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  • 1
    Electronic Resource
    Electronic Resource
    Sensitivity of CO2 washout to changes in acinar structure in a single-path model of lung airways (1991)
    Springer
    Annals of biomedical engineering 19 (1991), S. 679-697 
    Details
    ISSN: 1573-9686
    Keywords: Convection ; Diffusion ; Pulmonary gas exchange ; Numerical model ; Phase III slope
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A numerical solution of the convection-diffusion equation with an alveolar source term in a single-path model (SPM) of the lung airways simulates steady state CO2 washout. The SPM is used to examine the effects of independent changes in physiologic and acinar structure parameters on the slope and height of Phase III of the single-breath CO2 washout curve. The parameters investigated include tidal volume, breathing frequency, total cardiac output, pulmonary arterial CO2 tension, functional residual capacity, pulmonary bloodflow distribution, alveolar volume, total acinar airway cross sectional area, and gas-phase molecular diffusivity. Reduced tidal volume causes significant steepening of Phase III, which agrees well with experimental data. Simulations with a fixed frequency and tidal volume show that changes in blood-flow distribution, model airway cross section, and gas diffusivity strongly affect the slope of Phase III while changes in cardiac output and in pulmonary arterial CO2 tension strongly affect the height of Phase III. The paper also discusses differing explanations for the slope of Phase III, including sequential emptying, stratified inhomogeneity, and the issue of asymmetry, in the context of the SPM.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368076
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Noninvasive recovery of acinar anatomic information from CO2 expirograms (1994)
    Springer
    Annals of biomedical engineering 22 (1994), S. 293-306 
    Details
    ISSN: 1573-9686
    Keywords: Airway convection-diffusion ; Pulmonary function ; Emphysema ; Noninvasive pulmonary measurement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract A numerical single path model of respiratory gas exchange with distributed alveolar gas sources was used to estimate the anatomical changes in small peripheral airways such as occur in chronic obstructive pulmonary diseases (COPD). A previous sensitivity analysis of the single path model showed that decreasing total acinar airway cross-sectional area by an area reduction factor, R, results in computed gas expirograms with Phase III steepening similar to that observed in COPD patients. From experimental steady state CO2 washout data recorded from six healthy subjects and six COPD patients, optimized area reduction factors for the single path model were found that characterize peripheral airway anatomy for each subject. Area reduction factors were then combined with measured functional residual capacity data to calculate the normalized peripheral airspace diameters in a given subject, relative to the airspace diameters in the generations of an idealized standard lung. Mean area reduction factors for the patient subgroup were 63% of those for the healthy subgroup, which is related to the gas transport limitation observed in disease. Mean airspace sizes for the patient subgroup were 235% of the healthy subgroup, which characterizes the increase in size and reduction in number of peripheral airspaces due to tissue erosion in emphysema. From these results, the air-phase diffusive conductance in COPD patients was calculated to be 32% of the mean value in the healthy subjects. These findings correlated well with standard pulmonary function test data for the patients and yield the recovery of acinar airway information from gas washout by combining the single path model with experimental measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368236
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Evaluation of heavy water for indicator dilution cardiac output measurement (1989)
    Springer
    Journal of clinical monitoring and computing 5 (1989), S. 236-242 
    Details
    ISSN: 1573-2614
    Keywords: Monitoring: cardiac output ; Measurement techniques: indicator dilution thermodilution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine
    Notes: Abstract We evaluated deuterium oxide (D2O) as a tracer for cardiac output measurements. Cardiac output measurements made by thermodilution were compared with those made by indicator dilution with D2O and indocyanine green as tracers. Five triplicate measurements for each method were made at intervals of 30 minutes in each of 9 anesthetized, mechanically ventilated goats. Cardiac output ranged between 0.68 and 3.79 L/min. The 45 data points yielded a correlation coefficient of 0.948 for the comparison of D2O indicator dilution cardiac output measurements with thermodilution measurements and a linear regression slope of 1.046. D2O indicator dilution measurements were biased by −0.11±0.22 L/min compared with thermodilution measurements and had a standard deviation of ±0.12 L/min for triplicate measurements. Hematocrits ranging between 20 and 50 vol% had no effect on optical density for D2O. D2O is more stable than indocyanine green and approximately one-tenth the price (40 cents per injection compared with $4). The basic instrumentation cost of approximately $9,000 is an additional initial expense, but provides the ability to perform pulmonary extravascular water measurements with a double-indicator dilution technique. D2O has potential as a tracer for the clinical determination of indicator dilution cardiac output measurements and pulmonary extravascular water measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01618253
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Micropore membrane inlet mass spectrometer probes suitable for measurement of tissue surface gas tensions (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 563-571 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: New membrane inlet mass spectrometer (MIMS) probes are described that feature a micropore in a flat metal surface filled with a polymer membrane (Krytox high-vacuum fluorinated grease). In vitro assessment of spatial resolution, time response, stirring effect and calibration are reported. The small membrane area for this MIMS results in spatial resolution of about 30 μm, adequate for measuring gas tensions at an exposed tissue surface in experimental studies of tissue oxygenation and tissue gas exchange. These probes offer a unique combination of minimal stirring effect and rapid response speed for measurements of gas partial pressures in the per cent range in aqueous solutions. Several gases, including oxygen, carbon dioxide, helium, sulfur hexafluoride and argon, permeate the polymer membrane to give a detectable signal, and the membrane is highly impermeable to water. Membrane dimensions were calculated from time response characteristics and the measured gas sample rate for argon. The membrane area was independently confirmed by direct assessment of spatial resolution. This MIMS is highly linear, has an excellent signal-to-noise ratio and offers practical advantages over electrode approaches to the measurement of gas tensions in aqueous solution.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300407
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    Paper (German National Licenses)
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