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: Similarly , significant disturbances in myocardial energy metabolism were detected in the barium - exposed rats which were consistent with the reduced contractile element shortening velocity .
### Output Text:
Similarly , significant disturbances in myocardial energy metabolism were detected in the <span class="chemical">barium</span> - exposed rats which were consistent with the reduced contractile element shortening velocity . 