Funding for this research was provided by:
Ministry of Railways (2014Z005-C)
Received: 8 April 2019
Accepted: 31 October 2019
First Online: 21 November 2019
Ethics approval and consent to participate
: Approved by the ethics committee of Beijing shijitan hospital affiliated to capital medical university and China railway corporation (No. 2014Z005-C). Informed consent was obtained and written from all subjects before enrollment.
: Not applicable.
: The authors declare that they have no competing interests.