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

Pressure support (PS) is characterized by a pressure plateau, which is usua lly generated at the ventilator level (PSvent). We have built a PS device i n which the pressure plateau can be obtained at the upper airway level (PS, ,) or at the alveolar level (PSA). The effect of these different PS modes w as evaluated in seven healthy men during air breathing and 5% CO2 breathing . Minute ventilation during air breathing was higher with PSA than with PS, , and lower with PSvent (16 +/- 3, 14 +/- 3, and 11 +/- 2 l/min, respective ly). By contrast, there were no significant differences in minute ventilati on during 5% CO2 breathing (25 +/- 5, 27 +/- 7, and 23 +/- 5 l/min, respect ively). The esophageal pressure-time product per minute was lower with PSA than with PSaw and PSvent during air breathing (29 +/- 26, 44 +/- 44, and 4 8 +/- 30 cmH(2)O.s, respectively) and 5% CO2 breathing (97 +/- 40, 145 +/- 62, and 220 +/- 41 cmH(2)O.s, respectively). In conclusion, during PS, movi ng the inspiratory pressure plateau from the ventilator to the alveolar lev el reduces pressure output, particularly at high ventilation levels.