1 INTRODUCTION
The recommendations in this 1993 update do not differ materially from those in the previous report of the European Community for Steel and Coal [1]. However, the list of abbreviations has been extended with respect to the items covered; in addition the European Community has expanded since the previous report, and the report has accordingly been updated to cover the languages spoken in each of the member states.
2 SYMBOLS
2.1 Symbols for quantities
Symbols are used to designate specific quantities, including basic quantities (e.g. volume, time, pressure, amount of chemical substance) and derived quantities (e.g. volume by unit time). Letters from the Latin or Greek alphabet are commonly employed as symbols, either roman type as in the USA or italics as recommended by the European Society for Clinical Respiratory Physiology [2] and adopted in the 1983 report of the ECSC. As the number of letters available is limited, inevitably one symbol may be used to designate more than one quantity (e.g. concentration of chemical substance and compliance). Symbols for quantities may be specified by one or more subscripts and/or prescripts (abbreviations) and/or modifying signs (dashes, dots, primes), e.g. ΔV′50. Subscripts other than numbers are printed in roman small capitals or lower case letters. The order of specification is location (where), time (when), condition or quality (what, how). Specifications are printed either in line with the primary symbol or as subscripts. When more than one subscript is used, these are separated by a comma.
2.2 Symbols for units
Symbols for SI and non-SI units are roman lower case letters, unless the name of the unit is derived from a proper name, in which case it consists of a capital roman letter (except ohm, Ω), or a capital roman and a lower case letter. Prefixes are used to modify symbols for units and are single roman capitals or lower case letters (except deca, da). In respiratory physiology and medicine, the SI base units are extended with SI derived units and SI prefixes. Non-SI units which are widely applied in everyday life are retained for general use with the SI.
3 ABBREVIATIONS
Abbreviations are employed to facilitate written and spoken communication and are commonly specific to individual languages. However, there is a tendency for many abbreviations to be adopted in the various languages spoken within the European Community; they are also used in mathematical formulae and equations. Such abbreviations have acquired the attributes of symbols. Commonly accepted standard abbreviations for quantities are usually written in one or more capital letters, but there are many exceptions (e.g. Hb, cAMP, co-A, ATP-ase). The abbreviations can be specified by one or more subscripts and/or modifying signs (dashes, dots, primes). Subscripts are numbers or letters printed in roman small capital or small lower case type, e.g. FEV1.
4 UNITS
4.1 SI base units
4.2 Selected SI prefixes
4.3 Selected SI derived units
4.4 Selected non-SI units retained
Comments
1 The American and European recommendations differ with respect to pressure, amount of substance (gas) and time.
2 The working party recommends that time be reported in second for quantities which relate to instantaneous events; time averaged quantities should be reported in units which are appropriate to the length of time over which they are obtained (e.g. seconds, minutes, hours). For special purposes the units day (d), month (m) and year (a) may be used.
3 Volume of gas is usually expressed in lBTPS. Note that in this case the subscript refers to the unit. Unlike a previous recommendation the symbol for litre is now printed in italics, as the distinction between 1 (one) and 1 (for litre) with most fonts is commonly too subtle.
4 Amount of gas: mmol.
5 Partial pressure of gas: kPa.
6 Blood pressure: mmHg (temporarily permitted); kPa.
4.5 Special notations and mathematical operations
: mean value of X
X′: time derivative of X
X″: second time derivative of X
: time averaged value of 
(to be specified)
ΔXA: change of X for specification A
XA-B: difference between X-values for specifications A and B
XA,B: different specifications of X are separated by a comma
%X: Xas a percentage of the reference value
X%Y: X as a percentage of Y
X/Y: division is indicated by a solidus (stroke)
X·Y: multiplication is indicated by a raised dot
: examples of mathematical notations
Comments
1 In most American recommendations, the notation 
is used both for the instantaneous and the time-averaged value of the first time derivative of X, or the lower case form is used as well (e.g. 
). In accordance with the SEPCR recommendation [2] the working party recommends X′ for the instantaneous time derivative and 
for the averaged time derivative.
2 The second time derivative of X is usually indicated by 
in the USA; the present recommendation is X″.
3 The notation X/Y is allowed, except with complex notations. More than one solidus should never be used in a notation.
4.6 Abbreviations, symbols and units for lung function indices
The following tables contain abbreviation, symbols and units for some commonly used lung function indices. Gas volumes are at BTPS, unless indicated otherwise. Qualifying abbreviations are usually one or more roman lower case letters. However, for several qualifications, capital letters are (also) accepted.
Footnotes
The working party is very grateful to Prof. N. Siafakas, Drs. B. Bouros, N. Tzanakis and F. Vlaserou for the translation of the tables into Greek, and to Prof. J.H. Paiva de Carvalho for the translation into Portuguese.
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