OBJECTIVE: To investigate the effect of inspiratory time and inspiratory flow on the respiratory mechanics of intubated and ventilated neonates. DESIGN: Physiology study. SETTING:Tertiary university neonatal intensive care unit. PATIENTS: Neonates requiring mechanical ventilation with (group 1, n = 9) and without lung disease (group 2, n = 6). INTERVENTIONS: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. MEASUREMENTS: 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. MAIN 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.
RCT Entities:
OBJECTIVE: To investigate the effect of inspiratory time and inspiratory flow on the respiratory mechanics of intubated and ventilated neonates. DESIGN: Physiology study. SETTING: Tertiary university neonatal intensive care unit. PATIENTS: Neonates requiring mechanical ventilation with (group 1, n = 9) and without lung disease (group 2, n = 6). INTERVENTIONS: 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. MEASUREMENTS: 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. MAIN 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.