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: Orthostatic hypotension was determined by the average decrease ( % ) in mean arterial pressure ( MAP femoral ) over the 60 - s tilt period .
### Output Text:
Orthostatic hypotension was determined by the average decrease ( % ) in mean arterial pressure ( MAP femoral ) over the 60 - s tilt period . 