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A portable mechanical ventilator having a Roots blower is configured to provide a desired gas flow and pressure to a patient circuit. The mechanical ventilator includes a flow meter operative to measure gas flow produced by the Roots blower and an exhalation control module configured to operate an e

A portable mechanical ventilator having a Roots blower is configured to provide a desired gas flow and pressure to a patient circuit. The mechanical ventilator includes a flow meter operative to measure gas flow produced by the Roots blower and an exhalation control module configured to operate an exhalation valve connected to the patient circuit. A bias valve connected between the Roots blower and the patient circuit is specifically configured to generate a bias pressure relative to the patient circuit pressure at the exhalation control module. The bias valve is further configured to attenuate pulsating gas flow produced by the Roots blower such that gas flowing to the mass flow meter exhibits a substantially constant pressure characteristic. The bias pressure facilitates closing of the exhalation valve at the start of inspiration, regulates positive end expiratory pressure during exhalation, and purges sense lines via a pressure transducer module.

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1. An apparatus for use with a gas source for producing gas flow to a receiver circuit, comprising; a first valve connected to the receiver circuit;a control module configured to control the first valve;a second valve connected between the gas source and the receiver circuit, wherein the second valv

1. An apparatus for use with a gas source for producing gas flow to a receiver circuit, comprising; a first valve connected to the receiver circuit;a control module configured to control the first valve;a second valve connected between the gas source and the receiver circuit, wherein the second valve is configured to provide an elevated drive pressure at the control module relative to a downstream pressure at the receiver circuit;a poppet disposed within the second valve, the poppet having a mass sufficient to generate inertial damping of a gas flow between the gas source and the second valve, wherein the gas flow is received from the gas source. 2. The apparatus as claimed in claim 1, wherein the gas source includes a blower assembly. 3. The apparatus as claimed in claim 2, wherein the blower assembly includes a Roots blower. 4. The apparatus as claimed in claim 2, wherein the receiver circuit includes a patient circuit. 5. The apparatus as claimed in claim 4, wherein the control module includes an exhalation control module and an exhalation valve. 6. The apparatus as claimed in claim 5, further comprising: a pressure transducer module fluidly connected to the second valve, wherein the pressure transducer module receives a bias pressure due to the elevated drive pressure;a sense line system including at least one of an airway sense line and a flow sense line connected between the patient circuit and the pressure transducer module, wherein the pressure transducer module is operative to purge the sense line system using the bias pressure. 7. The apparatus as claimed in claim 4, wherein: the blower assembly is controlled by a blower control algorithm; and the second valve and blower control algorithm collectively regulates flow into and out of the patient circuit during performance of at least one of the following user-activated maneuvers: inspiratory-hold, expiratory-hold and regulation of mean inspiratory pressure/negative inspiratory force (MIP/NIF). 8. The apparatus as claimed in claim 2, wherein the second valve is configured to provide a substantially constant pressure differential across a flow range of the blower assembly. 9. The apparatus as claimed in claim 2, further comprising a flow meter interposed between the blower assembly and the second valve, wherein the flow meter is operative to measure a gas flow rate of the blower assembly. 10. The apparatus as claimed in claim 9, wherein the gas flow produced by the blower assembly is a pulsating gas flow. 11. The apparatus as claimed in claim 10 wherein: the second valve includes a cylinder and a poppet being configured to be reciprocatively slidable within the cylinder to define a substantially narrow poppet clearance between the poppet and cylinder, and wherein the poppet clearance is sized to generate viscous damping of the pulsating gas flow when gas passes through the poppet clearance during poppet reciprocation. 12. A ventilator apparatus comprising: a patient circuit;a blower assembly that produces a gas flow to the patient circuit;an exhalation valve connected to the patient circuit;an exhalation control module configured to operate the exhalation valve; anda bias valve connected between the blower assembly and the patient circuit, wherein the bias valve is configured to provide a bias pressure to the exhalation control module, the bias valve comprising a cylinder and a poppet, the poppet configured to be reciprocatively slidable within the cylinder to define a substantially narrow poppet clearance between the poppet and the cylinder, and the poppet clearance sized to generate viscous damping of the gas flow when gas passes through the poppet clearance during poppet reciprocation. 13. The ventilator apparatus of claim 12, wherein the bias valve is configured to provide a substantially constant bias pressure across a flow range of the blower assembly. 14. The ventilator apparatus of claim 12, wherein: the blower assembly is controlled by a blower control algorithm;the bias valve and blower control algorithm collectively regulate flow into and out of the patient circuit during performance of at least one of the following user-activated maneuvers:inspiratory-hold, expiratory-hold and regulation of mean inspiratory pressure/negative inspiratory force (MIP/NIF). 