Importance

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Abstract

A gas flow rate control device for a medical ventilator includes a variable-orifice valve for adjustment of the peak flow rate, and a waveform regulator which supplies controlled gas pressure to the orifice. The regulator maintains a fixed pressure differential between the upstream side of the orifice and a reference pressure. The reference pressure is variable between atmospheric pressure and a pressure which is essentially patient airway proximal pressure. When the reference pressure is patient airway proximal pressure, a constant pressure differential is maintained across the orifice so that a uniform flow rate is maintained. When the reference pressure is atmospheric pressure, a constant pressure is supplied to the upstream side of the orifice, so that the flow rate from the orifice decreases as patient airway proximal pressure on the downstream side of the orifice increases. In one embodiment, the invention uses a pneumatic switch to supply, as the reference pressure, either airway proximal pressure, whereby a uniform flow rate or 'square wave' is obtained, or atmospheric pressure, whereby a fixed flow rate deceleration or 'taper wave' is obtained for any given peak flow rate setting of the variable orifice. In another embodiment, a valve is used to vary the reference pressure between atmospheric pressure and airway proximal pressure to obtain adjustable values of flow rate deceleration for any given setting of the peak flow orifice.

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First Claim