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Negative-pressure ventilation assists inhalation by reducing the pressure outside the chest relative to that at the airway opening. A chamber encloses the torso while the mouth and nose communicate with gas outside the chamber. Lower external pressure allows chest expansion and makes alveolar pressure transiently lower than the airway opening, drawing gas into the lungs.

The original 1929 apparatus report by Philip Drinker and Louis A. Shaw describes a sheet-metal tank, a sealing neck collar and the head supported outside the tank. Alternating tank pressure moved the chest while the head remained exposed to atmospheric pressure.^[ref] This is a concrete distinction between applying a pressure change to the body surface and applying it through an airway interface.

An original static example uses transpulmonary pressure $P_L=P_{\mathrm{alv}}-P_{\mathrm{pl}}$. With an open airway and no flow, suppose alveolar pressure is zero on an atmospheric gauge. Changing pleural pressure from $-6$ to $-10$ cm H${}_2$O raises $P_L$ from 6 to 10 cm H${}_2$O. For stipulated lung compliance $0.05$ L/cm H${}_2$O, the linear model predictsDuring the actual filling transient, pressure differences also overcome airway resistance. The static calculation does not predict the instantaneous flow waveform.

Tank pressure is a boundary condition, not a direct measurement of pleural pressure. Chest-wall mechanics and body geometry affect pressure transmission. Consequently, an equal numerical pressure at a positive-pressure airway interface and a negative-pressure body chamber need not produce identical volume changes or circulatory effects. The useful unifying quantity for lung distension is the pressure difference across the lung, together with its mechanical response.

Philip Drinker coauthored the 1929 tank-respirator report with Louis A. Shaw. Its apparatus enclosed the body in a sheet-metal tank with a rubber collar at the neck, leaving the head outside at atmospheric pressure. Changing the tank pressure could then expand and compress the chest wall.^[ref]

The scientific principle is a driving pressure difference across the respiratory system. In an original passive linear model, let $v$ be added lung volume, $R$ total resistive coefficient, $C$ total respiratory-system compliance, $P_{\mathrm{ao}}$ airway-opening pressure and $P_b$ body-surface pressure. About a specified mechanical equilibrium,A negative change at the body surface can create a positive filling drive even when the airway remains open to room air. The pump acts on the enclosure; the resulting boundary-condition difference drives air through the airway.

For a stipulated step $P_{\mathrm{ao}}-P_b=10$ cm H${}_2$O, $R=10\mathrm{cm}{\mathrm{H}}_2\mathrm{O}\mathrm{s}{\mathrm{L}}^{-1}$ and $C=0.05\mathrm{L}(\mathrm{cm}{\mathrm{H}}_2\mathrm{O}{)}^{-1}$, the time constant is $RC=0.50$ s andThe initial volumetric flow rate is 1 L/s; after 0.50 s the added volume is about 0.316 L, still below the mechanical equilibrium increment 0.50 L. These are original model values, not measurements from Drinker's apparatus.

The equation also explains a limited equivalence: lowering body-surface pressure by a given amount or raising airway-opening pressure by that amount gives the same driving term in this model. It does not establish identical physiological effects in every respect. Upper-airway behavior, active muscles and departures from linear mechanics are absent from the calculation.

The report's importance lies in connecting an external mechanical apparatus to a sustained respiratory task with explicit pressure boundaries. The neck seal, accessible head and changing enclosure pressure describe how the intervention acts; independently observed gas movement and physiological responses establish what it achieves. The joint byline supports the coauthored contribution without assigning every construction or experimental step to one collaborator.