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: Objective signs of ischemia and factors increasing myocardial oxygen consumption were compared during epinephrine infusion and supine bicycle exercise .
### Output Text:
Objective signs of ischemia and factors increasing myocardial <span class="chemical">oxygen</span> consumption were compared during <span class="chemical">epinephrine</span> infusion and supine bicycle exercise . 