the progress of the measured blood property can be monitored regularly for a longer period of time. The device according to the invention can however also be used for more short-term applications, for instance in the case of acute thrombotic events, in which case the measuring device and the processing device are received in housings which remain outside the body of the patient. The catheter introduced into the patient via a peripheral vein is connected to the measuring device.
According to a very suitable embodiment the measuring device is combined with an implantable heart pacemaker unit and provided with two electrically separated circuits each having an individual power source, wherein the one circuit is adapted for the pacemaker function and the other circuit is adapted for the impedance measurement.
Heart pacemakers are generally known. The pacemaker unit herein contains, as can also be the case in the invention, an electrical power supply generally in battery form and the electronics required for the pacemaker function. The pacemaker unit is further also often provided with read-out means so that radiographic data can be read out in order to enable monitoring of the operation of the pacemaker and thus also the patient. The pacemaker unit is generally implanted on the chest under the skin. The device according to the invention, whether or not combined with a heart pacemaker, can be introduced in the same manner.
An electric catheter, referred to as the “lead” in professional jargon, is fixed to the device according to the invention when it is implanted under the skin. This electric catheter is inserted into the bloodstream at a suitable location and guided via the bloodstream to the heart. One or more electrodes are then placed on the electric catheter, generally on the end thereof. Via these electrodes it is then possible to generate an electrical stimulus which supports the working of the heart. As is generally known, current pulses in the order of 5 mA for 0.5 ms are herein generally more than sufficient. In older models of pacemakers a stimulus signal is
Martil Instruments B.V.
Nasser Robert L.
Zovko Mark
LandOfFree
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