# Camera-Based Continuous Heart and Respiration Rate Monitoring in the ICU
## 3 Results
### Respiration Rate Extraction  
First of all, we can see in Figure 8a how the overall performance of the RGB-based respiration rate measurement changed when we increased the threshold on our new breathing motion metric. A low threshold led to significantly higher overall agreement of the remaining segments. Furthermore, in Figure 8a, we can also see the performance of the NIR-based respiration rate measurement against our breathing metric threshold. Using NIR-based respiration, we can see a similar effectiveness of the breathing metric as in the RGB-based respiration. We also note that since the RGB and NIR cameras have different frame rates, the resolutions and bit depths threshold values between the two method were not comparable and had to be set separately. Finally, it is noted that in the RGB recordings, sometimes patients slid down the bed, which moved the chest ROI out of view of the camera, which explains why the coverage curve in Figure 8a did not reach 100% for high-threshold values of the metric. \begin{table}
\begin{tabular}{l r r r r r} \hline \hline
**Patient** & **Agreement (\%)** & **MAE (BPM)** & **Coverage (\%)** & **Time Gap (min)** & **Valid Time (min)** \\
**1** & **94** & **2,28** & **90.6** & **13** & **1166** \\ \hline
2 & 85.7 & 6.39 & 100 & 0 & 1056 \\
3 & 94.6 & 2.36 & 59.7 & 122 & 11  
Combining the respiration rate measurement of the NIR and RGB extraction methods requires that we choose threshold values of the breathing error metrics of the RGB and NIR measurements. Here, we chose cutoff values of 5.5 and 2.6 for the RGB and NIR, respectively, which resulted in an overall agreement of 90% for each recording type. Now, in Figure 8b, we see the combined and individual performance of the RGB and NIR measurements plotted against the brightness threshold of the chest ROI. The agreement, coverage, and MAE changed only slightly as we varied the brightness threshold. Over the range of brightness thresholds, the agreement of the combined respiration rate measurement changed very little. Next, to simplify the evaluation of the combined respiration rate measurement per patient, we chose the brightness threshold for the evaluation at 45. At this brightness threshold, RGB- and NIR-based measurements had approximately equal agreement. In Table 4, we present the 3 RPM agreement, MAE, coverage, largest time gap, and valid time for each patient. Patients for whom NIR contributed to the coverage of the respiration rate measurements have been highlighted in the table. For patients 29 and 30, no respiration rate reference was available, and thus, they have been excluded from the table. Now, in Table 4, we can see that the overall 3 RPM agreement was 91.1%, with an MAE of 1.12 RPM and a coverage of 59.1%. Of the two groups of patients, the postoperative group had a slightly higher agreement and coverage. Although the overall performance of the respiration rate extraction is decent, when we look at the performance of individual patients, there is still quite some variation in individual performance, especially for patient 22, who had the poorest agreement among the patients of 52.2%. The reason for this is likely because the patient suffered from a pneumothorax (collapsed lung) at the time of the recording. Although we will not go into the clinical details, it is likely that the assumptions of the breathing motion measurement were violated by the change in the physiology of the chest cavity. Furthermore, in Table 4, we report the largest time gap between measurements for each patient. For most patients, the largest gap between measurements was fairly short and dependent on the threshold of the breathing motion metric. In the current methodology, the only way to reduce the time gap would be to increase the threshold; however, this would also likely lower the agreement. For patient 24, the relatively longer time gap of 99 min  
Figure 8: (**a**) RGB- and NIR-based respiration rate extraction performance versus breathing motion metric.