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Sonic echocardiography: what does it mean when there are no bubbles in the left ventricle?

2011; American Physiological Society; Volume: 110; Issue: 1 Linguagem: Inglês

10.1152/japplphysiol.01241.2010

8750-7587

Hugh D. Van Liew, Richard D. Vann,

Cardiac Arrest and Resuscitation

Letters to the EditorSonic echocardiography: what does it mean when there are no bubbles in the left ventricle?Hugh D. Van Liew, and Richard D. VannHugh D. Van LiewBarnstable, Massachusetts; , and Richard D. VannDivers Alert Network, Duke Medical Center, Durham; and Center for Environmental Physiology and Medicine, Duke Medical Center, Durham, North CarolinaPublished Online:01 Jan 2011https://doi.org/10.1152/japplphysiol.01241.2010MoreSectionsPDF (30 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat the studies reported by Elliott and coworkers (3) in the Journal of Applied Physiology were prompted by criticisms of the way saline-contrast echocardiography results are interpreted (4–7). Our objective here is to rethink the interpretations in the light of our experience with bubbles in the body (1, 2).When a bubble is introduced into a vein, all gases in it immediately begin the diffusive exchanges with the surroundings that will eventually absorb it. A gas that diffuses rapidly comes close to equalizing its internal partial pressure with its partial pressure outside. Gases that diffuse less rapidly are left behind in the bubble, with relatively larger partial pressure gradients between inside and outside. The bubble persists until the least diffusive gas is gone. In subjects who have nitrogen in their tissues and blood, nitrogen is the least diffusive gas. If a non-air bubble is introduced into a vein, nitrogen immediately begins entering while the non-air gas exits; soon the partial pressure of nitrogen inside becomes higher than outside and the bubble shrinks. In the lung of a subject breathing pure oxygen, there is little or no nitrogen, so nitrogen exits a bubble several times more rapidly than when air is breathed; although oxygen would be in high concentration inside the bubble because it is high outside, it would be absorbed very rapidly when the nitrogen is gone.We recognize several uncertainties in echocardiography. What if bubbles appear in the left ventricle? 1) If they are larger than capillaries, they may have come through arteriovenous shunts. 2) If they are small, bubbles may have come through lung capillaries. One expects that small bubbles will be absorbed quickly. They would not reach the left ventricle if the time it takes to absorb the small bubbles is less than the time it takes for them to pass through the pulmonary capillaries. If the blood's passage is more rapid, as in exercise, the small bubbles may not be completely absorbed, so the inappropriate interpretation would be that there are open anastomoses. One experiment that could shed light on the time of passage through the lung vs. the absorption time would be to use bubbles that would last longer than air, such as the synthetic gas SF6 (1). 3) Arteriovenous shunts may be closed or nonexistent and therefore bubbles are stopped by capture at the precapillary level, but it is possible that as captured bubbles shrink they may escape and pass on into the left ventricle, leading to an interpretation that shunts are open, even if there are no shunts.What if bubbles do not appear in the left ventricle? 1) AV shunts may be closed so bubbles are stopped by capture at the precapillary level. 2) Bubbles may have passed through open shunts, but they may have been absorbed before they reach the left ventricle, leading to an incorrect interpretation that shunts are closed. 3) Bubbles may have passed through capillaries and then been absorbed.Why are no bubbles seen when exercising subjects breathe 100% oxygen? The strong potential for absorption due to lack of nitrogen in the pulmonary capillaries, pulmonary veins, and left atrium makes it likely that if they pass through the lung by any route—anastomoses, capillaries, or being freed from precapillary capture—bubbles will be absorbed before they reach the left ventricle. If so, the incorrect interpretation would be that oxygen closed the shunts so the bubbles were captured at the precapillary level.Elliott and coworkers substituted bubbles of pure oxygen, pure nitrogen, pure carbon dioxide, or pure helium for the usual air bubbles; the results were always similar to those with air bubbles. The likely explanation is that all these bubbles lost some of the special gas and gained some nitrogen from contact with the blood and tissue on the way from the antecubital vein and in passage through the heart and lungs, so they were all effectively the same as air bubbles.Nonbubble methods convince us that pulmonary shunts exist (4–7), but the uncertainties enumerated above lead us to question the reliability of saline-contrast echocardiography for studying shunts. In particular, we suspect that the lack of bubbles in exercising subjects who breathe oxygen is due to absorption in the pulmonary capillaries and veins, not to closure of arteriovenous anastomoses.DISCLOSURESNo conflicts of interest, financial or otherwise, are declared by the author(s).REFERENCES1. Burkard ME , Van Liew HD. Simulation of exchanges of multiple gases in bubbles in the body. Respir Physiol 95: 131–145, 1994.Crossref | PubMed | Google Scholar2. Burkard ME , Van Liew HD. Oxygen transport to tissue by persistent bubbles: theory and simulations. J Appl Physiol 77: 2874–2878, 1994.Link | ISI | Google Scholar3. Elliott JE , Choi Y , Laurie SS , Yang X , Gladstone IM , Lovering AT. Effect of initial gas bubble composition on detection of inducible intrapulmonary arteriovenous shunt during exercise in normoxia, hypoxia, or hyperoxia. J Appl Physiol (September 16, 2010). doi:10.1152/japplphysiol.00145.2010.ISI | Google Scholar4. Hopkins SR , Olfert IM , Wagner PD. Point: Exercise-induced intrapulmonary shunting is imaginary. J Appl Physiol 107: 993–994, 2009.Link | ISI | Google Scholar5. Hopkins SR , Olfert IM , Wagner PD. Rebuttal from Hopkins, Olfert, and Wagner. J Appl Physiol 107: 997–998, 2009.Link | ISI | Google Scholar6. Lovering AT , Eldridge MW , Stickland MK. Counterpoint: Exercise-induced intrapulmonary shunting is real. J Appl Physiol 107: 994–997, 2009.Link | ISI | Google Scholar7. Lovering AT , Eldridge MW , Stickland MK. Rebuttal from Lovering, Eldridge, and Stickland. J Appl Physiol 107: 998, 2009.Link | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: H. D. Van Liew, 100 Goodview Way, Barnstable, MA 02630 (e-mail: vanliew.hd@verizon.net). Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation Cited ByHyperoxia-induced stepwise reduction in blood flow through intrapulmonary, but not intracardiac, shunt during exerciseJames T. Davis, Jonathan E. Elliott, Joseph W. Duke, Alberto Cristobal, and Andrew T. Lovering21 June 2023 | American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, Vol. 325, No. 1 More from this issue > Volume 110Issue 1January 2011Pages 295-295 Copyright & PermissionsCopyright © 2011 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.01241.2010PubMed21228190History Published online 1 January 2011 Published in print 1 January 2011 Metrics