Effect of frequency of ventilation, positive end-expiratory pressure, PaO2 and PaCO2 on phrenic nerve activity. A study using a new valveless all-purpose ventilator.

The effect of changing the frequency of ventilation from 12 b.p.m. (NFV) to 80 b.p.m. (HFV) and applying PEEP on phrenic nerve activity (PNA) has been examined in anaesthetized dogs. HFV did not cause a greater decrease in PNA than the application of 0.5 kPa of PEEP. When the PEEP generated by HFV was removed by applying NEEP, PNA returned to control values. At a low normal PaCO2 (less than 5.3 kPa) and high PaO2 (greater than 30 kPa), HFV and PEEP (0.5 kPa) totally abolished PNA in some preparations. With a high normal PaCO2 (greater than 6.0 kPa) and high PaO2 (greater than 30 kPa), HFV and PEEP (0.5 kPa) decreased PNA by a mean of only 30%. When PaO2 was decreased to physiological values (less than 13.3 kPa), with a low normal PaCO2 (less than 5.3 kPa), the decrease in PNA by HFV and PEEP (0.5 kPa) was decreased to 25%. It was concluded that the frequency of ventilation per se has little or no effect on PNA in the range of frequencies studied.