HK1077725B - An apparatus and method for non-invasive blood pressure measurement - Google Patents

Description

Non-invasive blood pressure measuring device and method

Technical Field

The present invention relates generally to an electronic blood pressure measuring device and method, and more particularly to a non-invasive blood pressure measuring device and method that combines a cuff-type blood pressure measuring device with a separable cuff-less blood pressure measuring device based on pulse wave transmission time or pulse wave transmission speed theory.

Background

Currently, there are many different types of electronic blood pressure meters on the market, most of which use inflatable and deflatable cuffs. Many patents have been published relating to cuff-type sphygmomanometers, such as U.S. Pat. nos. 4,625,277, 5,215,096, and 6,602,200. Many cuff-type sphygmomanometers measure blood pressure using an oscillation method. The method comprises wrapping an inflatable/deflatable cuff around the arm of the user, and detecting pressure oscillations in the cuff by a pressure sensor disposed in the cuff by an electronically driven pump to increase the pressure in the cuff. In operation, the inflatable and deflatable cuff is automatically inflated to a value above the systolic pressure and then slowly deflated. Systolic blood pressure is detected when the amplitude of the pressure oscillations in the cuff begins to increase. When the pressure oscillation in the cuff reaches a maximum, the average pressure is detected. Diastolic pressure can be estimated by systolic pressure and mean pressure.

The traditional cuff type blood pressure measuring method can be used as a standard blood pressure measuring method for clinical application. However, the cuff-type sphygmomanometer has several disadvantages. First, the cuff can cause discomfort to the user. If the cuff is used frequently, the tissue and blood vessels under the cuff may be damaged due to frequent compression. In addition, since the cuff-type blood pressure measuring device uses a pump and a valve, it is generally bulky and consumes a large amount of power. Such devices are not convenient to carry around. Moreover, since a certain time is required for inflation and deflation, the cuff-type devices require a long time to complete one measurement, and they cannot realize continuous measurement of blood pressure. For the above reasons, this type of sphygmomanometer is not the most ideal choice for people who need to measure blood pressure frequently, and is not suitable for use outside home. However, it is still a convenient, reliable and accurate method for use at home.

Recent findings have made cuff-less, non-invasive blood pressure measurements possible. One of the methods is to predict the blood pressure using the pulse wave transmission speed. The pulse wave transmission speed refers to the speed at which a pulse wave is transmitted along an artery. Many different studies have shown that the pulse wave velocity is related to blood pressure. One commonly used method for measuring the velocity of the pulse wave is to measure the pulse wave transit time, i.e., the time required for the pulse wave to travel from the heart to a point on the artery. Methods for measuring blood pressure using pulse wave transmission time or pulse wave transmission speed are disclosed in U.S. Pat. nos. 5,649,543, 5,865,755, and 6,599,251, and european patent No. 0443267, etc. The pulse wave transit time can also be determined using a reference point on the electrocardiographic signal and a reference point on the pulse wave detected on the peripheral artery in the same cardiac cycle. The pulse wave can be detected by optical methods, which are photoplethysmography. Photoplethysmography characterizes the change in blood flow under tissue by impinging light on body tissue and measuring the reflected, transmitted or scattered light from the tissue, the light received by a photodetector. In addition, there are other methods of detecting pulse wave signals, such as using pressure sensors and impedance plethysmography.

The advantage of using the pulse wave transit time for measuring blood pressure is that it does not require the use of a cuff, thus providing a quick and comfortable measurement. Such measurements can be made frequently and continuously without causing any damage to the tissue or blood vessels under the cuff. In addition, the blood pressure change in a short time can be reflected by the continuous measurement. The cuff-less blood pressure measuring device does not need to use complex mechanical components, but only needs to use a plurality of dry electrodes to detect electrocardiosignals, and a pair of infrared light emitting diodes and a photoelectric detector are used for detecting the photoelectric plethysmographic signals. Because pumps and valves are not needed, the sphygmomanometer based on the method requires fewer electronic components, is simpler in mechanical part and consumes less power. The cuff-free sphygmomanometer can be small and portable and is suitable for being carried about. This type of device is suitable for persons who need to measure blood pressure often, such as persons who need to measure blood pressure several times a day.

However, there is also a disadvantage in measuring blood pressure using the pulse wave transit time, that is, calibration is performed for each user, that is, a relationship between the pulse wave transit time and the blood pressure of the user is established. The step of calibrating the cuff-less sphygmomanometer includes first measuring the blood pressure using a standard sphygmomanometer and then manually inputting the measured value into a control unit of the cuff-less sphygmomanometer so as to establish a calibration equation of the relationship between the blood pressure and the pulse wave transmission time. For example, U.S. patent 6,603,329 discloses a multifunctional blood pressure meter which provides a blood pressure measuring method based on the pulse wave transit time theory. The device comprises an input unit for inputting the blood pressure values required for calibration.

Calibration is usually required once a month, and more frequent calibration can improve the measurement accuracy of the cuff-less sphygmomanometer. Therefore, a user using a cuff-less sphygmomanometer may also need one cuff-type sphygmomanometer. This may greatly increase the expense for the user.

Japanese patent 2002-. The main feature of the invention is that the blood pressure value measured by the device for directly measuring blood pressure can be automatically transmitted to the electronic wrist watch sphygmomanometer for calibration thereof, so that the user does not need to manually input calibration data. Once the calibration is completed, the electronic wrist watch sphygmomanometer can estimate the blood pressure value of the user by calculating the pulse wave transmission time from the detected electrocardiosignals and the detected pulse wave signals. But this method requires that both separate measuring devices must have data transfer capabilities. Therefore, much development cost is increased compared to the blood pressure monitor having only a single microprocessor unit.

