The invention is in the medical field and in particular in the field of endovascular stent grafts.
In many medical fields it is desired to monitor a condition inside the body and alarm the patient when an abnormal situation develops. Prior art is mainly based on two technologies: electronic modules, being able to transmit a message to the outside of the body or non-electronic devices being periodically monitored by radiological means such as x-ray, MRI or CT. In both cases the detection of the abnormal condition relies on external equipment, requiring the patient to follow a schedule of periodic tests. An example of a common condition requiring monitoring is an aneurysm in an artery, typically the aorta, repaired by a stent graft. A common malfunction of such grafts is a leakage. Any leakage from the repaired area will cause internal bleeding. This can be detected by monitoring the pressure in the area surrounding the graft. Normal pressure in this area will be between 50 mmHg to 80 mmHg, well below systolic blood pressure. Should a leak develop, pressure in the aneurism area outside the graft will exceed 100 mmHg, as it is driven by the blood pressure inside the artery. An example of non-electronic prior art solutions is disclosed in U.S. Pat. No. 6,669,647 and 20060074479. These patents disclose sensors that can be read from outside the body by an X-Ray machine or other radiographic methods. They require the patient to undergo periodic radiography. It is an object of the invention to provide a warning to the patient without the use of any external equipment and without the patient being required to take any action to detect the warning. This will greatly shorten the duration of the period the abnormal condition exists. It is another object to provide a device with practically infinite lifetime. A further object is to provide a simple, low cost device that can be delivered percutaneously. These and further advantages of the invention will become clear from the disclosure and drawings.
An implant capable of sensing pressure, force, pH level or any other condition releases a chemical into the body when a pre-set limit is exceeded. The chemical is chosen to be detectable by the person without the need of any external equipment. Typical chemicals are dyes causing coloration visible to the person or chemicals causing a mild and clearly identified reaction such as odor, taste, or unique sensation. The released chemical can have therapeutic effects as well. The invention is particularly suitable for detection of abnormal increase of internal pressure in order to monitor stent grafts.
Many abnormal conditions inside the body can turn dangerous in a short time. Current methods of periodic testing have to trade off cost of monitoring with risk of delayed detection. For example, when an endovascular graft is installed to prevent an aneurysm from bursting, patients are typically monitored annually at a great cost to the medical system. Should bleeding develop detection time can be as long as twelve month with an average detection time of six months. The invention allows near-instant detection without the costs of periodic monitoring. In order to eliminate the need of external detection equipment and to provide practically infinite life and low cost, a chemical is released inside the body to alarm the patient when a preset limit was exceeded. The alarm mechanism takes advantage of the senses of the patient to detect the chemical, as explained later on.
An illustrative example of the invention is a detector for warning the patient against internal bleeding caused by a defect in an aneurysm repair by stent graft. Referring now to
It will be understood from the above examples that a detector for many other abnormal conditions can be made based on the same principle of releasing a chemical into the body. For example, a detector for pH level can be made by using a material which dissolves rapidly when pH is changes. Such a material can keep a detector as in
For a stent graft application, by the way of example, detector 5 is made of type 0.2 mm thick 316L stainless steel in the form of a cylinder having a diameter of 5 mm and a length of 30 mm. Holes 12 are about 3 mm diameter. Foil seals 11 are is made of 2 um thick type 316L stainless foil, laser welded to detector body. Foils down to 1 um thick are available from special suppliers such as Lebow (www.lebowcompany.com). Such supplier can supply the thin foil already bonded to housing. In this case a separate filling hole is used, later sealed by laser or micro-TIG welding. Clip 6′ and spikes 6 are made from the same piece of work-hardened type 316L stainless steel about 0.1 mm thick. The tips of spike 6 should be very sharp. Another good choice for clip 6′ and spikes 6 is Nitinol, because of high elasticity and relatively high hardness. In this case thickness should be increased to about 0.2 mm.
The size of the detector is ultimately determined by the amount of chemical required to cause the desired reaction in the patient. The disclosed mechanism can be scaled to any size, from below 1 mm to over 10 mm in diameter. The detector can be used inside or outside lumens in the body.
The released chemical can be selected from a large group of candidates according to the desired effect on the patient, but in general there are four main groups:
Dyes, such as Methylene Blue or Sudan Black, causing visible change in skin or urine color.
Chemicals causing an unusual sensation. Foe example, dimethyl sulfoxide (DMSO) causes a strong garlic smell and taste in the patient.
Therapeutic agents. The above materials can be mixed with a drug acting as a “first aid” to the detected condition.
Specialized viruses and biological agents. The advantage of this group is that the detectors can be highly miniaturized, as the released agent multiplies in the body and causes a mild reaction identified by the patient. Viruses are desirable as they can be preserved for a long time but other biological agents can be used.
In some cases, when the application limits the size of the detector and the volume of the released chemical, sensitivity to the released chemical can be increased by external means. For example, a wrist band containing a sensitive chemical test for the chemical released in the body will allow the implanted detector to be reduced significantly. An external chemical test based on a wrist band containing chemicals (typically soaked and dried) can detect a specific chemical down to parts per million levels. This allows the amount of the released chemical to be in milligram range. External detecting aids based on electro-optical properties such as fluorescence can detect down to parts per billion, but require a power source and are more costly.