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: Nitroprusside caused significant decreases in arterial blood pressure and systemic vascular resistance and increases in heart rate , but did not change cardiac output or QS / QT .
### Output Text:
<span class="chemical">Nitroprusside</span> caused significant decreases in arterial blood pressure and systemic vascular resistance and increases in heart rate , but did not change cardiac output or QS / QT . 