Respirators have become widely used in a large variety of applications by hospitals and medical practitioners. Respirators may be used to cure diseases such as pulmonary edema, central nervous system depressions, tetanus neonatorum, asphyxia neonatorum, respiratory distress syndromes, hyaline membrane disease as well as many others.
There are many different respirators available some of which are designed for specific diseases and others of greater complexity to provide a multitude of operational modes for different physiological requirements. For example, some respirators provide intermittent positive pressure breathing (IPPB), either with or without a positive end expiratory pressure (PEEP). Other respirators may also provide such respiratory supports known as intermittent mandatory ventilation (IMV) whereby a patient may be provided with inspirations with relatively long expirations, or continuous positive airway pressure (CPAP) to provide oxygen or other breathable gas mixtures at a constant pressure on a continuous, as needed, basis.
Respirators may involve electrical controls such as described in the U.S. Pat. to Wilson, No. 3,191,595 or a pneumatic control as described in the U.S. Pat. to Hoenig, No. 3,604,415. An intermittent positive pressure breathing respirator is described in the U.S. Pat. to Liston, No. 3,434,471.
The Hoenig patent describes a respirator using three basic pneumatic logic elements. The flow of breathable gas to the patient is not continuous but interrupted by a logic element whose opening and closure is controlled by other logic devices.
The Wilson patent describes a respirator which senses pressures generated in the gas tube leading to the patient mask to initiate control and operation of a main control valve.
Other respirators known to be available in the art provide a patient connection tube with a continuous flow of gas. The gas flow is permitted to pass through to a control valve which exhausts the gas to ambient in a controllable manner to thereby provide respiratory support at the patient mask. Such respirators utilize complex and expensive controls to generate the desired respiratory support.