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: Systemic vascular resistance was increased by PPA 28 % ( from 1710 + / - 200 to 2190 + / - 700 dyne X sec / cm5 ) and was further increased by propranolol 22 % ( to 2660 + / - 1200 dyne X sec / cm5 ) .
### Output Text:
Systemic vascular resistance was increased by <span class="chemical">PPA</span> 28 % ( from 1710 + / - 200 to 2190 + / - 700 dyne X sec / cm5 ) and was further increased by <span class="chemical">propranolol</span> 22 % ( to 2660 + / - 1200 dyne X sec / cm5 ) . 