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: Blood pressure was manipulated by one of the following schedules during 120 min of reperfusion : Control , normotensive reperfusion ; 90 / hypertension ( 90 / HTN ) , blood pressure was increased by 35 mm Hg during the initial 90 min of reperfusion only ; 15 / hypertension ( 15 / HTN ) , normotensive reperfusion for 30 min followed by 15 min of hypertension and 75 min of normotension .
### Output Text:
Blood pressure was manipulated by one of the following schedules during 120 min of reperfusion : Control , normotensive reperfusion ; 90 / hypertension ( 90 / HTN ) , blood pressure was increased by 35 mm Hg during the initial 90 min of reperfusion only ; 15 / hypertension ( 15 / HTN ) , normotensive reperfusion for 30 min followed by 15 min of hypertension and 75 min of normotension . 