Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
1999-05-24
2001-05-15
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S492000, C600S500000, C600S495000
Reexamination Certificate
active
06231517
ABSTRACT:
The invention relates to an apparatus and a method for non-invasive measurement of the arterial blood pressure according to the preamble of the independent patent claims.
Oscillometric blood pressure measurement was clinically introduced at the beginning of the 1980s. Although primarily intended to meet clinical requirements, the technology was additionally adapted to home-use devices with progress in both digital processing and memory technology. These advantages allowed the construction of inexpensive and highly transportable blood pressure measuring systems, widely applied in home use.
The oscillometric technology was originally developed to be applied at the brachial artery. This specific artery is also the site of the clinical reference measurement, performed by physicians and nurses. The brachial artery is covered by the biceps and triceps brachial muscles and is compressed in a well-defined manner by the cuff's compression at the upper limb. Since the brachium is located at the heart's level, the application site sufficiently fulfils the need of measuring at the correct position.
In order to place brachial cuffs correctly, clothes such as suits shirts or coats must be removed. Additionally, the application of the cuff requires a positioning manoeuvre by using the other arm. This procedure proves difficult in some elderly people and in patients suffering from certain diseases (e.g. brain stroke symptoms, neuro-system diseases, traumatic lesions of the upper limbs).
These limitations of the brachial arm blood pressure measurement were the basic motivation for several manufacturers to adapt the oscillometric measurement to new applications sites. So, in the early 1990s the wrist was introduced as an additional measurement site.
The human wrist is the interconnection between the forearm, composed of the radius and the ulna, and the carpal bones. The arteries passing the wrist supply all anatomical structures of the hand. There are two major arteries: the radial artery and the ulnar artery. Anatomical details are given in FIG.
1
.
Both arteries are compressed and gradually released during the course of the oscillometric measurement. Thus, both arteries independently produce pressure pulses, which are detected by the pneumatic pressure sensor within the measuring device.
Basically, the oscillometric technology refers to a certain pulse pattern, described as the pulse oscillogram. The shape of this pulse oscillogram is the basis for the determination of the measurement results, the systolic and diastolic arterial blood pressure. The individual anatomy of the application site leads to a certain change of the pulse oscillogram's shape. This is why the oscillometric blood pressure measurement results differ from each other.
Basically, the measurement at two different arteries, the radial and ulnar artery, results in the detection of two different pulse oscillograms. These oscillograms overlap each other. The shape of these pulse oscillograms are usually not identical. The pressure detection system receives the summary signal of both oscillograms.
The overlapping of the radial and the ulnar pulse oscillogram varies highly since the histological structure is interindividually different. Therefore the overlapped signal is not defined concerning the pulse oscillogram's rising and falling signal curves. Both arteries contribute to the degree of scattering in the state of the art technology.
Since two different arteries contribute to the pulse oscillogram's shape, the variation of the overlapped total signal is fairly high. The overlapped signal's variation greatly exceed the variation of the signal of one single vessel. This is one reason why the results of wrist-type oscillometric measurements are less reliable than those of brachial applications.
It is an object of the present invention to overcome the drawbacks of the prior art, especially to provide an apparatus and a method for non-invasive measurement of the arterial blood pressure which is applicable at the human wrist and which leads to reliable measurements.
According the invention, these objects are solved by an apparatus and a method with the features of the characterizing portion of the independent patent claims. The method presented refers to one artery and therefore is diminishing the amount of scattering.
The apparatus for non-invasive measurement of the arterial blood pressure consists substantially of a cuff having at least one inflatable measuring bladder. The cuff has a shape adapted to be placed in a predetermined position around the human wrist. This specific shape allows the cuff to be placed at a predefined position for each measurement.
The cuff has one measuring surface which is adapted to be applied over the ulnar artery of the wrist and a second measuring surface area adapted to be applied over the radial artery of the wrist. Due to the shape of the cuff which allows exact positioning, the first and second measuring surface areas will always lie over the ulnar artery (first measuring surface area) and over the radial artery (second measuring surface area). The measuring bladder is connected with a blood pressure monitor, which allows indication of the diastolic and systolic blood pressure using an oscillometric measuring method.
According to the present invention, each of the measuring bladders (one or two bladders) has an angular extension and is disposed within the cuff in such a way that it is arranged within only one of the first and the second measuring surface areas.
Due to this specific disposition of the bladders, the pulses of only one artery is taken into account for a specific cuff, such that there is no overlapping of the pulse signals. This includes the design that both arteries are contributing separately to the signals in their specific cuffs.
One or two measuring bladders may be provided. According to a first aspect of the invention, the cuff comprises one bladder which is arranged in such a way that it contacts the first measuring surface area, i.e. that it lies over the ulnar artery when the cuff is applied to the wrist.
In another aspect of the invention, the cuff comprises one bladder which is arranged in such a way that it contacts the second measuring surface area, i.e. that it takes into account the pulses provided by the radial artery of the wrist.
It is also conceivable to use a cuff which is provided with two bladders. In such an arrangement, a first bladder is arranged in such a way that it contacts only the first measuring surface area and a second bladder is arranged in such a way that it contacts only the second measuring surface area. With such an arrangement, it is important that the signals of the two bladders are treated separately in the blood pressure monitor. As the pulses of both arteries are treated separately, the stability of the measurement may be enhanced significantly. This is due to the fact that two blood pressure measurements are taken separately at the same time and consequently are used to minimise possible artefacts.
In a preferred embodiment, the cuff comprises at least one marking which allows positioning of the cuff around a wrist. The cuff already has a shape which is adapted to be placed in a predetermined position around the wrist. The marking facilitates positioning of the cuff for the user and ensures a correct application of the cuff.
In a further preferred embodiment, each bladder is provided with a pneumatic pressure tube which is connected by a connector to the blood pressure monitor. In the case of the two-bladder design, a pneumatic double tube is preferably used, each of the said bladders being connected with one of the tubes. This allows electronic signal processing of the two signals. The combined analysis of these two signals intends to enhance the artefact suppression as well as improve the measurement stability.
There may be basically three types of measuring apparatus according to the present invention. A first ulnar type has one bladder which is arranged in the first, ulnar, measuring surface area. A secon
Microlife Corporation
Nasser Robert L.
Shoemaker and Mattare Ltd.
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