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: In each group , SNP infusion resulted in an initial decrease in blood pressure from 86 torr and 83 torr , respectively , to 48 torr .
### Output Text:
In each group , <span class="chemical">SNP</span> infusion resulted in an initial decrease in blood pressure from 86 torr and 83 torr , respectively , to 48 torr . 