# Quality Evaluation Algorithm for Chest Compressions Based on OpenPose Model
## 2 System Architecture
### Research  
The AHA Guidelines point out that the compression depth of the chest should be between 5 and 6 cm [10]. Usually, the efficiency of standard CPR is only about 30% of the efficiency of autonomous cardiac pumping. When the compression depth is less than 5 cm, the efficiency of CPR is worse, which may cause the death of the patient. ERC has pointed out that, in the process of CCs, it is essential to maintain chest rebound [11]. Chest rebound can allow blood to flow back sufficiently to be fully \"ejected\" during the subsequent compression [18]. In the ERC guidelines from 2021, the frequency is at least 100 times/min [11]. Furthermore, it must be 100-120 times/min in the AHA guidelines [10]. If the frequency is less  
Figure 3: Front views of original and pose-estimated images: (**a**) front view of an original image; (**b**) front view of a pose estimated image by OpenPose. Figure 2: System architecture. than 100 times/min, the return of spontaneous circulation (ROSC) is significantly reduced. When the compression frequency is more than 120 times/min, due to the limitation of chest rebounds, myocardial perfusion and coronary blood flow both decrease, which reduces the success rate of the ROSC [19]. The correct compression position is the midpoint of the connection between the two nipples, which can withstand greater force [12]. If the position is offset during CPR, it is easy to fracture the patient's ribs [20]. Although there is no explicit requirement in major international CPR guidelines that states that the operator's elbows must be straight during compressions, during the actual operation, it was found that elbow straightness significantly influences the compression depth and frequency of the chest, which in turn affects the quality. At present, the relationship between them has not been accurately studied. Therefore, this section examines the relationship between elbow straightness and compression depth, frequency and chest rebound in a certain period, and then it explores the effects of elbow straightness on CC quality. To test the influence on depth, frequency, rebound and position of different elbow straightness, and to determine the appropriate elbow angle used for our algorithm, we recruited 34 volunteers to perform compression on a CPR manikin with real-time feedback under random conditions (referring to random within three groups of angles of 151-160\({}^{\circ}\), 161-170\({}^{\circ}\), and 171-180\({}^{\circ}\)). As shown in Table 1, a \(t\)-test was used for the measurement data, and a chi-squared test was used for the enumeration data. When \(p<0.05\), the difference was statistically significant. Continuous variables are expressed as mean \(\pm\) standard deviation (i.e., \(x\pm s\)). It can be seen from Figure 4 that the correct proportion of compression depth in the range of 171-180\({}^{\circ}\) is the highest, and the difference is statistically significant (\(p<0.05\)) compared with the other two groups. Moreover, the trend of correct rates in the frequency group and in the chest rebound group is consistent with the depth group. Therefore, it can be concluded that, when the elbow is bent during operation, the error rates of depth, frequency, and rebounds increase, affecting CC quality. In this study, experiments show that elbows should be kept as straight as possible to ensure quality and to improve the success rate of rescue, and elbow angles in the 171-180\({}^{\circ}\) range are acceptable. In the following study, operator elbow straightness is one of the key indicators to measure quality. Based on the above research on the five indicators, we specify five standardized operating parameters and eligibility requirements in Table 2. It is worth noting that we set a fault tolerance rate of 30%. Specifically, a qualified CC video requires that the correct rate of each inspection index must reach 70%, and each inspection index is qualified.