Negative pressure ventilation

Abstract

Negative pressure ventilation refers to a form of ventilatory assistance where the patient's body from the neck downwards, or just the trunk, is enclosed in a rigid container. The pressure inside the container is cyclically lowered below atmospheric pressure, resulting in the entrance of ambient air into the lungs. When the pressure inside the container returns to atmospheric levels, the elastic recoil of the lungs and chest wall stored during inspiration is released, causing passive expiration. Greater surface areas of the body exposed to the negative pressure swings, and greater levels of negative pressure result in larger tidal volumes. Due to lack of co-ordination between the respirator and the pharyngeal muscles of the patients, obstructive apnoeas may occur during negative pressure ventilation in asleep patients. Long-term negative pressure ventilation has proved useful in patients with respiratory failure secondary to a restrictive impairment of neuromusculoskeletal origin. Although negative pressure ventilation may be successfully used in acute-on-chronic respiratory failure in patients with chronic airflow obstruction, its use in the long-term management of this type of patients seems mnch less promising.