Negative-impedance ventilation and pressure support ventilation: a comparative study

Negative impedance ventilation (NIV) is a novel mode of assisted mechanical ventilation (AMV) in which the pressure support is regulated to continuously track inspiratory flow and/or volume. In this study, we have evaluated the efficacies of NIV and inspiratory pressure support (IPS) ventilation in a model of central airway obstruction in six rabbits. For both AMV modes there was an inverse relationship between the intrinsic work of breathing and alveolar pressure. Compared to IPS, NIV was found to: (1) achieve the same degree of ventilatory unloading and similar level of pulmonary ventilation with considerably lower alveolar pressure; (2) better restore the normal tidal volume and respiratory frequency; (3) yield a shorter inspiratory duty cycle, thereby helping to rest the respiratory muscles and preclude intrinsic positive end-expiratory pressure. We conclude that NIV is more efficacious than IPS in negating airway obstruction and offers a better trade-off between the risks of respiratory muscle fatigue and pressure induced complications.