Physiologic effects of negative pressure ventilation in acute exacerbationof chronic obstructive pulmonary disease

To assess the physiologic effects of continuous negative extrathoracic pres sure (CNEP), negative pressure ventilation (NPV), and negative extrathoraci c end-expiratory pressure (NEEP) added to NPV in patients with acute exacer bation of chronic obstructive pulmonary disease (COPD), we measured in seve n patients ventilatory pattern, arterial blood gases, respiratory mechanics , and pressure-time product of the diaphragm (PTPdi) under four conditions: (1) spontaneous breathing (SB); (2) CNEP (-5 cm H2O); (3) NPV; (4) NPV plu s NEEP. CNEP and NPV were provided by a microprocessor-based iron lung capa ble of thermistor-triggering. Compared with SB, CNEP improved slightly but significantly Pac(O2) and pH, and decreased PTPdi (388 +/- 59 versus 302 +/ - 43 cm H2O . s, respectively, p < 0.05) and: dynamic intrinsic positive en d-expiratory pressure (PEEPi) (4.6 <plus/minus> 0.5 versus 2.1 +/- 0.3 cm H 2O, respectively, p < 0.001). NPV increased minute ventilation ((V)over dot E), improved arterial blood gases, and decreased PTPdi to 34% of value duri ng SB (p < 0.001). NEEP added to NPV further slightly decreased PTPdi and i mproved patient-ventilator interaction by reducing dynamic PEEPi and nontri ggering inspiratory efforts. We conclude that CNEP and NPV, provided by mic roprocessor-based iron lung, are able to improve ventilatory pattern and ar terial blood gases, and to unload inspiratory muscles in patients with acut e exacerbation of COPD.