= Esophageal balloon occlusion test
The \b[esophageal balloon occlusion test] checks how well changes measured by an <esophageal balloon catheter> track changes in <pleural pressure>. During an inspiratory effort against an occluded airway at end-expiration, the comparison is between the pressure change in the balloon and that at the mouth. The original study by <Ahmet Baydur> and colleagues tested ten subjects in sitting, supine and lateral positions. Repositioning the balloon could improve agreement when a supine measurement initially differed.<A Simple Method for Assessing the Validity of the Esophageal Balloon Technique by Ahmet Baydur and others>[Abstract, end-expiratory occlusion protocol and positional findings]{ref}
The mechanical rationale is a change comparison. With no external flow and approximately fixed lung volume, the change in <transpulmonary pressure> is small in the simple static model. Consequently,
$$
\Delta P_{\rm alv}\simeq\Delta P_{\rm pl},\qquad
\Delta P_{\rm mouth}\simeq\Delta P_{\rm alv},\qquad
\frac{\Delta P_{\rm es}}{\Delta P_{\rm mouth}}\simeq1
$$
for a balloon that transmits pleural changes appropriately. The reasoning assumes communicating airways and a suitable measurement system; it does not establish equality merely because flow at one sensor is zero.
An original example uses simultaneous mouth-pressure changes $-3,-5,-4$ cm H$_2$O and balloon changes $-2.7,-4.5,-3.6$ cm H$_2$O. Their proportional response is 0.9. Repeating several efforts makes that relation more visible than interpreting one small pressure fluctuation in isolation.
Importantly, a successful change test does not determine the absolute offset. If a hypothetical sensor obeys $P_{\rm es}=aP_{\rm pl}+b$, the ratio of changes assesses $a$, while the constant $b$ cancels. A true pleural change from $-5$ to $-9$ recorded as 0 to $-4$ has unit change ratio despite a 5 cm H$_2$O offset. <Esophageal pressure measurement> therefore needs a clear distinction between tracking respiratory swings and assigning an absolute pressure for a transpulmonary calculation. The test interrogates pressure transmission, not every possible source of measurement error.
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