Pulse wave analyzer and blood pressure estimator using the same
In a pulse wave analyzer, an ECG signal and a pulse wave signal are detected from an object to be analyzed. A plurality of feature points are extracting from the acquired ECG signal, the feature points appearing in a waveform of the ECG signal. The acquired pulse wave signal is segmented into a plurality of pulse wave signal pieces based on times at which the feature points appear. Each of the pulse wave signal pieces is segmented every heart beat. A reference pulse wave is calculated based on the plurality of pulse wave signal pieces, by multiplying the pulse wave signal pieces by coefficients and averaging the pulse wave signal pieces multiplied by the coefficients. The reference pulse wave is used to estimate the blood pressure of the object.
1. A pulse wave analyzer comprising:
signal acquiring means for acquiring an ECG signal and a pulse wave signal which are detected from an object to be analyzed;
feature point extracting means for extracting a plurality of feature points from the acquired ECG signal, the feature points appearing in a waveform of the acquired ECG signal;
signal segmenting means for segmenting the acquired pulse wave signal into a plurality of pulse wave signal pieces based on times at which the plurality of feature points appear, each of the pulse wave signal pieces being segmented every heart beat;
calculating means for calculating, for estimation of a blood pressure of the object, a reference pulse wave based on the plurality of pulse wave signal pieces, by multiplying the plurality of pulse wave signal pieces by coefficients and averaging the plurality of pulse wave signal pieces multiplied by the coefficients, wherein the calculation of the reference pulse wave is performed repeatedly at intervals with a part of the plurality of pulse wave signal pieces interchanged with another new pulse wave signal piece; and
coefficient setting means for setting the coefficients based on a coefficient of correction between the new pulse wave signal piece and the reference pulse wave calculated immediately before the interchange such that the larger the coefficient of correlation, the larger a contribution of the pulse wave signal pieces to the reference pulse wave.
2. The pulse wave analyzer of claim 1 , wherein
the feature points are peaks of R-peaks of the waveform of the ECG signal.
3. The pulse wave analyzer of claim 2 , wherein
the feature point extracting means includes a low-pass filter whose cutoff frequency is present in a range of 15 to 30 Hz and means for extracting the feature points from the waveform of the ECG signal processed by the low-pass filter.
4. The pulse wave analyzer of claim 3 , wherein
the calculating means comprises adjusting means for adjusting a position of the new pulse wave signal piece in a time axis such that both the new pulse wave signal piece and the reference pulse wave calculated immediately before the interchange have the largest coefficient of correlation therebetween.
5. The pulse wave analyzer of claim 2 , wherein the calculating means is configured to adjust a position of the new pulse wave signal piece in a time axis such that both the new pulse wave signal piece and the reference pulse wave calculated immediately before the interchange have the largest coefficient of correlation therebetween.
6. The pulse wave analyzer of claim 1 , wherein
the calculating means comprises adjusting means for adjusting a position of the new pulse wave signal piece in a time axis direction such that both the new pulse wave signal piece and the reference pulse wave calculated immediately before the interchange are averaged to produce a new pulse wave having a waveform having a predetermined peak which presents the largest sharpness degree.
7. The pulse wave analyzer of claim 1 , further comprising
second coefficient setting means for setting the coefficient based on a parameter showing accuracy of measuring either the pulse signal or the ECG signal such that the higher the accuracy, the larger a contribution of the pulse wave signal pieces to the reference pulse wave.
8. The pulse wave analyzer of claim 7 , wherein
the parameter is a quantity based on either a first difference or a second difference, the first difference being between a heat rate interval obtained from the acquired ECG signal and a predetermined reference value thereof, the second difference being between a peak height of R-peaks appearing in the acquired ECG signal and a predetermined reference value thereof, and
the coefficient setting means is configured to set the coefficient such that the smaller either the first difference of the second difference, the larger the contribution.
