CN113670516B - Compression position positioning and pressure measuring method based on photoplethysmography imaging - Google Patents
Compression position positioning and pressure measuring method based on photoplethysmography imaging Download PDFInfo
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- CN113670516B CN113670516B CN202110923645.2A CN202110923645A CN113670516B CN 113670516 B CN113670516 B CN 113670516B CN 202110923645 A CN202110923645 A CN 202110923645A CN 113670516 B CN113670516 B CN 113670516B
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- pressure
- pressing
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- light volume
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- 238000013186 photoplethysmography Methods 0.000 title claims abstract description 45
- 238000000034 method Methods 0.000 title claims abstract description 26
- 238000003384 imaging method Methods 0.000 title claims abstract description 10
- 230000006835 compression Effects 0.000 title claims description 13
- 238000007906 compression Methods 0.000 title claims description 13
- 238000003825 pressing Methods 0.000 claims abstract description 60
- 230000008859 change Effects 0.000 claims abstract description 36
- 230000035487 diastolic blood pressure Effects 0.000 claims abstract description 17
- 239000008280 blood Substances 0.000 claims abstract description 16
- 210000004369 blood Anatomy 0.000 claims abstract description 16
- 230000035488 systolic blood pressure Effects 0.000 claims abstract description 10
- 238000005259 measurement Methods 0.000 claims abstract description 8
- 230000003287 optical effect Effects 0.000 claims description 8
- 238000003490 calendering Methods 0.000 claims description 6
- 238000010586 diagram Methods 0.000 claims description 6
- 238000009530 blood pressure measurement Methods 0.000 claims description 4
- 210000004204 blood vessel Anatomy 0.000 claims description 4
- 230000008602 contraction Effects 0.000 claims description 4
- 230000003205 diastolic effect Effects 0.000 claims description 4
- 230000004807 localization Effects 0.000 claims 1
- 230000008569 process Effects 0.000 description 3
- 238000003491 array Methods 0.000 description 2
- 230000036772 blood pressure Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000003993 interaction Effects 0.000 description 2
- 238000000691 measurement method Methods 0.000 description 2
- 206010005746 Blood pressure fluctuation Diseases 0.000 description 1
- 208000024172 Cardiovascular disease Diseases 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000017531 blood circulation Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000003745 diagnosis Methods 0.000 description 1
- 230000031700 light absorption Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000000541 pulsatile effect Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L25/00—Testing or calibrating of apparatus for measuring force, torque, work, mechanical power, or mechanical efficiency
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/021—Measuring pressure in heart or blood vessels
Abstract
The invention discloses a pressing position positioning and pressure measuring method based on photoplethysmography imaging. Before measurement starts, only one simple calibration work is needed, along with gradual enhancement of pressing force, the light volume signal characteristics corresponding to diastolic pressure and systolic pressure disappear one by one, two groups of pressure values and corresponding light volume signal intensity values are recorded, and a relation curve of pressure and blood light volume change can be fitted. Through the relation curve, the pressure values corresponding to the different blood light volume signal intensities can be obtained. The invention provides a non-contact measuring method for determining a pressing position and measuring pressure by a camera, which is different from the traditional technical route. The method is simple, does not need to install a pressure sensor, and can flexibly and conveniently measure a plurality of pressing areas on the surface of any object.
Description
Technical Field
The invention belongs to the field of machine vision analysis of limb photoplethysmography signals, and particularly relates to a pressing position positioning and pressure measuring method based on photoplethysmography imaging.
Background
In touch interactions, conventional implementations of pressure sensing require the provision of specific pressure sensing devices on the pressing surface. The sensing device comprises an element which generates strain along with pressure, and the pressure can be sensed by measuring corresponding parameters (such as resistance, capacitance and the like) of the element. Determining the absolute value of the pressure by the sensor requires calibration of the sensor prior to use to calibrate out the signal characteristics corresponding to the particular pressure. Such calibration operations are time consuming, laborious, complex in process and may drift over time making the measurements inaccurate.
