CHANGES IN PARAMETERS OF MECHANICS OF BREATHING DURING HIGH-FREQUENCYJET VENTILATION - WHAT IS THE CAUSE

In experiments on 51 healthy anaesthetized and paralyzed rabbits the c hanges in parameters of mechanics of breathing during high frequency j et ventilation (HFJV) were determined and the mechanisms responsible f or these changes were investigated. In the first series of experiments with two groups of animals ventilated by HFJV with relative inspirato ry time ti= 0.5 and ti = 0.7 airway resistance (Raw) after 5 h of HFJV in the ti=0.5 group increased from 1.14+/-0.05 to 2.31+/-0.09 kPa.l(- 1).s (P less than or equal to 0.001), in the ti=0.7 group from 1.22+/- 0.04 to 1.78+/-0.08 kPa.l(-1).s (P greater than or equal to 0.01). Dyn amic compliance (Cdyn) decreased in the ti=0.5 group from 0.041+/-0.00 4 to 0.017+/-0.001 1.kPa(-1) (P less than or equal to 0.01) and in the ti=0.7 group from 0.034+/-0.003 to 0.022+/-0.002 1.kPa(-1) (P less th an or equal to 0.01). In the second series of experiments a group of a nimals was ventilated by HFJV after cervical vagotomy. The deteriorati on of Raw and Cdyn was significantly reduced in vagotomized rabbits in comparison to the controls without vagotomy. Finally, the study of ph ospholipid content in bronchoalveolar lavage fluid revealed no signifi cant differences after 5 h of artificial ventilation or spontaneous br eathing. These data indicate that HFJV results in changes in the param eters of mechanics of breathing in healthy lungs, which may be attenua ted, but not fully eliminated, by bilateral cervical vagotomy. The dec rease in Cdyn and increase in Raw are probably not due to changes in t he pulmonary surfactant content.