Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2001-12-14
2004-05-25
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S500000, C600S494000, C600S490000
Reexamination Certificate
active
06740043
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressure-pulse-wave detecting apparatus which presses an artery of a living subject and detects a pressure pulse wave produced from the artery.
2. Related Art Statement
A pressure-pulse-wave detecting apparatus which includes a pressure-pulse-wave sensor, presses the sensor against an artery of a living subject via skin, and detects a pressure pulse wave produced from the artery, is employed in, e.g., a blood-pressure monitoring apparatus which successively determines blood-pressure values of the subject based on the pressure pulse wave, or a pulse-wave-propagation-velocity measuring apparatus which measures a pulse-wave propagation velocity based on at least the pressure pulse wave.
In the above-mentioned pressure-pulse-wave detecting apparatus, a magnitude of the pressure pulse wave detected by the pressure-pulse-wave sensor largely depends on a pressing force applied to the sensor, and additionally a phase of the pressure pulse wave more or less depends on the pressing force. Therefore, the pressure-pulse-wave detecting apparatus needs to press the artery with a pressing force (hereinafter, this pressing force will be referred to as an “optimum” pressing force) which assures that a portion of the wall of the artery is flattened. Meanwhile, usually, the pressure-pulse-wave sensor has a plurality of pressure-detecting elements that are arranged in an array in a widthwise direction of the artery, so that even if the sensor is more or less moved relative to the artery, at least one of the pressure-detecting elements remains positioned right above the artery to be able to detect the pressure pulse wave.
A method of determining the above-mentioned optimum pressing force is disclosed in, e.g., Japanese Patent Document No. 11-9562. This document discloses a blood-pressure monitoring apparatus including the above-explained pressure-pulse-wave detecting apparatus, and teaches that the pressure-pulse-wave sensor is worn on a wrist to detect a pressure pulse wave produced by a radial artery. According to this document, the optimum pressing force applied to the pressure-pulse-wave sensor is determined as follows: First, the pressing force applied to the sensor is continuously increased up to a value at which the entirety of the wall of the radial artery is flattened. Then, one of the pressure-detecting elements that detects, during the continuous increasing of the pressing force, the highest pressure of the respective pressures detected by all the elements is selected (as a highest-pressure detecting element), and a pressing force at which the pressure pulse wave detected by the selected element exhibits a maximal amplitude, or a pressing force that falls within a range whose center is equal to that pressing force, is determined as the optimum pressing force.
In the case where a pressure-pulse-wave sensor of, e.g., the pressure-pulse-wave detecting apparatus disclosed in the above-mentioned document, is worn on a wrist to detect a pressure pulse wave from a radial artery, the radial artery is sandwiched between the sensor and a radius. Therefore, as the pressing force applied to the sensor is increased, the radial artery can be substantially completely flattened. That is, since the radial artery is supported on the radius, the artery can be completely flattened. However, there are many arteries that are not supported on such bones. That is, if the pressing force applied to the sensor pressing an artery not supported on a bone is continuously increased, the artery cannot be completely flattened. Thus, in that case, an appropriate pressing force which causes only a portion of the wall of the artery to be flattened may not be determined.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a pressure-pulse-wave detecting apparatus which can determine an appropriate pressing force that causes only a portion of a wall of an artery to be flattened, without needing to flatten an entirety of the wall of the artery.
The Inventor has carried out extensive studies to achieve the above object, and has found that in a state in which the pressing force applied to the pressure-pulse-wave sensor causes a portion of a wall of an artery to be flattened, there is no phase difference between respective pressure pulse waves detected by respective pressure-detecting elements of the sensor that are positioned right above the flattened portion of the arterial wall, but there is a phase delay of a pressure pulse wave detected by a pressure-detecting element positioned right above a non-flattened portion of the arterial wall, from the phase of the pressure pulse waves detected by pressure-detecting elements positioned right above the flattened portion, owing to a visco-elasticity of the non-flattened portion. Thus, if a phase of a pressure pulse wave detected by a pressure-detecting element distant by a prescribed distance from the highest-pressure detecting element in a direction toward an end of the array of pressure-detecting elements, e.g., an pressure-detecting element next to the highest-pressure detecting element, is not delayed from the phase of the pressure pulse wave detected by the highest-pressure detecting element, or if the former phase is later than the latter phase by a short time only, it can be judged that a portion of the wall of the artery is flattened.
In addition, the Inventor has found that there is substantially no pulse-pressure difference between the respective pressure pulse waves detected by the respective pressure-detecting elements positioned right above the flattened portion of the arterial wall, but a pulse pressure of the pressure pulse wave detected by the pressure-detecting element positioned right above the non-flattened portion of the arterial wall is smaller than the pulse pressures of the pressure pulse waves detected by pressure-detecting elements positioned right above the flattened portion, owing to a pressure loss caused by the visco-elasticity of the non-flattened portion. Thus, if a pulse pressure of the pressure pulse wave detected by the pressure-detecting element distant by the prescribed distance from the highest-pressure detecting element in the direction toward the end of the array of pressure-detecting elements, is substantially equal to the pulse pressure of the pressure pulse wave detected by the highest-pressure detecting element, it can be judged that a portion of the wall of the artery is flattened. The present invention has been developed based on these findings.
The above object has been achieved by the present invention. According to a first aspect of the present invention, there is provided an apparatus for detecting a pressure pulse wave produced by an artery of a living subject, comprising a pressure-pulse-wave sensor which has a pressing surface, and a plurality of pressure-detecting elements that are arranged, in the pressing surface, in an array in a widthwise direction of the artery; a pressing device which presses, with a pressing force, the pressure-pulse-wave sensor against the artery via a skin of the subject, so that each of the pressure-detecting elements detects the pressure pulse wave produced by the artery; a highest-pressure-detecting-element selecting means for selecting, as a highest-pressure-detecting element, a first one of the pressure-detecting elements that detects a highest one of respective pressures corresponding to the respective pressure pulse waves detected by the pressure-detecting elements; and a pressing-force checking means for judging whether the pressing force of the pressing device applied to the pressure-pulse-wave sensor is appropriate, based on a time difference between a first time when a prescribed portion of the pressure pulse wave is detected by the highest-pressure-detecting element and a second time when the prescribed portion of the pressure pulse wave is detected by a second one of the pressure-detecting elements that is distant by a prescribed distance from the highest-pressure-detec
Colin Medical Technology Corporation
Nasser Robert L.
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