End-inspiratory hold

An 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.^[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 beThe 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.^[ref]