Physiological effects of alveolar, tracheal, and "standard" pressure supports.

Pressure support (PS) is characterized by a pressure plateau, which is usually generated at the ventilator level (PS(vent)). We have built a PS device in which the pressure plateau can be obtained at the upper airway level (PS(aw)) or at the alveolar level (PS(A)). The effect of these different PS modes was evaluated in seven healthy men during air breathing and 5% CO(2) breathing. Minute ventilation during air breathing was higher with PS(A) than with PS(aw) and lower with PS(vent) (16 +/- 3, 14 +/- 3, and 11 +/- 2 l/min, respectively). By contrast, there were no significant differences in minute ventilation during 5% CO(2) breathing (25 +/- 5, 27 +/- 7, and 23 +/- 5 l/min, respectively). The esophageal pressure-time product per minute was lower with PS(A) than with PS(aw) and PS(vent) during air breathing (29 +/- 26, 44 +/- 44, and 48 +/- 30 cmH(2)O. s, respectively) and 5% CO(2) breathing (97 +/- 40, 145 +/- 62, and 220 +/- 41 cmH(2)O. s, respectively). In conclusion, during PS, moving the inspiratory pressure plateau from the ventilator to the alveolar level reduces pressure output, particularly at high ventilation levels.