Figure 3. Phrenic nerve activity during adjustable artificial ventilation.

Steady-state measurement of phrenic nerve discharge, artificial ventilation and blood gases were recorded in anaesthetized, vagotomized, paralysed and artificially ventilated rats. By modifying the level of artificial ventilation, different levels of P_aCO2 could be achieved. Illustrative traces from a single experiment are shown (from top down): arterial blood pressure, integrated tracheal airflow, integrated phrenic activity (100 ms time constant) and raw phrenic nerve discharge. For each steady state, ventilation could be measured as integrated airflow and as phrenic minute activity. By determining the effect of varying airflow upon P_a,CO2 and the effect of P_a,CO2 upon phrenic minute activity, both curves and CO₂ respiratory controller equations could be derived simultaneously.