The Effects of Variations in Inspiratory Expiratory Ratio on Cardiorespiratory Function During Controlled Ventilation in Normo-, Hypo- And Hypervolaemic Dogs

Abstract

Changes in cardiorespiratory function resulting from the use of three different inspiratory: expiratory ratios (1:2, 0.5:2.5, and 2:1) have been studied in normo-, hypo-and hypervolaemic dogs. Deadspace/tidal volume ratio increased slightly with the 0.5:2.5 ratio in all the states of blood volume but the changes were not statistically significant. There was a significant increase in arterial-alveolar Pco 2 difference on the 0.5:2.5 ratio in the hypervolaemic state and there was a significant reduction in the Pco s difference with the 2:1 ratio in the normovolaemic state. There was a significant reduction in arterial Po, and a significant increase in venous admixture on the 0.5:2.5 ratio in the hypervolaemic state. Cardiac output was reduced after haemorrhage and increased after overtransfusion but there were no significant changes resulting from changes in the I: E ratio within each state of blood volume.

The Cardiorespiratory Effects of Haemorrhage and Overtransfusion in Dogs

“…The pooled results quoted in this paper were compiled from the studies on 16 dogs ventilated with a +o waveform as produced by a Cape ventilator (Sykes et al, 1970), a further 15 dogs ventilated with a sinusoidal flow pattern (Adams et al, 1970), and 16 dogs ventilated with a 1:2 inspiratory: expiratory ratio on the Bamet ventilator (Finlay et al, 1970). These results represented the control values in each of the studies mentioned and, although the inspiratory flow pattern was slightly different, the inspiratory: expiratory ratio of 1:2 and the frequency of 20 b.p.m.…”