Gas exchange in chronic pulmonary disease.
Patients with asthma, chronic obstructive lung disease and diffuse interstitial fibrosis were studied. These three groups of patients illustrate very different patterns of VA/Q mismatching in general, consistent with the known pathology of their disease. Some common threads run through all three groups. One is that the level of hypoxemia in an individual depends critically on the interplay between mixed venous PO2 and the degree of VA/Q mismatching. Thus patients with a high cardiac output can have little hypoxemia in the face of severe VA/Q mismatching, while patients with inadequate cardiac output can have moderately severe hypoxemia with relatively little VA/Q mismatching. In other words, the arterial PO2 alone cannot indicate the severity of VA/Q mismatch in any given situation. Another generalization that can be made is that in the obstructive diseases, evidence from our work suggests that it is obstruction due to mucus secretions and/or airway edema and inflammation that is important in causing areas of low VA/Q to be present. Bronchoconstriction on the other hand, is less likely to be responsible for abnormal gas exchange, even while it is the more important factor in terms of airflow rates and symptoms. Finally, the data we have obtained, particularly in obstructive lung diseases, suggests that collateral ventilation is an important phenomenon that protects the lung from collapse and helps to maintain arterial PO2 in the face of severe airways obstruction. Administration of 100% oxygen did not significantly change VA/Q relationships in any of these chronic lung diseases, indicating that at least in the patients that we studied, acute reversal of hypoxic vasoconstriction was not observed.(ABSTRACT TRUNCATED AT 250 WORDS)
D001249:Asthma / Q000503:physiopathology; D002908:Chronic Disease; D006801:Humans; D008171:Lung Diseases / Q000503:physiopathology*; D008173:Lung Diseases, Obstructive / Q000503:physiopathology; D011658:Pulmonary Fibrosis / Q000503:physiopathology; D011659:Pulmonary Gas Exchange; D014692:Ventilation-Perfusion Ratio