PubMed2006
In this paper we point out that there are different entities involved in the mathematical descriptions, or models, of the respiratory system: variables and parameters. These, in turn, can be divided into different types. Variables can be primary variables, difference variables, or change variables. Difference variables express the difference between primary variables measured simultaneously at 2 locations. Change variables are primary variables measured relative to fixed reference values. Parameters that appear in input-output models that are valid over a wide range of inputs can be interpreted as properties. There are 3 levels of properties, depending on the detail included in the model. If the model specifically includes the geometry of the system and the substances of which the system is composed, then the parameters in the model are material properties. If the model includes the general structures that compose the system, the parameters are structural properties. And if the model describes the behavior of the system as a whole with no detail included pertaining to internal makeup, then the parameters can be considered system properties. Parameters that appear in mathematical descriptions of input and/or output wave shapes can be interpreted as waveform characteristics. General waveform characteristics are attributes of arbitrary inputs and/or outputs. However, in those special cases in which a system is subjected to a well-defined, specialized input and the output waveform is described mathematically (even if only at a single point), the parameter(s) in such descriptions can be considered system response characteristic(s). We suggest that the symbols and names given to these various entities should follow well-defined guidelines that distinguish among the entity types. These guidelines should include symbol and name conventions and also sign conventions and expected unit ranges on appropriate measurement scales. One such set of conventions would be as follows. Italicize all variables. Use upper-case for primary (absolute) variables. Use the delta symbol (Delta) to denote difference variables (difference between 2 locations). Use lower-case letters for change variables (change relative to a reference, or operating, point) and for abbreviations (eg, "pl" for "pleural"). Use upper-case characters to represent the initial letters of words (eg, "AO" for "airway opening"). Make bold nonitalicized groups of letters used for properties (upper-case, lower-case, multi-height). Do not bold or italicize groups of letters used for characteristics (upper-case, lower-case, multi-height). Compound symbols are those that include subscripts and/or superscripts. Subscripts following a symbol indicate location, direction, or index (time); if more than one subscript, separate them by commas. Superscripts following a symbol indicate a component, or it can indicate a power if the symbol is enclosed in parentheses. Letters on the same line as initial letter but in smaller type are part of the generic symbol. Arguments are enclosed in parentheses; parentheses are also used to isolate compound symbols from powers or additional subscripts. Adapt currently standard symbols to retain their identity but conform to the above conventions. The sign of an entity is always dictated by and its interpretation is based on the model in which the entity is used. Units used are consistent with measurement resolution and accuracy. Copious examples of the applications of this set of suggested conventions are given in the text and in 4 tables. Our hope is that the presentation of these suggestions will start a dialogue in the field and will influence journal and book publishers to adopt a consistent set of conventions for the names and symbols used for respiratory-system-related terms.