How to retrieve specific element from open xml Word document mainpart

I am trying to read some specific text from a word document using open xml SDK. The structure of the document looks like this.

Requirement: Search for "Title of the chapter" - when found return everything under that section. in this case

   Author's notes: Some text here
    sometimes Author's notes are more than one line.

Document Structure is like this:

    1.1.1 Title of the Chapter

    Author's notes: Some text here
    sometimes Author's notes are more than one line.
    1.1.1.1 Title of the sub-chapter

    Some text here
    1.1.1.2 Title of the next sub-chapter

    Some text here.

    End of the Chapter