WO1992015241A1

WO1992015241A1 - Apparatus and method for determining in vivo the instantaneous velocity of the flow of blood in a living being

Info

Publication number: WO1992015241A1
Application number: PCT/US1992/001481
Authority: WO
Inventors: Young Cho; Kenneth Kensey
Original assignee: Kensey Nash Corporation
Priority date: 1991-03-04
Filing date: 1992-02-27
Publication date: 1992-09-17
Also published as: AU1644792A

Abstract

Apparatus (20) and a method of determining in vivo the instantaneous velocity of the blood flowing within the body of a living being. The apparatus (20) basically comprises respective first and second sensors (42, 44) which are arranged to be disposed at spaced apart locations within a blood vessel (26). The sensors (42, 44) are coupled to a control/analysis unit (24) located externally of the body of the being. The first sensor (42) is arranged to provide a heat pulse to the blood flowing thereby and to provide a first signal at that time. The second sensor (44) is located downstream of said first sensor and is arranged for providing a second signal when the first blood portion passes thereby. The control/analysis unit (24) measures the time period between those signals and based on that value and data representative of the distance separating the sensors, calculates the instantaneous blood velocity.

Description

APPARATUS AND METHOD FOR DETERMINING

IN VIVO THE INSTANTANEOUS VELOCITY OF THE

FLOW OF BLOOD IN A LIVING BEING

Field of the Invention

This invention relates generally to medical instruments for and methods of determining in vivo the velocity of the flow of blood in a living being.

Background Art

Conventional wisdom in the medical community used to be that heart attacks and strokes were primarily attributable to severe narrowing of the arteries due to vascular disease, e.g. , atherosclerosis and/or arteriosclerosis. However, it has been found that even in some patient's free of substantial arterial disease, or other high risk factors, e.g., high cholesterol, high blood pressure, etc. , the risk of heart attack/stroke is still great. Thus, today many investigators are focussing upon the blood's constituents, physical characteristics, and it effect(s) (sometimes referred to as "hemodynamic effects") upon the vascular system and associated organs to identify heart attack/ stroke risk factors and from that knowledge develop effective therapy. Moreover, the hemodynamic effects of the blood may, per se, play a role in the etiology of arterial disease.

Thus, one characteristic of the blood now being investigated from a hemodynamic standpoint is the so- called "stickiness" of the blood. For example, a recent study of male doctors has revealed that the riskiest time for a heart attack is in the morning. It has been suggested by one investigator, Dr. Paul Ridker, that this increased risk of a heart attack is the result of the fact that the blood is stickiest in the morning. If, in fact, increased blood viscosity is a factor in the etiology of vascular disease and/or the risk of heart attack or stroke, then apparatus and method for effectively determining the viscosity of the blood in real time, i.e., at virtually the same time that it is flowing through the body of the being, will be of considerable usefulness. Heretofore, measurement of blood viscosity has not been determined in real time. Instead it has been determined in-vitro with a substantial delay between the taking of the blood and its testing for viscosity. In this regard a blood sample is typically taken, via syringe, and the sample then sent to a laboratory for analysis. The major drawback of this in-vitro technique is that it does not present an accurate picture of the blood's viscosity at the time that it is flowing through the vascular system. This inaccuracy is the result of various factors, e.g. , viscosity may change as a result of the delay between the time the blood is withdrawn and tested and/or temperature changes from the time it is withdrawn until tested, and/or effects of contact with air, or other factors inherent in the in-vitro testing procedure.

In our copending United States Patent Application, Serial No. 07/664,262 filed on March 4, 1991, entitled Apparatus and Method Of Determining The Viscosity Of The Blood Of A Living Being, assigned to the same assignee as this invention and whose disclosure is incorporated by reference herein, there is disclosed and claimed apparatus which overcomes the deficiencies in the prior art for determining the viscosity of a being's blood. That -invention in one embodiment entails effecting the in-vivo determination of the instantaneous velocity of the blood flowing through the being's body to enable the determination of its viscosity to be calculated. The means and method for determining such blood viscosity constitutes the subject of this invention.

