# Wearable Sensors for Vital Signs Measurement: A Survey
## 2 Classification of Wearable Medical Sensors
### Classification and Application of Wearable Medical Sensors
#### 2.2.2 Wearable Medical Sensors for Detecting Breathing Intensity
This method is simple to implement, using a digital wearable medical sensor, and avoiding the need to filter and amplify analog signals related to temperature and humidity caused by the use of analog sensors to isolate DC processing. The difference in the digital wearable medical sensor data change is used to replace the average value extraction used in the previous analog circuit, and the enlarged design simplifies the apnea detection circuit. Perhaps, in the future, some occupations, such as pilots, can use wearable respiratory-intensity sensors to continuously monitor their physiological state. Even sooner, drivers will be able to use wearable respiratory-intensity sensors to undergo alcohol testing before driving, so that traffic accidents caused by drunk driving can be avoided. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Scholars** & **Sensor Types** & **Wearable Medical Sensor Model** & **Effect** \\ \hline [PERSON] et al. (2018) [22] & Pressure sensor & \begin{tabular}{c} BPNN-based respiratory \\ measurement device \\ \end{tabular} & \begin{tabular}{c} It effectively improved the \\ reliability of the newly \\ designed respiratory device. \\ \end{tabular} \\ \hline [PERSON] et al. (2019) [23] & Flexible sensor & \begin{tabular}{c} Wearable respiratory and HR \\ monitoring system \\ \end{tabular} & \begin{tabular}{c} It is suitable for matching \\ chest wall displacement and \\ can be used to monitor FR \\ and HR. \\ \end{tabular} \\ \hline [PERSON] et al. (2019) [24] & Optical fiber sensor & \begin{tabular}{c} HR detection model of perioperative \\ infants based on new optical \\ fiber sensor \\ \end{tabular} & \begin{tabular}{c} It was consistent with the \\ standard physiological \\ monitoring results. \\ \end{tabular} \\ \hline [PERSON] et al. (2020) [25] & Piezolectric film sensor & \begin{tabular}{c} Respiratory monitor based on \\ piezoelectric thin-film sensor \\ \end{tabular} & \begin{tabular}{c} The sensitivity of respiratory \\ characteristics was improved \\ by nearly 1.7 times. \\ \end{tabular} \\ \hline [PERSON] et al. (2020) [26] & Electrochemical sensor & \
\begin{tabular}{c} The strength of ROS (reactive oxygen \\ species) was used to detect sputum \\ samples selectively (volume less than \\ 500 \(\mu\)L) during COVID-19 \\ \end{tabular} &
\begin{tabular}{c} The accuracy and sensitivity \\ of response \\ calibration was 97\%. \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Review of different scholars’ research on respiratory intensity monitoring by wearable medical sensor. Figure 2 shows the specific steps of the algorithm flow. First, the latest eight temperature and humidity sampling points are taken at the current sampling time each time and cached in the array. Second, the difference between the temperature and humidity between every two adjacent sampling points in the array is measured to obtain the difference between the adjacent temperature and humidity sampling points. Third, with further sampling, the array that saves adjacent differences is constantly updated. At this point, the array can be processed in real time to calculate the corresponding breathing state and the time between breathing, thereby obtaining the frequency of breathing and the judgment of whether apnea has occurred. Fourth, observation of whether the difference between the temperature value of a certain sampling point in the current array and the previous sampling point is not negative is required, and also whether the difference between a certain humidity value and the previous sampling point is positive. Fifth, if the conditions of step 4 are met, and the conditions of step 4 can be maintained for more than 1.5 s (because the human body expiration time is generally about 1.5 s), it proves that the current subject is breathing, and the time of breathing will increase as the sampling continues to increase. If the conditions in step 4 are no longer met, it means that the subject's breathing state has ended, and the ending time will continue to increase with the sampling point interval.