5. The new influence regarding background heat and you will light-intensity
Comparative assessment are executed between your traditional fist BVP sensor and you can the device recommended when subjects are in state away from spontaneous respiration. 5 . It suggests that the newest noncontact device is much like get in touch with unit because a display screen out-of pulse rate ( Fig. 5(a) ), together with difference between the results measured by one another gadgets are within 3beat/minute. One another result of oxygen saturation are also within the an excellent contract having both ( Fig. 5(b) ).
Fig. 5 Spread out spot appearing noncontact device’s dimensions out-of pulse rate and you can fresh air saturation instead of the brand new get in touch with device’s measurement. (a) heart rate. (b) clean air saturation.
As can be seen from Fig. 5(a) , the heart rate obtained from the noncontact device proposed is generally in agreement with that of the finger BVP sensor. We have analyzed the results by Bland-Altman method in order to quantitatively describe the consistency of both devices. Figure 6(a) shows the Bland-Altman plot based on the results shown in Fig. 5(a) . Assuming that the mean difference between the devices is normally distributed, 95% confidence interval can be calculated at d ? ± 1.96 ? Sd ( d ? = 0.6238beat/min is the mean of the difference between measurements by both devices, and Sd is the standard deviation between measurements of both devices). The difference between measurements by both devices is within the limitation of confidence interval. It indicates that the results measured by the non-contact device are in good agreement with that by the finger BVP sensor, and they can be used interchangeably. The consistency of the SPO2 measured by both devices by Bland-Altman method is also assessed. Figure 6(b) shows a Bland-Altman plot. One among the 30 groups of data lies beyond the limitation of d ? – 1.96 ? Sd and d ? + 1.96 ? Sd . It indicates that the accuracy of measurement by the non-contact device proposed can’t reach the level of clinical application.
Following analysis decide to try that have 29 volunteers, the newest calculating outcome of one another products get for the Fig
Fig. 6 Bland-Altman plot of the mean of the measurements by both devices for each subject versus the difference between the measurements by both devices for each subject. (a) heart rate, (b) SPO2 (The number next to the data point is the sample number at that location).
This procedure utilizes the brand new ambient white once the light source, that the newest PPG signal are delicate. Therefore the background light intensity has to be felt because of its has an effect on into test results. Y. Sun et al shown the dimension from heartrate is almost blind on background white alter . The new try detecting the new influences out-of ambient white transform on the blood oxygen saturation is carried out from inside the darkroom with the exact same setups just like the men and women shown into the Fig. dos . The distinctions try light-averaging layer and you can strength changing light Led number put into play with as the illumination resource to simulate the background lights criteria below individuals weather. The cousin intensity of new ambient light is described as the latest mediocre grey worth of the human face pixel accumulated by CCD which have 520nm filter.
Table 1 summarizes the descriptive statistics for critical evaluation of the proposed method compared to a finger BVP sensor at different ambient light intensity. It shows that the relatively stable ambient light intensity has no obvious influences on SPO2 (the average gray value fluctuation is within ± 5). Temperature is also the factor that should be considered. The test is conducted under conditions with controllable temperature and stable ambient light while the temperatures are controlled as 16 ± 1°C, 20 ± 1°C, 24 ± 1°C, 28 ± 1°C, 32 ± 1°C respectively. The blood oxygen saturation of the volunteers is measured respectively after they stayed in the conditions with different temperature for 45 minutes. It turns out that the temperature almost has no influences on the test results.