Concern has been raised that altering the fraction of inspired O₂ (Fi(O₂)) could accelerate or decelerate microbubble dissolution time within the pulmonary vasculature and thereby invalidate the ability of saline contrast echocardiography to detect intrapulmonary arteriovenous shunt in subjects breathing either a low or a high Fi(O₂). The present study determined whether the gaseous component used for saline contrast echocardiography affects the detection of exercise-induced intrapulmonary arteriovenous shunt under varying Fi(O₂). Twelve healthy human subjects (6 men, 6 women) performed three 11-min bouts of cycle ergometer exercise at 60% peak O₂ consumption (Vo(2peak)) in normoxia, hypoxia (Fi(O₂) = 0.14), and hyperoxia (Fi(O₂) = 1.0). Five different gases were used to create saline contrast microbubbles by two separate methods and were injected intravenously in the following order at 2-min intervals: room air, 100% N₂, 100% O₂, 100% CO₂, and 100% He. Breathing hyperoxia prevented exercise-induced intrapulmonary arteriovenous shunt, whereas breathing hypoxia and normoxia resulted in a significant level of exercise-induced intrapulmonary arteriovenous shunt. During exercise, for any Fi(O₂) there was no significant difference in bubble score when the different microbubble gas compositions made with either method were used. The present results support our previous work using saline contrast echocardiography and validate the use of room air as an acceptable gaseous component for use with saline contrast echocardiography to detect intrapulmonary arteriovenous shunt during exercise or at rest with subjects breathing any Fi(O₂). These results suggest that in vivo gas bubbles are less susceptible to changes in the ambient external environment than previously suspected.

Concern has been raised that altering the fraction of inspired O2 (FIO2) could accelerate or decelerate microbubble dissolution time within the pulmonary vasculature and thereby invalidate the ability of saline contrast echocardiography to detect IPAV shunt. The current study determined if the gaseous component used for saline contrast echocardiography affects the detection of exercise‐induced IPAV shunt under varying FIO2's. Eleven healthy subjects (6 female) performed three, 11 min bouts of cycle ergometer exercise at 60% VO2max, in hyperoxia (FIO2 = 1.0), normoxia (FIO2 = 0.21) and hypoxia (FIO2 = 0.14). Five different gases were used to create saline contrast bubbles and were injected in the following order at 2 min intervals: room air, 100% N2, 100% O2, 100% CO2 and 100% He. During exercise, for any FIO2, there was no significant difference in shunt score when using the different bubble gas compositions. Breathing hyperoxia prevented exercise‐induced IPAV shunt whereas breathing hypoxia and normoxia resulted in a significant level of exercise‐induced IPAV shunt. The current results support our previous work and validate the use of room air as the gaseous component of saline contrast bubbles to detect IPAV pathways during exercise in any FIO2. These results call into question the validity of the 100% O2 technique to detect and quantify right‐to‐left shunting via inducible IPAV pathways. Funding: OHSU MRF 0820

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