Passive, Proportional, Valveless Gas Sampling and Delivery

Respiratory gas analysis is widely used in indirect calorimetry to measure oxygen consumption and carbon dioxide production, and derive metabolic parameters such as energy expenditure and respiratory exchange ratio. Traditional metabolic carts provide accurate measurements by collecting and mixing exhaled breaths, but their multi-liter mixing chambers, gas sensors, flow sensors, and supporting equipment make them relatively large and poorly suited to unrestricted mobile use. Portable breath-by-breath systems eliminate the large chamber, but they require rapid measurements of gas concentration and flow, together with careful temporal alignment of signals from physically separated sensors. Conventional respiratory systems also commonly rely on pumps and mechanical check valves to direct or sample airflow. These components can increase size, complexity, cost, respiratory burden, and calibration requirements. Constant-rate side-stream sampling introduces an additional measurement problem because it can disproportionately sample low-flow portions of an exhalation and can bias measured gas concentrations; the patent reports an example in which constant-rate sampling produced nearly a 10% energy-expenditure error for one breath. Similarly, conventional inhalers can require coordinated actuation and inhalation, and may lose medicine through environmental release or deposition in the mouth and throat. A passive system that uses respiratory airflow itself to perform directional, proportional sampling or delivery can address these limitations without adding active flow-control hardware.

Technology Description

This technology uses a specially shaped flow tube as a fluid-dynamic valve that selectively directs a proportional fraction of a person's breath without requiring active pumps or mechanical valves. In gas-sampling mode, an impedance such as a constriction creates a pressure differential during exhalation that diverts a fraction of each breath into a mixing chamber at a rate proportional to the instantaneous respiratory flow. When the user inhales, the flow geometry produces little or no pressure difference across the sampling ports, preventing ambient air from diluting the collected sample. The proportional samples can be mixed across multiple breaths and analyzed for oxygen, carbon dioxide, volatile organic compounds, water vapor, and other constituents. The same fluidic principle can be operated in the opposite direction to proportionally introduce aerosolized, powdered, vaporized, or liquid medicine into inhaled air. Unlike conventional metabolic carts that collect large volumes of exhaled breath or portable breath-by-breath systems that require high-speed sensors, pumps, and precise synchronization between gas concentration and flow measurements, this approach performs proportional sampling passively. Sampling only a small fraction of each breath can dramatically reduce the required mixing-chamber volume while preserving representative gas concentrations; the patent describes, for example, reducing a nominal 3-liter chamber to approximately 30 mL with 1% proportional sampling. The passive architecture can also accommodate slower, less expensive sensors and eliminates moving parts from the flow tube. For drug delivery, the same approach naturally meters and mixes medicine with the inhaled airflow over one or multiple breaths, reducing dependence on precise inhaler actuation timing and potentially reducing medicine lost to the environment or deposited in the mouth and throat.