The conventional pressing measurement technology requires a set of sensor arrays if the spatial position of the touch point is to be located, and requires high consistency of response characteristics of different sensor units in the arrays, so that the problem is that the spatial resolution is generally low, the accuracy of locating the position is low, the complexity and the manufacturing cost of the device are increased, and the large-scale use is inconvenient.
Disclosure of Invention
Aiming at the defects of the existing pressure sensing interaction technology, the invention provides a pressing position positioning and pressure measuring method based on photoplethysmography imaging.
The invention aims at realizing the following technical scheme: a compression position location and pressure measurement method based on photoplethysmography imaging, comprising the steps of:
(1) The method comprises the steps of placing a camera near a pressing area to be detected, collecting video through the camera, and collecting the change of the light volume signal intensity of the pressing area to be detected in each frame of image channel of the video through photoplethysmography to measure the change of the light volume, so as to measure the change of blood volume in tissue blood vessels of the pressing area of a human body.
(2) Before the measurement starts, performing calibration; the finger touches the pressing area, the pressure is gradually increased, and along with the enhancement of the pressing force, the photoplethysmography signal intensity under different pressures is obtained, so that the photoplethysmography signal characteristics of the diastolic pressure and the systolic pressure disappear one by one; firstly, the characteristics of the diastolic calendaring plethysmographic signal disappear, and the corresponding light volume signal intensity v at the moment is recorded 1 Diastolic pressure p 1 The method comprises the steps of carrying out a first treatment on the surface of the With increasing compression force, the features of the subsequently contracted calendered plethysmographic signal disappear and the corresponding photoplethysmographic signal intensity v at that time is recorded 2 Pressure p of contraction 2 The method comprises the steps of carrying out a first treatment on the surface of the Obtaining waveform change diagram of optical volume signal intensity of the pressing region, and corresponding diastolic pressure p at the moment when the optical volume signal intensity characteristics of systolic pressure and diastolic pressure disappear respectively 1 Shrink pressure p 2 Namely the value of the external pressure; completing calibration work;
(3) Fitting an approximate relationship between pressure and blood light volume change: determining the equivalent moments of different external pressure and diastolic pressure and systolic pressure according to the waveform change diagram of the light volume signal intensity of the pressing area obtained in the step (2); and (3) fitting to obtain an approximate relation curve of the change of the photoplethysmography signal and the external pressure according to the corresponding relation of the two groups of photoplethysmography signals obtained in the step (2) and the external pressure.
(4) And (3) positioning the pressing position and measuring the pressure, and obtaining the pressing position and the applied pressure value according to the approximate relation curve of the photoplethysmography signal change and the applied pressure obtained in the step (3).
Further, the relationship of the photoplethysmography signal change in step (3) to applied pressure is determined by compliance.
Further, the step (4) specifically comprises: and identifying the pressing areas pressed by multiple points through a camera to obtain a change relation curve of the intensity of the external pressure and the blood light volume signal corresponding to each pressing area, and obtaining the pressing position of each position and the pressure value corresponding to each pressing position according to the change relation curve.
The beneficial effects of the invention are as follows: the invention provides a non-contact measuring method for determining a pressing position and measuring pressure by a camera, which is different from the traditional technical route. The method is simple, does not need to install a pressure sensor, and can flexibly and conveniently measure a plurality of pressing areas on the surface of any object. The invention is carried out before starting measurement, and only one simple calibration work is needed.
Drawings
FIG. 1 is a schematic view of the positional relationship between a camera and a pressing area to be detected in the pressing position locating and measuring method of the present invention;
fig. 2 (a) is a schematic representation of the photoplethysmography signal intensity versus time in the absence of compression in accordance with this invention;
fig. 2 (b) is a waveform variation of the optical volume signal intensity during the calibration process of the present invention;
FIG. 3 is a graph model fitted with data points obtained by simple calibration showing the relationship of pressure measurements of the present invention to changes in the intensity of the blood photoplethysmographic signal;
Detailed Description
Photoplethysmography (PPG) is an optical measurement technique of biomedical tissues, and light with a specific wavelength is absorbed and scattered by tissues to attenuate after passing through the tissues. The change in blood volume within the tissue vessel can be monitored by the attenuated light volume signal. Photoplethysmography acquires the blood volume of blood vessels surrounding the site and its pulsatile changes with the heartbeat by recording the light absorption of tissues (e.g., finger tips, nasal lobes) of the measured portion in real time. The photoplethysmography is widely used in the areas of physiological detection and cardiovascular disease diagnosis and treatment.
