Relative assessment are performed amongst the traditional finger BVP detector and you will the computer proposed whenever sufferers have been in county out-of spontaneous respiration. 5 . It suggests that the newest noncontact device is comparable to contact product given that a monitor of pulse rate ( Fig. 5(a) ), and difference between the outcome measured by the both gizmos is actually in this 3beat/minute. Both result of outdoors saturation also are inside the a beneficial arrangement having both ( Fig. 5(b) ).
Fig. 5 Spread spot indicating noncontact device’s aspect from heart rate and you may outdoors saturation versus the fresh contact device’s measurement. (a) heartrate. (b) oxygen 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.
After the review take to that have 29 volunteers, the fresh new measuring consequence of one another gadgets are given inside 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 makes use of the new background white since source of light, to which the fresh PPG signal are sensitive and painful. And so the ambient light intensity should be believed for its affects towards the test results. Y. Sunshine ainsi que al shown the measurement out-of heartbeat try almost blind towards the background white change . The fresh check out detecting the new affects of background white change towards the blood outdoors saturation is conducted inside the darkroom with the exact same configurations since those individuals found within the Fig. 2 . The differences was light-averaging piece and you will strength modifying light Added array put into have fun with due to the fact lighting effects resource to help you imitate brand new background lighting conditions below some climate. Brand new cousin concentration of the fresh new background white means new mediocre grey value of the human being deal with pixel compiled by CCD having 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.