Article History
Received: 19 September 2017
Accepted: 26 January 2018
First Online: 14 February 2018
Compliance with ethical standards
:
: None of the authors have any conflict of interest associated with the study.
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The study was approved by the local ethics committee of Peking University People’s hospital.