Moreover, it is believed that the determination of the instantaneous velocity of the blood flowing through the body of a living being may prove useful in evaluating hemodynamic effects on the etiology of vascular disease and/or risk factors for heart attack or stroke.

Objects of the Invention Accordingly, it is the general object of this invention to provide apparatus and a method determining in vivo the instantaneous velocity of the blood flowing within the body of a living being. It is a further object of this invention to provide apparatus which can be readily introduced into the vascular system of a living being to effect the in-vivo determination of the instantaneous velocity of the blood then flowing.

It is still a further object of this invention to provide apparatus to effect the in-vivo determination of the instantaneous velocity of the blood flowing through a living being and which is simple in construction, easy to use and accurate.

Summary of the Invention These and other objects of the instant invention are achieved by providing apparatus and a method for determining in vivo the instantaneous velocity of the flow of blood through the body of a living being.

The apparatus basically comprises implantable means and monitoring means. The implantable means is arranged for disposition within a blood vessel of the being and comprises first sensor means for providing a signal at a time that a first portion of said blood passes thereby, and second sensor means located downstream of said first sensor means. The second sensor means is arranged for providing a signal when the first blood portion passes thereby. The monitoring means operates on those signals to calculate the instantaneous blood velocity.

In accordance with a preferred embodiment of the invention the first sensor means is arranged to provide a pulse of heat to the first portion of blood as it flows thereby to heat it and to provide a signal indicative thereof to the monitoring means. The second sensor means is arranged to sense the passage of the heated blood portion thereby and to provide a signal indicative thereof to said monitoring means, whereupon said monitoring means determines the time period between said signals to calculate the instantaneous blood velocity. Brief Description of the Drawings Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

Fig. 1 is a section view, partially schematic, showing an implantable apparatus constructed in accordance ^• with this invention for effecting in-vivo measurement of instantaneous blood velocity; and

Fig. 2 is an enlarged sectional view taken along lines 2-2 of Fig. 1.

Detailed Description of the Preferred Embodiment

Referring now in detail to the drawing wherein like reference characters refer to like parts, there is shown at 20 in Fig. 1 apparatus constructed in accordance with one aspect of the subject invention. The apparatus 20 is arranged for effecting the in-vivo measurement of the instantaneous velocity of the blood flowing through the vascular system of a living being and basically comprises a pair of components, namely, an implantable monitor unit 22, and an associated externally located control/ analysis unit 24.

The monitor unit 22 will be described in detail later. Suffice it for now to state that it is arranged to be implanted within a suitable blood vessel 26, e.g., femoral artery, of the being. The monitor unit includes electrical leads, to be described later, connecting it to the control/analysis unit 24. That unit is arranged to be located outside the body of the being and serves to provide electrical signals to the monitor unit and to receive electrical signals therefrom. These signals are used by the control/analysis unit 24 to calculate the velocity of the blood using software in it, without requiring manual interaction.

The monitor unit 22 basically comprises a small diameter, e.g., 8 or 9 mm outside diameter, tube 28 of any material, e.g., stainless steel, suitable for location within interior 30 the being's blood vessel 26. The tube is preferably of very thin wall thickness, e.g., 0.5 mm, and its distal end 32 is tapered so that blood can flow readily into its interior without interference by the distal end of the tube.

The signals which the external unit 24 utilizes to calculate the instantaneous velocity of the blood are provided from velocity sensing probe means 40 in the unit 22. The velocity sensing probe means 40 basically comprises a pair of electrical resistance heating probes 42 and 44 projecting a short distance, e.g., 2 mm, radially inward into the interior of the tube 28 from the inner surface thereof. The probes are longitudinally spaced apart from each other by a predetermined distance, e.g., 2 cm. Each of the probes is connected via a pair of conductors 46 and 48 (although only one of each is shown in the interest of drawing simplicity) to a probe velocity controller 50 forming a portion of the control/analysis unit 24.

