Exercise-Induced Intrapulmonary Arteriovenous Shunting and Pulmonary Gas Exchange

Stickland, Michael K.; Lovering, Andrew T.

doi:10.1249/00003677-200607000-00003

Cited by 45 publications

(45 citation statements)

References 13 publications

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“…Indeed, we would suggest that the magnitude of the exercise-induced anatomic arteriovenous shunting in the human may be greater than in the dog (32), because of the larger relative increases in cardiac output, pulmonary vascular pressures, and (a-a)Do 2 typically observed in humans with exercise. The lack of right-to-left shunt documented during exercise by gas exchange-dependent techniques, despite solid evidence of an anatomic I-P shunt, is controversial and may be explained by either gas exchange occurring proximal to (34) or within (35) arteriovenous anastomotic vessels (36). Notably, a substantial range in shunt fraction (range, 0.2-3.1% of cardiac output) was found in the three exercising dogs for which shunt fraction could be calculated.…”

Section: Shunt Consequencementioning

confidence: 99%

Exercise-induced Arteriovenous Intrapulmonary Shunting in Dogs

Stickland

Lovering²,

Eldridge³

2007

Am J Respir Crit Care Med

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Rationale:We have previously shown, using contrast echocardiography, that intrapulmonary arteriovenous pathways are inducible in healthy humans during exercise; however, this technique does not allow for determination of arteriovenous vessel size or shunt magnitude. Objectives: The purpose of this study was to determine whether large-diameter (more than 25 m) intrapulmonary arteriovenous pathways are present in the dog, and whether exercise recruits these conduits. Methods: Through the right forelimb, 10.8 million 25-m stable isotope-labeled microspheres (BioPAL, Inc., Worcester, MA) were injected either at rest (n ϭ 8) or during high-intensity exercise (6-8 mph, 10-15% grade, n ϭ 6). Systemic arterial blood was continuously sampled during and for 3 minutes after injection. After euthanasia, tissue samples were obtained from the heart, liver, kidney, and skeletal muscle. In addition, 25-and 50-m microspheres were infused into four isolated dog lungs that were ventilated and perfused at constant pressures similar to exercise. Measurements and Main Results: Blood and tissue samples were commercially analyzed for the presence of microspheres. No microspheres were detected in the arterial blood or tissue samples from resting dogs. In contrast, five of six exercising dogs showed evidence of exercise-induced intrapulmonary arteriovenous shunting, as microspheres were detected in arterial blood and/or tissue. Furthermore, shunt magnitude was calculated to be 1.4 ؎ 0.8% of cardiac output (n ϭ 3). Evidence of intrapulmonary arteriovenous anastomoses was also found in three of four isolated lungs. Conclusions: Consistent with previous human findings, these data demonstrate that intrapulmonary arteriovenous pathways are functional in the dog and are recruited with exercise.Keywords: intrapulmonary arteriovenous anastomoses; shunt; pulmonary gas exchange; pulmonary circulationThe classic understanding of the normal pulmonary circulation is that all the blood leaving the right ventricle passes through the pulmonary microcirculation via capillaries before returning to the left side of the heart through the pulmonary venous circulation. Studies using saline contrast echocardiography in humans have demonstrated that exercise results in the transpulmonary passage of contrast bubbles, suggesting that large-diameter intrapulmonary (I-P) arteriovenous pathways are recruited with exercise (1-3). These findings are controversial in that they are in contrast with prior research, using inert gas and/or inspired 100% Previous studies, using contrast echocardiography, suggest that intrapulmonary shunts are recruited during exercise in health. However, the size of the contrast is unknown, and thus arteriovenous diameter is undefined. What This Study Adds to the FieldLarge-diameter intrapulmonary arteriovenous shunts are functional in healthy animals, and exercise recruits these vessels.oxygen (4)(5)(6)(7)(8), that has failed to detect substantial right-to-left physiological I-P shunt during exercise.Despite an absence of right-to-left I-P...