Chinese patent CN 1440722a proposes a design concept of integrating two blood pressure measurement units together. The electronic sphygmomanometer comprises a unit for measuring blood pressure by using an oscillation method and a unit for measuring blood pressure by using an SPD method. The SPD method relies on the relationship of the arterial pulse wave waveform and cuff pressure to estimate blood pressure. Unlike the oscillatory method, the SPD method does not require the pressure within the cuff to vary over a dynamic range. It only needs to estimate the blood pressure using the pulse wave detected when the cuff pressure is a certain value. Therefore, the time required for measurement thereof is greatly shortened as compared with the conventional oscillation method. At the same time, however, the accuracy of the measurement may be reduced. The advantage of using the device is that it allows the user to select the blood pressure measurement mode according to different situations. For example, the user may choose to quickly measure blood pressure using the SPD method while working. The two measurement modes are integrated into one device, and only one microprocessor is used, so that the development cost can be saved. However, both blood pressure measuring methods of this apparatus require a cuff to be wrapped around the upper arm of the user, and therefore it is not suitable for frequent blood pressure measurement.

The idea of integrating a cuff-type blood pressure measurement and a non-cuff-type blood pressure measurement into one unit is disclosed in us patent 5,752,920 and european patents 0875200, 0821910 and 1312301. However, the cuff-type device is generally bulky and inconvenient to carry because it includes a cuff, a pump, and a valve.

Therefore, in order to achieve convenient and comfortable cuff-less blood pressure measurement, it is necessary to provide a novel blood pressure monitor which can provide cuff-less blood pressure measurement on the same unit in addition to cuff-less blood pressure measurement, and which can be separated from a bulky cuff-less device for portability.

Disclosure of Invention

The invention aims to provide a novel sphygmomanometer and a method for measuring blood pressure by using the sphygmomanometer, which can overcome the defects of large volume and inconvenience in carrying caused by the fact that a cuff, a pump and a valve are included in the traditional electronic sphygmomanometer, is suitable for frequent blood pressure measurement, and does not excessively increase the cost.

To achieve the above object, according to a first aspect of the present invention, there is provided a non-invasive sphygmomanometer comprising a main body part and a separable unit, wherein the main body part includes a cuff-type blood pressure measuring device, and the separable unit includes a non-cuff-type blood pressure measuring device, and the separable unit is detachably mounted on the main body part and electrically connected to the main body part, characterized in that the separable unit includes a control unit for controlling the cuff-type blood pressure measuring device of the main body part to perform blood pressure measurement and calibrating the non-cuff-type blood pressure measuring device of the separable unit according to a result of the blood pressure measurement by the cuff-type blood pressure measuring device of the main body part. According to the calibration result, the blood pressure value of the tested person can be determined by the parameters detected by the non-cuff type blood pressure measuring device of the separable unit.

According to an embodiment of the present invention, the non-invasive sphygmomanometer may further include: a control unit provided on the main body portion for automatically controlling the operation of the main body portion and performing the calculation of the blood pressure value when the blood pressure is measured in a cuff manner.

According to an embodiment of the present invention, in the above non-invasive sphygmomanometer, the cuff type blood pressure measuring apparatus of the main body portion includes: a cuff which can be placed on the arm of a subject and pressurizes and depressurizes the subject by inflation and deflation; a pump that inflates the cuff to an initial pressure; a valve for releasing the pressure in the cuff; the signal detection device detects signals when the cuff pressure changes and converts the signals into corresponding electric signals so as to determine one or more parameters of diastolic pressure, systolic pressure and average pressure; the first signal preprocessing circuit is used for preprocessing the signal input by the signal detection device; and a first input/output circuit for exchanging signals with the detachable unit.

The separable unit non-cuff blood pressure measuring device includes: the physiological signal acquisition unit is used for detecting the physiological signal of the tested person and converting the physiological signal into a corresponding electric signal; the second signal preprocessing circuit is used for preprocessing the electric signal input by the physiological signal acquisition unit; and the second input/output device is used for being connected with the first input/output device of the main body part and exchanging signals.

In addition, according to a preferred aspect of the present invention, the non-invasive sphygmomanometer may further include: a main body operation unit provided on the detachable unit and/or the main body part for a user to start a blood pressure measurement operation and a calibration operation; a display unit provided on the detachable unit and/or the main body part for displaying a final result of the measurement or other information.

The physiological signal acquisition unit may include a sensor unit for detecting a peripheral blood flow (peripheral blood flow) signal and a bioelectric signal.

In the sphygmomanometer with the main body part and the detachable unit according to the present invention, the detachable unit may be put back into the main body to provide cuff-based blood pressure measurement, or separated from the main body to provide cuff-less blood pressure measurement.

According to another aspect of the present invention, there is provided a method of cuff-less blood pressure measurement using the sphygmomanometer according to the first aspect of the present invention, comprising the steps of:

when the detachable unit is mounted on the main body portion,

the cuff type blood pressure detection device of the main body part detects the blood pressure of the tested person;

the control unit of the separable unit establishes the relation between the measurement parameter of the non-cuff type blood pressure measurement device and the actual blood pressure value according to the blood pressure value detected by the main body part and the reference value detected by the non-cuff type blood pressure measurement device of the separable unit; and

when the blood pressure measurement is performed using the detachable unit,

the control unit of the detachable unit determines an actual blood pressure value corresponding to the parameter value according to the parameter value measured by the non-cuff blood pressure measuring device using the established relationship.

