Measuring and testing – Fluid pressure gauge – Diaphragm
Reexamination Certificate
1999-04-06
2002-02-05
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Diaphragm
C073S708000
Reexamination Certificate
active
06343514
ABSTRACT:
The present invention relates generally to pressure, temperature and flow measurements, in particular in the medical field, and especially to in situ measurements of the intracoronary pressure, distally of a stricture, using a guide wire having a pressure sensor mounted at its distal end.
In particular it concerns a combined flow, pressure and temperature sensor.
BACKGROUND OF THE INVENTION
In order to determine or assess the ability of a specific coronary vessel to supply blood to the heart muscle, i.e. the myocardium, there is known a method by which the intracoronary pressure distally of a stricture in combination with the proximal pressure is measured. The method is a determination of the so called Fractional Flow Reserve (see “Fractional Flow Reserve”, Circulation, Vol. 92, No. 11, Dec. 1, 1995, by Nico H. j. Pijls et al.). Briefly FFR
myo
is defined as the ratio between the pressure distally of a stricture and the pressure proximal of a stricture, i.e. FFR
myo
=P
dist
/P
prox
. The distal pressure is measured in the vessel using a micro-pressure transducer, and the proximal pressure is the arterial pressure.
A limitation in measuring only the blood pressure and the pressure gradient, alternatively the Fractional Flow Reserve, is that there is no control of the flow in the coronary vessel. As an example, a vessel having a significant stricture would not yield any pressure drop if the myocardium is defective and has no ability to receive blood. The diagnosis will incorrectly show that the coronary vessel is healthy, when instead the conclusion should have been that the myocardium and possibly the coronary vessel are ill.
A diagnosis method for diagnosing small vessel disease is performed as follows:
The Fractional Flow Reserve is determined. If the FFR is <0.75 the coronary vessel should be treated.
If FFR is >0.75 there are two possibilities:
a) either the patient is healthy with respect to the actual coronary vessel (the most plausible), or
b) there is a low blood flow distally of the distal pressure measurement due to either an additional stricture or a sickly myocardium.
In order to investigate whether alternative b) is at hand, it is desirable to obtain knowledge regarding the health status of the myocardium, by measuring Coronary Flow Reserve (CFR), or in the alternative the Coronary Velocity Reserve (CVR). The idea is to determine by how many times a patient is able to increase his/her blood flow during work. A healthy patient should be able to increase the blood flow by 2.5-5 times, depending on the patient's age. Work is simulated by the addition of a so called vaso dilating pharmaceutical/medicament, e.g. Adenosine, Papaverin or the like. This medicament dilates the capillaries which increases the blood flow. The same medicament is used for determining FFR.
CFV is defined as
CFV
=
Q
work
/
Q
rest
=
Q
during
vaso
dilatation
/
Q
rest
(Q is the flow).
This being a ratio and assuming that the cross sectional area is constant during one velocity measurement, it will suffice to measure the velocity.
CFR is defined as
CFR=Q
work
/Q
rest
=[V
work
*K]/[V
rest
*K]=V
work
/V
rest
Since the desired parameter is a flow increase, it will be sufficient to obtain it as a relative quantity
CFR=[K*V
work
]/[K*V
rest]
wherein K is a constant.
Researchers have devised methods where the pressure and flow velocity in the coronary vessel are measured, the results being presented as so called “pressure-velocity loops” (di Mario). Thereby it becomes possible to distinguish patients suffering from the so called “small vessel disease” from others. In patients with “small vessel disease” the pressure gradient, corresponding to a low FFR, and the velocity of flow will be low, whereas healthy patients will have a low pressure gradient, corresponding to a high FFR, and a high flow.
In some investigations the applicant's system for pressure measurements in vivo, Pressure Guide™ (Radi Medical Systems) and the flow sensor sold under the trade name Flowmap™ (Cardiometrics) have been tested.
It is a great drawback to have to introduce two sensors into the coronary vessel, compared to a situation where both sensors are mounted on a “guide wire”. Thus, it has been suggested to provide a guide wire with two sensors, but this presents several technical problems with the integration of two sensors in a thin guide wire.
SUMMARY OF THE INVENTION
The object of the invention is therefor to make available means and methods for carrying out such combined pressure and flow measurements with a single unit, thus facilitating investigations of the outlined type, and making diagnosing more reliable.
The object outlined above is achieved according to the invention with the sensor as defined in claim 1, whereby the problems of the prior art have been overcome. The key is to use the temperature sensitive element for obtaining a flow parameter. Thus, there is provided a single sensor having the ability to measure both the pressure and to determine the velocity of flow or the volume flow. A great advantage with such a solution is that only one electrical circuit needs to be provided in a guide wire.
In a preferred embodiment, the sensor is an electrical sensor of a piezoresistive type. However it is contemplated that other pressure sensitive devices may be used, e.g. capacitive devices, or mechanically resonating sensors.
In accordance with the invention there is also provided a method of determining pressure, temperature and flow in a coronary vessel, as defined in claim 20.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
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Pijls, N., et al., “Fractional Flow Reserve: A Useful Index to Evaluate the Influence of an Epicardial Coronary Stenosis on Myocardial Blood Flow,” Circulation, vol. 92, No. 11, pp. 3183-3193 (1995).
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Aw-Musse Abdullahi
Foley & Lardner
Oen William
Radi Medical Systems AB
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