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Section: Shunt Consequencementioning

confidence: 99%

Exercise-induced Arteriovenous Intrapulmonary Shunting in Dogs

Stickland

Lovering²,

Eldridge³

2007

Am J Respir Crit Care Med

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“…The prevalence of PAVMs and grossly distended capillaries that result from rare diseases such as hepatopulmonary syndrome and hemorrhagic hereditary telangiectasia is considered to be very small, on the order of 1 in 50,000 (Khurshid & Downie, 2002;Liu et al, 2010). However, we have found that greater than 95% of healthy humans have intrapulmonary arteriovenous anastomoses that are closed at rest but open up during exercise (Stickland & Lovering, 2006;Lovering et al, 2010). Furthermore, the existence of these pathways in baboon lungs suggests that they may not be evolutionary disadvantageous since humans, gorillas and chimpanzees diverged from the old world monkeys (baboons, macaques, etc.)…”

Section: Right-to-left Intrapulmonary and Intracardiac Shuntmentioning

confidence: 97%

“…Typically, 0.5-1 ml of air and 4-10 ml of saline are used to manually agitate between two syringes connected by stopcocks for a total injection volume of 10 ml (Otto, 2004;Feigenbaum, 2005;Woods et al, 2010). In a research setting, equal success has been achieved in detecting right-to-left shunts via intrapulmonary arteriovenous anastomoses using 0.5-1 ml of air and 3-5 ml of saline, for a total injection volume of 5 ml (Stickland & Lovering, 2006;Laurie et al, 2010;Lovering et al, 2010;Elliott et al, 2011a). The agitated saline mix solution should be injected as a bolus, forcibly by hand.…”

Section: Equipment Instrumentation and Techniquementioning

confidence: 99%

“…Furthermore, increasing exercise intensity increases the amount of saline contrast that is detected in the left ventricle, which is indicative of increased intrapulmonary shunting (Stickland et al, 2004). It has been suggested that blood flowing through intrapulmonary arteriovenous anastomoses is acting as a "true" shunt (Stickland & Lovering, 2006;Lovering et al, 2009a), however the physiologic role of these vessels remains highly controversial and as of yet, unproven (Hopkins et al, 2009). …”

Section: Research Using Echocardiography In Healthy Humans During Exementioning

confidence: 99%

“…First, they allow deoxygenated blood to mix with oxygenated blood, thereby reducing the overall efficiency of pulmonary gas exchange. Thus, the opening of either intrapulmonary or intracardiac shunts at rest and/or during exercise may play a role in determining pulmonary gas exchange efficiency (Sun et al, 2002;Stickland & Lovering, 2006;Lovering et al, 2011). The opening of these shunts may also explain why some people with pulmonary diseases such as chronic obstructive pulmonary disease (COPD) desaturate so profoundly during even mild exercise (Miller et al, 1984;Dansky et al, 1992).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Detection of Intracardiac and Intrapulmonary Shunts at Rest and During Exercise Using Saline Contrast Echocardiography

Lovering¹,

Goodman²

2012

Applied Aspects of Ultrasonography in Humans

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Pulmonary Circulation at Exercise

Naeije¹,

Chesler

2012

Comprehensive Physiology

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The pulmonary circulation is a high flow and low pressure circuit, with an average resistance of 1 mmHg.min.L−1 in young adults, increasing to 2.5 mmHg.min.L−1 over 4–6 decades of life. Pulmonary vascular mechanics at exercise are best described by distensible models. Exercise does not appear to affect the time constant of the pulmonary circulation or the longitudinal distribution of resistances. Very high flows are associated with high capillary pressures, up to a 20–25 mmHg threshold associated with interstitial lung edema and altered ventilation/perfusion relationships. Pulmonary artery pressures of 40–50 mmHg, which can be achieved at maximal exercise, may correspond to the extreme of tolerable right ventricular afterload. Distension of capillaries that decrease resistance may be of adaptative value during exercise, but this is limited by hypoxemia from altered diffusion/perfusion relationships. Exercise in hypoxia is associated with higher pulmonary vascular pressures and lower maximal cardiac output, with increased likelihood of right ventricular function limitation and altered gas exchange by interstitial lung edema. Pharmacological interventions aimed at the reduction of pulmonary vascular tone have little effect on pulmonary vascular pressure-flow relationships in normoxia, but may decrease resistance in hypoxia, unloading the right ventricle and thereby improving exercise capacity. Exercise in patients with pulmonary hypertension is associated with sharp increases in pulmonary artery pressure and a right ventricular limitation of aerobic capacity. Exercise stress testing to determine multipoint pulmonary vascular pressures-flow relationships may uncover early stage pulmonary vascular disease.

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Exercise-Induced Intrapulmonary Arteriovenous Shunting and Pulmonary Gas Exchange

Cited by 45 publications

References 13 publications

Exercise-induced Arteriovenous Intrapulmonary Shunting in Dogs

Exercise-induced Arteriovenous Intrapulmonary Shunting in Dogs

Detection of Intracardiac and Intrapulmonary Shunts at Rest and During Exercise Using Saline Contrast Echocardiography

Pulmonary Circulation at Exercise

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