# Camera-Based Continuous Heart and Respiration Rate Monitoring in the ICU
## 4 Discussion  
In this work, our objective was to provide new insights into the performance and coverage of camera-based continuous heart and respiration rate monitoring using state-of-the-art methods in ICU patients. Furthermore, we aimed to evaluate the usability of camera-based monitoring to replace spot-check-based monitoring in the general ward. In terms of RGB-based heart rate extraction, the brightness level was the only factor limiting agreement and coverage in 18 of 35 RGB recordings. In these recordings, segments with a brightness level greater than 25 showed a 97.3% 5 BPM agreement and a coverage of 80.1%. Only one of these recordings was from the emergency group, as more emergency patients faced challenging monitoring conditions compared to the postoperative group. Key challenges were identified in RGB-based heart rate measurements from the remaining 17 patients. First, irregular heart rates complicate Fourier spectrum analysis because the rhythm is not represented by a single peak. This occurred for three postoperative and for seven emergency patients. Further investigation into the type of rhythm and the effect on the heart rate measurement is left for future work. Second, RGB-based heart rate measurements often became inaccurate due to limited face visibility and often resulted in poor face ROI detection, especially when staff or visitors obstructed the camera view. The camera view was defined by our measurement setup. We used one RGB and one NIR camera at the bed's foot end with fixed lens magnification, which was chosen to always keep the patient within the camera's field of view. Future research should include how the current camera monitoring setup can be improved to increase agreement and coverage where the system of this work failed. Future improvements may include adding multiple cameras at different room locations for better visibility, ensuring the patient's chest and face are always visible, or splitting monitoring tasks between different cameras with increased lens magnification for more detailed ROIs. Of course, this could also be facilitated by a single camera with a higher resolution. In terms of the NIR-based heart rate extraction, we found that the ICU environment was suboptimal for evaluating the efficacy of the NIR-based monitoring system. Many recordings did not aid in heart rate measurement coverage because the room never became sufficiently dark for RGB-based measurements to fail. Where NIR-based measurements did work, their performance was decent, but their coverage was limited by the presence of patient motion. To improve the usability of the NIR camera for heart rate monitoring, there are a few things to consider. First, in one patient, there was a problem with illumination variation caused by a blinking light that illuminated the patient. For RGB-based monitoring this is not problematic, since the POS method for extraction is robust against illumination variations. This is not the case for NIR monitoring. To avoid this issue, visible light filters on the camera lens could be used. However, in that case, a more powerful IR light source could be needed. The current light source was chosen with the primary goal being safe with regard to infrared light exposure of the ICU patient, but with careful consideration of safety standards, more could potentially be achieved. Furthermore, in some patients, the NIR-based extraction could not be used, because the IR light source was not pointed correctly at the patient. Here, an IR light source with a wider angle of illumination could prevent this from occurring. In the evaluation of the combined heart rate extraction using RGB and NIR measurements, a 5 BPM agreement of 81.5%, an MAE of 6.52 BPM, and a coverage of 81.9% were achieved. The agreement in the postoperative patients was 91%, while it was only 62.6% in the emergency patients. Relative to the sizes of the two groups, more patients had an irregular heart rate in the emergency group, which negatively impacted the monitoring performance.