## 4 Discussion
### Application of BCG/SCG in Medical Treatment and Health Care
#### 4.3.3 BCG/SCG's Field Implementation  
Despite the rapid development of the research of BCG/SCG technology, the applications of this technology in real life have been still very few. This is mainly because this technology is still on the rise and has not reached full maturity, with the main manifestations:  
Figure 9: The types of data under the concern.  
Standardization and Reference  
The lack of physiological standards of BCG/SCG waveforms and the existence of many variabilities, resulting in the difficulty to guarantee the signal quality so that it is often applied to a specific scene. In [PERSON]'s review [6], he mentioned that there is a naming issue between BCG and SCG and a confused terminology when it comes to the description of specific features (peaks and valleys). Finally he proposed standardization on indication of the site of measurements, specs and orientation of sensors which will facilitate works based on BCG/SCG literature.  
Noise and Interference  
According to [PERSON] et al. [6], sensor and circuit noise, motion artifacts and floor vibration can potentially corrupt BCG and SCG measurements. The sensor and circuit noise were characterized and reduced for weighing-scale-based BCG systems using an ac-bridge amplifier approach. This approach led to a SNR improvement of 6 dB. Motion artifact detection for standing BCG measurements was accomplished using auxiliary sensors as noise references; then, gating the BCG signal based on the detection of excessive noise. Floor vibration poses challenges for measurements taken on vehicles and planes. [PERSON] [95] gave an successful example of BCG measurement by using an auxiliary sensor for vibration detection and adaptive noise cancelling to cancel floor vibration artifacts.  
Effect of Respiration, Posture, Sensor Adherence  
In recent research of SCG signals, the authors presented some limitations concerning this relatively new measurement and their proposition of solutions regarding those points [96]. SCG has variability on its morphology decided by respiration, sensor location, subject posture etc. conforming with the conclusion of [PERSON] [6; 8] where BCG had similar variability due to their nature of measurements. It needs further research to ameliorate SCG's utility. [PERSON] et al. [96] proposed to make a comprehensive SCG signal database which will play an important role in stimulating basic research and medical device development. The combination of ECG, BCG, SCG and other electro-mechanical signals was equally mentioned for more efficient diagnostics.  
Modern _ballistocardiography_ and seismocardiography systems may be capable of monitoring slow, longitudinal changes in cardiac function associated with a number of cardiovascular diseases. Timely noninvasive detection of subtle changes in cardiac pathophysiology may one day enable daily drug dosage adjustments, thus reducing costly and morbid rehospitalizations [97]. Recent study has shown BCG and SCG potentiality in sleep quality assessment in terms of detecting obstructive sleep apnea [98].  
But BCG/SCG's the poor universality, which leads to high dependence on other reference signals, and makes it difficult to give full play to its advantages in practical applications. Despite the large number of published studies, as shown in Figure 6, the analysis found that 68% of BCG/SCG technology was implemented in a strictly controlled laboratory environment and still some way from being put in market applications.