Apparatus and method for measuring blood pressure

1. A blood pressure measuring apparatus comprising:

a sensing unit comprising a plurality of sensors each sensing a sphygmus wave at a same measurement site;

an analysis unit which

filters each sphygmus wave,

generates an envelope for each filtered sphygmus wave, and

calculates a waveform characteristic value for each envelope from slopes or slope variations of the each envelope;

a comparison unit comparing the characteristic values of the envelopes to determine the smallest or largest characteristic value, among the characteristic values of the envelopes;

a selection unit selecting one sensor of the plurality of sensors which sensed the sphygmus wave, the envelope of which has the smallest or largest characteristic value; and

a blood pressure estimation unit estimating blood pressure of the measurement site based on the sphygmus wave which is sensed by the selected one sensor.

2. The blood pressure measuring apparatus of claim 1 , wherein

the analysis unit filters the each sphygmus wave through a high-pass filter to pass a high-frequency component of the each sphygmus wave, and determines a maximum amplitude of the each filtered sphygmus wave; and

the comparison unit compares the determined maximum amplitudes of the filtered sphygmus waves to determine the largest maximum amplitude.

3. The blood pressure measuring apparatus of claim 2 , wherein the selected one sensor sensed the sphygmus wave, of which the filtered sphygmus wave has the largest maximum amplitude.

4. The blood pressure measuring apparatus of claim 1 , wherein the analysis unit

filters the each sphygmus wave through a low-pass filter to pass a low-frequency component of the each sphygmus wave,

generates the envelope from each low-pass filtered sphygmus wave, and

calculates the characteristic value for the each envelope from the slopes or the slope variations of the each envelope.

5. The blood pressure measuring apparatus of claim 4 , wherein

the analysis unit

determines for the each envelope, an envelope inflection zone where a slope of the envelope consecutively increases and decreases, and

calculates for the each envelope, a maximum slope and a difference between the increasing slope and the decreasing slope in the envelope inflection zone, and

the comparison unit compares the maximum slopes and the differences, to determine the largest maximum slope and the largest difference, and

wherein

the selected one sensor sensed the sphygmus wave, the envelope of which has the largest maximum slope, or

the selected one sensor sensed the sphygmus wave, the envelope of which has the largest difference.

6. The blood pressure measuring apparatus of claim 4 , wherein

the analysis unit

determines for the each envelope, an envelope inflection zone where a slope of the envelope consecutively decrease and increases, and

calculates for the each envelope, a minimum slope and a difference between the decreasing slope and the increasing slope in the envelope inflection zone, and

the comparison unit compares the minimum slopes and the differences, to determine the smallest minimum slope and the largest difference, and

wherein

the selected one sensor sensed the sphygmus wave, the envelope of which has the smallest minimum slope, or

the selected one sensor sensed the sphygmus wave, the envelope of which has the largest difference.

7. The blood pressure measuring apparatus of claim 4 , wherein the analysis unit

interpolates peaks of the each low-pass filtered sphygmus wave to generate a peak envelope,

interpolates valleys of the each low-pass filtered sphygmus wave to generate a valley envelope, and

generates the envelope of the each low-pass filtered sphygmus wave using the peak and valley envelopes.

8. The blood pressuring measuring apparatus of claim 1 , wherein

the analysis unit

filters the each sphygmus wave through a high-pass filter to pass a high-frequency component of the sphygmus wave,

curve-fits peaks within each filtered sphygmus wave, to generate a peak envelope,

calculates a maximum width of each peak envelope, and

calculates the width of the each peak envelope having a predetermined ratio with respect to the maximum width; and

the comparison unit compares the widths of the each peak envelope having the predetermined ratio, such that the selected one sensor sensed the sphygmus wave, the peak envelope of which has the smallest width having the predetermined ratio.

9. The blood pressure measuring apparatus of claim 1 , wherein the sensing unit comprises a sensor array in which a plurality of a rigid substrate is arrayed, each of the rigid substrates being moveable relative to neighboring rigid substrates, and each of the rigid substrates comprising at least two sensors arrayed thereon.

