Lung
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Nitric oxide (NO) and carbon monoxide (CO) are synthesized at high levels in asthmatic airways. NO can oxidize hemoglobin (Hb) to methemoglobin (MetHb). CO binds to heme to produce carboxyhemoglobin (COHb). ⋯ Venous COHb was similar among groups, and thus, arteriovenous COHb (a-v COHb) concentration difference was greater in asthma compared with controls. Venous MetHb was lower in asthma compared to controls (p = 0.01) and correlated to venous NO (p = 0.009). The greater a-v COHb in asthma suggests CO offloading to tissues, but lower than normal MetHb suggests countermeasures to avoid adverse effects of high NO on gas transfer.