Humans breathe with negative pressure by exerting their diaphragm and chest muscles to inhale air. Mechanical ventilation is used when a patient is paralyzed (e.g. during surgery) or too sick to breath on their own. Mechanical ventilation is positive pressure breathing, where air is actually forced into the lungs. Pressure Support Ventilation (PSV) is a cross between positive and negative pressure ventilation. Instead of actively forcing air into the lungs at predetermined intervals, PSV assists a patient who is attempting to breathe but is not strong enough to breathe completely on their own. PSV senses the patient’s effort to breathe and supports them by providing a positive air pressure. This positive pressure reduces the "work of breathing" (WOB) required by the patient. By altering the level of PSV given to a patient the clinician can control the work required by the patient. By gradually increasing the work needed for the patient to breathe, the clinician can slowly strengthen the patient’s muscles and wean them from the ventilator much faster than with standard ventilatory modes.

The vast majority of ventilators built today use a proportional flow control valve (PFCV) to deliver air to the patient. As the name implies, control signals to the valve determine the amount of air flow to the patient. PSV and other modes of ventilation, however, require a constant pressure in the patient, not a constant flow. Control algorithms are used to determine the flows required to maintain a constant pressure. Most ventilators, however, use antiquated PID controllers to implement this task. The result is that the ventilators create pressure waveforms that are far from optimal. Worse yet, the results will vary widely from patient to patient, forcing the ventilator manufacturer to tune the PID in a very conservative manner. The goal of this project was to create a pressure control algorithm that provides much better and consistent pressure waveforms. The typical goal of a PSV breath is to deliver as close to a square waveform of pressure once the patient’s effort to breathe is detected.

Ventilator Home | Next Page

Products | Support | Order | Download | Search | Contact

Product questions? Contact info@nd.com Website questions? Contact webmaster@nd.com
Web Site Design and Implementation Copyright © 2002 NeuroDimension, Inc.