In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Mean changes in MSDBP and mean sitting systolic BP ( MSSBP ) were analyzed at the 8 - week core study end point .
### Output Text:
Mean changes in MSDBP and mean sitting systolic BP ( MSSBP ) were analyzed at the 8 - week core study end point . 