Uneven ventilation-perfusion ratio distribution during acute exacerbation of chronic pulmonary diseases

We studied ventilation-perfusion ratio (VA/Q) unevenness in terms of alveolar-arterial gas tension difference (AaDO2 and aADN2) and of multiple inert gas elimination technique during the chronic stable periods and the acute exacerbation periods of seven cases with chronic pulmonary diseases. Three had idiopathic pulmonary fibrosis, 2 had pulmonary emphysema, 1 had bronchiolitis and the other had a sequelae of pulmonary tuberculosis. Sulfur hexafluoride and cyclopropane dissolved in saline were infused into a peripheral vein at a constant rate and these 2 gases were used as the indicator gases to make analysis of two compartmental VA/Q. During exacerbation all cases showed lower PaO2 than in the stable period. All cases except idiopathic pulmonary fibrosis showed higher PaCO2. Five cases also had higher AaDO2 and aADN2. One case with pulmonary emphysema and one with bronchiolitis actually had lower AaDO2 and aADN2 values during acute exacerbation than during the chronic stable period. We introduced the difference between the logarithm of higher VA/Q and lower VA/Q values (log [(VA/Q)H/(VA/Q)L)] as an index of VA/Q unevenness. Two compartmental VA/Q analysis revealed greater VA/Q differences in all cases during acute exacerbation. This included cases who showed lower AaDO2 and aADN2 values in the acute exacerbation period. In conclusion, worsened VA/Q distribution, during the acute exacerbation period, was elucidated quantitatively using the multiple inert gas elimination technique.