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A New Noninvasive Method of Measuring Pulmonary Gas Exchange in Patients with Lung Disease
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A5847 - A New Noninvasive Method of Measuring Pulmonary Gas Exchange in Patients with Lung Disease
Author Block: J. B. West1, D. L. Wang2, G. Prisk3; 1Univ of California At San Diego, La Jolla, CA, United States, 2Nedicine, Univ of California At San Diego, La Jolla, CA, United States, 3Medicine, Univ of California At San Diego, La Jolla, CA, United States.
Rationale: We have developed a noninvasive method for measuring gas exchange in patients with lung disease, and so reduce the need for repeated arterial punctures.
Methods: The patient breathes through a mouthpiece and the Inspired and expired PO2 and PCO2 are continually measured by small rapidly responding analyzers. The arterial PO2 is calculated from the oximeter reading and the oxygen dissociation curve, using the end-tidal PCO2 to allow for the Bohr effect. The PO2 difference between the end-tidal gas and the calculated arterial value is called the Oxygen Deficit.
Results: Measurements on 31 normal subjects showed that the Oxygen Deficit is very small with a mean value of 2 mm Hg in young subjects, and a modest increase with age. Measurements on outpatients with lung disease gave much higher values with a mean Oxygen Deficit of 49 mm Hg. The Oxygen Deficit is related to the classical Alveolar-arterial PO2 difference based on ideal alveolar gas. However that traditional index is heavily biased by lung units with low-ventilation perfusion ratios, whereas the new index has a broader physiological basis because it includes contributions from the whole lung. A major advantage of the Oxygen Deficit is that an arterial sample is not required.
Conclusion: The results to date suggest that the new method will be valuable in assessing hypoxemia in the clinical environment
Author Block: J. B. West1, D. L. Wang2, G. Prisk3; 1Univ of California At San Diego, La Jolla, CA, United States, 2Nedicine, Univ of California At San Diego, La Jolla, CA, United States, 3Medicine, Univ of California At San Diego, La Jolla, CA, United States.
Rationale: We have developed a noninvasive method for measuring gas exchange in patients with lung disease, and so reduce the need for repeated arterial punctures.
Methods: The patient breathes through a mouthpiece and the Inspired and expired PO2 and PCO2 are continually measured by small rapidly responding analyzers. The arterial PO2 is calculated from the oximeter reading and the oxygen dissociation curve, using the end-tidal PCO2 to allow for the Bohr effect. The PO2 difference between the end-tidal gas and the calculated arterial value is called the Oxygen Deficit.
Results: Measurements on 31 normal subjects showed that the Oxygen Deficit is very small with a mean value of 2 mm Hg in young subjects, and a modest increase with age. Measurements on outpatients with lung disease gave much higher values with a mean Oxygen Deficit of 49 mm Hg. The Oxygen Deficit is related to the classical Alveolar-arterial PO2 difference based on ideal alveolar gas. However that traditional index is heavily biased by lung units with low-ventilation perfusion ratios, whereas the new index has a broader physiological basis because it includes contributions from the whole lung. A major advantage of the Oxygen Deficit is that an arterial sample is not required.
Conclusion: The results to date suggest that the new method will be valuable in assessing hypoxemia in the clinical environment
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