Abstract 218

Introduction : Irregular breathing in surfactant depleted cats is improved by CPAP and surfactant instillation. Proportional assist ventilation (PAV) combines resistive and elastic unloading during inspiration and resistive unloading during expiration with a preset end-expiratory pressure. PAV has been shown to increase tidal volume (Vt) and respiratory rate (RR), and to decrease mean phrenic nerve activity (PNA) in healthy young cats. Aim : To compare the variability of breathing and the effect on PNA and Vt during PAV and CPAP in surfactant depleted young cats before and after surfactant instillation.

Methods : Compliance decreased by 57±2% after lung lavages (30 mL/kg×7) and increased by 36±19% after surfactant instillation(100 mg/kg). CPAP was applied with 5 cm H2O, and PAV with resistance=10 cm H2O/L/s, elastance=0.35 cm H2O/L and PEEP=5 cm H2O. The duration and amplitude of the integrated PNA was recorded; the duration of inspiration (It) and expiration (Et) was analyzed. The coefficient of variation (CV) was calculated.

Results : In lung lavaged cats PAV gave a larger Vt and a higher RR than CPAP (p<0.01); a reduced amplitude and duration of PNA (p<0.01); and a decrease in It giving a lower I:E ratio (p<0.02). The CV of RR increased from 2.5% during CPAP to 6.4% during PAV (p<0.01). After surfactant instillation Vt and RR remained higher with PAV than with CPAP and mean PNA was low. The other parameters did not differ significantly.

Conclusion : The variability of breathing after lavage was higher during PAV than during CPAP, and depth and rate of breathing was increased during PAV with less PNA.