Effect of increasing inspiratory time on respiratory mechanics in mechanically ventilated neonates.
OBJECTIVE
To investigate the effect of inspiratory time and inspiratory flow on the respiratory mechanics of intubated and ventilated neonates.


METHODS
Physiology study.


METHODS
Tertiary university neonatal intensive care unit.


METHODS
Neonates requiring mechanical ventilation with (group 1, n = 9) and without lung disease (group 2, n = 6).


METHODS
All infants were ventilated with a Servo 900C Siemens ventilator in the volume-controlled constant-flow mode. Flow and pressure were measured at the Y-piece, while different inspiratory times (25%, 33%, 50%, and 67% of the respiratory cycle) were applied randomly without changing tidal volume.


METHODS
The constant flow end-inspiratory airway occlusion technique allowed partitioning of the total respiratory system resistance (R(tot,rs)) into a standard intrinsic flow resistance (R(int,rs)) and a lung/thorax tissue viscoelastic component (DeltaR(rs)), and it allowed partitioning of the dynamic respiratory system elastance (E(dyn,rs)) into a static (E(st,rs)) and a lung/thorax tissue viscoelastic component (DeltaE(rs)). A two-compartment model of the respiratory system was applied to the experimental data.


RESULTS
All respiratory mechanics components were significantly higher in group 1 compared with group 2. Both groups showed increasing R(int,rs) with increasing flow and increasing DeltaR(rs) with increasing inspiratory time. DeltaR(rs) represented 40% to 75% of R(tot,rs) whatever the group. E(dyn,rs) and E(st,rs) changed with inspiratory time in the very low (<0.4 secs) and the very long inspiratory time range (>1.0 secs). No change was found when clinically, commonly used inspiratory times were applied (0.4-1.0 secs). DeltaE(rs) represented 17% to 19% of E(dyn,rs). The relationship between DeltaR(rs) and increasing inspiratory time fitted the exponential two-compartment model (r =.99, p <.001).


CONCLUSIONS
Total respiratory mechanics and its components in ventilated newborns with and without lung disease showed inspiratory time dependence. DeltaR(rs) increased with increasing inspiratory time as predicted by the two-compartment lung model, whereas standard R(int,rs) and E(dyn,rs) decreased.
Riou
Yvon
Y
Department of Respiratory Physiology, Hôpital Jeanne de Flandre, Chru de Lille, France.
Leclerc
Francis
F
Scalfaro
Piétro
P
Abazine
Abdel
A
Neve
Véronique
V
Storme
Laurent
L