Abstract: A method and apparatus for non-invasive assessment of lung inhomogeneity by accurate high temporal resolution measurement of respiratory gas flows at the mouth during steady state breathing and inert gas wash-in or wash-out and using these measurements to fit a mathematical model of the inhomogeneous lung. The model of the lung is based on modelling the lung as plural alveolar compartments each having an identical volume at functional residual capacity, but varying in its fractional share of total lung compliance, total pulmonary vascular conductance and total anatomical deadspace. A bivariate log-normal distribution of the lung compliance and pulmonary vascular conductance is used, together with a normal distribution of deadspace fraction.

Abstract: A molecular flow sensor includes a flowmeter integrated with an in airway laser gas analyser. The laser gas analyser spectroscopically analyses the concentrations of gases in a measurement space. The gas flow is measured by measuring the pressure drop across the flow-sensing mesh screens using a differential pressure sensor. Helical baffles are provided upstream and downstream of the measurement space to provide a low resistance gas flow path while blocking ambient light from entering the measurement space, and flow-conditioning elements of mesh or metal foam are provided between the helical baffles and the flow-sensing meshes. Pressure averaging is conducted circumferentially around the gas flow path. At least two independent pressure sensors may be provided, switchable out independently to allow regular calibration while the other is still measuring. The flow sensor is particularly useful for measuring respiratory gas exchange such as oxygen consumption or carbon dioxide production by a respiring subject.

Abstract: A device for measuring oxygen uptake and carbon dioxide production by a respiring subject based on the use of absorption spectroscopy. An absorption spectrometer using cavity enhanced absorption spectroscopy at 763 nm to measure oxygen concentration and direct absorption or wavelength modulation spectroscopy at 2.0035 ?m for carbon dioxide concentration is incorporated into a breathing tube in proximity to the respiring subject. This provides measurements of oxygen and carbon dioxide concentration with a good temporal resolution which can be combined with measurements of flow rate as a function of time to obtain oxygen uptake and carbon dioxide production on a breath-by-breath basis. The device can also measure the concentration of water vapour and of anaesthetic gases in exhaled breath.