Increased arteriovenous carboxyhemoglobin differences in patients with inflammatory pulmonary diseases

Purpose: Exhaled carbon monoxide and arterial blood carboxyhemoglobin concentrations increase in inflammatory pulmonary diseases. The present study was undertaken to elucidate whether arteriovenous carboxyhemoglobin (a-vHb-CO) concentration differences are also useful to define the site of inflammation, either in the lung or organs other than the lung. Materials and methods: We examined concentrations of carboxyhemoglobin in both arterial and peripheral venous blood and exhaled carbon monoxide in patients with acute pulmonary inflammation including bronchial asthma (n = 18) and pneumonia (n = 33), and those in patients with extrapulmonary inflammatory diseases, including acute pyelonephritis (n = 28) and active rheumatoid arthritis (n = 16). Results: The values of carboxyhemoglobin in both arterial and peripheral venous blood were significantly higher in patients with pulmonary and extrapulmonary inflammation compared with those in control subjects (n = 22). Furthermore, a-vHb-CO differences in patients with inflammatory pulmonary diseases were higher than those in patients with acute pyelonephritis and patients with rheumatoid arthritis, and than those in control subjects. The a-vHb-CO differences correlated with the WBC count of peripheral venous blood in patients with pneumonia. In patients with bronchial asthma, the a-vHb-CO differences inversely correlated with FEV₁, although they did not correlate with WBC count of peripheral venous blood. The a-vHb-CO differences in patients with acute pyelonephritis were higher than those in patients with active rheumatoid arthritis. Conclusion: The present study suggests that a-vHb-CO differences may be a useful means to define the site of inflammation, either in the lung or organs other than the lung, in patients with a fever of unknown origin. The large a-vHb-CO differences may be caused by carbon monoxide production in pulmonary inflammation.