This application is the U.S. national phase of International Application No. PCT/KR2016/013057 filed 14 Nov. 2016, which designated the U.S. and claims priority to KR Patent Application No. 10-2015-0173149 filed 7 Dec. 2015, and KR Patent Application No. 10-2016-0120252 filed 20 Sep. 2016, the entire contents of each of which are hereby incorporated by reference.

BACKGROUND

Field

Apparatuses and methods consistent with the present disclosure relate to an apparatus for measuring blood pressure and a method of measuring blood pressure using the same, and more particularly, to an apparatus for measuring blood pressure and a method of measuring blood pressure using the same for detecting, from the wrist, a periodic change occurring when blood flows in a blood vessel via cardiac impulse to measure blood pressure of radial artery.

Description of Related Art

In general, a non-invasive method that does not damage a human body is a method of measuring blood pressure in a hospital and a home. The non-invasive method is broadly classified into a Korotkoff-sound method and an oscillometric method.

In the Korotkoff-sound method, blood pressure is measured by listening to sound generated in a blood vessel through a stethoscope while increasing and reducing pressure in a cuff in a state in which the cuff is wound around an upper arm and the stethoscope is positioned adjacent to the blood vessel. Systolic blood pressure corresponds to cuff pressure at a time point when stethoscope sound is begun to be first heard (or a time point when two or more pulses of stethoscope sound are begun to be heard). Diastolic blood pressure corresponds to cuff pressure at a time point when stethoscope sound completely disappears by continuously reducing cuff pressure.

However, in the Korotkoff-sound method, a measurer measures blood pressure via stethoscope sound heard through a stethoscope and, thus, the measurer needs high proficiency to accurately measure blood pressure. In addition, because a sense in terms of a time point when stethoscope sound is heard is difference for each measurer, different blood pressure is disadvantageously measured for each measurer.

The oscillometric method is a method of measuring blood pressure using an automated machine and has been most widely used, recently. In the oscillometric method, a cuff is wound around an upper arm and pressure in the cuff is continuously measured while cuff pressure is increased and, then, is gradually reduced. When the pressure in the cuff is continuously measured, a periodic pressure change of blood in a blood vessel is transmitted to the cuff and, in this case, this pressure change in blood changes cuff pressure. In this case, the systolic blood pressure and the diastolic blood pressure are measured by estimating that cuff pressure at a time point when a cuff pressure change due to a blood pressure change is highest is equal to average blood pressure of a user.

However, in the oscillometric method, high pressure needs to be applied to a cuff and, thus, a blood vessel or textus is damaged due to repeated measurement in the case of a hypertensive patient or the old and the inform with inflexible textus. In addition, currently, numerous devices have been introduced but most devices have a large volume and, thus, a user has a difficulty in measuring blood pressure using such a device while carrying the device.

The above two methods of measuring blood pressure commonly use a cuff. Conversely, there is a method of measuring blood pressure using a light sensor instead of a cuff. In the blood pressure measuring method, a pulse transit time (PTT) is calculated using electrocardiogram and photo-plethysmograph (PPG) measured at a finger and blood pressure is estimated using the calculated value. Here, the PPG indicates a pulsation component that is used as a bio signal obtained by irradiating the human body with light in a specific wavelength band and detecting reflected or transmitted light and is generated due to a cardiac impulse. Bio signal measurement using PPG is a non-restraint and non-invasive method and it is possible to detect a multiple signal such as pulse, respiration, and oxygen saturation using a single sensor. A time interval of detecting a pulse wave of PPG from an electronic signal of electrocardiogram (ECG) is referred to as PTT and has a correlation with blood pressure. As such, the method using the PTT measures blood pressure without using of a separate cuff and simultaneously measures PPG and electrocardiogram and calculates the PTT to estimate blood pressure.

However, the PTT is changed by not only a change in blood pressure but also other causes and, thus, there is a problem in that a high measurement error occurs depending on a state of a measurer compared with the above methods using a cuff.

SUMMARY

The present disclosure provides a blood pressure measuring apparatus that is small sized to be worn on the wrist and measures blood pressure in consideration of both a pulse transit time (PTT) and an arterial stiffness index (ASI) that are calculated through photo-plethysmograph (PPG) and electrocardiogram (ECG) to more accurately measure blood pressure, and a blood pressure measuring method using the blood pressure measuring method.

According to an aspect of the present disclosure, a blood pressure measuring method includes calculating a pulse transit time (PTT), measuring an arterial stiffness index (ASI), and calculating systolic blood pressure and diastolic blood pressure using the PTT and the ASI, wherein the ASI is measured in each of at least two or more postures with different hand shapes.