The invention discloses a pressing position positioning and pressure measuring method based on photoplethysmography imaging, which specifically comprises the following steps:
(1) The method comprises the steps of placing a camera near a pressing area to be detected, collecting video through the camera, collecting the change of the light volume signal intensity of the pressing area to be detected in one channel of each frame of image RGB channels of the video through photoplethysmography to measure the change of the light volume, and further reacting to the change of limb pressing force through the change of blood flow pressure in tissue blood vessels of the pressing area of a human body. The schematic diagram of the position relation between a camera and a pressing area to be detected is shown in fig. 1, the camera faces the pressing area to be detected, the position where the pressing occurs is determined by shooting the pressing action of a finger, and the change of photoplethysmography signals of the finger area is collected.
The amount of blood in the vicinity of the pressed area of the human body is affected by the combination of the intravascular pressure and the applied pressure, and changes to different extents when the finger applies pressure of different intensities. As shown in fig. 2 (a), a schematic diagram of a photoplethysmography signal of the compression region a in fig. 1 is shown as a function of time. In the absence of external compressions, the change in the photoplethysmography signal is indicative of a change in blood pressure in the vicinity of the area of the body's compression caused by the heart beat. The peak of the signal indicates that the pressure in the vessel at this time is systolic, labeled systolic peak in the figure, and the second maximum peak formed over time is diastolic peak.
(2) Before the measurement starts, performing calibration; taking the pressing area a in fig. 1 as an example, the pressing area a is touched by a finger, the pressure is gradually increased, the photoplethysmography signal intensity under different pressures is obtained along with the enhancement of the pressing force, and when the pressure reaches a certain value, the photoplethysmography signal characteristics of the diastolic pressure and the systolic pressure disappear one by one. Firstly, the characteristics of the diastolic calendaring plethysmographic signal disappear, and the corresponding light volume signal intensity v at the moment is recorded 1 Diastolic pressure p 1 . As the compression force increases, the features of the subsequently contracted calendered plethysmographic signal disappear and the corresponding photoplethysmographic signal intensity v at that time is recorded 2 Pressure p of contraction 2 . The diastolic pressure p 1 Shrink pressure p 2 May be obtained by instrumental measurements or approximated by average values in the population. The diastolic pressure p 1 Pressure p of contraction 2 I.e. the value of the applied pressure. The waveform change of the optical volume signal intensity of the pressing area a is obtained, and as shown in fig. 2 (b), the optical volume signal intensity characteristics of the systolic pressure and the diastolic pressure are respectively disappeared at the moment, and the corresponding applied pressure value, that is, the value of the equivalent blood pressure at the moment, is obtained. And (5) completing the calibration work.
(3) Fitting an approximate relationship between pressure and blood light volume change: by estimating the compression force by the change in the waveform of the photoplethysmographic signal intensity as shown in fig. 2 (b) using the change in the peak-to-peak blood pressure morphology characteristic in the photoplethysmographic signal, the times at which the different applied pressures are equivalent to the diastolic and systolic pressures can be determined, respectively. According to the corresponding relation between the two groups of photoplethysmography signals and the applied pressure, a relation curve of photoplethysmography signal intensity and pressure can be obtained. The relationship between photoplethysmography signal intensity and applied pressure is determined by compliance (compliance), which can be considered constant over a small range of applied pressure under conditions of small tissue deformation, where blood photoplethysmography signal intensity and pressure are linear. Using the two sets of data points (p 1 ，v 1 ) And (p) 2 ，v 2 ) Can fit photoplethysmography informationThe approximate relationship between the number intensity and applied pressure is shown as a bold line in fig. 3. The approximate relationship curve between the photoplethysmography signal intensity and the external pressure can be used for obtaining external pressure values corresponding to different blood photoplethysmography signal intensities.
