Funding for this research was provided by:
National Natural Science Foundation of China (81600299)
Received: 28 August 2019
Accepted: 8 January 2020
First Online: 14 January 2020
Compliance with ethical standards
: The authors declare that they have no conflict of interest.
: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
: Due to the retrospective nature of the study, informed consent was waived.