2.2.1. Experimental Equipment and Test Principle
Laser Speckle Contrast Imaging (LSCI), a non-contact testing technology for testing the blood flow of human-surface-skin microcirculation, has been widely used in clinical research in recent years because of its high sensitivity and accuracy [
12,
13]. LSCI is a non-contact imaging technology based on the principle of speckle contrast analysis. Speckle occurs because large amounts of light interfere with each other due to scattering and diffuse reflection when a laser beam irradiates an object with a rough surface. At this time, if the rays are superimposed with each other, bright spots will appear. Such images are called laser speckle patterns.
LSCI has excellent temporal and spatial resolution and has the advantage of full-field measurement. At present, this technology has been applied in many aspects, such as cerebral-blood-flow monitoring and skin-microcirculation monitoring in medicine. Therefore, the use of LSCI is of great significance in measuring medical-related parameters such as blood-flow velocity and microcirculation blood perfusion, studying the pathogenic mechanism in the pathology related to microcirculation perfusion disorder, diagnosing various diseases, and preventing the need for health care and alleviating pain.
The instrument used to test the promotion effect of fabrics on the blood flow of human-skin microcirculation involved in this paper was the BVI microcirculation-blood-flow imager provided by Shenzhen Shengqiang Technology Co., Ltd. (Shenzhen, China). The experimental apparatus, test schematic diagram, and curves of dynamic blood-flow rate were obtained by covering 1+3 simulated rib samples of GP-0.0% and GP-0.2% at two test points of the arm, as shown in
Figure 2.
Table 3 shows the average values of dynamic blood-flow rate at three periods of two test points, which were intercepted from the curves obtained by covering 1+3 simulated rib samples of GP-0.0% and GP-0.8% at two test points of the arm.
The instrument is divided into three parts: host, clamp, and support. The host includes a power supply, optical system, electronic processing, and control system. According to the principle of LSCI imaging, when human living tissue is irradiated by infrared light, the hemoglobin in blood vessels contained in the tissue has a more obvious absorption effect on light than surrounding tissues. After conversion by the instrument image processing system, a visible image of veins can be formed on the display screen. The principle advantage of the instrument is that it can capture the blood-flow-velocity imaging of living tissues’ microcirculation within a large area. The largest test area of the instrument is 18 cm × 12 cm, and the laser is launched by the host machine. When the surface of the measured object is uneven, the incident light will backscatter, and the optical path of the light reaching the imaging surface of the camera is different, so random interference will occur on the imaging surface. Thus, speckle patterns with different light and dark effects are produced.
2.2.2. Experimental Materials and Test Methods
According to the arm circumference of the 10 subjects and considering that no pressure should be applied when wrapping the arm of the sample, the size of the sample was set as follows: the width was 10 cm, the length of the test point, C1, near the wrist was 20–23 cm, and the length of the test point, C2, near the elbow was 23–27 cm. To facilitate the test, a 2 cm × 2 cm square hole was set in the middle of each sample.
- 2.
Pre-Test Preparation Requirements.
Because the test results of blood-flow rate on the human-body-skin microcirculation are easily affected by the physiological factors of the tested person and the external environment, the impact of these factors were avoided as much as possible during the test. Before the experimental test, the samples were humidified for 24 h according to the standard GB/T 6529-2008 [
14]. The ambient temperature of the laboratory was controlled at 25 °C and the relative humidity was 65%. The room was kept in a non-ventilated state, and all light aside from the indoor light was shielded. The inside of the non-dominant arm of the tested person was observed in advance and marked with a 2 cm × 2 cm square test point. To ensure the validity of the test data, the tested person’s test position was be contaminated with water within 30 min of the test and they did eat food that may have caused human excitement, including functional drinks such as tea, coffee, etc., with 24 h of the test. The tested person also needed to sit still for 30 min in the test environment to adapt to the environmental conditions. After the tested person was in a calm state, the arm was placed on the test platform for 20 min. The whole process needed to be kept in a static state.
- 3.
Conditions of the Subjects and Test Sites.
To control the influencing factors of the experiment, we increased the number of samples and reduced the impact of individual differences on the experimental results. A total of 10 healthy adult males aged 22–26 years were selected for this study, with a height of 160–170 cm and a weight of 55–70 kg.