Further, according to a preferred aspect of the present invention, in establishing a relationship of the measurement parameter of the non-cuff type blood pressure measuring apparatus with the actual blood pressure value to calibrate the separable unit, the estimated blood pressure value, the time and date of each calibration and each measurement, and other parameters extracted from physiological signals (electrocardiographic signals and photoplethysmographic signals), such as the pulse wave transmission time and the area of the pulse wave, are recorded by the separable unit. When the following occurs: 1) the detachable unit has not been calibrated for more than a certain time frame (e.g., one month); 2) when the estimated blood pressure value and at least one other parameter value extracted from the physiological signal are compared with the values recorded at calibration, which change over a reference value or reference ratio, the detachable unit may give an alarm message on its display unit to alert the user that recalibration by cuff-type blood pressure measurement should take place. The alarm message may also be issued when the comparison result is greater than a preset value based on a comparison with a previous measurement result.

In addition, the invention also provides a method for automatically starting the cuff type blood pressure measurement when the separable unit detects certain physiological changes of the user. The function can be used for the situation that the cuff needs to be continuously wound on the wrist of a user for long-term blood pressure monitoring, so that the user can carry out clinical standard cuff type blood pressure measurement when needed.

In addition, the invention also provides a method for measuring the heart rate by using the sphygmomanometer, which is characterized by comprising the following steps of: detecting a physiological signal of the subject using the main body part or the detachable unit; calculating, by a control unit of the detachable unit or a control unit of the main body portion, a heart rate of the subject based on the detected physiological signal; the control unit of the detachable unit controls the output of the calculated heart rate value.

The device provided by the invention can not only allow a user to select a cuff type method for measuring the blood pressure, but also can utilize a rapid, comfortable and convenient cuff-free type method for measuring the blood pressure at any time and any place. The cuff-free blood pressure measuring unit of the device is small and exquisite and can be separated from the main body of the device, and the cuff-free blood pressure measuring unit can work as an independent blood pressure measuring device and can provide quick, comfortable and convenient blood pressure measurement at any time and any place. The blood pressure can be regularly and frequently measured by the user, and the method is particularly suitable for the user when the user is not at home. Meanwhile, compared with the existing blood pressure measuring device, the device of the invention also reduces the cost.

Drawings

Fig. 1 is a block diagram showing the structure of a conventional cuff-type electronic blood pressure monitor;

FIG. 2 is a schematic view of a sphygmomanometer in accordance with a first embodiment of the present invention;

FIG. 3 is a schematic view of a body in a first embodiment of the invention;

FIG. 4 is a block diagram of the main body in the first embodiment of the present invention;

FIG. 5a is a front view of the detachable unit in the first embodiment of the present invention;

FIG. 5b is a rear view of the detachable unit in the first embodiment of the present invention;

fig. 6 is a block diagram showing the construction of a detachable unit according to the first embodiment of the present invention;

FIG. 7 is a flow chart of the calibration of the detachable unit in the first embodiment of the present invention;

FIG. 8 illustrates the start and end of a calibration time window in an oscillatory manner, the selection of which is determined by the time at which a characteristic blood pressure value is detected;

FIG. 9 is a flow chart of blood pressure measurement using the detachable unit of the first embodiment of the present invention;

FIG. 10 is a flow chart for detecting the need to restart cuff blood pressure measurement;

FIG. 11 is a schematic view of a sphygmomanometer in accordance with a second embodiment of the present invention;

fig. 12 is a block diagram of a main body in a second embodiment of the present invention.

Detailed Description

Fig. 1 is a block diagram showing the structure of a conventional cuff-type sphygmomanometer using an oscillation method. In this device, an inflatable and deflatable cuff 101 is included, which is wrapped around the upper arm or wrist of the subject in use. The pump 104 is used to inflate the cuff 101 to the initial pressure. The valve 103 is used to release air from within the cuff to reduce the pressure. The pressure sensor 102 detects the pressure in the cuff and the pressure oscillation in the cuff generated by the pulsation of the subject's artery. The preprocessing circuit 108 processes the signal obtained from the sensor 102 and transmits the processing result to the control unit 105. A control unit 105, typically a microprocessor, automatically controls the pump 104 and the valve 103 and calculates the blood pressure value. The operation unit 106 includes buttons for the user to operate the sphygmomanometer, so that the user can operate the sphygmomanometer. The display unit 107 is used to display the blood pressure value calculated and output by the control unit 105.

The cuff-based blood pressure measuring device measures blood pressure by the following method. First, the inflatable and deflatable cuff 101 is wrapped around the upper arm of the user, the start button on the operation unit 106 is pressed, the control unit 105 provides a signal to drive the pump 104 to increase the pressure in the cuff 101, and the pressure sensor 102 in the cuff 101 detects the pressure oscillation in the cuff. When the pressure in the cuff 101 rises above the systolic pressure, the control unit 105 provides a signal to the valve 103 to release air from the cuff 101 and the cuff 101 is gradually deflated slowly. In the case of the oscillatory method, the systolic pressure is detected when the amplitude of the pressure oscillations in the cuff starts to increase; when the pressure oscillation in the cuff reaches a maximum, the average pressure is detected. Diastolic pressure can be estimated from systolic pressure and mean pressure. Algorithms required for signal processing and blood pressure value calculation may be stored in the control unit 105. The control unit 105 may calculate blood pressure values, such as systolic pressure and diastolic pressure, and display them on the display unit 107.

