= Esophageal balloon
An \b[esophageal balloon] is a thin-walled pressure-sensing balloon placed in the <oesophagus> and connected to a pressure-measurement system. Its mechanical purpose is to couple surrounding pressure to the gas inside it. An <esophageal balloon catheter> supplies the pneumatic connection; <esophageal pressure measurement> concerns the interpretation of the resulting signal as evidence about <pleural pressure>.
A useful idealization separates the contributions:
$$
P_{\rm measured}=P_{\rm surrounding}+P_{\rm balloon}+P_{\rm wall}+b,
$$
where balloon tension, tissue reaction and an instrumental offset $b$ can affect the reading. This additive model is bookkeeping, not a universal constitutive law for the tissue or balloon. A pressure change can be transmitted well even when the baseline has an offset.
The primary physiological study by <Francesco Mojoli> and collaborators changed balloon filling and compared pressure transmission with baseline contributions from the esophageal wall. Its observations demonstrate that favorable transmission of pressure swings does not by itself remove the <esophageal balloon filling artifact>.<In vivo calibration of esophageal pressure in the mechanically ventilated patient makes measurements reliable by Francesco Mojoli and others>[Abstract and Results: filling, transmitted changes and wall-pressure contribution]{ref}
For a constructed example, suppose surrounding pressure changes from 6 to $10\,\mathrm{cm\,H_2O}$ while a fixed added pressure is $2\,\mathrm{cm\,H_2O}$. The balloon reads 8 and 12: it reproduces the $4\,\mathrm{cm\,H_2O}$ change exactly but overestimates both absolute values by two. Consequently, agreement of a change measurement is a different validation claim from agreement of absolute pressure. Neither the balloon's name nor its presence inside the chest makes those claims automatic.
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