10. The blood pressure measuring apparatus of claim 1 , wherein the sensing unit comprises a sensor array in which a plurality of a semiconductor chip is packaged on a flexible printed circuit board, each of the semiconductor chips comprising a plurality of sensors disposed thereon.

11. The blood pressure measuring apparatus of claim 1 , wherein the sensing unit comprises a sensor array in which a plurality of sensors are disposed on a flexible printed circuit board.

12. The blood pressure measuring apparatus of claim 1 , wherein each of the sensors has a sensing width which is equal to or smaller than a diameter of an arterial blood vessel at the measurement site.

13. The blood pressure measuring apparatus of claim 1 , wherein the measurement site is a wrist region of a subject, and the sensing unit senses sphygmus waves transferred from a radial artery to local skin surfaces of the wrist region by using the plurality of sensors sensing the transferred sphygmus waves.

14. The blood pressure measuring apparatus of claim 1 , wherein the blood pressure estimation unit estimates blood pressure based on the sphygmus wave sensed by the selected one sensor, according to an oscillometric method.

15. The blood pressure measuring apparatus of claim 1 , further comprising a pressurizing element configured to flexibly conform to a shape of the measurement site.

16. The blood pressuring measuring apparatus of claim 1 , wherein

the analysis unit

filters the each sphygmus wave through a high-pass filter to pass a high-frequency component of the sphygmus wave,

curve-fits peaks and curve-fits valleys within each filtered sphygmus wave, to form a peak envelope and a valley envelope, respectively,

generates a peak-valley envelope for the each filtered sphygmus wave by subtracting the valley envelope from the peak envelope,

calculates a maximum width of each peak-valley envelope, and

calculates the width of the each peak-valley envelope, having a predetermined ratio with respect to the maximum width; and

the comparison unit compares the widths having the predetermined ratio, such that the selected one sensor sensed the sphygmus wave, the peak-valley envelope of which has the smallest width having the predetermined ratio.

17. The blood pressuring measuring apparatus of claim 1 , wherein

the analysis unit

filters the each sphygmus wave through a high-pass filter to pass a high-frequency component of the sphygmus wave,

curve-fits peaks and curve-fits valleys within each filtered sphygmus wave, to form a peak envelope and a valley envelope, respectively,

generates a peak-valley envelope for the each filtered sphygmus wave by subtracting the valley envelope from the peak envelope,

calculates a maximum width of each peak-valley envelope,

calculates the width of the each peak-valley envelope, having a predetermined ratio with respect to the maximum width, and

determines a portion of the width of the each peak-valley envelope, occurring before the mean arterial pressure of the each peak-valley envelope; and

the comparison unit compares the width portions occurring before the mean arterial pressure of the each peak-valley envelope, such that the selected one sensor sensed the sphygmus wave, the peak-valley envelope of which has the smallest width portion occurring before the mean arterial pressure of the each peak-valley envelope.

18. A blood pressure measuring method comprising:

a plurality of sensors each sensing a sphygmus wave at a same measurement site;

an analysis unit

filtering each sphygmus wave,

generating an envelope for each filtered sphygmus wave, and

calculating a waveform characteristic value for each envelope from slopes or slope variations of the each envelope;

comparing the characteristic values of the envelopes to determine the smallest or largest characteristic value, among the characteristic values of the envelopes;

selecting one sensor of the plurality of sensors which sensed the sphygmus wave, the envelope of which has the smallest or largest characteristic value; and

estimating blood pressure of the measurement site based on the sphygmus wave which is sensed by the selected one sensor.

19. A computer readable recording medium storing instructions which control at least one processor to perform a method of measuring blood pressure, the method comprising:

a plurality of sensors each sensing a sphygmus wave at a same measurement site;

an analysis unit

filtering each sphygmus wave,

generating an envelope for each filtered sphygmus wave, and

calculating a waveform characteristic value for each envelope from slopes or slope variations of the each envelope;

comparing the characteristic values of the envelopes to determine the smallest or largest characteristic value, among the characteristic values of the envelope;

selecting one sensor of the plurality of sensors which sensed the sphygmus wave, the envelope of which has the smallest or largest characteristic value; and

estimating blood pressure of the measurement site based on the sphygmus wave which is sensed by the selected one sensor and outputting the results of the estimating blood pressure to a user.