Exovent: a study of a new negative-pressure ventilatory support device in healthy adults.

Abstract

Negative-pressure ventilation may have several advantages compared with positive-pressure ventilation. Negative-pressure ventilation simulates natural lung movements, does not require tracheal intubation and may reduce the incidence of barotrauma and adverse cardiovascular events. A group of engineers, doctors and nurses designed and bench-tested the Exovent, a new, lightweight, torso-only, negative-pressure ventilatory support system. We aimed to test the comfort, nursing acceptability and ventilatory support capabilities of the Exovent in healthy adult volunteers. We measured the effect of continuous negative extra-thoracic pressure on functional reserve capacity and the efficacy of ventilation produced by a combination of negative-pressure ventilation and negative end-expiratory pressure. Six members of the development team volunteered to test the device. The application of continuous negative extra-thoracic pressure did not change tidal volumes from baseline levels; however, functional reserve capacity increased by a mean (SD) of 1.1 (0.05) ml.kg-1 .cmH2 O-1 (p=0.0002). The combination of negative-pressure ventilation and negative end-expiratory pressure produced effective ventilation, with the resting tidal volume being exceeded by the application of -4 cmH2 O of extra-thoracic negative pressure. All the volunteers found the experience comfortable and none had ventilator dysynchrony. The Exovent allowed good nursing and monitoring access and was comfortable in both the semi-recumbent and prone positions. The Exovent delivered effective continuous negative extra-thoracic pressure and negative-pressure ventilation plus negative end-expiratory pressure to healthy adults. Further trials are needed to investigate the clinical utility of the device.