Fig. 2 is a schematic view of the sphygmomanometer 1 according to the first embodiment of the present invention. The sphygmomanometer 1 includes a main body portion 2 and a detachable unit 3. The detachable unit 3 may be built into the body portion 2. The sphygmomanometer can measure blood pressure by wrapping the cuff 201 around the upper arm of the user using the oscillation method as explained above. Further, in the case where the detachable unit 3 is placed in the main body portion 2, the user can also choose to calibrate the detachable unit 3 when measuring the blood pressure by the cuff method. In calibration, the user needs to place a finger on the sensor units 301, 302, 303, 304 and 305 to obtain physiological signals, including electrocardiographic signals and photoplethysmographic signals. Once the calibration is complete, the detachable unit 3 can be operated independently as a stand-alone blood pressure measuring device.

Fig. 3 shows an external appearance of the main body portion 2 in the first embodiment. Fig. 4 shows a block diagram of the structure of the constituent units of the main body portion 2. The main body part 2 comprises the components of a conventional cuff-type blood pressure measuring device, such as an inflatable/deflatable cuff 201, a pressure sensor 202, a pre-processing circuit 205, a valve 203 and a pump 204. A pressure sensor 202 is disposed within the inflatable cuff 201 to detect the pressure within the cuff and its changes (e.g., oscillations). The pump 204 and valve 203 are located within the housing 21. In this embodiment of the sphygmomanometer 1, the main body part 2 does not comprise a microprocessor unit, and it will therefore rely on the control unit in the detachable unit 3 to provide control signals to drive the pump 204 and the valve 203, as well as to calculate the blood pressure value from the signal obtained by the pressure sensor 202.

As shown in fig. 3 and 4, the housing 21 of the main body part 2 has a slot 208 for receiving the detachable unit 3. The socket 208 has electrically conductive contacts 209 for transmitting signals between the body part 2 and the detachable unit 3. The socket 208 may also be provided with further electrically conductive contacts 210 for enabling the battery charging unit 211 to charge the battery of the detachable unit 3. The main body 2 further comprises an operating unit 206 which includes buttons for the user to operate the sphygmomanometer, such as a power switch button, a sphygmomanometer start button, a calibration button, and the like. It is obvious that the operation unit 206 may not be provided on the main body portion 2, and the operation unit 308 on the detachable unit 3 may be used instead of the function of the operation unit 206, such as starting cuff-type blood pressure measurement or the like.

Fig. 5a and 5b are front and rear views of the detachable unit 3 separated from the main unit 2. Fig. 6 is a block diagram showing the structure of a corresponding detachable unit. The detachable unit 3, which may be a stopwatch, an electronic watch, an electronic toy or other device that can be worn by the user, comprises electrodes 301, 302 and 303 for acquiring bioelectrical signals from the finger, and optical sensors 304 and 305 for acquiring photoplethysmographic signals from the finger. The electrodes 301, 302 and 303 may be metal dry electrodes such as stainless steel or steel sheets. The optical sensor that acquires the photoplethysmograph signal of the finger may include a near infrared light emitting diode 304 and a photodetector 305. The wavelength of a near infrared light emitting diode is typically 880 or 940 nanometers. To reduce the influence of ambient light, the optical sensor may be built into a finger cuff made of a material that shields light.

The preprocessing circuit 306, the control unit 307, the memory unit 312, and the rechargeable battery 311 are disposed in the housing 31 of the detachable unit 3. The control unit 307 may employ a conventional microprocessor or microcontroller that executes applications to calculate blood pressure values for cuff or non-cuff blood pressure measurements and to provide control signals to the pump 203 and valve 204 for cuff blood pressure measurements. Since the control unit 307 may need to control both measurement modes at the same time, an oscillating circuit with a higher operating speed is required. While the memory 312 needs to have sufficient RAM and ROM to store various applications and to implement various control functions. An operation unit 308 and a liquid crystal display unit 309 are provided at the front end of the detachable unit 3, and the liquid crystal display unit 309 displays the blood pressure and heart rate value calculated by the control unit 307. At the rear end of the detachable unit 3, there is provided a conductive contact 313 for a signal input/output unit 315, which allows signals to be transmitted between the detachable unit 3 and the main body unit 2. Since the detachable unit 3 is operated by the rechargeable battery 311, a conductive contact 314 for power input to charge the rechargeable battery 311 is also provided in the detachable unit 3.

The detachable unit 3 needs to be calibrated before use. The calibration process includes measuring blood pressure using a cuff-based method and acquiring physiological signals (electrocardio-signals and photoplethysmography signals) using a non-cuff-based method, which may be performed simultaneously or sequentially. The synchronous calibration process can be seen in the flow chart of fig. 7. During calibration, the detachable unit 3 needs to be inserted into the slot 208 of the main body part 2, as shown in fig. 2. Before calibration, the user needs to select the calibration mode by pressing a button on the operation unit 308. In the first step of calibration (step SA1), the user needs to wrap the inflatable and deflatable cuff 201 around the upper arm for a cuff-based blood pressure measurement (e.g., using an oscillation method). Step SA2 is synchronized with step SA1, and the user puts a finger on the sensor unit of the detachable unit 3. One finger of the left hand is placed on electrode 301 and one finger of the right hand is placed on electrode 303, and one finger of either hand is placed on electrode 302, so that a cardiac electrical signal can be obtained. A finger placed on the intermediate electrode also touches both the light emitting diode 305 and the photodetector 304, thus obtaining a reflected photoplethysmographic signal.

