PHYSIOLOGICAL-EFFECTS OF POSITIVE END-EXPIRATORY PRESSURE AND MASK PRESSURE SUPPORT DURING EXACERBATIONS OF CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

To assess physiologic effects of continuous positive airway pressure ( CPAP) and positive end-expiratory pressure (PEEP) during noninvasive p ressure support ventilation (PSV) in patients with acute exacerbation of chronic obstructive pulmonary disease (COPD), we measured in seven patients the breathing pattern, lung mechanics, diaphragmatic effort ( PTPdi), and arterial blood gases under four conditions: (1) spontaneou s breathing (SB); (2) CPAP; (3) PSV of 10 cm H2O; and (4) PSV plus PEE P (PEEP+PSV). CPAP and PEEP were set between 80 and 90% of dynamic int rinsic PEEP (PEEPi(dyn)) measured during SB and PSV, respectively. PEE Pi(dyn) was obtained (1) from the decrease in pleural pressure (Delta Ppl) preceding inspiration, and (2) subtracting the fall in gastric pr essure (Delta Pga) caused by relaxation of the abdominal muscles from the Delta Ppl decrease. Abdominal muscle activity made PEEPi(dyn) over estimated in almost all instances (p < 0.0001). PSV increased minute v entilation, improved gas exchange, and decreased PTPdi. PEEP added to PSV, likewise CPAP compared with SB, further significantly decreased t he diaphragmatic effort (PTPdi went from 322 +/- 111 to 203 +/- 63 cm H2O.s) by counterbalancing PEEPi(dyn), which went from 5.4 +/- 4.0 to 3.1 +/- 2.3 cm H2O. These data support the use of low levels of PEEP ( 80 to 90% of PEEPi(dyn)) to treat acute exacerbation of COPD by means of mask PSV.