Wednesday, September 20, 2006

Diseases as Dependent Continuants

In a comment submitted to this blog, Dr William Goossen, researcher and consultant at Acquest Research, Development and Consulting in the Netherlands quotes from my remark in a ">previous posting to the effect that the RIM could effect considerable improvements by adding a new backbone class, called ‘Dependent Continuant’ since this would allow a coherent treatment of diseases, which could be classified under this heading, leaving observations of disease to be classified, properly, as Acts. The new class of Dependent Continuant could then include not only diseases but also qualities such as temperature, blood pressure, etc.

As Dr Goossen would have it:
Currently the comments refer to the RIM. However, the actual standards are based on the RIM and formed in the Domain Message Information Models (D-MIM). For example the Care Provision D-MIM. The structure suggested above is already in there. It is called clinical or care statements and it allows to express any observation and each observation can be linked to another, e.g. a disease (value pneumonia) can be visible through observations of temperature (e.g. value 39 degrees Celcius), breathing pattern (e.g. shorness of breath), x-ray (showing the pneumonia in the lungs) etc. The suggestion to have this additional class is therefore not necessary at all. This disease and its underlying observations on which the clinician has based his conclusion of "pneumonia" can further be linked to the treatment given and can be tracked in the care statement collector. In other words: what you ask for is already in the HL7 v3 standard, but the RIM is not the whole standard. You look at the wrong sections .
As Werner Ceusters points out, however, if Dr Goossen is right about the Care Provision D-MIM, then this is one more reason why the Dependent Continuant class should indeed by added to the RIM forthwith. This is because HL7 itself asserts that:
The Domain Message Information Model (D-MIM) is a subset of the RIM that includes a fully expanded set of class clones, attributes and relationships that are used to create messages for any particular domain.
If the D-MIM is a subset, then surely it cannot add anything.

It is however gratifying to see that, by the evidence of this D-MIM, HL7-ers working in the area of patient care have recognized that entities such as diseases, temperature qualities and the like, which exist longer than any observation, cannot themselves be identified as observations. They have thus created the notion of Condition, which they define as:
An observable finding or state that persists over time and tends to require intervention or management and is, therefore, distinguished from an observation made at a point in time.
This definition is in line with our proposal according to which a Condition (Dependent Continuant) is something out there on the side of the patient.

But there are problems with the definition nonetheless. First, there are presumably (for example in the very early stages of most every disease) Conditions at the molecular level which are not observable. Second there are Conditions – for instance a normal temperature, a normal blood pressure – which do not ‘tend to require intervention or management’.

Moreover, there are problems with the D-MIM documentation, for example when it asserts that ‘if a state or observation is used as a “reason” for intervention or management, it qualifies as a “Condition.”’ First, what if a state (e.g. of chronic depression) is not ‘used as a “reason” for intervention or management’ – is it then not a Condition? Second, must it not quite generally be the case that Conditions exist prior to any Acts in which they are used as reasons for intervention? Thirdly, we are told in the just-quoted passage that observations themselves can be instances of Condition (which means, given what we assume to be the rules governing the RIM’s backbone classes) that Conditions themselves would have to be accepted, after all, as a subtype of Act, which brings us back to the very same confusions with which we started.

Question, therefore, for Dr Goossens and the authors of this D-MIM: Is what has been added here truly a special kind of Act, called ‘Condition’? And if so, is it reasonable to identify, e.g. a chest pain in a patient as an Act? And if so, who is the agent of this Act?

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