Connecting medical devices: GDT, HL7 and FHIR at a glance

In a rehabilitation clinic, a diagnostic centre or a performance diagnostics lab, ten or twenty devices from different manufacturers quickly add up. Each one produces valuable data, and almost every one stores it in its own software. Anyone who wants to connect medical devices therefore has to answer two questions: which interface does the device offer, and where should the data ultimately flow? This guide explains the common standards, shows options for devices without a standard interface and describes how a connection project runs.

Why device data is scattered

Data silos are rarely a deliberate decision. A device fleet grows over years, across different departments and budgets. Each manufacturer supplies its own software, designed for its own device. A shared view of the person is not part of this model.

Many facilities know the consequences:

• Duplicate entry: name, date of birth and case number are typed in again at every device.
• Media breaks: results are printed out, retyped or filed in the record as a PDF.
• No history: anyone wanting to see how a person has developed across several devices has to open several programs.
• Dependency: the data stays in the manufacturer’s software. Switching devices often means a break in the history.

A device connection only solves these problems if it works in both directions: person data and order to the device, readings back into a shared data foundation.

The key standards for medical device interfaces

Healthcare has established standards for data exchange. They differ in their field of application, their technology and how finely they represent data.

Standard	Purpose	Typical devices and systems	Technology
GDT	Exchange between device and practice or hospital software in German-speaking countries	ECG, lung function, ergometry, EMG, visual field testing	Files in a shared directory, line-by-line field identifiers
HL7 v2	Messages between the HIS and subsystems	Laboratory, functional diagnostics, cardiopulmonary exercise testing, therapy documentation	Event-based messages, usually via TCP/IP
FHIR R4	Modern exchange of individual data objects	Newer device software, apps, platforms, applications related to the German electronic patient record (ePA)	REST interface, JSON or XML
DICOM	Image data and associated information	X-ray, ultrasound, MRI, CT	Own protocol and file format, worklists for examinations
IHE XDS	Exchange of documents between facilities	Findings reports, progress documents	Profile based on existing standards

GDT interface

In German-speaking countries, GDT is the most widespread way of connecting a diagnostic device to practice software or the HIS. The specification is maintained by the Qualitätsring Medizinische Software (QMS). The principle is simple: the software places a file with patient data and the examination order in a shared directory, the device software reads it, carries out the measurement and places a results file back.

The advantage is the low barrier to entry, as many devices support GDT out of the box. The limitation lies in the structure: how detailed the returned results are depends heavily on the manufacturer. Some deliver individual readings, others only a reference to a report.

HL7 v2

HL7 v2 is the standard for messages between the hospital information system and a hospital’s subsystems. Typical messages are patient admissions, orders and results. In this way, a subsystem receives the master data and the order from the HIS and sends the results back.

HL7 v2 is widespread and available in almost every HIS. The downside: the standard leaves room for interpretation, so each interface has to be agreed between the parties involved.

FHIR

FHIR (Fast Healthcare Interoperability Resources) is the newer standard from HL7 International. It describes data as individual resources, such as Patient, Observation for a reading or DiagnosticReport for a finding, and uses common web technologies. Version R4 is the most widely supported today.

FHIR is interesting for connecting medical devices because a reading is transmitted as a self-contained object with unit and time. Many manufacturers are developing their interfaces in this direction. Tyromotion, for instance, is working on a bidirectional FHIR interface for its rehabilitation robotics.

DICOM

DICOM governs the exchange of image data and the associated information. It is the established standard for imaging. For therapy and functional devices, DICOM plays a smaller role, but can become relevant when images or videos belong to an examination.

Connecting medical devices without a standard interface

Therapy and training devices, motion analysis and performance diagnostics in particular often lack a standard. That does not mean a connection is impossible. Typical options are:

• Manufacturer interface: many manufacturers offer their own programming interface or SDK. This can be used to hand over orders and retrieve results, in some cases bidirectionally.
• File export: the device software outputs results as XML, CSV or in a proprietary format. A program reads the files in automatically.
• Connection via intermediate software: some devices are connected via the software that controls them anyway, such as cross-manufacturer training software.
• Reading out at the device: a small program on the device computer reads the data directly and forwards it in standardised form.