At step SA3, the resulting two signals are first filtered, amplified and reference point detected by the vertex detection circuit by the preprocessing circuit 306. The reference point of the electrocardiographic signal can be the peak of the R-shaped wave, and the reference point of the photoplethysmographic signal can be the peak or the bottom of the pulse signal. These reference points may also be detected by the first or second derivative of the signal. The control unit 307 determines the time to detect the reference point according to step SA 3.

Meanwhile, in step SA4, the control unit 307 detects a first characteristic blood pressure based on the pressure signal obtained by the pressure sensor 202. If the blood pressure is measured by oscillation, the first characteristic blood pressure value may be the systolic blood pressure, as shown at 801 in FIG. 8. When the control unit 307 detects the first characteristic blood pressure, it initializes a calibration time window in step SA5, and the pulse wave transit time recorded in the calibration time window is used for calibration.

According to one embodiment of the invention, a cuff-based blood pressure measurement may be used to detect the blood pressure value for each cardiac cycle and to measure the pulse wave transit time synchronously using a cuff-less method. For example, this embodiment may be implemented using existing instrumentation that measures blood pressure values per cardiac cycle in a cuff-like manner (e.g., Finapres manufactured by Finapres medical systems, the Netherlands). The blood pressure value of each cardiac cycle can be obtained as long as the cuff is wrapped around the finger of the user, and the control unit 307 achieves more reliable calibration of the detachable unit 3 corresponding to each cardiac cycle by using the blood pressure value of each cardiac cycle measured by the apparatus.

Then, in step SA6, a pulse wave transit time is calculated from a time difference between a reference point on the electrocardiographic signal and a reference point on the photoplethysmographic signal within the same cardiac cycle. According to step SA8, the calibration time window is ended when a second characteristic blood pressure is detected in step SA7 by the pressure signal obtained by the pressure sensor 202, or after a given time frame (e.g., 10 seconds). If the blood pressure is measured by oscillation, the second characteristic blood pressure value may be the mean or diastolic blood pressure, as shown at 802 and 803 in FIG. 8. If the number of valid pulse wave transit times within the calibration time window is lower than the preset value in the control unit 307 due to the interference of noise (e.g., motion noise), the whole calibration process is performed again according to step SA 9. Simultaneously with the calculation of the pulse wave transit time, in step SA10, the control unit 307 synchronously calculates the systolic pressure, the diastolic pressure, and/or the average pressure based on the cuff-type blood pressure measurement, such as the oscillation method. Finally, the blood pressure value is displayed on the liquid crystal display unit 309 of the detachable unit 3.

The blood pressure values measured by the cuff-like method and the corresponding pulse wave transit times obtained in the calibration time window can be used as calibration data. In order to determine the relationship between blood pressure and the calculated parameters, two sets of calibration data are typically required. The control unit 307 performs step SA11 to determine whether the calibration data is sufficient, for example, whether two sets of pulse wave transmission time and corresponding blood pressure values are obtained simultaneously. If the data is not enough, after a while, steps SA1 through SA10 are called again. When sufficient calibration data is obtained, the control unit 307 executes step SA12 to establish a calibration equation describing the relationship between the blood pressure and the calculated parameter value. The calibration equation may be obtained by conventional regression analysis (regression) or other similar methods. The obtained calibration constant is then stored in the control unit 307 or other memory unit 312 in step SA 13. The calibration constant can then be called when the blood pressure is measured with the detachable unit 3.

When the physiological signal acquisition required for calibration is performed in sequence with the cuff-based blood pressure measurement, the procedure is similar to that described above, except for the initialization of the calibration time window. When the pressure signal obtained by the pressure sensor 202 indicates that the cuff blood pressure measurement has been completed, the control unit 307 initializes a calibration time window. The calibration time window may be 10 seconds, and the pulse wave transmission time recorded in the calibration time window may be calibrated in the control unit 307.

Once the calibration is complete, the detachable unit 3 can be detached from the main unit 2 and operated as a stand alone unit. The cuff-less blood pressure measurement process can be described by the flowchart of fig. 9. The first step is SB1, and the user places his finger on the electrodes 301, 302 and 303 and the optical sensors 304 and 305 to obtain the ecg and ppg signals. In step SB2, the two signals obtained are first filtered and amplified by the preprocessing circuit 306, and the reference point is detected by the vertex detection circuit. The reference point detection may also be performed in the control unit 307 by a pre-programmed program.

Once the desired signal is obtained, the control unit 307 in the detachable unit 3 performs step SB 3. In step SB3, the control unit 307 executes a program to calculate a time difference between a reference point on the electrocardiographic signal and a reference point on the photoplethysmographic signal in the same cardiac cycle as a pulse wave transmission time. If the number of valid pulse wave transit times within the calibration time window is lower than the preset value in the control unit 307 due to the disturbance of noise (e.g., motion noise), the detection of the electrocardiographic signal and the photoplethysmographic signal is resumed in step SB 4. When the sufficient pulse wave transit time is obtained, the control unit 307 executes step SB5 to calculate the diastolic and systolic pressures based on the pulse wave transit time and the previously stored calibration equation. Meanwhile, the heart rate can be calculated by utilizing the time interval between the peaks of the R-shaped wave of the electrocardiosignal or the time interval between the peaks of the photoplethysmography signal. The blood pressure value and the heart rate value calculated in step SB6 may be displayed on the liquid crystal display unit 309.

The user can carry the detachable unit 3 with him or her to measure the blood pressure outdoors at any time. Since the detachable unit 3 is used every day, the detachable unit 3 of the present invention is provided with a rechargeable battery 311, and thus, the battery does not need to be frequently replaced. The main unit 2 is provided with a charging unit comprising a charging circuit which may be of any existing circuit design. When the user returns home, the detachable unit 3 can be put back into the slot 208 of the main unit 2 to charge the battery 311. The user may also choose to recalibrate the detachable unit 3 if desired.