The probe velocity controller 50 is arranged to provide an electrical signal via conductors 46 to the distally located probe 42 to cause it to heat up quickly and thereby produce a heat pulse in the portion of the blood flowing thereby. The propagation of the heat pulse to the proximally located probe 44 resulting from the flow of the heated blood portion thereby is sensed by that probe and a signal indicative thereof is provided via conductors 48 to the probe velocity controller 50. That controller measures the delay or propagation time for the heat pulse from the distal probe to reach the proximal probe and provides output signals via lines 52 to a computer and signal processor 54 also forming a part of the external control/analysis unit 24. The computer and signal processor 54 can be of any suitable construction, e.g., a microprocessor and associated storage means, having software in it to effect the calculation of the blood's instantaneous velocity from the electrical signals provided to it. To achieve that end the computer and signal processor 54 has stored therein data representing the distance separating the probes 42 and 44.

Without further elaboration, the forgoing will so fully illustrate our invention that others may, by applying current or future knowledge, readily adopt the same for use under various conditions of service.

Claims

CLAIMSWhat is claimed is:

1. Apparatus for determining the instantaneous velocity of the blood flowing within the body of a living being, said apparatus being characterized bv implantable means and monitoring means, said implantable means being arranged for disposition within a blood vessel of said being and comprising first sensor means for providing a first signal at a time that a first portion of said blood passes thereby, and second sensor means located downstream of said first sensor means, said second sensor means for providing a second signal when said first blood portion passes thereby, said first sensor means being arranged to provide a pulse of heat to said first portion of said blood as it flows thereby to heat said first blood portion and to provide said first signal indicative thereof to said monitoring means, and wherein said second sensor means is arranged to sense the passage of said heated blood portion thereby and to provide said second signal indicative thereof to said monitoring means, said monitoring means operating on said first and second signals to calculate the instantaneous blood velocity by determining the time period between said first and second signals.

2. The apparatus of Claim 1 characterized in that said implantable means comprises a support member defining a wall portion along which said blood may flow, said wall portion supporting said sensors at a predetermined spacing from each other.

3. The apparatus of Claim 2 characterized in that said sensors project from said wall portion.

4. The apparatus of Claim 1 characterized in that each of said sensors comprises an electrical resistance heating member coupled via a respective electrical conductor to said monitoring means.

5. The apparatus of Claim 1 characterized in that said monitoring means is located outside the body of said being.

6. The apparatus of Claim 2 characterized in that said monitoring means is located outside the body of said being.

7. The apparatus of Claim 3 characterized in that said monitoring means is located outside the body of said being.

8. The apparatus of Claim 4 characterized in that said monitoring means is located outside the body of said being.

9. A method for determining in vivo the instantaneous velocity of the blood flowing within the body of a living being via the use of implantable means comprising first and second spaced apart sensor means, said method being characterized bv the steps of: inserting said implant¬ able means within a blood vessel in said being so that said second sensor means is located downstream of said first sensor means, providing a first signal at a time that a first portion of said blood passes by said first sensor means, providing a second signal when said first blood portion passes said second sensor means, and utilizing said signals to calculate the instantaneous blood velocity.

10. The method of Claim 9 characterized in that calculation of instantaneous blood velocity is effected by determining the time period between said first and second signals.

11. The method of Claim 9 characterized in that said method includes the steps of causing said first sensor means to provide a pulse of heat to said first portion of said blood as it flows thereby to heat said first blood portion and to provide said first signal, said second sensor means being arranged to sense the passage of said heated blood portion thereby and to provide said second signal.

12. The method of Claim 10 characterized in that said method includes the steps of causing said first sensor means to provide a pulse of heat to said first portion of said blood as it flows thereby to heat said first blood portion and to provide said first signal, said second sensor means being arranged to sense the passage of said heated blood portion thereby and to provide said second signal.