= Arthur B. DuBois
{c}
\b[<Arthur B. DuBois>] is first author of the 1956 primary report introducing a rapid plethysmographic measurement of <thoracic gas volume> and comparing it with a nitrogen-washout measurement of <functional residual capacity> in normal subjects.<A rapid plethysmographic method for measuring thoracic gas volume by Arthur B. DuBois and others>[Title and primary byline, JCI 35, pp.322–326]{ref} The experiment turns a gas-compression relation into an observable pressure-volume slope.
The apparatus enclosed the subject in a sealed chamber, used a mouthpiece shutter and recorded chamber and mouth-pressure signals with capacitance manometers on a cathode-ray oscillograph. Chamber calibration related its pressure signal to changes in body volume.<A rapid plethysmographic method for measuring thoracic gas volume by Arthur B. DuBois and others>[Method, p.323 and Figure 1]{ref} This supplied simultaneous signals rather than an estimate from one uncalibrated pressure reading.
An original <Boyle's law> example follows the paper's derivation. For an approximately isothermal closed gas compartment,
$$
P_0V_0=(P_0+\Delta P)(V_0+\Delta V),\qquad
V_0=-\frac{(P_0+\Delta P)\Delta V}{\Delta P}.
$$
Here $\Delta V$ is the signed change in gas volume, not a raw chamber-pressure signal. If $|\Delta P|\ll P_0$, the approximation is $V_0\approx-P_0\Delta V/\Delta P$. The original article derives the same exact-to-small-change distinction.<A rapid plethysmographic method for measuring thoracic gas volume by Arthur B. DuBois and others>[p.324, equations 1–4]{ref}
For stipulated $P_0=100$ kPa, compression $\Delta V=-0.030$ L and pressure rise $\Delta P=1$ kPa, the exact expression gives 3.03 L and the small-change approximation gives 3.00 L. Their 0.03 L difference is an approximation effect in the chosen gas model, not observed instrument error in the study.
The experiment also depends on the relationship between mouth and alveolar pressure. The paper explicitly discusses failures when that relationship is disrupted.<A rapid plethysmographic method for measuring thoracic gas volume by Arthur B. DuBois and others>[Method, p.323, unsatisfactory tracings]{ref} DuBois's contribution combines the physical law, pressure sensing, chamber calibration and tests of the assumptions needed to interpret the signal.
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