CHAPTER 10 Mechanics of proportional - assist ventilation

Proportional-assist ventilation (PAV) is an effective and improved mode of ventilation over the conventional pressure-support ventilation due to its attractive features of better patient harmony and comfort. The conventional ventilation systems in hospitals will either deliver a specified tidal volume to the patient or raise the airway pressure to a preset level during the inspiratory phase of each breath. These systems do not take into consideration the patient’s breathing patterns and varying requirements during each inspiration. To assist patients with breathing difficulties, PAV has been used as a mode of synchronized partial ventilatory support, by applying airway pressure in proportion to volume and flow rate to overcome the patient’s higher respiratory elastance and resistance, respectively, as a result of pulmonary disease. A new PAV system using a proportional solenoid valve to control the air supply to patients suffering from respiratory disabilities, was studied. The outlet flow and pressure from the valve at various air-supply pressures were tested and proven to be suitable for pressure and flow control in a PAV system. In vitro tests using a breathing simulator, which has been proven to possess the general characteristics of the human respiratory system in spontaneous breathing tests, were conducted and the results demonstrated the viability of this PAV system in normalizing the breathing patterns of patients with abnormally high resistances and elastances as well as neuromuscular weaknesses. In vivo tests using this PAV system were also conducted on healthy volunteer subjects with artificial resistance and elastance incorporated. The test subjects felt comfortable to breathe, with reduced breathing effort when PAV was active, demonstrating the positive assist effect of PAV. www.witpress.com, ISSN 1755-8336 (on-line) WIT Transactions on State of the Art in Science and Engineering, Vol 24, © 2006 WIT Press doi:10.2495/978-1-85312-944-5/10 188 Human Respiration