Detachable unit 3 alerts the user when to recalibrate detachable unit 3 by recording the time of each calibration, the time of each cuff measurement after calibration, and detecting large changes in the estimated blood pressure value or other body parameters to ensure the accuracy of the cuff-less blood pressure measurement. During calibration, the cuff-less blood pressure measuring device 3 may record the estimated blood pressure value, the calibration time and data, and other parameters extracted from the electrocardiographic signal and the photoplethysmographic signal (such as the pulse wave transmission time, the pulse wave area of the photoplethysmographic signal, etc.) in the memory 312. Such a parameter is at least one of pulse wave transmission speed-related information, pulsatile blood volume change-related information, or heart rate-related information. Typically, in estimating the blood pressure, the control unit 307 averages the values of these parameters over a time window. Control unit 307 may determine whether detachable unit 3 has not been calibrated for more than a certain time range (e.g., one month) by comparing the measured time with the calibration time stored in memory unit 312; the control unit 307 may also compare the estimated blood pressure value, the other parameter values extracted from the electrocardiographic signal and the photoplethysmographic signal with the values recorded at calibration stored in the memory unit 312 to determine whether the change in the estimated blood pressure value or the change in the at least one other parameter exceeds a reference value (e.g., a blood pressure value of 20 mmHg) or a reference proportion (e.g., 20%). When this occurs, the detachable unit 3 may give an alarm message on the liquid crystal display unit 309 to remind the user to recalibrate the detachable unit 3 by cuff-type blood pressure measurement.

Another way to give alarm information is: each time a cuff-less blood pressure measurement is made using detachable unit 3, detachable unit 3 may record in memory unit 312 the estimated blood pressure value and other parameters extracted from the electrocardiographic and photoplethysmographic signals. During measurement, the control unit 307 compares the current estimated blood pressure value and other parameter values with the result of the previous measurement stored in the memory unit 312, and when the change in the estimated blood pressure value or the change in at least one other parameter exceeds the reference value or reference ratio, an alarm message is given on the liquid crystal display unit 309 to remind the user to recalibrate the detachable unit 3 by cuff-type blood pressure measurement.

The other functions of the sphygmomanometer of the present invention are: when the detachable unit 3 detects a certain change of the physiological condition of the user, the cuff-based blood pressure measurement is initiated. This function can be used in situations where the cuff needs to be wrapped continuously around the user's wrist for long-term monitoring of blood pressure. In calibration, the detachable unit 3 may store the estimated blood pressure values and other parameters extracted from the electrocardiographic signal and the photoplethysmographic signal in the memory 312. Such a parameter is at least one of pulse wave transmission speed-related information, pulsatile blood volume change-related information, or heart rate-related information. Typically, when estimating the blood pressure, the control unit 307 averages the values of these parameters over a time window. The detection process can be illustrated by fig. 10 when measuring. First, the control unit 307 obtains the current estimated blood pressure value in step SC1, and then compares the current value with the value stored in the memory unit 312 obtained at the time of calibration. In step SC2, the control unit 307 checks whether the change in the estimated blood pressure value exceeds a predetermined threshold value, which may be a numerical value (e.g., 15mmHg) or a ratio (e.g., 15%). If not, the checking process ends, otherwise, the control unit 307 performs steps SC3, SC4, and SC 5. At this time, the control unit 307 obtains three types of variation of parameters: information on the change in the pulse wave propagation velocity is obtained in step SC3, information on the change in the pulsatile blood volume is obtained in step SC4, and information on the change in the heart rate is obtained in step SC 5. Then, in step SC6, the control unit 307 compares each of the three parameters with the corresponding value of the above parameter obtained during calibration, and detects whether the variation of at least one parameter exceeds a predetermined threshold, which may be a value or a ratio. If not, the examination is ended, otherwise the control unit 307 in step SC7 sends a control signal to the main body part 2 to initiate the cuff-based blood pressure measurement.

The parameter for initiating cuff-type blood pressure measurement or giving recalibration information is at least one of pulse wave transmission speed related information, pulsatile blood volume change related information or heart rate related information. The information on the pulse wave transmission speed includes the pulse wave transmission time, which is the time difference between a reference point on the electrocardiographic signal and a reference point on the photoplethysmographic signal in the same cardiac cycle. The information related to the change of the volume of the pulsating blood comprises various information obtained from the waveform of the photoplethysmography signal, including the rising edge time and the falling edge time of the pulse wave, the area of the normalized pulse wave, the high-order moment of the normalized pulse wave, and the first derivative and the second derivative of the signal. The information related to the heart rate comprises the time interval between two pulse waves and the time interval between two R-type waves of said bioelectric signal.

As shown in fig. 6, the detachable unit 3 may also include a data transfer port 310 for transferring the recorded blood pressure data to a peripheral device, such as a desktop computer, a Personal Digital Assistant (PDA), a mobile phone or other electronic products equipped with a display. The transmission may be via a wired connection or a wireless connection (e.g., infrared or radio). The function can lead the user to store the long-term blood pressure change data in the peripheral equipment, and can also assist the blood pressure monitoring in the remote medical treatment.

