MHD or "Mobile Health Document" is a system defined by IHE and is synonymous with exchanging information in health, be it images, lab reports or simply supporting various workflows . The MHD profile simplifies the registration, distribution and access to patient data.
This MHD profile is useful for sharing CDA documents and specifically specifies the rules for deriving MHD envelope metadata from the CDA header.
By opposition to XDS, MHD is using REST to exchange documents (>< SOAP). As such, the syntax the norm is using is FHIR.
The following profile are used in the different transactions that will go through :
HL7 FHIR R4 :

• DocumentReference
• DocumentManifest
• List
• Patient
• Practitioner
• OperationOutcome
• Bundle

More information on MHD profiles can be found at https://www.ihe.net/uploadedFiles/Documents/ITI/IHE_ITI_Suppl_MHD.pdf