I can't provide actual examples as design documentation is confidential but I can provide some guidance.
You need to consider the requirements at different levels, top level being the User requirements which should be considered under the following headings:
• Intended use
• Intended patient population
• Intended users / Usability
• Intended locations for use
• Intended functions and features
• Intended markets
• Intended maintenance regimen
• Regulatory approvals required
• Relevant international standards
• Treatment guidelines from medical bodies
• HeartSine business requirements
• Improvements required for existing device
• Backward compatibility requirements
Once the user requirements are agreed you can then look at the detailed features and functions that the product will require to fulfill the user requirements. The product requirements may then be broken down into lower level requirements such as hardware or software. I find it useful to document in tabular form, each user requirement may link to multiple product requirements.
Once the requirements are documented in tabular form this can be the basis of a traceability matrix, where each requirement is linked to the verification or validation activity which tested it.