Hyperoxia prevents exercise-induced intrapulmonary arteriovenous shunt in healthy humans

Department of Human Physiology, 1240 University of Oregon, Eugene, OR 97403-1240, USA.
The Journal of Physiology (Impact Factor: 5.04). 08/2008; 586(Pt 18):4559-65. DOI: 10.1113/jphysiol.2008.159350
Source: PubMed


The 100% oxygen (O(2)) technique has been used to detect and quantify right-to-left shunt for more than 50 years. The goal of this study was to determine if breathing 100% O(2) affected intrapulmonary arteriovenous pathways during exercise. Seven healthy subjects (3 females) performed two exercise protocols. In Protocol I subjects performed an incremental cycle ergometer test (60 W + 30 W/2 min; breathing room air, FIO2 = 0.209) and arteriovenous shunting was evaluated using saline contrast echocardiography at each stage. Once significant arteriovenous shunting was documented (bubble score = 2), workload was held constant for the remainder of the protocol and FIO2 was alternated between 1.0 (hyperoxia) and 0.209 (normoxia) as follows: hyperoxia for 180 s, normoxia for 120 s, hyperoxia for 120 s, normoxia for 120 s, hyperoxia for 60 s and normoxia for 120 s. For Protocol II, subjects performed an incremental cycle ergometer test until volitional exhaustion while continuously breathing 100% O(2). In Protocol I, shunting was seen in all subjects at 120-300 W. Breathing oxygen for 1 min reduced shunting, and breathing oxygen for 2 min eliminated shunting in all subjects. Shunting promptly resumed upon breathing room air. Similarly, in Protocol II, breathing 100% O(2) substantially decreased or eliminated exercise-induced arteriovenous shunting in all subjects at submaximal and in 4/7 subjects at maximal exercise intensities. Our results suggest that alveolar hyperoxia prevents or reduces blood flow through arteriovenous shunt pathways.

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    • "We found that 3 of 4 Sherpas had resting blood flow through IPAVA at HA breathing 100% O 2 . It has been previously shown that breathing 100% O 2 prevents blood flow through IPAVA during exercise (Lovering et al. 2008b; Elliott et al. 2011) and in 80% of resting subjects who demonstrate blood flow through IPAVA (Elliott et al. 2013). In Elliott et al. (2013), we also reported that a subset of healthy young asymptomatic subjects (6/31 or 20%) with blood flow through IPAVA at rest (near SL) continue to have blood flow through IPAVA despite breathing 100% O 2 . "
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    ABSTRACT: Incidence of blood flow through intracardiac shunt and intrapulmonary arteriovenous anastomoses (IPAVA) may differ between Sherpas permanently residing at high altitude (HA) and sea-level (SL) inhabitants as a result of evolutionary pressure to improve gas exchange and/or resting pulmonary hemodynamics. To test this hypothesis we compared sea-level inhabitants at SL (SL-SL; n=17), during acute isocapnic hypoxia (SL-HX; n=7) and following 3 weeks at 5,050m (SL-HA; n=8 non-PFO subjects) to Sherpas at 5,050m (n=14). SpO2, heart rate, pulmonary artery systolic pressure (PASP) and cardiac index (Qi) were measured during 5min of room air breathing at SL and HA, during 20min of isocapnic hypoxia (SL-HX; PETO2 = 47mmHg) and during 5min of hyperoxia (FiO2=1.0; Sherpas only). Intracardiac shunt and IPAVA blood flow was evaluated by agitated saline contrast echocardiography. Although PASP was similar between groups at HA (Sherpas: 30.0±6.0 mmHg; SL-HA: 32.7±4.2 mmHg; P=0.27), it was greater than SL-SL (19.4±2.1 mmHg; P<0.001). The percent of subjects with intracardiac shunt was similar between groups (SL-SL: 41%; Sherpas: 50%). In the remaining subjects, IPAVA blood flow was found in 100% of subjects during acute isocapnic hypoxia at SL, but in only 4 of 7 Sherpas and 1 of 8 SL-HA subjects at rest. In conclusion, differences in resting pulmonary vascular regulation, intracardiac shunt and IPAVA blood flow do not appear to account for any adaptation to high altitude in Sherpas. Despite elevated pulmonary pressures and profound hypoxaemia, IPAVA blood flow in all subjects at HA was lower than expected compared with acute normobaric hypoxia.
    The Journal of Physiology 01/2014; 592(6). DOI:10.1113/jphysiol.2013.266593 · 5.04 Impact Factor
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    • "We also observed no relationship between aerobic capacity ( ˙ V O 2,peak ) and the onset of shunt in exercising women. The high degree of between-subject variation we observed is consistent with other reports that have studied mainly male subjects (Lovering et al., 2006, 2008b; Stickland et al., 2004). However, Stickland et al. (2004) observed in trained males ( ˙ V O 2,max = 55 ml kg −1 min −1 ) performing upright cycling that shunt occurred at all work rates with a CO of more than 24 l min −1 and was significantly correlated with cardiac output (r = 0.76) and mean pulmonary artery pressure (r = 0.73). "
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    ABSTRACT: The purpose of this study was to determine if healthy young women of various aerobic fitness levels are vulnerable to intrapulmonary arteriovenous shunts (IPAVS) at sub maximal work rates. Female volunteers (n=24) performed semi-recumbent cycling exercise to exhaustion and agitated saline contrast echocardiography was used to determine the presence of IPAVS at rest, during exercise, and post exercise. Subjects were classified as untrained (UT, n=8), moderately trained (MT, n=6) and highly trained (HT, n=10) based on their respective (V(O(2,peak)) (UT=35±5; MT=43±1 and HT = 50 ± 3 ml kg(-1) min(-1)). We found that the % (V(O(2,peak)) at IPAVS onset was not significantly different between women of varying fitness (P>0.05). The majority of individuals exhibited IPAVS during modest levels of exercise intensity. In conclusion, there is no association between aerobic capacity or exercise intensity at IPAVS onset in women performing semi-recumbent cycle exercise.
    Respiratory Physiology & Neurobiology 04/2012; 181(1):8-13. DOI:10.1016/j.resp.2012.01.004 · 1.97 Impact Factor
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