The list of compatible systems shows how different this looks in practice. Noraxon is connected bidirectionally via GDT, OCULUS via GDT through the Twinfield software, COSMED via HL7 through the Omnia software. Biodex is connected via an XML export because there is no open manufacturer interface, and with BTS Bioengineering the analysis results are imported without a standardised interface. Hocoma and CONTEMPLAS are connected via bidirectional manufacturer interfaces with Order Entry.

For reading out at the device, Datico^® has the Datico^® Agent. It reads the data directly at the device and transmits it in standardised form, for example via HL7. If only a single device is to be connected to a hospital system, this is also possible without a complete platform using the Datico^® Agent Standalone.

PDF report or discrete individual values?

Every device connection raises the question of what form the results come back in. The difference is bigger than it first appears.

	PDF report	Discrete individual values
Content	Finished document with tables and charts	Individual parameters with value, unit, time and person
Filing in the record	Yes	Yes, and a report can also be generated
History over time	Only by reading several reports	Automatic
Comparison with other devices	Not possible	Possible
Classification in reference ranges	Only as specified by the manufacturer	According to your own references
Use for scores and studies	Not possible	Possible

A PDF is sufficient for documentation. For therapy management, quality assurance and research, you need the individual values. That is why the Device Connector does not just import reports, but discrete readings and analysis results that can be combined with other sources.

Connecting therapy and diagnostic devices: the steps of a project

A connection project usually follows the same sequence, regardless of whether you are connecting therapy, diagnostic or training devices.

1. Inventory: which devices are there, with which software and version? Which interfaces do they offer according to the manufacturer?
2. Define the target: where should the data flow: into the HIS, into a platform for analysis, or both? Which values are actually needed?
3. Clarify the order route: do orders come from the HIS or practice software? If so, define which order triggers which examination on which device.
4. Choose the interface per device: a standard where available, otherwise a manufacturer interface or file export. This also clarifies which fields come back.
5. Map parameters: each reading is given a unique parameter with a unit, so that values from different devices become comparable.
6. Test with real measurements: person assignment, completeness and return transmission are checked with real examinations.
7. Operation and expansion: new devices are added step by step without changing the existing connections.

With Order Entry, step 3 is mapped in the Datico^® Life Hub: an order from the HIS is assigned via a procedure to an examination workflow that defines devices, parameters and sequence. The HIS Connector then returns findings, histories and scores to the target system via HL7, FHIR, GDT or IHE XDS. For devices without their own HIS interface, the Datico^® Life Hub thus takes on the role of an interoperability platform.

Several devices at once: live connection

Some applications need more than importing finished results. In altitude and climate chambers, in performance diagnostics or in group testing, several devices and sensors run simultaneously, and their values have to match in time.

This is what Live Control is for. It displays the readings from several devices in sync at a central workstation, stores them per person and session, and controls devices such as treadmills or altitude chambers directly. Additional information such as perceived exertion on the Borg scale is recorded via tablet at the exact moment. Examples include connecting h/p/cosmos treadmills via the coscom protocol or ergoline ergometers via the ergoline protocol in real time.

Staying manufacturer-independent

A device connection is an investment that should outlast several device generations. Pay attention to three points:

• The data belongs to you: the readings should sit in a data foundation that you control and be exportable in open formats.
• One connection to the HIS: if a platform bundles the devices, the HIS only needs one interface to that platform instead of one to each device.
• Expandable: it should be possible to add new devices and older systems without tying yourself to a single device manufacturer.

The Device Connector is designed for these goals. According to its feature page, more than 60 systems from medicine, rehabilitation, sport and research are compatible. The article Therapy devices from different manufacturers describes what this looks like in the day-to-day running of a rehabilitation clinic.

From connection to decision

Connecting devices is the first step, not the goal. Once readings are available in structured form, they can be classified and condensed: with Reference Sets into evaluation zones, with Index Management into scores that combine several devices and questionnaires. Many individual measurements thus become a history that supports therapy and training as a basis for decisions.

If you would like to go through your device fleet, arrange a personal initial consultation. System manufacturers who would like to have their devices connected will find information under System partners.