Phrenic nerve activity and ventilation during lung oedema in rabbits

Single fibre and "integrated" phrenic nerve activity was recorded in anaesthetized spontaneously breathing rabbits, during experimentally induced lung oedema. Tidal volume, blood pressure, end-tidal CO2, were monitored. In oedema the number of impulses in each volley slightly decreased while the discharge frequency was increased relatively to control values. The latter effect was due to the increased respiratory rate. "Integrated" phrenic nerve activity was also increased, contrary to tidal volume which was diminished. Minute ventilation obtained from pneumotachograph records [f per V(T)] was compared to the neural output in terms of tidal phrenic amplitude times frequency [f per V(T) eq]. The minute ventilation rose insignificantly by 45 +/- 40 percent and neural output was increased on the average by 150 percent.