jdh71

epiphany at nine thousand six hundred feet
10+ Year Member
Dec 14, 2006
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FEMA Camp, USA
Status
Attending Physician
"PEEP increases the pressure around structures in the thorax and, to a lesser extent, in the abdominal cavity, relative to atmospheric pressure. Because the rest of the circulation is at atmospheric pressure, this results in a pressure differential, with most of the systemic circulation being under lower pressure than the left ventricle and the thoracic aorta. Thus, increased ITP, at constant arterial pressure, decreases the force necessary to eject blood from the left ventricle in a manner exactly analogous to decreased arterial pressure, at constant ITP"

ITP = intrathoracic pressure

Though it's nuanced. Read the section on afterload: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1414045/