1. Field of the Invention
The present invention is broadly concerned with an improved ventilator compressor system adapted for use with as a part of or in conjunction with a medical ventilator. More particularly, the invention is concerned with such compressor systems which include a hollow fiber membrane drying module for dehumidifying pressurized air from a compressor and significantly reducing the dew point pressure thereof; this insures that compressed air delivered to the ventilator is free of condensed water. Preferably, a recycle line is provided for delivery of pressurized, dehumidified air back to the compressor inlet during low demand operation of the system, to reduce the moisture level of incoming air to the compressor.
2. Description of the Prior Art
Many critically ill patients require breathing assistance by way of supplemental oxygen or through the use of a ventilator. A ventilator either forces pressurized gas into the lungs (a positive pressure ventilator) or expands the chest cavity of the patient to draw gas into the lungs (a negative pressure ventilator). Ventilators typically provide mixtures of pressurized air and oxygen to a patient according to a prescribed schedule, such as a specific pressure profile or a specific gas volume delivery profile over time. Moreover, many ventilators can be adjusted to either force breaths or respond only to a patient's attempts to breath and assist in such breathing, or operate in some more complex pattern.
In order to provide a source of pressurized air, ventilators may be coupled to hospital wall air which provides high quality, dehumidified and pressurized air. To this end, many hospital wall systems employ dryers in the pressurized air lines for dehumidification purposes, typically refrigerant or desiccant dryers. Membrane type dryers have also been used in this context. In addition, portable ventilators are commonly equipped with a portable compressor system either to meet the full demand of the ventilator or as a backup for ventilators using hospital wall air. A problem with such portable compressor systems is that they tend to provide high humidity air which can condense and cause damage to internal components of the ventilator and potentially loss of breath support to a patient. Previous methods for controlling humidity in such compressor systems has included the use of copper coils or heat exchangers for cooling and condensing of compressor output air. The cooling of such copper coil or heat exchanger occur within the confines of the compressor module itself, and is therefore warmer than ambient air outside the compressor module. Therefore, any outlet air that is exposed to ambient air can cool and cause condensation of the saturated air delivered to the ventilator. A typical solution is to compress the gas to above the required output pressure, pass it through a heat exchanger/condenser, and then regulate it down to a lower pressure. This expands the partially de-humidified air to try to bring the dew point below the ambient temperature. The problems introduced by this approach are decreased efficiency (to overpressurize the air), added heat in the compressor, decreased compressor life, and potential for inadequate dew point depression if the heat balance and pressure ratios are not adequate for all potential environments and air demand conditions.