Abstract
To assess the impact of the endotracheal tube (ETT) and of different flow waveforms on estimates of alveolar cyclic recruitment (CR) and overdistension (AO). Numerical simulation of the respiratory system plus ETT (inertance L plus a flow-dependent resistance, K 1 and K 2), with the following non-linear equation of motion
(P AW pressure at the airways opening, V volume), under volume-controlled mechanical ventilation. An index %E 2 = 100·(E 2·V T)/(E 1 + E 2·V T) can be calculated where %E 2 > 30% represents AO and %E 2 < 0% represents CR. Parameters were estimated by the least-squares method, either with the complete equation or supressing L, K 2 or both. %E 2 is always underestimated (down to −152 percent points) with incomplete equations of motion. The estimation of %E 2 may be strongly biased in the presence of an ETT excluded from the estimation model.
Abbreviations
- ALI:
-
Acute lung injury
- AO:
-
Alveolar overdistension
- CR:
-
Cyclic recruitment
- E 1 :
-
Linear elastance
- E 2.V :
-
Volume-dependent elastance
- %E 2 :
-
Contribution of the volume-dependent elastance to the total elastance
- ETT:
-
Endotracheal tube
- K 1 :
-
Linear resistance of the ETT
- \( K_{2} \left| {\left. {\ifmmode\expandafter\dot\else\expandafter\.\fi{V}({\text{t}})} \right|} \right. \) :
-
Flow-dependent resistance of the ETT
- L :
-
Inertance
- P 0 :
-
Airways pressure when volume and respective derivatives are zero
- P AW :
-
Pressure at the airways opening
- Pel:
-
Elastic component of the airways pressure
- Pel-V:
-
Elastic pressure–volume relationship
- PEEP:
-
Positive end-expiratory pressure
- Pinf:
-
Mathematical inflection point of the Pel-V curve
- Pmcd:
-
Point of maximal decrease of compliance
- Pmci:
-
Point of maximal increase of compliance
- Rrs:
-
Resistance of the respiratory system
- RS:
-
Respiratory system
- VCV:
-
Volume-controlled ventilation
- V T :
-
Tidal volume
- V(t):
-
Volume
- \( \ifmmode\expandafter\dot\else\expandafter\.\fi{V}({\text{t}}) \) :
-
Flow
- \( \ifmmode\expandafter\ddot\else\expandafter\"\fi{V}({\text{t}}) \) :
-
Time-derivative of the flow
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Acknowledgments
The authors wish to thank Dr. J. Venegas for his kindness in providing the experimental data for this study. This work was partially supported by grants of CNPq and FAPERJ.
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Jandre, F.C., Modesto, F.C., Carvalho, A.R.S. et al. The endotracheal tube biases the estimates of pulmonary recruitment and overdistension. Med Bio Eng Comput 46, 69–73 (2008). https://doi.org/10.1007/s11517-007-0227-5
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DOI: https://doi.org/10.1007/s11517-007-0227-5