Human skin is widely distributed with free nerve endings overlapping each other in a certain range, which makes it highly sensitive. According to relevant studies, the distribution of nerve endings is more extensive in human limbs, which indicates that the skin on the limbs is more susceptible to external stimuli and generates responses [
15]. Therefore, the visible superficial veins on the skin surface needed to be avoided as much as possible when testing the blood velocity of microcirculation on the human-skin surface. The test position was selected at least 5 cm away from the wrist and 2.5 cm away from the cubical fossa, and the size of the test position was 2 cm × 2 cm. The marking diagram of the position of the test point on the arm is shown in
Figure 3 [
16].
- 4.
Test Steps for Blood-Flow Promotion Multiples of Microcirculation on Human-Surface Skin.
Under the above pre-test preparation requirements, we tried to keep the subject in a relatively stable state after they adapted to the laboratory environment.
First, the visible distribution of superficial veins in the arm of the subject was observed, and the test positions of 2 cm × 2 cm were marked with a black marker.
After the arm of the tested person was placed on the test bench for 20 min and reached a stable state, the GP-0.0% sample was covered at test point C1, and the C2 was kept blank. After 20 min, the dynamic blood-flow velocity values of 5 min at C1 and C2 were framed and tested by the computer software(software version number: Laser Microcirculation Winform), and then the original ratio of blood-flow changes on the skin microcirculation was calculated according to the average value of blood-flow velocity in the two areas automatically obtained by the test software. After this test, the subject had to sit still for 10 min for the next test.
Next, we covered the GP-0.0% sample and the GP-0.1% sample at test points C1 and C2, respectively. After 20 min, we repeated the steps of testing the original ratio of blood-flow-rate change to obtain the average value of blood-flow rate after covering the sample at test points C1 and C2 and calculated the ratio of blood-flow change in human-skin microcirculation. After the test, the tested person needed to remain calm for 10 min.
The sample at test point C1 remained unchanged. We replaced the sample at test point C2 with GP-0.2% and GP-0.8%, respectively, and repeated the above test steps.
- 5.
Fabrics Test Scheme.
The test point C1 was covered with GP-0.0% samples, and test point C2 was covered with GP-0.1%, GP-0.2%, and GP-0.8% samples, respectively. The two test points C1 and C2 had to correspond to the samples with the same structure during each test.
We selected two test points on the inner side of the arm of the subject. The state of the uncovered sample and microcirculation-blood-flow imaging are shown in
Figure 4(a1,a2). After covering the GP-0.0% sample at C1 for 20 min, we tested the original ratio of blood-flow change in human-skin microcirculation at C1 and C2. The test state and blood-flow imaging are shown in
Figure 4(b1,b2). Then, after covering GP-0.1%, GP-0.2%, and GP-0.8% samples in sequence at the C2 test point for 20 min, we tested the change ratio of blood flow of human-skin microcirculation at C1 and C2. The coverage state and blood-flow imaging of the GP-0.1% sample are shown in
Figure 4(c1,c2); The coverage state and blood-flow imaging of the GP-0.2% sample are shown in
Figure 4(d1,d2); The coverage state and blood-flow imaging of GP-0.8% sample are shown in
Figure 4(e1,e2).
- 6.
Calculation of Blood-Flow Promotion Multiple of Human-Surface-Skin Microcirculation.
The effect of fabric on promoting blood-flow velocity of microcirculation on human skin can be shown by the change in blood-flow velocity and the ratio of blood-flow velocity. Refer to the LSCI detection method to test the original ratio of blood-flow change and the ratio of blood-flow change, and take the blood-flow promotion multiple (
) obtained after covering the sample as the evaluation index of the effect of the sample on promoting blood-flow velocity of microcirculation on human skin. The calculation formulas are shown in (1) and (2):
where
is the blood-flow value of microcirculation of human skin at test point
C1;
is the blood-flow value of microcirculation of human skin at test point
C2;
is the ratio of blood-flow rate;
is the original ratio of microcirculatory blood-flow changes;
is the change ratio of microcirculatory blood flow; and
is the blood-flow promotion multiple after covering the sample.