Abstract
With the use of constant flow, end-inspiratory airway occlusion, respiratory system resistance (Rrs) can be partitioned into a flow resistive component (Rint) and an additional component (ΔR), reflecting viscoelasticity and time constant inequality. Similarly, respiratory system elastance (Edyn) can be partitioned into static elastance (Est) and elastance due to viscoelasticity and time constant inequality (ΔE). We measured Rrs and Edyn and their subdivisions (Rint and ΔR, Est and ΔE, respectively) and studied their flow and volume dependence in eight otherwise healthy children (median age 3.6 y; range 1.9–5.2 y) undergoing general anesthesia for oral rehabilitation. With a constant inspiratory flow (VI) of approximately 15 mL/s/kg and tidal volume of 12 mL/kg, the mean values of Rrs, Rint, and ΔR were: 0.20, 0.11, and 0.10 cmH2O/mL/s·kg. Under the same conditions, the mean Est and ΔE were: 1.04 and 0.12 cmH2O/mL/kg. With increasing VI and under constant VT, ΔR decreased (p< 0.001) progressively. Rint also decreased paradoxically (p< 0.001). Hence, Rrs decreased (p< 0.001) with increasing VI. Est decreased (p< 0.001) with increasing VI, whereas ΔE increased (p< 0.005). With increasing VT and under constant VI, Rint decreased (p< 0.001) and ΔR tended to increase (p= 0.058); Rrs did not change. With increasing VT under constant VI, both Est and ΔE decreased (p< 0.001 and p= 0.001, respectively). Thus, in contrast to the findings in adults, Rint and Est decreased in children with increasing flow and under constant tidal volume, probably reflecting decreased functional residual capacity in anesthetized children, compared with adults. The flow and volume dependence of ΔR and ΔE were similar to those in adults, whereas Rrs did not necessarily follow the direction of changes of ΔR.
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Abbreviations
- C:
-
compliance
- ΔE:
-
elastance of the respiratory system due to tissue viscoelasticity and time constant inequality
- Edyn:
-
dynamic elastance of the total respiratory system
- Est:
-
static elastance of the total respiratory system
- ET tube:
-
endotracheal tube
- FRC:
-
functional residual capacity
- Pao:
-
airway opening pressure proximal to ET tube
- PEEP:
-
positive end-expiratory pressure
- ΔR:
-
respiratory system resistance due to tissue viscoelasticity and time constant inequality
- Rint:
-
intrinsic flow resistance
- Rrs:
-
total respiratory system resistance
- TI:
-
inspiratory time
- ΔV:
-
gas volume
- VI:
-
constant inspiratory flow
- VT:
-
tidal volume
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Acknowledgements
The authors thank David Chasey for his editorial assistance.
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Supported by intramural funds of the Department of Anesthesiology and Critical Care Medicine, University of Pittsburgh and Children's Hospital of Pittsburgh.
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Kaditis, A., Motoyama, E., Seki, I. et al. Flow and Volume Dependence of Respiratory Mechanics in Anesthetized Children. Pediatr Res 46, 419 (1999). https://doi.org/10.1203/00006450-199910000-00010
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DOI: https://doi.org/10.1203/00006450-199910000-00010
