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: RESULTS : Five hundred seventy - nine patients were studied , 205 with PPH and 374 with pulmonary hypertension from other causes ( secondary pulmonary hypertension [ SPH ] ) .
### Output Text:
RESULTS : Five hundred seventy - nine patients were studied , 205 with PPH and 374 with pulmonary hypertension from other causes ( secondary pulmonary hypertension [ SPH ] ) . 