Lung-Volume-Dependent Effects of Varying Inspiratory Time during High-Frequency Oscillation of Surfactant-Deficient Rabbits

Abstract

Background

High-frequency oscillatory ventilation (HFOV) has been used to treat diffuse alveolar disease in neonates. The SensorMedics 3100 oscillator provides for varying inspiratory time (%IT), but little evidence exists for the clinical utility of this option. Because %IT has important effects on lung volume (LV), tidal volume (VT), and blood gas values during conventional mechanical ventilation, it is important to know whether such effects are present when HFOV is used.

Materials & Methods

We studied 12 New Zealand White rabbits after saline lung lavage to determine the effects of varying %IT on a/A02, PaCO2, cardiac output (C.O.), and VT and to discover whether these effects were dependent on LV. Animals were randomized to high LV (HLV) or low LV (LLV) and placed in a body plethysmograph. HLV and LLV were defined as baseline LV (BLV) ±33%. We collected data at 33, 50, and 70 %IT using both BLV and LLV and BLV and HLV. We tested our hypotheses using analysis of variance with repeated measures.

Results

No effect of varying %IT was dependent on LV (p > 0.05). At HLV, oxygenation (a/A_O2) was significantly higher (p = 0.006), whereas C.O. was lower (p = 0.04), across all %ITs. The effect of %IT on VT and PaCO2 was highly significant (p < 0.0005) across all LVs.

Conclusion

In a saline-lavaged rabbit model, the cardiorespiratory effects of using 33, 50, and 70 %IT are independent of LV.

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