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

To assess the physiologic effects of continuous negative extrathoracic pressure (CNEP), negative pressure ventilation (NPV), and negative extrathoracic end-expiratory pressure (NEEP) added to NPV in patients with acute exacerbation of chronic obstructive pulmonary disease (COPD), we measured in seven 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 plus NEEP. CNEP and NPV were provided by a microprocessor-based iron lung capable 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 end-expiratory pressure (PEEPi) (4.6 0.5 versus 2.1 +/- 0.3 cm H2O, respectively, p < 0.001). NPV increased minute ventilation ((V)over dotE), improved arterial blood gases, and decreased PTPdi to 34% of value during SB (p < 0.001). NEEP added to NPV further slightly decreased PTPdi and improved patient-ventilator interaction by reducing dynamic PEEPi and nontriggering inspiratory efforts. We conclude that CNEP and NPV, provided by microprocessor-based iron lung, are able to improve ventilatory pattern and arterial blood gases, and to unload inspiratory muscles in patients with acute exacerbation of COPD.