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: Regional analysis showed a reduction in the worst affected segment 15 and 30 minutes after exercise ( - 27 . 9 ( 7 . 2 ) % and - 28 . 6 ( 5 . 7 ) % , both p < 0 . 01 ) , and at 30 minutes after dobutamine ( - 32 ( 5 . 3 ) % , p < 0 . 01 ) .
### Output Text:
Regional analysis showed a reduction in the worst affected segment 15 and 30 minutes after exercise ( - 27 . 9 ( 7 . 2 ) % and - 28 . 6 ( 5 . 7 ) % , both p < 0 . 01 ) , and at 30 minutes after <span class="chemical">dobutamine</span> ( - 32 ( 5 . 3 ) % , p < 0 . 01 ) . 