FIG. 11 is a schematic view of a second embodiment of the sphygmomanometer of the present invention. Fig. 12 is a block diagram of the main body part 2 in the second embodiment of the present invention. The sphygmomanometer comprises a main body part 2 and a detachable unit 3. Unlike the first embodiment, the main body part 2 has its own independent control unit 214, and the main body part 2 can still be used as an independent cuff type sphygmomanometer after the detachable unit 3 is detached from the main body part 2. Control unit 214 is typically a microcontroller or microprocessor that executes programs to perform the cuff-based blood pressure measurement (e.g., using the oscillation method explained above) and to provide control signals to pump 203 and valve 204 during the cuff-based blood pressure measurement. The main body part 2 displays the calculated blood pressure values including the systolic pressure and the diastolic pressure through its liquid crystal display unit 207. The other parts of the sphygmomanometer 1 according to the second embodiment are the same as those of the first embodiment.

The calibration process of the detachable unit 3 in the second embodiment can be seen in the flowchart of fig. 7, and the cuff-type blood pressure measurement is synchronized with the acquisition of the physiological signal. During calibration, the detachable unit 3 needs to be inserted into the slot 208 of the main body part 2, as shown in fig. 2. Before calibration, the user needs to select the calibration mode by pressing a button on the operation unit 308. The first step in calibration is SA1, where the user needs to wrap the inflatable and deflatable cuff 201 around the upper arm for cuff based blood pressure measurement (e.g., using an oscillation method). Step SA2 is synchronized with step SA1, and the user puts his or her finger on the sensor unit of the detachable unit 3. One finger of the left hand is placed on electrode 301 and one finger of the right hand is placed on electrode 303, and one finger of either hand is placed on electrode 302, so that a cardiac electrical signal can be obtained. A finger placed on the middle electrode also touches both the led 305 and the photodetector 304, thus obtaining a reflected photoplethysmographic signal.

Step SA3 is performed after step SA2, and the resulting two signals are first filtered, amplified, and reference point detected by the vertex detection circuit by the preprocessing circuit 306. The reference point of the electrocardiographic signal is usually the top point of the R-type wave, and the reference point of the photoplethysmographic signal is usually the top point or the bottom point of the pulse signal. These reference points may also be detected by the first or second derivative of the signal. The control unit 307 on the detachable unit 3 selects the time at which the reference point is detected in step SA 3.

Meanwhile, in step SA4, the control unit 214 of the main body part 2 detects a first characteristic blood pressure based on the pressure signal obtained by the pressure sensor 202. If the blood pressure is measured by oscillation, the first characteristic blood pressure value may be the systolic blood pressure, as shown at 801 in FIG. 8. When the control unit 214 detects the first characteristic blood pressure, it sends a synchronization message to the control unit 307, and informs the control unit 307 to initialize a calibration time window in step SA5, in which the recorded pulse wave transmission time can be used for calibration. The subsequent calibration process is the same as the above embodiment and is performed independently by the control unit 307. This step may also be the detection of the first characteristic blood pressure value by the control unit 307, the subsequent calibration process being as in the first embodiment above, and the control unit 214 being responsible for controlling the main body part 2 to measure blood pressure independently only when no separate unit is present.

If the cuff type blood pressure measurement can measure the blood pressure value of each cardiac cycle, each blood pressure value measured by the cuff type method and the pulse wave transmission time measured by the cuff-free method are synchronized. The same can be achieved with Finapres as described above. The blood pressure value for each cardiac cycle can be obtained by simply wrapping the cuff around the user's finger, and the control unit 214 uses the measured blood pressure value to achieve a more reliable calibration of the detachable unit 3 for each cardiac cycle.

Then, step SA6 calculates the pulse wave transit time from the time difference between a reference point on the electrocardiographic signal and a reference point on the photoplethysmographic signal within the same cardiac cycle. According to step SA8, the calibration time window is ended when a second characteristic blood pressure is detected in step SA7 or after a given time frame (e.g., 10 seconds). If the blood pressure is measured by oscillation, the second characteristic blood pressure value may be the mean or diastolic blood pressure, as shown at 802 and 803 in FIG. 8. When the control unit 214 detects the second characteristic blood pressure value in step SA7, the control unit 214 sends another synchronization message to the control unit 307, so that the control unit 307 ends the calibration time window in step SA 8. This step may also be performed by the control unit 307 detecting the second characteristic blood pressure value and ending the calibration time window, the control unit 214 being responsible for controlling the main part 2 to measure the blood pressure independently only when the separate unit is not present. If the number of valid pulse wave transit times within the calibration time window is lower than the preset value in the control unit 307 due to the interference of noise (e.g., motion noise), the whole calibration process is performed again according to step SA 9. When the control unit 307 in the detachable unit 3 calculates the pulse wave transmission time, such as by the oscillation method, the control unit 214 on the main body portion 2 synchronously calculates the systolic pressure, the diastolic pressure, and/or the average pressure in step SA 10. Finally, the blood pressure value is displayed on the liquid crystal display unit 207 of the detachable unit 2.

The blood pressure values measured by the cuff-like method are transmitted by the control unit 214 on the main body part 2 to the control unit 307 on the detachable unit 3. These blood pressure values and the corresponding pulse wave transit times obtained in the calibration time window can be used as calibration data. In order to determine the relationship between blood pressure and the calculated parameters, two sets of calibration data are typically required. The control unit 307 executes step SA11 to determine whether the calibration data is sufficient. If the data is not enough, after a while, steps SA1 through SA10 are called again. When sufficient calibration data is obtained, the control unit 307 executes step SA12 to establish a calibration equation describing the relationship between the blood pressure and the calculated parameter values, including the pulse wave transit time. The obtained calibration constant is then stored in the control unit 307 or other memory unit 312 in step SA 13. The calibration constant can then be recalled when measuring blood pressure with the detachable unit 3. Once the calibration is complete, the detachable unit 3 can be removed from the main body portion 2 and operated as a stand alone unit.

