Original polygraph recordings during a change from continuous positive-pressure ventilation (CPPV) to continuous negative-pressure ventilation (CENPV) in patient 6. The pressure-time profiles of endotracheal pressure (AWP) during CPPV and tank pressure were similar during inspiration and expiration. During CENPV, endotracheal airway pressure increased during inspiration and decreased after a short initial peak. This patient had high intraabdominal pressure despite an open abdomen that decreased impressively during CENPV. (To convert pressure values from millimetres of mercury to centimetres of water, multiply by 1.33.) ECG, electrocardiogram; AWP, airway pressure (measured in the trachea); CVP, central venous pressure; AP, arterial pressure; IAP, intraabdominal pressure, exp. CO2, expired carbon dioxide.