The invention is applied to a device for non-invasive measurement of heart rate information, in particular to a heart rate monitor used in connection with exercise and sports.
The measurement of heart beat frequency is an interesting field of application in connection with exercise. On the basis of the heart beat frequency, i.e. the heart rate, it is possible to obtain information e.g. on a persons stress level, recovery and development of physical condition, and consequently the proportion of training exercises and rest can be monitored and planned better.
The heart rate is measured on a person""s skin on the basis of an electrocardiographic (ECG) signal generated by a heart beat. Additional information on ECG is available in the following publication by Guyton, Arthur, C., Human Physiology and Mechanisms of Disease, third edition, W. B. Saunders Company, 1982, ISBN 4-7557-0072-8, Chapter 13: The Electrocardiogram, which is incorporated herein as reference. The electrocardiographic signal is an electromagnetic signal originating from a heart beat, which is detected on the body of a person to be measured. The signal is measured by means of electrodes, which are in contact with the body at least at two points. By a polarization vector, the electrode that is located closest to the heart often acts in practice as the actual measuring electrode, while the other electrode serves as ground potential, to which the voltage measured by the measuring electrode is compared as a function of time.
The heart rate monitor electrodes to be placed on the chest are arranged in a known manner in a belt-like structure, i.e. a so-called electrode belt. The electrode belt is thus a ring-shaped attachment means that goes round the whole chest and can be tightened round the human chest. A structure of this kind is shown in FIG. 1. The electrode belts are known to have structures that comprise an electronic unit in the middle of the belt, with an electrode on both sides. The electrodes measure the electric pulse transmitted by the heart and transmit the measurement results to the electronic unit through an interface connecting the electrode and the electronic unit. The components included in the electrode belt, such as the electronic unit and the electrodes, are generally coated with plastic or rubber in order to protect the components against moisture, for instance. Depending on the structure of the electrode belt, the electronic unit often also comprises means for transmitting an electric pulse as an analog burst to a receiver and display unit worn on the wrist, for instance. Alternatively, the electrode belt itself may comprise the means for storing and displaying the electric pulses.
In general, the electrode belts have a structure in which the rubber or plastic support structure covering the components of the electrode belt is relatively rigid. These electrode belts are, in general, poorly suited for long-term, continuous use, and they chafe the skin easily. The belt-like structure of the electrode belt also limits its optimal positioning substantially at the heart with persons having large quantities of muscular or other tissue in the chest area. Also slim adults and children have troubles in wearing the rigid electrode belt, because it does not bend sufficiently to follow the contours of a human body with a narrow chest. In some prior art solutions, the problem is approached such that the plastic support structure between the electronic unit and the electrode is pleated, whereby the electrode belt bends immediately outside the electronic unit. However, this solution only reduces rigidity in bending the electrode belt, because the electrode belt is still ring-shaped and attachable round the chest.
The prior art solution has a serious drawback: it is difficult to fit the rigid electrode belt optimally round the chest to achieve the best measurement result, in particular in long-term, continuous use, when the electrode belt also chafes the skin easily.
The object of the invention is to provide an improved electrode structure and heart rate measuring arrangement for measuring an electrical heart beat signal on a human body such that the above problems can be solved. This is achieved with the following electrode structure for measuring an ECG signal on the chest of a person. The electrode structure comprises a band-like component having an inner surface to be placed against the skin of the person""s chest and an outer surface opposite thereto, and which electrode structure comprises a first electrode at a first end and a second electrode at a second end of the electrode structure, and the inner surface of the electrode structure is an adhesive surface for attaching the electrode structure to the skin of the person""s chest, and the electrode structure is arranged to measure a potential difference between the first and the second electrodes caused by the ECG signal.
The invention also relates to a heart rate measuring arrangement for measuring the ECG signal on the skin of a person""s chest. The heart rate measuring arrangement comprises an electrode structure placed on a person""s chest and a wrist-worn receiver unit, the electrode structure comprising a band-like component having an inner surface against the skin of the person""s chest and an outer surface, opposite thereto, and which electrode structure comprises a first electrode at a first end and a second electrode at a second end of the electrode structure, the inner surface of the electrode structure being an adhesive surface for attaching the electrode structure to the skin of the person""s chest, and the electrode structure being arranged to measure a potential difference between the first and the second electrodes caused by the ECG signal, the electrode structure further comprising ECG processing means communicating with the electrodes for measuring the potential difference between the first and the second electrodes caused by the ECG signal and for producing heart rate information on the basis of the measured potential difference, and the electrode structure further comprising a transmitter for transmitting the heart rate information to the wrist-worn receiver which comprises a receiver for receiving the heart rate information transmitted from the electrode structure, the wrist-worn receiver further comprising a display for presenting the heart rate information.
