Catheter and process for the temperature measurement of the vascular wall
FIELD OF THE INVENTION The present invention relates to endovascular catheters specially designed to identify temperature discrepancies inside the human vascular wall (arterial or vein) or the wall of concave biological organs associated with ongoing process of inflammation and a process of identifying such temperature discrepancies.
BACKGROUND OF THE INVENTION
Heart attacks and stroke incidences are growing fast in the industrial nations tending to be the number one case of death among other diseases. Prognosis and prevention of such a situation would be of outmost importance.
It is now well accepted that atherosclerotic plaques are composed by cholesterol, proliferating smooth muscle cells, and inflammatory cells all covered by collagen that forms a fibrous cap. Macrophages migrate into the plaque causing inflammation. Rupture and erosion of these plaques lead to acute syndromes and sudden cardiac death.
The role of inflammation is believed to be of critical importance since, pathology studies have shown that plaque rupture is found at sites of increased local temperature variations probably due to macrophage accumulation. It is difficult to detect vulnerable plaques with conventional angioscopy, since the majority of them occur in coronary arteries with hemodynamically insignificant stenoses or mild stenoses.
Almost 50% of patients with myocardial infractions have not had previous symptoms justification for temperature measurements on other organs. Studies have shown the existence of thermal heterogeneity in vulnerable plaques compared to normal artery wall. Thus it is necessary to obtain an accurate temperature measurement inside the human body and more
specifically inside the vasculatory system in order to detect and treat the vulnerable plaques. This temperature measurement however inside the vasculatory system is not a trivial job since it is influenced by the background temperature of the human body. This factor cannot be ignored during the measurements since, on the opposite case, it can lead to false interpretations. The blood, as it circulates around, tends to cool down the hot spots by taking away the excess heat so the cooling effect must be somehow eliminated or minimized. On the other hand, the thermal sensor(s), used for measurements, should have fast response time, very high sensitivity, and be encapsulated in the catheter in such a way, that ensures contact only with the area of interest and not with the other sources of heat that may interfere with the readings of the area of interest. Moreover, the device itself, the catheter together with the sensor(s), should be designed in a way that, during the use of the device, the risk the patient is exposed to, due to possible injuries, e.g. rupture of the plaque, are the minimum possible.
JP2001149481 A describes a catheter for measuring the temperature of a biological intratubular wall. In such embodiment the cooling result of the blood flow is not encountered. The blood itself circulates around the distal end side of the catheter where the temperature sensor is attached and as a result it takes away part of the excess heat. This catheter is probably underestimating the actual temperature of the area of interest. In view of the above, specially designed catheters, able to measure thermal discrepancies or hot spots on the vascular wall (arterial or vein) or the wall of concave biological organs would be desirable.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide such a catheter and a process for the temperature measurement of the vascular wall or the wall of concave biological organs.
To this effect, the invention provides a cathether for temperature measurement of the vascular wall or the wall of concave biological organs comprising 3 internal lumens, one or more thermal sensors placed at the distal end of the catheter, wires connected with the thermal sensors passing through the first of the internal lumens, a guide wire facilitating the advancement of the catheter to the human body concave entering at the proximal end of the catheter and passing through the second of the internal lumens and characterized in that it also comprises controlled expansion means at the distal end of the catheter, placed in such a way that by expansion of said means, full contact of said thermal sensors with the vascular wall or the internal wall of the concave biological organ is achieved, thus allowing the measurement of the temperature thereof. Furthermore the invention provides a process for temperature measurement of the vascular wall or the wall of a concave biological organ, comprising the insertion within a human body of a catheter comprising 3 internal lumens, one or more thermal sensors placed at the distal end of the catheter and controlled expansion means at the same end of the catheter, placed in such a way that by expansion of said means, full contact of said thermal sensors with the vascular wall or the internal wall of the concave biological organ can be achieved, the expansion of the controlled expansion means to make the temperature measurement(s), and the measurement(s) of the temperature.
The current invention refers to special catheters that use thermal sensors called thermistors; the thermistors come in contact in a controlled mode with the internal wall of the concave biological organs by external handling of the catheters, for the recording of the temperature.
Moreover, in cases where the blood flow is dominant, e.g. coronary arteries, the preferred embodiment would be the one that could eliminate the flow itself leaving the area of interest to be measured alone without the background temperature to interfere. In another case, where the blood flow is not dominant in the way that is present but in a somehow statistic condition, the preferred embodiment will not need to eliminate the flow during the measurement, e.g. lungs, urinary blade. According to the invention, this is achieved: 1) By using a chamber filled with gas or liquid placed at the distal tip of the catheter in such a way that it alters the distal shape of the catheter in a predefined shape which can take advantage of the blood flow for passive contact with the area of interest eg. the plaque inside the coronary vessel wall. The chamber is externally supplied with gas or liquid and has the ability to achieve different volumetric shapes to accommodate different diameters of the vasculatory vessel walls. By the expansion of the chamber, the tip of the catheter, where the thermistor(s) are placed, will come in contact with the vascular wall (artery or vein), regardless of the diameter of the vessel, or with the internal surface of other biological organ(s). The advantage of such a catheter is that it facilitates contact with the vulnerable plaque in order to make temperature measurements by using only the actual blood flow as the mean to push the distal tip of the catheter against the vessel wall and at the same time to block partially the blood flow in the area opposite to the shaped tip where the thermistor(s) is/are and eliminate the cooling effect.
