Positive pressure is frequently applied to the airway during resuscitation, inhalation therapy, and anesthesia, and plays an important role in aviation medicine. It has long been known that pressure in the airWay affects the circulation,19 but only recently have these effects on the systemic and pulmonary circulation been thoroughly investigated.1-17,20-23,25
For all practical purposes principally three methods are used, namely: continuous positive pressure, intermittent positive pressure, and alternating positive-negative pressure.
Whenever air is forced into the lungs, there is interference with the circulation. The degree varies with the method.1,4,5,7,10, 12-14,25
Continuous positive pressure always results in circulatory depression, and the extent depends on magnitude and duration of the applied pressure. The higher the pressure and the longer it is maintained, the more pronounced the depression (Fig. 1).
With intermittent positive pressure the effect on the circulation varies with the mean airway pressure and the duration of the