I am looking for a refruibished ECG in order to understand if I can use it to simulate electrically its functioning.

But before the purchase, I want to check their technical specification, and in particoular their circuits specifications.
Do you know where is it possible to find the patents? I would like to find the electronic design of ECGs.

I am looking for something like a patent or a technical design of how the inner power electronics work.

Thank you