According to one aspect of the present invention, there is provided ventilator apparatus comprising: a pump including a negative-pressure chamber having an inlet for drawing air into the chamber, and a positive-pressure chamber having an outlet for outletting pressurized air; delivery means for delivering pressurized air to a patient; an exhalation valve assembly producing breathing cycles in which the delivery means is first connected to the patient to effect inhalation, and then is vented to the atmosphere to permit exhalation; and a control valve operated by the pump for controlling the breathing cycles of the exhalation valve; characterized in that the pump is a cyclically-operated reciprocating pump is a cyclically-operated reciprocating pump and has a low volume-displacement, operates at a cyclical speed to effect at least 2 cycles of operation for each breathing cycle of the exhalation valve, and includes an expansible member in the flow path of the air from the positive pressure chamber to the delivery means to damp oscillations produced by the reciprocating pump.
In the described preferred embodiment, the low volume displacement pump includes two pistons reciprocated within a cylinder, each of the pistons having a diameter of less than 40 mm, preferably about 32 mm (1.25 inch), and is operated at about 20-30 cycles per breath. A pump having this order of displacement is considered to be a low volume-displacement pump, as distinguished from that commonly used in the present portable ventilators, operated at a speed of one cycle per breath, and having a piston diameter of 250-280 mm (10-12 inches). The novel construction, using a low volume-displacement pump operated at a high cyclical speed (each cycle of operation including a suction stroke and a pressure stroke), as distinguished from the large volume-displacement pumps operated at a relative low cyclical speed in existing ventilators, and including an expansible member, enables the ventilator of the present application to be selectively operated to perform the different functions of the many different types of existing ventilators as described above. The novel construction also more accurately meters the quantity of air supplied, and even obviates the need for seals between the pistons and the cylinder.
According to another feature, the ventilator apparatus further includes an air inlet into the negative-pressure chamber, an oxygen inlet into the negative-pressure chamber, and proportioning means controlling the proportion of the air and oxygen inletted via their respective inlets.
According to a still further feature, the ventilator apparatus further includes a relief valve communicating with the delivery means for preventing the pressure in the delivery means from rising above a predetermined peak; a sensor for sensing the pressure in the delivery means; and control means effective to energize the pump when the sensed pressure in the delivery means is below the peak value, and to deenergize the pump when the sensed pressure is substantially equal to the peak value.
The latter feature makes the novel ventilator apparatus particularly useful as a CPAP ventilator for alleviating obstructive apnea during sleep. In this application, the relief (i.e., the PEEP) valve would be set at a predetermined peak pressure, and the sensor and its control systems (i.e., the storage device and the comparator circuit in the described preferred embodiment) would be effective to intermittently operate the pump so as to avoid wasting power, as well as oxygen and moisture when oxygen and moisture are supplied with the pressurized air to the patient. This makes the CPAP ventilator very efficient and quiet, and enables it to save oxygen and moisture, as well as electrical power. Also, the electrical sensing circuit senses the PEEP pressure upon each exhalation cycle, and memorizes it so that it controls the pump according to that pressure, thereby eliminating the need for any adjustment on behalf of the user.