9. The pulse wave analyzer of claim 7 , further comprising
disturbance strength acquiring means for acquiring a strength of a disturbance influencing the accuracy,
the quantity is based on the strength of the acquired disturbance, and
the coefficient setting means is configured to set the coefficient such that the weaker the disturbance, the larger the contribution.
10. The pulse wave analyzer of claim 9 , wherein
the disturbance strength acquiring means comprises a group of sensors including a vibration sensor, a temperature sensor, and a pressure sensor sensing a pressure between a pulse wave sensor sensing the pulse wave signal and the body, and
the disturbance strength acquiring means is configured to acquire the strength of the disturbance based on signals from one or more sensors selected from the group of sensors.
11. The pulse wave analyzer of claim 7 , wherein
the coefficient setting means is configured to calculate the reference pulse wave repeatedly at intervals with a part of the plurality of pulse wave signal pieces interchanged with another new pulse wave signal piece,
the parameter is a quantity based on a coefficient of correlation between the new pulse wave signal piece and the reference pulse wave calculated immediately before the interchange, and
the coefficient setting means is configured to calculate the coefficient such that the larger the coefficient of the correlation, the large the contribution.
12. The pulse wave analyzer of claim 11 , wherein
the coefficient setting means is configured to positionally adjust the new pulse wave signal piece in a time axis such that both the new pulse wave signal piece and the reference pulse wave calculated immediately before the interchange have the largest coefficient of correlation therebetween, and
the quantity is based on the coefficient of correlation obtained when the new wave pulse signal piece is positionally adjusted in the time axis.
13. The pulse wave analyzer of claim 11 , wherein
the coefficient setting means is configured to positionally adjust the new pulse wave signal piece in a time axis the new pulse wave signal piece and the reference pulse wave calculated immediately before the interchange are averaged to produce a new pulse wave having a waveform having a predetermined peak which presents the largest sharpness degree, and
the quantity is based on the coefficient of correlation obtained when the new wave pulse signal piece is positionally adjusted in the time axis.
14. The pulse wave analyzer of claim 12 , wherein
the coefficient setting means is configured to positionally adjust the new pulse wave signal piece in the time axis through an interval of time of .+−.30 msec.
15. The pulse wave analyzer of claim 12 , wherein
the coefficient setting means is configure to set the coefficient of the correlation such that the smaller an amount of adjustment of the new pulse wave signal piece in the time axis, the larger the contribution.
16. The pulse wave analyzer of claim 1 , wherein
the calculating means is configured to calculate the reference pulse wave repeatedly at intervals with a part of the plurality of pulse wave signal pieces interchanged with another new pulse wave signal piece, check if a coefficient of correlation between the new pulse wave signal piece and the reference pulse wave immediately before the interchange is less than 0.7, and exclude the new pulse wave signal piece from calculating the reference pulse wave if it is checked that the coefficient of the correlation is less than 0.7.
17. The pulse wave analyzer of claim 1 , wherein
the pulse wave analyzer is mounted in a vehicle and the object is a crew in the vehicle.
18. The pulse wave analyzer of claim 1 , wherein the calculating means is configured to adjust a position of the new pulse wave signal piece in a time axis such that both the new pulse wave signal piece in the reference pulse wave calculated immediately before the interchange have the largest coefficient of correlation therebetween.
19. A method of analyzing a pulse wave, comprising steps of:
acquiring an ECG signal and a pulse wave signal which are detected from an object to be analyzed;
extracting a plurality of feature points from the acquired ECG signal, the feature points appearing in a waveform of the acquired ECG signal;
segmenting the acquired pulse wave signal into a plurality of pulse wave signal pieces based on times at which the plurality of feature points appear, each of the pulse wave signal pieces being segmented every heart beat; and
calculating a reference pulse wave based on the plurality of pulse wave signal pieces, by multiplying the plurality of pulse wave signal pieces by coefficients and averaging the plurality of pulse wave signal pieces multiplied by the coefficients,
wherein the calculation of the reference pulse wave is performed repeatedly at intervals with a part of the plurality of pulse wave signal pieces interchanged with another new pulse wave signal piece.