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: This resulted in a significant decrease in CMRO2 ( to 1 . 73 + / - 0 . 16 ml / 100 g min - 1 ) , while CBF was unchanged .
### Output Text:
This resulted in a significant decrease in CMRO2 ( to 1 . 73 + / - 0 . 16 ml / 100 g min - 1 ) , while CBF was unchanged . 