TRANSITIONAL EFFECTS OF INSPIRED CO2 ON LUNG-MECHANICS IN ANESTHETIZED RABBITS

In eight anesthetized, spontaneously breathing New Zealand rabbits air flow, tidal volume, tracheal and esophageal pressures were measured. F requency, inspiratory and expiratory durations, respiratory system and lung resistances, and elastances, total postinspiratory muscle pressu re and its timing parameters were determined. The measurements were pe rformed: (a) under control condition; (b) continuously, during the fir st 90 sec of the inhalation of a mixture of 5% CO2 + 95% O-2, (carboge n, CI); and (c) 6 min after the start of CI. During CI both lung resis tance and elastance decreased: and inspiratory driving pressure and po stinspiratory muscle pressure increased. No modification could be dete cted in either the pattern or the duration of postinspiratory muscle a ctivity. In conclusion, mechanical changes precede and facilitate the ventilatory adjustment to CO2 in rabbits.