= End-inspiratory hold
An \b[end-inspiratory hold] is a pause after inflation during which the airway is occluded and external flow is interrupted. Under passive, leak-free conditions, the resulting pressure trace helps distinguish flow-related <airway resistance> from the pressure remaining at approximately fixed lung volume. A stable endpoint provides a <plateau airway pressure> for interpreting <respiratory-system compliance>.<How to measure driving pressure by Hamilton Medical>[End-inspiratory hold; passive and leak-free measurement conditions]{ref}
Stopping flow does not imply that every compartment instantaneously reaches a common pressure. <Stress relaxation>, redistribution between lung regions and the apparatus response can produce a continuing pressure change after the rapid resistive drop. The measured value should therefore identify the observation interval, rather than treating the first post-interruption sample as universally equilibrated.
For an original illustrative trace, suppose flowing peak pressure is 26 cm H$_2$O and stopping flow immediately removes 4 cm H$_2$O. Let the subsequent relaxation be
$$
P_{\rm hold}(t)=18+4e^{-t/(0.5\,\mathrm s)}\quad\text{cm H}_2\text O.
$$
The initial hold value is 22 cm H$_2$O, about 19.47 remains after 0.5 s, and about 18.20 after 1.5 s. The model's long-time value is 18. The change from 26 to 22 and the later change from 22 toward 18 represent different mechanisms in this constructed example.
With total end-expiratory pressure 8 cm H$_2$O, using the initial hold value gives a nominal <respiratory driving pressure> of 14, whereas using the asymptotic value gives 10 cm H$_2$O. The difference demonstrates the importance of time and model assumptions; it does not prescribe a hold duration. Continued muscle activity, leakage or airway closure can invalidate the simple static interpretation. The experimental pilot study compares static and dynamic measurement methods rather than assuming all displayed pressure estimates are interchangeable.<Static and Dynamic Measurements of Compliance and Driving Pressure: A Pilot Study by Pierre Tawfik and others>[Figure 1 and Study Procedures]{ref}
\Image[/end-inspiratory-pressure-relaxation.png]
{title=Constructed end-inspiratory pressure trace separating flow interruption from later relaxation}
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