I can try, but to be totally clear this is only an idea that I have in my head, and is far from fully formed.
But as far as I understand, it should be possible for a user on a blockchain, to have their set of data encrypted in the ledger. It should also be possible to implement a sort of permission scheme.
So I am imagining, instead of relying on things like Epic Systems and other EHR systems, that control your data and might have incentives to not share them with other systems. One could imagine a EHR system based on a blockchain. The patient can then grant permission to, say a hospital, to read certain data from the ledger. This could be scoped to what is necessary in the context of their visit or procedure.
After the visit to the hospital, the patient has full transparency to read what data has been added to their own records.
Anyway, I am not capable to give a full technical solution, since I have not thought it fully through, and not nearly knowledgable enough to actually know. So I might be very wrong in my assumptions, and would gladly be told otherwise if that is the case.
Then there's the whole issues of how do you get existing systems as Epic to integrate with said "blockchain EHR".
Edit:
This might be of interest:
https://journals.sagepub.com/doi/full/10.1177/14604582198663...