THE PROBLEMS RELATED TO BREATH-BY-BREATH MEASUREMENT OF RESPIRATORY GAS EXCHANGE

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  • Breath-by-breathによるガス交換測定法における問題点の検討
  • Breath by breath ニ ヨル ガス コウカン ソクテイホウ ニ

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The problems of breath-by-breath measurement of respiratory gas exchange to analyze the transient responses during complex load work are described and treated. With review for the experimental systems developed by other investigators, our signal transducers and data processing were improved. We found the computer-processed data were in good agreement with those obtained from simultaneous Douglas bag gas collection.<BR>1) Errors in the measurement of volume arose from errors in the flow signals such as nonlinearity, base-line drift, noise, and frequency response, as well as composition and temperature of gas, water vapor condensation, quantization errors, and breathing valve leakage. ±1.74% error in the flow integration reproducibility resulted from the modification of the upstream geometry of the pneumotachometer and the pressure tubing as well as a compensation for base-line drift and filter smoothing.<BR>2) Errors in the gas concentration signals were attributed to inaccuracy, drift, noise, and water vapor concentration. The transport delay of gas concentration signals was overestimated in order to cancel the underestimation in Vco2and Vo2·Other compensation methods for the response time were discussed.<BR>3) Error magnitudes below±0.97% in the A/D amplitude quantization were found by means of signal simulation.<BR>4) The optimal compromises between breath recognition threshold and the fluctuation in flow signal were examined to permit identification of irregular breath.<BR>5) Since the breathing valve dead space was modified to tidal volume dependent, errors in the gas exchange variables were reduced.<BR>6) To validate the accuracy of the equipment operation and the gas exchange algorithm, problems in signal simulation and the model lung were described.

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