The present invention relates to ventilator apparatus, and particularly to portable ventilator apparatus useful for providing mechanical ventilation of a patient at home or during transport.

Ventilating apparatus is widely used for mechanically forcing air into the lungs of a patient requiring ventilatory assistance. Some ventilators are designed for continuous use in hospitals, such as in intensive care units; and others are designed as portable units for use in the home or during transport. Examples of the latter are described in U.S. Pat. Nos. 3,499,601, 4,215,681 and 4,493,614. The present invention is particularly applicable to ventilators of the portable type for use in the home or during transport.

Ventilators are usually also divided into the following types:

1. Pressure ventilators, usually including a source of compressed air administered by a solenoid valve at a rate of one cycle per breath, 10-30 breaths per minute.

2. Volume ventilators, usually including a large reciprocating piston driven by an electric motor for compressing air into the patient's lungs at a preset fixed volume with the cycling frequency of one cycle per breath, 5 to 40 breaths per minute.

Both of the above type ventilators usually include large-size pistons (e.g., 10-12 inch diameters) having sealing surfaces with respect to the cylinders in which they move, and in general are characterized by bulky construction precluding portability, high power consumption because of continuous operation precluding the use of batteries, and/or poor control of the volume the patient inhales with each breath. Such ventilators are also generally characterized by inability to attain high frequencies required for baby respiration, poor control of the volumes when they are set very low since the piston stroke becomes very critical, and/or poor mechanical efficiency since most of the energy is expended in overcoming friction in the piston seal and in the transmission from the motor to the piston.

3. Continuous positive airway pressure (CPAP) ventilators, usually including a compressor providing continuous positive pressure at a low pressure level. Such ventilators are commonly used only for applying a positive pressure to the patient's lungs in order to help alleviate obstructive apnea during sleep while the patient breathes against the continuous pressure. The presently used CPAP ventilators generally include small turbines, such as vacuum cleaner turbines, generating high air flow rates with low pressure, and a relief valve, commonly called a "PEEP" (Positive End Expiratory Pressure) valve, which releases the pressure to the atmosphere when the pressure in the delivery conduit rises above a predetermined value. However, such known CPAP ventilators are usually not only noisy but also wasteful of power, oxygen and moisture since they generate air flow far in excess of the patient's needs and while the patient is exhaling.

4. High-frequency positive-pressure ventilators, in which a source of compressed air is controlled to deliver air to the patient at controlled volumes and at rates between 60 and 120 breaths per minute. Such ventilators are usually of bulky construction and therefore are primarily used in clinical applications.

5. High-frequency jet ventilators, which include compressors delivering high pressure air directly to the lungs at frequencies of up to 400 cycles per minute.