ABSTRACT
The worldwide poliomyelitis epidemic in the middle of the twentieth century resulted in many cases of ventilatory failure. An ingenious, albeit palliative, answer to this type of ventilatory failure was the development of the iron lung, an external negative pressure ventilator that saved the lives of countless patients who developed respiratory failure during the epidemic. Assisted ventilation was instituted not to restore the function of the motor neurons, but to take over the work of the failing muscles. Even though poliomyelitis is now very infrequent in the developed parts of the world, the use of ventilators has increased and the machines have evolved in sophistication and capability. Close to half of all patients admitted to intensive care units require mechanically assisted ventilatory support. Almost all the ventilatory support currently uses positive rather than negative pressure, but the overall aims and principles remain the same: to be as unobtrusive and effective as possible. In addition, the incorporation of microprocessor technology to mechanical ventilation has resulted in a giant leap forward in the way machines can operate under difficult and frequently changing physiologic conditions. Respiratory patterns can be altered to satisfy an individual patient's needs and to fulfill specific therapeutic goals.
