Non-invasive measurement of the mean alveolar O(2) tension from the oxygen uptake versus tidal volume curve.
OBJECTIVE
The classical equations for measuring the mean and the ideal alveolar O(2) tension are based on assumptions, which are shown to be invalid. So we thought to develop a new, non-invasive method for measuring the mean alveolar P,O(2) within the volume domain (PA,O(2(Bohr))). This method is based on the oxygen uptake vs. tidal volume curve (VO(2) vs. VT) obtained during tidal breathing of room air and/or air enriched with oxygen.


METHODS
PA,O(2(Bohr)) and the ideal alveolar PO(2) (PA,O(2(ideal))) were simultaneously measured in 10 healthy subjects and 34 patients suffering from chronic obstructive pulmonary disease (COPD) breathing tidally room air at rest. Additionally, 10 subjects (three healthy subjects and seven COPD patients) were studied while breathing initially room air and subsequently air enriched with oxygen.


RESULTS
According to the results, PA,O(2(Bohr)) considerably differed from PA,O(2(ideal)) (P = 0.004). The cause of the difference, at the individual's R, is: (1) the difference between the arterial and Bohr's alveolar CO(2) tension, mainly in COPD patients, and (2) the inequality between Bohr's alveolar part of the tidal volume for CO(2) and O(2). Furthermore, end-tidal gas tension (PET,CO(2) and PET,O(2)) differed from Pa,CO(2) and PA,O(2(Bohr)) respectively.


CONCLUSIONS
The deviation of PA,O(2(Bohr)) from PA,O(2(ideal)) has a definite impact on Bohr's dead space ratio for O(2) and CO(2), and on the alveolar-arterial O(2) difference. The difference (PA,O(2(Bohr)) - PA,O(2(ideal))) is not related to the pathology of the disease. So, gas exchange within the lungs should be assessed at the subject's R from PA,O(2(Bohr)) and PA,CO(2(Bohr)) but not from PA,O(2(ideal)) nor Pa,CO(2).
Jordanoglou
J
J
Respiratory Function Laboratory, Department of Respiratory Medicine, University of Athens Medical School, 'Sotiria' Hospital for Diseases of the Chest, Athens, Greece. jbj@hol.gr
Latsi
P
P
Chroneou
A
A
Koulouris
N G
NG
D000280:Administration, Inhalation; D000328:Adult; D000368:Aged; D000465:Algorithms; D001944:Breath Tests; D002245:Carbon Dioxide / Q000032:analysis / Q000097:blood; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000378:metabolism*; D029424:Pulmonary Disease, Chronic Obstructive / Q000378:metabolism; D011659:Pulmonary Gas Exchange; D013990:Tidal Volume
D002245:Carbon Dioxide; D010100:Oxygen