Funding for this research was provided by:
Capital's Funds for Health Improvement and Research (2018-2-2-24)
Article History
Received: 7 October 2018
Accepted: 15 April 2019
First Online: 9 May 2019
Ethics approval and consent to participate
: The study was performed with the approval of the ethics committee of the Beijing Friendship Hospital and the written informed consent was obtained from each participant.
: Not applicable.
: The authors declare that they have no competing interests.
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