When the physiological signal acquisition required for calibration is performed in sequence with the cuff-type blood pressure measurement, the procedure is similar to that described above. The difference is that the control unit 214 sends a message to the control unit 307: when the pressure signal obtained by the pressure sensor 202 indicates that the cuff-type blood pressure measurement is completed, the control unit 307 initializes the calibration time window. The calibration time window may be 10 seconds, and the pulse wave transmission time recorded in the calibration time window may be used for calibration in the control unit 307.

The invention has been described in detail with reference to certain preferred embodiments. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Claims (14)

1. A non-invasive sphygmomanometer comprising a main body part and a separable unit, wherein the main body part comprises a cuff-type blood pressure measuring device, the separable unit comprises a non-cuff-type blood pressure measuring device, and the separable unit is detachably mounted on the main body part and electrically connected with the main body part,

the separable unit includes a control unit for controlling the cuff-type blood pressure measurement device of the main body portion to perform blood pressure measurement, calibrating the non-cuff-type blood pressure measurement device of the separable unit according to a blood pressure measurement result of the cuff-type blood pressure measurement device of the main body portion, and determining a blood pressure value according to a parameter detected by the non-cuff-type blood pressure measurement device of the separable unit using the calibration result.

2. The non-invasive sphygmomanometer according to claim 1, further comprising: a control unit provided on the main body portion for automatically controlling the operation of the main body portion and performing the calculation of the blood pressure value when the blood pressure is measured in a cuff manner.

3. Non-invasive sphygmomanometer according to claim 1 or 2,

the cuff type blood pressure measuring device of the main body portion includes:

a cuff which can be placed on the arm of a subject and pressurizes and depressurizes the subject by inflation and deflation;

a pump that inflates the cuff to an initial pressure;

a valve for releasing pressure within the cuff;

the signal detection device detects signals when the cuff pressure changes and converts the signals into corresponding electric signals so as to determine one or more parameters of diastolic pressure, systolic pressure and average pressure;

the first signal preprocessing circuit is used for preprocessing the signal input by the signal detection device; and

a first input/output circuit for exchanging signals with the detachable unit;

the separable unit non-cuff blood pressure measuring device includes:

the physiological signal acquisition unit is used for detecting the physiological signal of a measured person and converting the physiological signal into a corresponding electric signal;

the second signal preprocessing circuit is used for preprocessing the electric signal input by the physiological signal acquisition unit;

and a second input/output device for connecting and exchanging signals with the first input/output circuit of the main body portion.

4. The non-invasive sphygmomanometer according to claim 3, further comprising:

a main body operation unit provided on the detachable unit and/or the main body part for a user to start a blood pressure measurement operation and a calibration operation;

a display unit provided on the detachable unit and/or the main body part for displaying a final result of the measurement or other information.

5. The non-invasive sphygmomanometer of claim 4, wherein the signal detection device comprises a pressure sensor; the physiological signal acquisition unit comprises a sensor unit for detecting peripheral blood flow signals and bioelectric signals.

6. A non-invasive sphygmomanometer according to claim 5, wherein the sensor unit is selected from the group consisting of:

one or more light emitting diodes and one or more photodetectors to obtain a signal indicative of peripheral blood flow, the obtained signal being a photoplethysmographic signal; or/and

a pressure sensor for obtaining a signal indicative of peripheral blood flow, said signal indicative of peripheral blood flow being a pressure pulse signal; or/and

dry electrodes for deriving a signal indicative of peripheral blood flow, said signal indicative of peripheral blood flow being an impedance plethysmography signal; or/and

and the dry electrode is used for obtaining a bioelectric signal, and the bioelectric signal is an electrocardiosignal.

7. The non-invasive sphygmomanometer according to claim 6, wherein the one or more light emitting diodes and the one or more photodetectors are disposed in a finger cuff made of a material that shields light.

8. A non-invasive sphygmomanometer according to claim 1 or claim 2, wherein the main body portion further includes a socket for receiving the separable unit, the socket and the separable unit each including a conductive contact through which the main body portion and the separable unit input/output signals.

9. A non-invasive sphygmomanometer according to claim 8, wherein the separable unit includes a rechargeable battery, the main body portion includes a charging unit for charging the rechargeable battery of the separable unit, and the socket and the separable unit each include respective electrically conductive contacts for charging the battery of the separable unit, the charging unit having a charging circuit disposed therein.

10. A non-invasive sphygmomanometer according to claim 1 or claim 2, wherein the detachable unit includes a data transmission port for transmitting data to a peripheral device, the data transmission port being one of a wireless connection port and a wired connection port.

11. A non-invasive sphygmomanometer according to claim 10, wherein the peripheral device is a computer, a palm top computer, a mobile phone or other electronic products with display function.

12. A non-invasive sphygmomanometer according to claim 1 or claim 2, wherein the detachable unit is a stopwatch, an electronic watch, an electronic toy or other device that can be worn with the user.

13. The non-invasive sphygmomanometer according to claim 1, wherein the non-invasive sphygmomanometer is configured to calibrate the non-cuff blood pressure measuring apparatus of the separable unit while measuring blood pressure using the cuff-type measuring apparatus of the main body part.

14. The non-invasive sphygmomanometer according to claim 1, wherein the non-invasive sphygmomanometer is configured to calibrate the non-cuff blood pressure measuring apparatus of the separable unit after completion of blood pressure measurement using the cuff-type measuring apparatus of the main body part.