Respiratory and hemodynamic effects of diminished expiratory flow during artificial ventilation

The supposition, that a diminished expiratory flow (DEF) during artificial ventilation will improve blood-gas exchange. especially in obstructive pulmonary disease and that DEF improves blood-gas exchange better than a comparable positive end-expiratory pressure (PEEP. producing the same rise in mean tracheal pressure) was explored in experiments using Yorkshire piglets, without altering respiratory rate, tidal volume, inspiratory time~ inspiratory hold or expiratory time. During mechanical ventilation the effects of DEF and a comparable PEEP on hemodynamics, gas exchange and pulmonary mechanics were studied. These effects were compared to each other and to intermittent positive pressure ventilation (IPPV) in health and disease induced by histamine. acetylcholine or oleic acid in order to evaluate hypothetic mechanisms of the effects of DEF. Additionally the validity of cardiac output estimation by the thermodilution method and the cyclic modulation of these estimates during the three modes of mechanical ventilation were analysed in order to find the most appropriate way of calculating mean cardiac output from the smallest number of estimates. In chapter II the experimental model and the methods are described. In chapter III cardiac output estimations by the thermodilution method are evaluated. The results of hemodynamic and respiratory effects (pulmonary mechanics and gas exchange) of DEF and PEEP are presented in chapter IV and discussed in chapter v. In chapter VI the effects of the expiratory flow on the exchange of carbon dioxide during mechanical ventilation are studied using single breath analyses