Negative airway pressure generation (Paw) (following airway occlusion), inspired volume, end-tidal PCO2, oxygen saturation, mean blood pressure and heart rate are plotted every 30 min during continuous inspiratory muscle pacing with HF-SCS after bilateral phrenicotomy. Results are means ± SE. Airway pressure and inspired volume generation remained constant throughout the initial 5.5 hours of stimulation. End-tidal PCO2 and oxygen saturation were also maintained around 40 mmHg and 94%, respectively. Mean blood pressure and heart rate also remained stable throughout this period. After 5.5 hour of continuous pacing, stimulus parameters were increased (indicated by arrows) resulting in an increase in inspired volume and consequent fall in PCO2, which was sustained over a 30 min period. These results indicate that adequate levels of ventilation can be maintained over a prolonged period with HF-SCS of the intercostal muscles alone.