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: Hemodynamic measurements in 1 of the patients demonstrated an increase in total peripheral resistance and essentially no change in cardiac output following propranolol therapy .
### Output Text:
Hemodynamic measurements in 1 of the patients demonstrated an increase in total peripheral resistance and essentially no change in cardiac output following <span class="chemical">propranolol</span> therapy . 