Surgery – Truss – Pad
Patent
1992-11-25
1995-07-11
Sykes, Angela D.
Surgery
Truss
Pad
128633, 128687, A61B 500
Patent
active
054311705
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention relates to pulse responsive devices and more particularly but not solely to pulse rate meters and pulse oximetry devices.
2. Description of the Prior Art
Pulse oximetry devices, and some other pulse responsive devices, utilise the effect that there is a change in the light transmitted through or reflected from body tissues, due to the pulsing of the blood flow or flow of other body fluid. Such pulse responsive devices include light sensors which produce electrical output signals which can be analyzed to determine various parameters such as pulse rate or blood oxygen saturation for example. Advantages of these devices are that they are non-invasive and they can monitor the relevant parameter on a continuous basis. However, we have found that movements of the body can generate spurious noise in the output signal of the light sensor, thus masking the signal which is to be monitored. We have now devised a device which overcomes this problem.
SUMMARY OF THE INVENTION
In accordance with this invention, there is provided a pulse responsive device, having a light emitter, a light sensor for receiving light from the emitter after transmission through or reflection from body tissue and providing an electrical signal having a component varying according to pulsations in blood or other fluid flow through the body tissue, and a transducer responsive to movement or vibration of the body and providing an electrical signal varying according to the body movements or vibrations but independent or relatively independent of the blood or other fluid flow pulsations, and means for comparing one electrical signal with the other.
The electrical signal provided by the light sensor includes, in addition to the component varying according to the pulsations in the blood flow, a noise component due to the body movements or vibrations. Accordingly, by comparing one electrical signal with the other, the noise component due to body movements can be cancelled and an output signal is produced which various with the blood pulsations and independently of the body movements.
The movement transducer may comprise a light sensor responsive to light transmitted through or reflected from the body tissue, this light being of a wavelength that is unaffected or substantially unaffected by the pulsations in the flow of blood or other body fluids. As an example, we have found that yellow light is suitable for this purpose. However, as an alternative, the movement transducer may comprise a pressure or vibration sensor or an accelerometer. The two electrical signals may be compared by subtracting one from the other to cancel the noise component. Alternatively, the signal from the movement transducer may be analyzed to identify one or more ranges of frequencies corresponding to noise, and the corresponding frequencies are filtered out from the signal from the light sensor. The frequency analysis of each signal may be carried out by fast Fourier Transform techniques.
An adaptive cancellation technique may be used for subtracting the one electrical signal from the other in which cross-correlation is performed between the two electrical signals, and the technique is therefore able to cancel the noise component even if the phase and amplitude relations of the two signals vary with time.
The pulse responsive device in accordance with this invention may comprise a pulse rate meter. This may be adapted for use by joggers. Preferably in this case the light sensor and movement transducer are applied to the forehead. Preferably a read-out device is provided for wearing on the wrist or the back of the hand. Preferably a short wave radio system communicates output signals from the elements on the forehead to the read-out device on the wrist or hand, but instead the read-out unit may be connected to the elements on the forehead by a cable: the read-out unit may be carried in a pocket or clipped onto the user's clothing. In a modification, the read-out device may also be mounted to the h
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Schindler Edwin D.
Sykes Angela D.
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