http://www.ncbi.nlm.nih.gov/pubmed/6608638 : Data relating to the hemodynamic efficaciousness and mechanism of action of a pulmonary artery catheter or vent used for left ventricular venting during cardiac operations are presented.

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Note added at 11 mins (2014-01-23 08:44:18 GMT)
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A vent is placed in the right superior pulmonary vein and passes through the left atrium into the left ventricle to decompress the left ventricle during the procedure

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Note added at 11 mins (2014-01-23 08:44:40 GMT)
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http://www.ctsnet.org/sections/clinicalresources/congenital/...

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Note added at 13 mins (2014-01-23 08:46:38 GMT)
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Powyższy link odnosi sie do zacytowanego zdania "a vent is placed..."