ISO/IEEE 11073 Personal Health Device (PHD) standards are a group of standards addressing the interoperability of personal health devices (PHDs) such as weighing scales, blood pressure monitors, blood glucose monitors and the like. The standards draw upon earlier IEEE11073 standards work, but differ from this earlier work due to an emphasis on devices for personal use (rather than hospital use) and a simpler communications model.

Background Demographics changes (the rapidly aging population in many industrialised countries) and an increase in chronic diseases (such as diabetes and heart disease) has led many to ask how technology can be used to ease the burden on health care professionals and provide useful tools to the elderly and infirm – and in particular how technology can help people cope with their conditions within their own homes. This is leading to the development of "personal health devices" which allow people to monitor their own conditions within their own homes and provide the information that such devices obtain to health care professionals and other carers.

Concern that incompatible systems will slow the roll-out of useful personal health devices has prompted moves towards ensuring interoperability. The Continua Alliance is a group of companies and bodies seeking to promote the growth of this personal health market. They are working with the IEEE Standards Association, and the IEEE-EMBS affiliated 11073 Personal Health Data Working Group is formulating standards for data formats and communications to ensure device interoperability.

In the words of IEEE 11073-20601-2008, that standard:

...addresses a need for an openly defined, independent standard for converting the information profile [of personal health devices] into an interoperable transmission format so the information can be exchanged to and from personal telehealth devices and compute engines (e.g., cell phones, personal computers, personal health appliances, and set top boxes).

Previous standards The IEEE 11073 Personal Health Device standardsFor published standards search for '11073' at IEEE, http://shop.ieee.org/ieeestore or ISO, http://www.iso.org/iso/search.htm?qt=11073&searchSubmit=Search&sort=rel&type=simple&published=true (ISO store catalogue). ISO and CEN standards may be purchased from your national standards organisation or bookstore (e.g. AFNOR, BSI, DIN, JIS, UNI, etc.). family is based around a single "framework" standard:

IEEE Std 11073-20601 - Application profile - Optimized exchange protocol IEEE Std 11073-20601a - Application profile - Optimized exchange protocol (amendment)

and a number of "device specialization" standards - the following exist at present:

IEEE Std 11073-10404 - Device specialization - Pulse Oximeter IEEE Std 11073-10406 - Device specialization - Basic Electrocardiography (ECG) (1‐ to 3‐lead ECG) IEEE Std 11073-10407 - Device specialization - Blood Pressure Monitor IEEE Std 11073-10408 - Device specialization - Thermometer IEEE Std 11073-10415 - Device specialization - Weighing Scale IEEE Std 11073-10417 - Device specialization - Glucose Meter IEEE Std 11073-10419 - Device specialization - Insulin Pump IEEE Std 11073-10420 - Device specialization - Body composition analyzer IEEE Std 11073-10421 - Device specialization - Peak flow IEEE Std 11073-10425 - Device specialization - Continuous Glucose Monitor (CGM) IEEE Std 11073-10441 - Device specialization - Cardiovascular fitness and activity monitor IEEE Std 11073-10442 - Device specialization - Strength fitness equipment IEEE Std 11073-10471 - Device specialization - Independent living activity hub IEEE Std 11073-10472 - Device specialization - Medication monitor

IEEE 11073-20601 is the framework standard which defines the generic data types, message types and communication model. This supports any number of (relatively small) "device specialization" standards (such as the IEEE 11073-10408 standard for thermometers) which need only define the data model for that particular type of personal health device.

This modular approach makes it relatively easy to add support for a new type of device. More device specialization standards are in the course of preparation, including:

IEEE P11073-10406 - Device specialization - Basic ECG (1 to 3-lead) IEEE P11073-10413 - Device specialization - Respiration rate monitor IEEE P11073-10418 - Device specialization - INR (blood coagulation) IEEE P11073-10419 - Device specialization - Insulin pump

Revisions to existing standards: IEEE Std 11073-10404 - Device specialization - Pulse Oximeter (revision) IEEE Std 11073-10417 - Device specialization - Glucose Meter (revision) IEEE Std 11073-10441 - Device specialization - Cardiovascular fitness and activity monitor (revision to add 3D accelerometer / physical activity monitor data)

Architectural overview Architectural decisions include:

A point-to-point connection is made between "agent" and a "manager". Transport agnostic (to facilitate porting to new communications channels). Object-oriented philosophy (to facilitate code re-use and simplify the introduction of new devices). Agents are self-describing (so Managers can understand the characteristics of the Agents). Extensible (to encompass new types of agent, and custom specializations of already-defined agents) ASN.1 used to represent data structures and messages (to simplify parsing of messages).

