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: Response was defined as MSDBP < 90 mm Hg or a > or = 10 mm Hg decrease compared to baseline .
### Output Text:
Response was defined as MSDBP < 90 mm Hg or a > or = 10 mm Hg decrease compared to baseline . 