Importance

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Abstract

A method and device for effective delivery of a gas such as oxygen for inhalation is provided by sequentially diluting room air to the flow of gas during a respiratory cycle. A mask assembly is described that comprises an inspiratory and expiratory limb each containing a very low resistance one-way valve, and a sequential dilution conduit (leading from the atmosphere to the inspiratory limb) with a one-way valve that has a slightly positive cracking pressure. A gas reservoir is also attached to the inspiratory limb. During expiration, the reservoir is filled with oxygen, for example, flowing from the oxygen source. During inspiration, oxygen from the oxygen source and the reservoir are drawn preferentially. If the oxygen flow is equal to or greater than the minute ventilation of the subject, no atmospheric air is entrained into the mask assembly and the subject gets pure oxygen. If the minute ventilation (tidal volume) exceeds the oxygen flow, the reservoir is depleted. The sequential dilution valve subsequently opens and the remainder of the inspired gas is drawn from the atmosphere. Because the gas is inhaled sequentially, i.e., oxygen then room air, the alveoli receive pure oxygen, while room air inspired at the end of inspiration is delivered to the anatomical dead space of the respiratory system. Thus, due to the sequential delivery of oxygen and air, the minimum oxygen flow needed to provide an FIO2 of 1.0 is equal to the alveolar, not minute, ventilation, i.e., only about 2/3 of the minute ventilation at rest. The mask assembly delivers 100% or less than 100% oxygen to the alveolus while using significantly lower flow rate than conventional masks.

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