2) By placing, at the distal end of the catheter, a coil, which can be withdrawn and expanded by external maneuvers. The thermistor(s) is/are placed on the coil so that they can come in contact with the vascular wall (artery or vein), when the coil is expanded, regardless of the diameter of the vessel or with the internal surface of other biological organ(s).
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1A -1 D illustrates a thermistor catheter in accordance with one embodiment of the invention. Figure 2A-2D illustrates a thermistor catheter in accordance with a second embodiment of the invention.
Figure 3A-3D illustrates a thermistor catheter in accordance with a third embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention is described below, with reference to the attached figures. A first embodiment of the thermography catheter is illustrated in figures 1A- 1D. The catheter comprises three internal lumens. One or more thermal sensors (3) is/are fixed at the distal tip of the catheter and is/are connected with two wires passing through the first internal lumen, (figure 1A, number 3). The catheter further comprises a guide wire, which enters at the proximal end of the thermography catheter (figure 1A, number 6) and passes through the second lumen (figure 1 A, number 4). The guide wire facilitates the advancement of the catheter to the target site of the vascular wall or the concave biological organ(s).
At the distal tip of the catheter, there is a metallic cylinder 1 ,5 cm long with diameter the same as the shaft of the catheter's tip with a slot at the one side just opposite of the thermistors band. Inside the cylinder, a piece of elastic material (for example: Latex) is placed (figure 1C, number 9). This piece of elastic material is expandable either by gas or liquid. In its expanded form a chamber is created (figure 1 B, number 8). The gas (e.g. Helium) or liquid are inserted through the third lumen of the thermography catheter (figure 1 B, number 5). The size of the chamber is determined by the amount of gas or liquid that is inserted through the lumen. The thermal sensors are embedded inside the distal tip of the catheter opposite to the chamber (figure 1C, number 3) in order not to overhang and degrade the smoothness of the catheter shaft.
The catheter is placed at the site of the vessel wall, on which temperature measurements will be performed, and thereafter the chamber is expanded by the insertion of gas or liquid. The positioning of the catheter on the vascular wall after the expansion of the elastic material is shown in figure 1 D. The chamber comes in contact with one side of the vascular wall (figure 1D, number 10), and more precisely in the internal wall of the vessel or of the other biological organ (figure 1D, number 11). By this way, complete contact is accomplished between the thermal sensor(s) and the side of the wall, on which temperature measurements will be performed, while the flow of biological fluids (e.g. blood in vessels) is restored.
A second embodiment of the catheter is illustrated in Figures 2A-2D. This has the same general characteristics with the first embodiment. A balloon that has the ability to expand controllably only on one side of the catheter (figure 2A, 2B), when gas or liquid is inserted in it, is placed around the distal end the catheter, as an alternative to the elastic material. The distal shape of the catheter is altered in a predefined shape, which can take advantage of the blood flow for passive contact with the area of interest eg. the plaque inside the coronary vessel wall. The thermography catheter (figure 2A,) comprises three internal lumens. One or more thermal sensors is/are fixed at the distal tip of the catheter and is connected with two wires passing through the first lumen, (figure 2A, number 3). The thermal sensor(s) is/are embedded inside the distal tip of the catheter opposite to the chamber (figure 2C, number 3) which is formed after expansion of the balloon, in order not to overhang and degrade the smoothness of the catheter shaft.
A guide wire, which enters at the proximal end of the thermography catheter (figure 2A, number 6), passes through the second lumen (figure 2A, number 4). The guide wire facilitates the advancement of the catheter to the target site of the vascular wall or the concave biological organ(s).
A third embodiment of the catheter is illustrated in Figures 3A-3D. The thermography catheter used for temperature measurements on vascular
walls or on the internal surface of other concave biological organ(s) (figure 3A, number 1), comprises three internal lumens. One or more thermal sensors (3) is/are fixed at the distal tip of the catheter and is/are connected with two wires passing through the first internal lumen, (figure 3A, number 3). Wires connected to the thermal sensor(s) are inserted in the first lumen (figure 3A, number 3), and exerted through the proximal tip of the catheter (figure 3A, number 7). A guide wire (figure 3A, number 4) passes through the second lumen of the catheter. It is used to facilitate the easy advancement of the catheter inside the cavities of the human body. The guide wire is inserted through the proximal end of the catheter (figure 3A, number 6).
Over the whole length of the third lumen, there is a wire (preferably Nitinol) (figure 3A, number 5), which forms at least one, preferably one coil (figure 3A, number 6) at the distal tip of the catheter. The section of this wire, which consists of the coil, is protected by a sheath (figure 3A, number 2). Thermal sensors are placed on the coil 1 cm each apart of the wire (figure 3A, number 3). When the sheath is withdrawn, the coil expands and its diameter increases (figure 3B). The positioning of the catheter on the vascular vessel wall is demonstrated in figure 3D. By expanding the coil the thermal sensor(s) come in contact with the wall (figure 3D, number 10), and more accurately with the internal surface of the wall (figure 3D, number 11) thus enabling the measurement of the temperature thereof.