System model The overall IEEE 11073 system model is divided into three principal components, each of which is treated separately in IEEE 11073-20601, and each of which are treated in more detail later in this article:

The Domain Information Model represents an agent as a set of objects. Each object has one or more attributes. Attributes describe measurement and status data that are communicated to a manager. The service model provides commands such as Get, Set, Action, and Event Report that are sent between the agent and manager to exchange data from the DIM. The communication model establishes a state machine for the Agent and the Manager, including states related to connection, association, and operation. The communication model also converts the abstract data modeling used in the Domain Information Model into a binary message format for transfer using the communication model

Detail

Agents and managers

The IEEE 11073 PHD standards has the concept of "agents" and "managers". Agents and managers may operate in staggered architectures with multiple layers of agents as well as of managers. The agents are the personal health devices and are generally small, inexpensive battery-powered devices that lack much in the way of displays and other user interfaces. The managers are typically small computers or smart phones with greater computing resources and required routing capabilities to convey information autonomously from delivering source to named class of sink.

All communications between agents and managers is preferably mobile and autonomous, as the carrying patient of nurse is a mobile subject himself. When the agents transmit their data to more capable managers then the data can be processed and displayed on the managers, and then perhaps transferred through the Intranet to people's carers and to health care professionals. A transfer via Internet is technically viable, however of lesser level of security and protection of privacy for data.

The standards assume that each agent communicates with a single manager at a time. A manager could communicate with more than one agent. Communications is bi-directional to enable transaction security. The manager may be able to maintain its own copy of the transmitted agent's objects (data), however a layered server architecture provides for legally secure archiving.

Transport independence The IEEE 11073 PHD standards define messages that travel between agent and manager but not how those messages should be moved.

Three transports were defined: Bluetooth Health Device Profile USB Personal Healthcare Device Class Zigbee Health Care Profile Others may be defined in the future.

Object oriented The IEEE 11073 family of standards use the object-oriented systems management paradigm. Data (measurement, state, and so on) are modeled in the form of information objects that are accessed and manipulated using an object access service protocol. Note that this does not mean that Agents or Managers must be implemented using object oriented programming languages.

This approach ensures flexibility and is what allows new device specialisation standards to be added easily: all Agents are instances of a "Medical Device System" object, and contain an appropriate mix of other objects pre-defined by the IEEE 11073-20601 framework standard.

Self-describing and extensible An agent may either implement one or more standard configurations, or may implement an extended (custom) configuration. When an agent first associates with a manager it states its configuration. Usually the manager will already have knowledge of the object model of agents with this configuration code - either because it was given this knowledge at birth, or because it has previously associated with this Agent and has already learned its object model. If the manager does not have knowledge of this configuration it asks the agent to describe its characteristics (by listing its objects).

The use of standard configurations, and the exchange of object models when an Agent with a new configuration appears for the first time, significantly reduces the exchange of data required when an Agent associates with a Manager.

ASN.1 representation of data Each object, and all of its attributes, are formally defined using Abstract Syntax Notation One (ASN.1). ASN.1 provides a set of formal rules for describing the structure of objects that are independent of machine-specific encoding techniques.

ASN.1 objects are converted into binary data streams using Medical Device Encoding Rules (MDER) which is a subset of Basic Encoding Rules (BER). The use of MDER allows agents to store predefined transmission templates ("canned messages") and modify just the fixed location, varying parts before sending.

System model in more detail The overall IEEE 11073 system model is divided into three principal components: the Domain Information Model (DIM), the service model, and the communications model. These three models work together to represent data, define data access and command methodologies, and communicate the data from an Agent to a Manager. They are considered in turn.

Domain Information Model The IEEE 11073 standards represent the agent as a set of objects (in the object-oriented programming sense of the word).

Each object has one or more attributes. Attributes describe measurement data that are communicated to a Manager as well as elements that control behavior and report on the status of the Agent. As well as attributes, the objects can possess methods (such as GET and SET) by which the Manager can interact with the Agent. And the Agent can generate Events - typically to inform the Manager that some data has changed.

The IEEE 11073-20601 defines these classes (which are instantiated as objects): Medical Device System (MDS) – each Agent has one MDS object, which identifies it and reports its status. The attributes of the MDS object identify it to the Manager, represent the time and status, and provide other information. The MDS then contains zero or more of some of the objects represented by the classes below. Metric Class is the base class for all objects representing measurements, status and context data. However, the Metric Class is never instantiated itself: rather, it is used as the base class for the Numeric, Real-Time Sample Array and Enumeration classes.

For each object there are a range of attributes – some mandatory and some optional. These attributes include timestamps, descriptive strings, validity and units.