THE EFFECTS OF VARIATIONS IN INSPIRATORY: EXPIRATORY RATIO ON CARDIORESPIRATORY FUNCTION DURING CONTROLLED VENTILATION IN NORMO-, HYPO- AND HYPERVOLAEMIC DOGS BY

Changes in cardiorespiratory function resulting from the use of three different inspira-tory: 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 Pco2 difference on the 0.5:2.5 ratio in the hypervolaemic state and there was a significant reduction in the Pcos 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. In recent years the authors have been interested in the effects of mechanical ventilation on cardio-respiratory function with particular reference to the patient who has undergone open-heart surgery under cardiopulmonary bypass. This paper des-cribes the effect of different inspiratory: expiratory ratios on cardiorespiratory function in normo-, hypo- and hypervolaemic dogs