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

Greyhound dogs were given oleic acid i.v. to induce controlled pulmonary oedema. These animals were then studied using intermittent positive pressure ventilation (IPPV) with four different inspiratory flow waveforms, each at three different inspiratory times, in a fixed respiratory cycle of 4 s at a constant tidal volume. Although there were statistically significant differences in airway and oesophageal pressures between the different waveforms and times, there was little variation in the other physiological parameters studied except for arterial carbon dioxide tension. (PaCO2) which showed statistically significant improvement with reversed ramp and sine wave inputs and at the longer inspiratory time of 2.2s. Venous admixture (Qs/Qt) was also less with the longer inspiratory time of 2.2s.