The assessment of gas exchange by automated analysis of O 2 and CO 2 alveolar to arterial differences
International journal of clinical monitoring and computing(1986)
摘要
Summary A computer program to measure breath by breath alveolar pressure (PA) and alveolar to arterial difference (AaD) for O2 and CO2, by a mass-spectrometer has been implemented. The program allows the determination of alveolar gas by different methods:
1. Bohr's equation (BE); 2. ideal alveolar air equation for O2 (IDO2); 3. end-tidal (ET); 4. by the Rahn's definition of ‘mean alveolar gas’, i.e., alveolar pressures are defined when instantaneous
respiratory exchange ratio (IRQ) equals mean respiratory exchange ratio (MRQ). This automated technique has been used in 16
patients with chronic obstructive lung disease (COLD) and 15 patients with pulmonary embolism (APE). In both groups of patients
it was always possible to find in each breath the point where IRQ=MRQ and therefore to measure AaD by RD. IDO2 was significantly lower than PAO2 by the other methods. Also ET values of O2 and CO2 were significantly different from RD and BE in both groups of patients, however the difference was consistently higher in
COLD patients. The different shape of the expirograms (steeper expirograms in COLD) is responsible for this different result.
RD and BE AaD characterize gas exchange more precisely than ET, because the contribution of high VA/Q units is also evaluated.
This is particularly important in COLD patients.
Consideration on dead space measurements are also reported both for COLD and APE patients. In conclusion this automated technique
provides the assessment of gas exchange for the use in clinical respiratory physiology and for the monitoring of gas-exchange
in critically ill patients.
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关键词
complete program, gas exchange, respiratory failure, pulmonary embolism
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