PULM6: Exploratory In Vivo Testing Of A Non-Invasive Ventilation Assist Device

Abstract

Background: Mechanical ventilation is normally accomplished by positive pressure, either invasively through an endotracheal tube, or non-invasively through a mask or nasal prongs. Positive pressure ventilation (PPV) is associated with ventilator induced lung injury (VILI), especially in infants. Negative pressure ventilation (NPV) is more physiologic and preferentially opens posterior areas of the sick lung refractory to opening with positive pressure ventilation alone. However, NPV is not widely used due to the cumbersome negative air pressure chambers requiring torso and neck seals. Methods: We have developed a more practical device for achieving NPV. The Torso Expander consists of flexible tubes attached to a base layer which adheres to the torso with a silicone skin adhesive. Positive air pressure applied to the tubes causes elongation of the tubes and a distending pressure on the torso. The distending pressure may be static or cycled on and off (Torso Assist Ventilation - TAV) at a manual rate, or synchronized to the patient’s respiration (spontaneous or ventilator induced). The Torso Expander, sized for infants, was tested acutely in 5 piglets (3.1+/- 0.2 kg) during normal physiologic states as well as simulated ARDS by saline lavage surfactant washout, and simulated neuromuscular dysfunction by rocuronium paralysis, in order to study the biomechanics and potential clinical applications with various testing modes. Results: In the ARDS model, when static inflation (up to 400 mmHg) was added to the synchronized intermittent mandatory ventilation (SIMV) for a period of 17 min, intra-abdominal pressure was reduced by 1.0-1.5 cm-water per 100 mmHg inflation pressure, average tidal volume (TV) was increased by 5ml, and average respiratory rate was decreased by 27/min compared to the baseline SIMV. Gastric pressure, which may be measured less invasively in clinical use, correlated linearly (r2 > 0.94) with intra-abdominal pressure. TAV, synchronized with spontaneous and ventilator breaths, was demonstrated, resulting in increases in TV. During static and TAV support oxygenation improved (PaO2/FiO2 increased from 69 to 222 mmHg on average after the interventions). TAV alone was able to support a TV of 5 ml/kg with the animal paralyzed. Discussion: Exploratory studies demonstrated the beneficial effects of this novel non-invasive method of NPV. Additional studies are underway to further quantify these observations and test the technology in adults. This technology may reduce the time on PPV, or avoid PPV in some cases.