15. The ventilator apparatus of claim 12, further comprising: a pressure transducer module fluidly connected to the bias valve, wherein the pressure transducer module receives the bias pressure;a sense line system including at least one of an airway sense line and a flow sense line connected between the patient circuit and the pressure transducer module, wherein the pressure transducer module is operative to purge the sense line system using the bias pressure. 16. The ventilator apparatus of claim 12, further comprising: a flow meter interposed between the blower assembly and the bias valve, wherein the flow meter is operative to measure a gas flow rate of the blower assembly. 17. The ventilator apparatus of claim 16, wherein the gas flow produced by the blower assembly is a pulsating gas flow. 18. The ventilator apparatus of claim 17, wherein the poppet has a mass sufficient to generate inertial damping of the pulsating gas flow for measurement by the flow meter. 19. A bias valve apparatus for use with a gas source producing a gas flow and a flow-receiving device fluidly connected to and located downstream of the bias valve apparatus, comprising: a gas-receiving end and a gas-excreting end;a valve seat that receives fluid flow from the gas source at the gas receiving end of the bias valve apparatus;a poppet engageable to the valve seat wherein the poppet alternates between closed and open positions for respectively preventing and allowing gas to flow out of the bias valve apparatus;a spring configured to bias the poppet against the valve seat such that an elevated drive pressure is provided at the gas-receiving end of the bias valve apparatus relative to a downstream pressure of the flow-receiving device;a pressure transducer module fluidly connected to receive the elevated drive pressure; anda sense line system including at least one of an airway and flow sense line connected between the flow-receiving device and the pressure transducer module, wherein the at least one of an airway and flow sense line module is configured to measure pressure and flow at the flow-receiving device and the pressure transducer module is operative to purge the sense line system using the drive pressure. 20. The bias valve apparatus as claimed in claim 19, wherein the gas source includes a blower assembly. 21. The bias valve apparatus as claimed in claim 20, wherein the blower assembly includes a Roots blower. 22. The bias valve apparatus as claimed in claim 20, wherein the flow-receiving device includes a patient circuit connected to the gas-excreting end of the bias valve apparatus. 23. The bias valve apparatus as claimed in claim 22, further comprising: an exhalation control module connected to the gas-receiving end of the bias valve apparatus; and an exhalation valve controlled by the exhalation control module and connected to the patient circuit. 24. The bias valve apparatus of claim 20, wherein the bias valve apparatus is configured for use in conjunction with a ventilator apparatus having a flow meter interposed between the blower assembly and the bias valve apparatus and wherein the flow meter is operative to measure a gas flow rate of the blower assembly. 25. The bias valve apparatus of claim 24, wherein the gas flow produced by the blower assembly is a pulsating gas flow; and the poppet has a mass sufficient to provide inertial damping of the pulsating gas flow for measurement by the flow meter. 26. The bias valve apparatus of claim 25, further comprising a mass element attached to the poppet, wherein: the poppet reacts against the pulsating gas flow at a forcing frequency;the poppet and the spring are reciprocative at a poppet natural frequency; andthe poppet and mass element are sized and configured to provide the highest degree of inertial damping when the forcing frequency is substantially higher than the poppet natural frequency. 27. The bias valve apparatus of claim 25, wherein the bias valve apparatus is configured to provide viscous damping of the pulsating gas flow for measurement by the flow meter. 28. The bias valve apparatus of claim 27, wherein the bias valve apparatus is configured to maximize viscous damping when the forcing frequency is substantially equal to the poppet natural frequency. 29. The bias valve apparatus of claim 24, wherein the flow meter is configured as a heated wire mass flow meter. 30. The bias valve apparatus of claim 19, wherein the spring has a spring constant sufficient to bias the poppet against the valve seat such that the elevated drive pressure is substantially constant across a flow range of the gas source. 31. The bias valve apparatus of claim 19, wherein the bias valve apparatus is configured to provide a drive pressure sufficient to prevent flow into and out of the flow- receiving device during performance of a user-activated maneuver. 32. The bias valve apparatus of claim 31, wherein the user-activated maneuver includes at least one of the following: inspiratory-hold, expiratory-hold and regulation of mean inspiratory pressure/negative inspiratory force (MIP/NIF). 33. A ventilator apparatus comprising: a blower assembly producing a pulsating gas flow;an exhalation control module;an exhalation valve connected to the patient circuit;a patient circuit, wherein the exhalation control module is configured to operate the exhalation valve; anda bias valve comprising: a valve seat connected to the blower assembly;a poppet engageable to the valve seat, the poppet configured to be reciprocatively slidable within a cylinder to define a substantially narrow poppet clearance between the poppet and the cylinder, to generate viscous damping of the pulsating gas flow when gas passes through the poppet clearance during poppet reciprocation, wherein the poppet alternates between closed and open positions for respectively preventing and allowing gas to flow from the blower assembly to the patient circuit; anda spring configured to bias the poppet against the valve seat such that a bias pressure is provided at the exhalation control module for regulation of the exhalation valve, wherein the exhalation control module is fluidly connected to one side of the bias valve and the patient circuit is fluidly connected to an opposite side thereof.