# Unobtrusive Vital Sign Monitoring in Automotive Environments--A Review
## 3 ECG Monitoring in a Car
### Capacitive ECG Monitoring
In a joint effort by the Karlsruhe Institute of Technology (KIT) and Daimler (DAIMLER AG, Mercedesstrasse 137, D-70327 Stuttgart, Germany), textile integration into the car seat was further demonstrated by [PERSON] et al. in the same year [58]. A two electrode design featuring two textile electrodes placed horizontally and rather lumbar has been presented which provided decent ECG measurements in pilot trials. Around that time, [PERSON] and colleagues from ETH Zurich in Switzerland obtained cECG test equipment from the Philips Chair at RWTH Aachen University. Based on the European SEAT project (EU 6 th Framework Program, contract number: AST5-CT-2006-030958), the authors investigated if capacitive ECG measurements would be feasible for passenger monitoring in an airplane seat [47; 62]. In their 2012 publication, [PERSON] et al. pointed out that the signal quality of unobtrusive sensing during various passenger activities might not always be sufficient for continuous monitoring [47]. The authors hence introduced a signal class label that reflects the signal quality and called it the _quality label_ (QL). In addition in 2012, [PERSON] et al. from the FZI Research Center for Information Technology in Karlsruhe, Germany, developed a framework for vital sign measurements inside a vehicle including a textile seat cover [48]. The design features two textile electrodes located horizontally in the lumbar region of the back and a driven seat electrode above the two active sensing electrodes. The design was demonstrated in an Audi Q5. In the same year, [PERSON] and coworkers from Pukyong National University presented another capacitive ECG monitoring system with two horizontal electrodes integrated into a car [49]. In this design, the active measurement electrodes were again planar copper plates located horizontally in the backrest, while the driven right leg electrode was made of conductive fabrics and located on the seat. In the presented trial, the authors investigated HRV analysis on measurements obtained from \(n=5\) subjects without any heart disease. At the 2012 EXPO in Chicago, IL, USA, Plessey Ltd. (Plessey Semiconductors Ltd., Plymouth PL6 7 BQ, UK) announced the availability of their capacitive ECG sensor system EPIC(tm). About two years later, the EPIC(tm) system was tested in an office chair [63]. In addition, a three-electrode system integrated into the car seat was announced in the media [59]. In 2014, [PERSON] et al. demonstrated that a local release of water vapor can dramatically increase the SNR of capacitive ECG [60]. As an underlying principle, it was shown that the increase of local air humidity can improve the ohmic coupling (hence the coupling will not be exclusively capacitive anymore). At the same time, this allows static charge difference induced by triboelectric effects to flow to ground. It hence reduces the impact of triboelectricity on capacitive monitoring. [PERSON] et al. proposed using conductive textile electrodes that are permeable for water vapor and to place chambers with silica gel as a source or sink for humidity behind the textile electrodes, but also other concepts for humidification are conceivable [64]. Figure 2h presents the arrangement of the electrodes used for prooving the concept. In 2015, the RWTH Aachen group presented a multi-electrode design integrated into a Ford S-Max commercial test vehicle (Ford Motor Company, Dearborn, MI, USA). While in this design the electrodes remained solid metal, their shape was changed to round and the contract area was reduced as compared to previous designs. Note that the textile driven ground has now been completely integrated into the seat. In the same year, some of these authors started clinical trials with survivors of heart attacks or heart surgery in the Rosenquelle rehabilitation hospital in Aachen. Results from this study have been published in [55; 61]. In this trial, patients (\(n=10\)) were asked to drive in a driving simulator equipped with capacitive ECG in the seat and classical ECG monitoring for reference.