Effects of positive and negative pressure ventilation on cardiac performance.

We have critically reviewed our present understanding of the complex hemodynamic events occurring during spontaneous and mechanical ventilation. It is clear that the physiologic events occurring during normal conditions are present but may be relatively less important under pathophysiologic conditions. Furthermore, since spontaneous ventilation and mechanical ventilation are not simply opposites, evaluation of one ventilatory mode aids in understanding the hemodynamic events in the other. While we have not discussed the hemodynamic events during high frequency oscillation, only with a full understanding of both spontaneous respiration and conventional IPPV can the full implications of this new mode of ventilation be appreciated. It seems a reasonable assumption that in the critically ill patient with cardiopulmonary dysfunction, one mode of ventilation will be optimal and another either less so or even detrimental. Only with an understanding of the hemodynamic effects of respiration can the optimal therapeutic modality be tailored to each patient.