In HealthVault, if you have custodian access to the record, it will be migrated with any other records and you will retain your access as you did before. The sharing section in Lydia shows the linkage to any other custodians that have also migrated their accounts and allows you the same control as you had in HealthVault.
If you have access to a record in HealthVault but it is not custodian access (View or View and Modify), you do not have sufficient privileges to migrate the record and your access to it will be revoked in the migration process. Even if the custodian of the record has or will migrate his/her account to Lydia, he/she will need to repeat the sharing process from Lydia for you to regain access.
To learn more about sharing in Lydia, click here.