Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-08-12
2002-06-04
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S459000, C600S504000, C623S002220
Reexamination Certificate
active
06398734
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to the use of ultrasonic transducers to monitor flow and velocity, and more specifically, to the use of such sensors to monitor flow and velocity of blood through a cardiac valve, so as to determine the condition of the valve.
BACKGROUND OF THE INVENTION
A cardiac valve that is diseased or defective can be surgically excised and replaced with an artificial valve. Once the valve has been replaced, it will be desirable to carefully monitor the condition of the valve, to ensure that it continues to function properly. While it is possible to externally examine a patient and reach some nominal diagnosis concerning the condition of a replacement valve and its proper functionality, an external examination may fail to identify incipient problems. If the valve subsequently fails catastrophically, the patient may die before surgery can correct the problem. Imaging techniques and other diagnostic evaluations of the proper functioning of an artificial valve may be impractical, patent application particularly because of expense and because they require the patient to visit facilities where such evaluations can be carried out. Accordingly, it will be apparent that means for performing such an evaluation on a continuing basis while a patient remains mobile and continues to lead a normal daily routine that does not involve frequent visits to a medical facility would be very desirable.
Often, a patient's natural cardiac valve may be diseased, but still capable of functioning to at least a limited extent. Again, it would be helpful to monitor the condition of the natural cardiac valve on a continuous basis to enable surgery to be performed to replace the valve before the patient suffers a serious heart attack caused by a failure of the valve. Currently, the most effective technique to evaluate the condition of either an artificial cardiac valve or a natural valve is to monitor the flow of blood through the valve. However, there is no convenient way to accomplish this monitoring on a continuing basis. The velocity and volume of blood flowing through a cardiac valve are ideal parameters for determining whether the valve is functioning properly. Distal and proximal fluid pressure across a valve are a further indication of its condition.
Ideally, it would be desirable to employ means for monitoring the condition of fluid flow through a cardiac valve remotely, either continually or only periodically, upon demand. The means used for monitoring the condition of a cardiac valve should enable a physician to evaluate the parameters noted above at a remote location outside the patient's body, without resorting to an invasive procedure. Further, the monitoring means should at least periodically be supplied power from an external source, since it is unlikely that a battery could provide the power required by sensors and circuitry required to monitor flow and other parameters indicative of a condition of a cardiac valve for an extended period of time.
Various techniques are known in the prior art for monitoring flow and velocity of a fluid inside a blood vessel, but in each case, the devices employed for this purpose are intended for relatively short-term use immediately following surgery and are not acceptable for the extended period for monitoring fluid flow, as noted above. For example, one type of volume flow measurement system described in U.S. Pat. No. 4,227,407 uses two piezoelectric ultrasonic transducers that are alternately activated to produce ultrasonic waves. The ultrasonic waves pass into a vein or artery and are modified by the flow of blood in the vessel interposed between the two transducers. When one transducer is actively transmitting an ultrasonic wave, the other transducer serves as a receiver of the wave. The two transducers are oriented at an acute angle relative to the longitudinal axis of the blood vessel, so that the ultrasonic sound wave propagating through the blood vessel has a component in the direction (or opposite to the direction) of blood flow through,the vessel. In an alternative embodiment disclosed in this patent, the transducers are located on the same side of the blood vessel, spaced apart along its longitudinal axis, and a reflective plate is disposed on the opposite side of the vessel, intermediate the positions of the two transducers. An ultrasonic wave transmitted from either transducer passes through the blood vessel, is reflected from the reflective plate, and is received by the other transducer. The difference in the transit times for the sound waves transmitted from the two transducers (in both embodiments) is indicative of the flow through the blood vessel. If transducers used only extend over a small portion of the diameter of the vessel, the difference in transit time would be indicative of the velocity of blood flowing in the blood vessel. However, since the transducers shown in this prior art reference are sufficiently large so that the diameter of the blood vessel is fully encompassed by the sound waves the transducers emit, the transit time is indicative of the flow of blood flowing through the vessel, i.e., volumetric flow. The flow is thus determined without any consideration of the internal cross-sectional area of the blood vessel. While this prior art apparatus is useful for monitoring blood flow (or velocity) through a blood vessel that is surgically exposed, the transducers are too large to be implanted within a patient's body and are unsuitable to monitor the fluid flow status through a blood vessel associated with a cardiac valve. Also, to provide a good acoustic path between the transducers and the adjacent surface of the vessel, it may well be necessary to apply the transducers against the surface of the vessel with sufficient force to distort the wall of the vessel into the notch in the apparatus that is formed adjacent the sloping face of each transducer. Such distortion of the vessel may adversely affect the accuracy of the measurements and is undesirable over an extended period of time.
Another prior art approach for determining the velocity and/or flow of blood in a vessel employs Doppler sensing using either a pulsed or continuous wave ultrasonic signal that is emitted at a defined angle relative to the longitudinal axis of the blood vessel. If only a single transducer is used, the angle must be accurately known, and any error in the angle must be corrected. However, if a transmitting transducer is disposed on one side of the blood vessel and a receiving transducer is disposed on the opposite side of the blood vessel, angled so that the ultrasonic beam reflected from the blood flowing through the vessel is directed to the receiving transducer, an angle correction is not required.
Examples of apparatus for Doppler monitoring of blood flow are disclosed in U.S. Pat. Nos. 5,289,821 and 5,588,436. In the first of these two patents, an ultrasonic transducer wire assembly is secured to a strip of biologically inert or absorbable material, which is wrapped around and in contact with a blood vessel to form a cuff, preferably disposed downstream from an anastomosis of the vessel, such as may be performed during microvascular surgery. The wire from the transducer exits the patient's body through a slit and is coupled to ultrasonic processing means that determine the velocity of blood flowing through the vessel by the Doppler processing of an ultrasonic wave that is transmitted by the transducer and received as a reflection from the blood in the vessel. After monitoring the velocity of blood flow for about three to seven days to determine if any thromboses has formed that would impede blood flow, the wire and transducer can be pulled from the strip and removed from the body through a small incision, leaving the strip behind. This device is not usable for an extended period of time (much beyond seven days), since the slit in the skin where the wires penetrate represents a pathway for infection. Further, the patent teaches that the invention is primarily intended for us
Cimochowski George E.
Keilman George W.
Anderson Ronald M.
Jaworski Francis J.
VascuSense, Inc.
LandOfFree
Ultrasonic sensors for monitoring the condition of flow... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ultrasonic sensors for monitoring the condition of flow..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ultrasonic sensors for monitoring the condition of flow... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2913842