The preferred embodiments of the invention are disclosed in the dependent claims.
In the solution of the invention, it is intended that the electrode structure is placed on the skin of the user""s chest. In one embodiment, the band-like component of the electrode structure is of flexible, soft material that fits the skin closely, and as a consequence it is comfortable and inconspicuous to wear and does not chafe the skin, and hence it is well suited for long-term use in ECG measuring. In one embodiment the band-like component of the electrode belt is continuous, in which both electrodes and their attachment means are integrated. The band-like component is disposable and economical to manufacture. In terms of design, it is a plaster-like sticker, for instance.
The electrode structure has a first electrode at a first end and a second electrode at a second end. The first and the second electrodes of the electrode structure are electrically separated from one another in order to enable the measurement of the potential difference between the electrodes. For optimal measurement of the heart rate signal, the first and the second electrodes should be located sufficiently far apart from one another so as to detect an electric ECG signal generated by a heart beat. The electrodes are thus advantageously placed at the ends of the electrode structure. Naturally, there may be more than said two electrodes.
According to a preferred embodiment, the inner surface of the electrode structure is an adhesive surface for attaching the electrode structure on the skin of the person""s chest. An advantageous manner to implement the adhesive surface and the electrodes is the embodiment, in which the electrodes located at the ends of the band-like component of the electrode structure are made of electrically conductive adhesive. Hence, the adhesive attaches the electrode structure on the skin of the person""s chest. In a second embodiment the first electrode and the second electrode of the electrode structure consist of an electrically conductive membrane at both ends of the electrode structure, at the electrode. On the inner surface of the membrane, which is placed against the person""s skin there is an electrically conductive adhesive. The adhesive is preferably an electrically conductive glue. Further, a third manner to implement the electrodes and the adhesive surface is an embodiment, in which the first electrode and the second electrode of the electrode structure consist of an electrically conductive membrane at both ends of the electrode structure, at the electrode, and the electrodes at both ends of the electrode structure are narrower than the band-like component. Around the electrodes, on the outer edges of the band, on the inner surface thereof, there is an adhesive, with which the electrode structure is attached to the person""s skin. In this case, the adhesive need not be electrically conductive. Because the inner surface of the electrode structure is that portion of the electrode structure which is against the person""s skin, the electrodes are preferably located on the inner surface of the band. The electrode structure can also be designed such that the electrodes are partly or completely located on both the inner surface and the outer surface of the band. Further, the electrode structure can be designed such that the electrodes are located on the inner surface of the band, but they have interfaces also on the outer surface of the band.
The electrode structure also comprises an electronic unit communicating with the electrodes. The electronic unit is an electronic component attached to the band-like part of the electrode structure with one or more gripping means. The electrodes of the electrode structure communicate with the electronic unit. The electronic unit comprises ECG processing means, by which the potential difference caused by the ECG signal between the first and the second electrodes is measured, and an estimate for detected heart beat time instants is formed from the heart rate signals measured by the electrodes, and further the heart beat rate is calculated on the basis of the detected heart beat time instants. The electronic unit also comprises a transmitter for transmitting heart rate information to a wrist-worn receiver, which comprises a receiver for receiving the heart rate information transmitted from the electrode structure, and a display for presenting the heart rate information.
The wrist-worn receiver is located in a watch-like device that the user wears on his wrist, such as a heart rate monitor or a wrist computer. Transmission of information between the electrode structure and the heart rate monitor is thus carried out in known manners, for example through a connecting line, optically or electromagnetically. In the embodiment in question, the display for presenting the heart rate information is also preferably located in the wrist-worn receiver.
The electronic unit is preferably arranged in a casing which comprises one or more gripping means for attaching the electronic unit to the stap-like component of the electrode structure. The gripping means are most preferably located on that surface of the electronic unit casing which is against the person""s skin. The preferable structures of the gripping means include attachment slots, a pivoted, clamping clip, or the like, that are in the central unit casing. The gripping means or the central unit casing comprises conductive connecting means, through which the ECG signal measured with the electrodes is applied from the electrodes to the electronic unit.
The invention also has an advantage that the electrode structure is inconspicuous, comfortable and well suited for long-term use as compared with the known solutions.