(4) Press position location and pressure measurement are performed: the camera and the pressing area to be detected are arranged according to the step (1), and the change of the light volume is measured by collecting the change of the light volume signal intensity of the pressing area to be detected in each frame image channel of the video through photoplethysmography. In the use process, the pressed limb part is identified by the camera, so that the multi-point pressing sensing identification can be performed, each pressing area corresponds to a respective relation curve of the applied pressure and the blood light volume signal intensity, and the numerical value of the applied pressure of each pressing area can be measured simultaneously. And (3) obtaining the pressing position and the applied pressure value according to the approximate relation curve of the photoplethysmography signal intensity and the applied pressure obtained in the step (3).
In summary, the present invention provides a non-contact measurement method for determining a pressing position and measuring pressure by a camera, which is different from the conventional technical route. The method is simple, does not need to install a pressure sensor, and can flexibly and conveniently measure a plurality of pressing areas on the surface of any object.
Claims (3)
1. A compression position locating and pressure measuring method based on photoplethysmography imaging, characterized by comprising the steps of:
(1) Placing a camera near a pressing area to be detected, collecting video through the camera, and collecting the change of the light volume signal intensity of the pressing area to be detected in each frame of image channel of the video through a photoplethysmography method to measure the change of the light volume, thereby measuring the change of blood volume in tissue blood vessels of the pressing area of a human body;
(2) Before the measurement starts, performing calibration; the finger touches the pressing area and gradually increases the pressure, and along with the enhancement of the pressing force, the photoplethysmography signal intensity under different pressures is obtained, so that the photoplethysmography of the diastolic pressure and the systolic pressure is obtainedTrace signal features disappear one by one; firstly, the characteristics of the diastolic calendaring plethysmographic signal disappear, and the corresponding light volume signal intensity v at the moment is recorded 1 Diastolic pressure p 1 The method comprises the steps of carrying out a first treatment on the surface of the With increasing compression force, the features of the subsequently contracted calendered plethysmographic signal disappear and the corresponding photoplethysmographic signal intensity v at that time is recorded 2 Pressure p of contraction 2 The method comprises the steps of carrying out a first treatment on the surface of the Obtaining waveform change diagram of optical volume signal intensity of the pressing region, and corresponding diastolic pressure p at the moment when the optical volume signal intensity characteristics of systolic pressure and diastolic pressure disappear respectively 1 Shrink pressure p 2 Namely the value of the external pressure; completing calibration work;
(3) Fitting an approximate relationship between pressure and blood light volume change: determining the equivalent moments of different external pressure and diastolic pressure and systolic pressure according to the waveform change diagram of the light volume signal intensity of the pressing area obtained in the step (2); fitting to obtain an approximate relationship curve of the change of the photoplethysmography signal and the external pressure according to the corresponding relationship between the two groups of photoplethysmography signals obtained in the step (2) and the external pressure;
(4) And (3) positioning the pressing position and measuring the pressure, and obtaining the pressing position and the applied pressure value according to the approximate relation curve of the photoplethysmography signal change and the applied pressure obtained in the step (3).
2. The photoplethysmography imaging based compression position localization and pressure measurement method of claim 1 in which the photoplethysmography signal change versus applied pressure in step (3) is determined by compliance.
3. The method for positioning and measuring pressure of pressing locations based on photoplethysmography imaging according to claim 1, characterized in that said step (4) is specifically: and identifying the pressing areas pressed by multiple points through a camera to obtain a change relation curve of the intensity of the external pressure and the blood light volume signal corresponding to each pressing area, and obtaining the pressing position of each position and the pressure value corresponding to each pressing position according to the change relation curve.
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