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: Nitroglycerin , up to 0 . 3 micrograms / kg , selectively increased circumflex artery diameter ( CxAD ) without simultaneously affecting any other cardiac or systemic hemodynamic parameter .
### Output Text:
<span class="chemical">Nitroglycerin</span> , up to 0 . 3 micrograms / kg , selectively increased circumflex artery diameter ( CxAD ) without simultaneously affecting any other cardiac or systemic hemodynamic parameter . 