The hand shapes may be taken by any one of spreading all fingers or folding at least one finger, closing a first or spreading at least one finger while the first is closed, by folding a finger, allowing at least two fingers to contact each other, and spacing all fingers apart from each other. In this case, the hand shape may be taken by bending the wrist in any one direction.

The hand shape may be taken by bending the wrist in any one direction and may be taken by bending the wrist at a predetermined angle.

According to another aspect of the present disclosure, a blood pressure measuring method includes measuring calibration systolic blood pressure and calibration diastolic blood pressure, calculating a pulse transit time (PTT) and an arterial stiffness index (ASI) in a state in which at least two different hand shapes are taken, and calculating the calibration systolic blood pressure and calibration diastolic blood pressure, calibration pulse transit time and calibration ASI, and systolic blood pressure and diastolic blood pressure through the calculated PTT and ASI.

The PTT may be calculated using the PPG signal and the electrocardiogram signal.

The ASI may be calculated according to a following math formula by measuring reference pressure applied to a wrist and fluctuation pressure according to cardiac impulse under the reference pressure with respect to each hand shape and obtaining a graph satisfying values corresponding to the reference pressure and the fluctuation pressure:
y−a·ebx+c

where x is the reference pressure, y is the fluctuation pressure, b is the ASI, and ‘a’ and ‘c’ are constants.

The diastolic blood pressure may be calculated according to following math formulae:
PSD0=PS0−PDO

where PS0is calibration systolic blood pressure and PDOis calibration diastolic blood pressure.

PSD=PSD⁢⁢0(ebeb0)⁢(PTT0PTT)2

where PTT0is a calibration pulse transit time, PTT is a pulse transit time during blood pressure measurement, b0is a calibration ASI, and b is an ASI during blood pressure measurement.

PD=eb⁡(b0-b)0.018+ebeb0⁢(PD⁢⁢0+k0⁢PSD⁢⁢0)-kPSD

where PDis diastolic blood pressure during blood pressure measurement and k is a constant.

The systolic blood pressure may be obtained according to a following math formula:
PS=PD+PSD

where PSis systolic blood pressure during blood pressure measurement.

The k may be calculated according to a following math formula:

k=∫ab⁢f⁡(x)Bb-Ba·H

where ∫abf(x) is an area of a waveform configured by fluctuation pressure, Bb-Ba is a width of a fluctuation waveform, and H is a height of the fluctuation waveform.

The blood pressure measuring method may further include guiding a first hand shape, measuring a first pressure deviation applied to a wrist for a predetermined time, re-guiding the first hand shape when the first pressure deviation is not within a predetermined range and measuring a first ASI when the first pressure deviation is within the predetermined range, guiding a second hand shape, determining whether a first inclination of pressure applied to the wrist is greater than a second inclination of pre-measured pressure applied to the wrist as a hand shape is changed to the second hand shape from the first hand shape, re-guiding the second hand shape when the first inclination is less than the second inclination and measuring a second pressure deviation applied to the wrist for a predetermined time when the first inclination is greater than the second inclination, and re-guiding the second hand shape when the second pressure deviation is not within a predetermined range and measuring a second ASI when the second pressure deviation is within the predetermined range.

The first and second hand shapes may be guided to at least one of an image, a text, and voice.

The measuring of the ASI may include guiding a predetermined wearing posture of a blood pressuring measuring apparatus according to whether an ECG signal is detected.

According to another aspect of the present disclosure, a blood pressure measuring apparatus includes a wearing portion configured to be worn to be wound around a wrist of a user, a sensor disposed on the wearing portion and configured to detect a pulse transit time (PTT) and an arterial stiffness index (ASI) of the user, a controller configured to calculate systolic blood pressure and diastolic blood pressure of the user using the PTT and the ASI detected by the sensor, and a display configured to display the systolic blood pressure and diastolic blood pressure calculated by the controller, wherein the sensor detects pressure in a state in which at least two different hand shapes are taken to vary a degree pressurized to the wrist by the wearing portion.

The sensor may include a PPG sensor, an electrocardiogram sensor, and a pressure sensor.

The sensor may detect reference pressure applied to a wrist of a user and fluctuation pressure varied according to cardiac impulse under the reference pressure as pressure of a cell, which is installed on the wearing posture and into which air is injected, to pressurize the cell according to a hand shape.

The sensor may be disposed on one surface of the wearing portion to directly detect pressure applied to a wrist of a user according to a hand shape.

The sensor may be disposed between the wearing portion and the wrist.

