Effects of varying inspiratory flow waveform and time in intermittent positive pressure ventilation: emphysema.

Emphysema was induced in mongrel dogs by four weekly inhalations of papain. The effects of IPPV were studied using four different inspiratory flow waveforms and each at three different inspiratory times. Tidal volume and respiratory frequency were kept constant and inspiratory time and flow waveform were varied independently. There were statistically significant differences in a number of physiological variables. With a longer inspiratory time of 2.2s and with the reversed ramp flow waveform VD/VT was decreased. With the reversed ramp flow waveform there was a greater total compliance, increased (PAo2-Pao2) and reduced PaCO2. There were statistically significant differences in mean airway and oesophageal pressures which indicate valid differences in the flow waveforms and times.