CARDIORESPIRATORY EFFECTS OF CHANGING INSPIRATORY TO EXPIRATORY RATIO DURING HIGH-FREQUENCY OSCILLATION IN AN ANIMAL-MODEL OF RESPIRATORY-FAILURE

To examine the effects of varying inspiratory/expiratory ratio (I/E) on cardiorespiratory function during high-frequency oscillation (HFO), 11 saline-lavaged rabbits were ventilated at I/E = 1:2, 1:1.5, 1.5:1, and 2:1 in a paired comparison to a baseline of I/E = 1:1. HFO was delivered by a SensorMedics model 3100 oscillator at a frequency of 10 Hz. Pressure amplitude and proximal mean airway pressure (PPawBAR) were held constant as I/E was varied from baseline to the experimental I/E. During each paired observation, Pa(O2), Pa(CO2), cardiac output, blood pressure, and distal mean airway pressure (DPawBAR) were measured. We found that as I/E was increased or decreased from 1:1, no significant changes in Pa(O2), Pa(CO2), blood pressure, or cardiac output occurred. We conclude that in this model, varying I/E has no significant effect on oxygenation, ventilation, or cardiovascular function.