# Unobtrusive Vital Sign Monitoring in Automotive Environments--A Review
## 3 ECG Monitoring in a Car
### Conductive ECG Monitoring  
Placing electrodes on the steering wheel has been one of the early research targets. The available literature dates back at least a decade. In an attempt to quantify driver stress levels, in 2007, [PERSON] and colleagues [20] from Yonsei University in Korea investigated driver task load and stress response looking at heart rate variability (HRV) obtained with a steering wheel-based pair of dry ECG electrodes.  
Similarly, in the same year, [PERSON] and coworkers from Seoul National University in Korea reported about their study using dry electrodes integrated into the steering wheel [21]. These tape-type dry electrodes were made of copper tape (3M). Three male students were recruited as test drivers and asked to drive a route of 16 km in about 40-50 min. Heart rate variability was assessed using a modified Tompkins algorithm for R-peak detection and computation of R-peak intervals, heart rate, SDNN, RMSSD and pNN50. While just an abstract without providing any details, [PERSON] and colleagues also reported on the integration of ECG into the steering wheel in 2008 [22].  
In 2010, [PERSON] et al. [23] and later [PERSON] et al. [24] from Pukyong National University in Busan, Korea, presented steering wheel electrodes based on conductive fabric. In parallel, a multisensor system allowing to measure SpO\({}_{2}\), temperature and skin temperature at the steering wheel of a Mercedes S-Class vehicle (DAIMLER AG, Mercedesstrasse 137, D-70327 Stuttgart, Germany) was published by [PERSON] and colleagues [25] from Karlsruhe Institute of Technology, Germany. Around the same time, [PERSON] and colleagues from the Technical University of Munich demonstrated a multisensor system  
Figure 2: Electrode locations for conductive and low-contact ECG monitoring around a car seat. Red blocks indicate tested locations for sensing electrodes, blue blocks indicate published locations for the driven ground electrode.  
integrated into the steering wheel of a BMW 730d test vehicle (BMW AG, Petuelring 130, D-80788 Munchen, Germany) [26; 27] featuring SpO\({}_{2}\) and conductive ECG sensing as well. The authors used a design similar to [20], integrating the electrodes into the steering wheel, the shift lever and the left arm rest. However, the precise electrode position was not revealed in this work.  
In 2012, [PERSON] and [PERSON] [28] from the Universitat Politecnica de Catalunya in Barcelona, Spain, presented a steering wheel-based ECG-measurement demonstrator which was based on dry ECG electrodes and wireless communication. Similarily, in that year, [PERSON] and colleagues [29] from IT/IST-UTL in Lisbon, Portugal, demonstrated that dry Ag/AgCl electrodes on a steering wheel can produce ECG measurements of similar quality as traditional electrodes.  
Another Korean project from Pukyong National University was presented in 2014. [PERSON] and colleagues [24] proposed a design featuring a steering wheel with two conductive fabric electrodes, similiar to [29]. This electronic circuit design was based on an MSP 430 microcontroller and a Chipcon CC2420 RF Transceiver (both manufactured by Texas Instruments Inc., P.O. Box 660199, Dallas, TX, USA) for wireless data transmission at 2.4 GHz.  
In 2015, [PERSON] et al. of Takata corporation (Takata corporation, Tokio, Japan) presented a steering wheel with sensors measuring the heart frequency. The actual integration is not well documented in the publication; it can only be assumed that it is similar to [PERSON] [21] and [PERSON] [29].  
Figure 3 gives an overview of different electrode placements.  
We note that ECG monitoring using steering wheel-based approaches is a feasible option for heart rate tracking but requires both hands to touch two different conductive parts of the wheel. Hence, significant steering movements with changes of the location of gripping and the quite common habit of steering with one hand pose a problem for this technique.