= J. Bartels
{c}
\b[<J. Bartels>] is the first named author of the 1954 primary study comparing <respiratory dead space> measurements using single-breath analysis of <oxygen>, <carbon dioxide>, <nitrogen> or <helium>. The journal supplies the initial-only byline; it does not establish a fuller personal name. The measurement contribution concerns the relationship between expired gas composition and expired volume.<The Respiratory Dead Space Measured by Single Breath Analysis of Oxygen, Carbon Dioxide, Nitrogen or Helium by J. Bartels and others>[p. 41, primary byline, study title and opening measurement description]{ref}
A single expired breath is not compositionally uniform. Conducting-airway gas appears before gas from exchanging regions, with a transition that depends on mixing and measurement response. Pairing mouth-flow recording with gas-fraction recording allows elapsed time to be converted into an expired-volume coordinate. Synchronization matters because a gas analyser can respond later than the flow sensor.
An original idealized washout curve makes the volume interpretation concrete. Suppose a tracer fraction is zero over the first 100 mL, rises linearly to its plateau over the next 100 mL, and then stays at a plateau value $F_A$. The equivalent sharp-boundary volume under this flat-plateau model is
$$
V_D=\int_0^{V_T}\left[1-\frac{F(V)}{F_A}\right]dV
=100+\frac{100}{2}=150\,\mathrm{mL}.
$$
The transition contributes half its width. This synthetic equal-area construction explains a measurement principle; it is not a reported observation from Bartels's subjects.
A sloping plateau, incomplete tracer equilibration or analyser delay can change the inferred boundary. Comparing tracers therefore tests a physiological measurement model as well as an instrument. Bartels's verified authorship belongs to that gas-analysis experiment, without claiming that the initial-only name identifies a particular namesake or that every definition of <respiratory dead space> gives an identical volume.
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