Received: 2 March 2019
Accepted: 7 August 2019
First Online: 14 August 2019
Ethics approval and consent to participate
: This study was approved by the Ethics Committee of Kunming Medical University prior to the commencement of research. Written informed consent was obtained from all persons participating in the study, and the Ethics Committee of Kunming Medical University approved this consent procedure.
: Not applicable.
: The authors declare that they have no competing interests.