the decline in pao2 and sao2 during exercise has been termed as exercised - induced arterial hypoxemia ( eiah ) and has been classified into mild ( arterial oxygen saturation , sao2 = 93 - 95% ) , moderate ( sao2 = 88 - 93% ) , and severe ( sao2 < 88%).1 ) eiah has been well documented in highly fit male endurance athletes during heavy and even submaximal exercise and have been reported to occur in approximately 50% of highly trained runners.2 ) however , the determining factor which is responsible for the development of eiah in those patients is unclear . we report a highly fit male complaining of dyspnea during strenuous exercise who underwent cardiopulmonary treadmill exercise test and agitated saline contrast echocardiography at peak exercise . a 51-year - old man presented to the outpatient department because of dyspnea with strenuous aerobic exercise . as an amateur rollerblader , he has rollerbladed twice a week for the past 5 years . about 9 months ago , dyspnea occurred abruptly during rollerblading at full speed for over ten minutes . at that time , he felt like collapsing but his symptom improved completely within 3 minutes after stopping the exercise . , he was asymptomatic and physical examination revealed clear lung sound and normal heart sounds without murmurs . oxygen saturation was 99 at room air and pulmonary function test was also normal at rest . after a baseline echocardiogram , agitated saline contrast echocardiography was performed to evaluate intra- or extracardiac shunt as a cause of the dyspnea . only a few air bubbles appeared in the left heart after 9 cardiac cycles from the onset of right heart opacification ( fig . 1 ) . to assess for the presence of intrapulmonary ( ip ) shunt , such as pulmonary arteriovenous malformation ( avm ) , computed tomography of the chest ( fig . 2a ) and pulmonary angiography ( fig . 2b ) were performed and they showed no significant abnormality . since the patient complained of dyspnea during strenuous exercise , a cardiopulmonary treadmill exercise test ( quark b2 , cosmed , rome , italy ) with arterial blood gas analysis ( abga ) was performed . while increasing the exercise intensity , the patient suddenly complained of dyspnea at 205 watts of exercise and the values obtained from cardiopulmonary exercise test and abga at that time were as follows ( table 1 ) . we confirmed the presence of severe exercise - induced arterial hypoxemia and an excessive alveolar - arterial oxygen tension difference ( a - ado2 ) widening in this patient . bilateral breathing sounds were normal in auscultation during the dyspneic episode . when an exercise echocardiography was done within one minute after stopping the exercise however , the agitated saline contrast echocardiography revealed that large amount of microbubbles appeared in the left atrium and leaded to complete left heart opacification after > 5 cardiac cycles from the onset of right heart opacification ( fig . the patient 's dyspnea and hypoxemia in pulse oxymetry were completely normalized within one minute of rest . this patient showed a severe eiah with a widening of a - ado2 during strenuous exercise . the severity of eiah is significantly correlated with gas - exchange efficiency as quantified by the a - ado2 . potential mechanisms of eiah with a widening of a - ado2 include ventilation - perfusion mismatching , diffusion limitation , and right - to - left shunting.1 ) although prior studies , using the multiple inert gas elimination techniques and/or inspired 100% oxygen have failed to detect significant right - to - left physiological ip shunt during exercise,3)4 ) there are substantial studies documenting the presence of anatomical arteriovenous anastomoses in the isolated lung and the recruitment of ip shunts during exercise using the agitated saline contrast echocardiography technique.5)6 ) the recruitment of ip shunt might be a response to increasing pulmonary arterial pressure and/or cardiac output during dynamic exercise to reduce the potential damaging effects of high perfusion pressure during exercise.6 ) also , recent studies have reported that oxygen tension might play a crucial role in the regulation of these shunt vessels.7 ) however , determinants regulating these shunt vessels during exercise in some highly fit subjects and their contribution to the components of gas exchange has not been fully elucidated . the present case indicates that the existence of exercise - induced ip shunt has a close connection with dyspnea by impairing gas exchange with widening of the a - ado2 . additionally , considering the lung 's role as a biologic filter and the increased risk of stroke in patients with pulmonary avm , the recognition of exercise - induced ip shunt among patients complaining of exertional dyspnea is crucial because this condition might serve as another potential source of embolic stroke .
a 51-year - old highly fit man presented for dyspnea with strenuous aerobic exercise . the patient was asymptomatic and all tests were normal at rest . with increasing exercise intensity , he suddenly complained of dyspnea and showed a severe exercise - induced hypoxemia with an excessive alveolar - arterial oxygen tension difference . in agitated saline contrast echocardiography at peak exercise , 
 a large amount of left to right shunt was identified after > 5 cardiac cycles , which suggests the presence of exercise - induced intrapulmonary arteriovenous shunt in this patient .