Gas bubble composition does not affect the detection of exercise‐induced intrapulmonary arteriovenous shunt in hypoxia, normoxia or hyperoxia

Abstract

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