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: Total peripheral vascular resistance fell from 15 . 1 to 12 . 2 mm Hg / l / min ( SED + / - 1 . 03 , p less than 0 . 05 ) .
### Output Text:
Total peripheral vascular resistance fell from 15 . 1 to 12 . 2 mm Hg / l / min ( SED + / - 1 . 03 , p less than 0 . 05 ) . 