Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-04-24
2002-10-22
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C607S023000, C607S024000
Reexamination Certificate
active
06468219
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to cerebral blood flow velocity monitoring system and method specifically a transcranial Doppler ultrasound device adapted for implantation into the human body, for detecting microembolic signals and changes in cerebral blood flow velocity and operatively connected to a drug delivery system.
Human implantable physiological and/or chemical sensors and/or implantable fluid delivery systems of various forms are used in present day clinical practice. U.S. Pat. No. 5,484,404 is an example of such a system and is incorporated herein by reference.
U.S. Pat. No. 5,188,106 describes an apparatus and method that provides for monitoring of heart contractility and blood flow output from the heart to control an implantable cardiac assist or therapy device to maintain cardiac output without invading the left heart or the arterial system of the patient. The '106 patent is incorporated herein by reference.
While the '106 patent describes a system in which the physiologic parameter of interest for hemodynamic control is the cardiac output, that is, the amount of blood flow from the heart per unit time, the required indicia for brain blood supply is determined by peripheral reactions influencing the resistance and capacitance of cerebral blood vessels. The hemodynamic differences between the cardiovascular and cerebrovascular systems are further illustrated by the applicability of the “windkessel” model to the former as described in an article by Frank O. entitled “Die Grundform des arteriellen pulses,” published in Z Biol, vol. 37, pp. 483-526 (1899), but not to the latter, as argued in an article by Njemanze P. C. et al., entitled “Fourier analysis of the cerebrovascular system,” published in Stroke, vol. 22, pp. 721-726 (1991). Furthermore, there appears to be distinct regulatory mechanisms of blood flow in the cerebrovascular system as compared to the cardiovascular system. Cerebrovascular autoregulation has been characterized using transcranial Doppler technique in an article by Aaslid R. et al., entitled “Assessment of cerebral autoregulation dynamics from simultaneous arterial and venous transcranial Doppler recordings in humans,” published in Stroke, vol. 22, pp. 1148-1154 (1991). The possibility that failure of cerebrovascular flow regulatory mechanisms such as in syncope may not be accompanied by fall in mean arterial blood pressure has been raised in an article by Njemanze P. C., entitled “Cerebral circulatory dysfunction and hemodynamic abnormalities in syncope during upright tilt test,” published in Can J Cardiol, vol. 9, pp. 238-242 (1993). This work further emphasis the difference between cerebrovascular and cardiovascular systems thus requiring different monitoring approaches. Other publications by Njemanze P. C., entitled “Isoproterenol induced cerebral hypoperfusion in a heart transplant recipient,” published in PACE vol. 16, pp. 491-495 (1992) and another article by same author entitled “Cerebrovascular dysautoregulation syndrome in a heart-lung transplant recipient,” published in J Cardiovascular Tech, vol. 10, pp. 227-232 (1992), suggest that cardiopulmonary reflexes may not be implicated in this mechanism. Even more importantly the changes in cerebral circulation may precede changes in cardiovascular system as suggested in a report by Njemanze P. C. entitled “Cerebrovascular dysautoregulation syndrome complex—brain hypoperfusion precedes hypotension and cardiac asystole,” published in Jpn Circ J, vol. 58, pp. 293-297 (1994). It therefore follows that the '106 patent may not be applicable to the cerebrovascular system. What is therefore desirable is a device that is responsive to blood flow changes detected in the cerebrovascular system in conditions such as stroke.
The annual incidence of stroke is approximately 700,000 per annum in the United States according to the statistics provided in a work by Broderick J., et al., entitled “The Greater Cincinnati/Northern Kentucky Stroke Study: preliminary first-ever and total incidence rates of stroke among blacks,” published in Stroke, vol. 29, pp. 415-421 (1998). Ischemic strokes account for 80% of all stroke types. The high incidence and associated burden of disease of stroke have led to an interest to develop accurate predictors and prevention strategies. It is therefore desirable to have noninvasive techniques to identify surrogate markers of stroke events and their associated outcome. One such approach has been to utilize non-invasive cerebral blood flow velocity monitoring using transcranial Doppler ultrasound to measure microembolic signals also called high-intensity transient signals known to precede stroke events. Microembolic signals have been observed in patients with implanted mechanical and prosthetic devices and there are also spontaneously occurring microembolic signals in a variety of clinical conditions. Microembolic signals are identified by criteria set forth by the Consensus Committee of the Ninth International Cerebral Hemodynamic Symposium in a publication entitled “Basic identification criteria of Doppler microembolic signals,” published in Stroke, vol. 26, pp. 1123 (1995).
The occurrence of microembolic signals has been recorded during open-heart surgery, carotid endarterectomy and in patients with prosthetic heart valves, ventricular assist devices and those with atrial fibrillation. The association of microembolic signals with neurological and neuropsychological deficits in patients after open-heart surgery has been described in an article by Clark R. E., et al., entitled “Microemboli during coronary artery bypass grafting genesis and effects on outcome,” published in J Thorac Cardiovasc Surg, vol. 109, pp. 249-258 (1995).
Spencer M. in an article entitled “Transcranial Doppler monitoring and causes of stroke from carotid endarterectomy,” published in Stroke, vol. 28, pp. 685-691 (1997), ascribed postoperative cerebral ischemia in patients with carotid endarterectomy to the high rates of microembolic signals during surgery and in the immediate postoperative period. The enormity and severity of the problem of symptomatic and asymptomatic microemboli remains to be fully elucidated.
One object of the present invention is to use it in conjunction with ventricular assist devices. Considering that while tens of thousands of United States patients need a donor heart each year, only about 2,000 receive one. The ventricular assist devices have been shown to add months, even years, to patients' lives while the wait for donor heart to become available. Close to three thousand patients have received ventricular assist devices in Europe and America. One major limitation of the ventricular assist devices is the occurrences of clinical thromboembolism in up to 30%, dependent on device type and implantation center. Wagner W. R., and Johnson P. C., in an article entitled “Therapeutic techniques for reducing thrombosis after cardiovascular implants, published in a book by Klizman B., (ed.) entitled “Problems in General Surgery”, published by JB Lippincott Co., Philadelphia, Pa.: chapter 11, pp. 241-246 (1994), have suggested that thromboembolism remains a significant impediment to the choice application of ventricular assist devices. However, they demonstrated prolonged life of the patients with cardiomyopathy using ventricular assist devices until heart transplantation, which makes identification and prevention of thromboembolism an important strategy in patient care for prevention of strokes in this population. Wilhelm C. R., et al., in an article entitled “Measurement of hemostatic indexes in conjunction with transcranial Doppler sonography in patients with ventricular assist devices,” published in Stroke vol. 30, pp. 2554-2561 (1999), have demonstrated that microembolic signals identified using transcranial Doppler are related to increased hemostatic activity in patients with ventricular assist devices. Ventricular assist devices of different designs are now in clinical use. Left ventricular assist device (Novacor Left Ventricular Assist Sys
Jain Ruby
Lateef Marvin M.
Njemanze Philip Chidi
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