RATIONALE: High-frequency jet ventilation (HFJV) is often used to treat infants with pathologies associated with gas trapping and abnormal lung mechanics, who are sensitive to the adverse effects of suction. OBJECTIVE: This study aimed to investigate the effect of closed suction (CS), catheter size, and the use of active post-suction sighs on tracheal pressure (P(trach)), and global and regional end-expiratory lung volume (EELV) during HFJV. METHODS: Six anaesthetized and muscle-relaxed adult rabbits were stabilized on HFJV. CS was performed using all permutations of three CS methods (Continual negative pressure, negative pressure applied during Withdrawal, and HFJV in Standby) and 6 French gauge (6 FG) and 8 French gauge (8 FG) catheter, randomly assigned. The sequence was repeated using post-suction sighs. P(trach), absolute (respiratory inductive plethysmography) and regional (electrical impedance tomography; expressed as percentage of vital capacity for the defined region of interest, %Z(VCroi) ) EELV were measured before, during and 60 sec post-suction. RESULTS: CS methods exerted no difference on ΔP(trach), ΔEELV(RIP), or Δ%Z(VCroi) . 8FG catheter resulted in a mean (95%CI) 20.0 (17.9,22.2) cm H(2)O greater loss of P(trach) during suction compared to 6FG (Bonferroni post-test). Mean (± SD) ΔEELV(RIP) was -6(±3) and -2(±1) ml/kg with the 8 and 6 FG catheters (P < 0.0001; Bonferroni post-test). ΔEELV was 31.7 (21.1,42.4) %Z(VCroi) and 24.8 (10.9,38.7) %Z(VCroi) greater in the ventral and dorsal hemithoraces using the 8 FG. Only after 8 FG CS was post-suction recruitment required to restore EELV. CONCLUSIONS: In this animal model receiving HFJV, ΔP(trach), ΔEELV, and need for post-suction recruitment during CS were most influenced by catheter size. Volume changes within the lung were uniform.