= Esophageal balloon catheter
An \b[esophageal balloon catheter] is the tube-and-balloon instrument used to transmit a pressure signal from a balloon in the <oesophagus> to a pressure sensor. The <esophageal balloon> is the coupling element; the <catheter> also introduces a gas-filled line, connections and an external measurement chain. Those components can affect both baseline pressure and dynamic response.
The physiological filling study by <Francesco Mojoli> and collaborators shows why treating the assembly as an ideal pressure wire is inadequate: changing balloon filling altered pressure-change transmission and wall-related baseline pressure.<In vivo calibration of esophageal pressure in the mechanically ventilated patient makes measurements reliable by Francesco Mojoli and others>[Abstract, Methods and Results]{ref} This establishes a measurement dependence, not one universal filling volume for every catheter and surrounding pressure.
A minimal model of <pneumatic response lag of an esophageal catheter> is
$$
\tau\frac{dP_m}{dt}+P_m=P_s,
$$
where $P_s$ is a varying source pressure and $P_m$ the sensor output. For a step from $P_0$ to $P_1$, the response is
$$
P_m(t)=P_1+(P_0-P_1)e^{-t/\tau}.
$$
With a stipulated $\tau=0.10\,\mathrm s$, 63.2 percent of the step appears after 0.10 s and 95.0 percent after 0.30 s. These are model calculations, not specifications of a clinical device.
This dynamic error differs from a fixed offset: waiting longer removes the modeled step-response lag but not a baseline bias. A comparison against a known pressure waveform can test the instrument's response, while an <esophageal balloon occlusion test> addresses transmission in the measurement setting. Neither validation alone proves that esophageal pressure equals regional <pleural pressure> throughout the lung.
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