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Old 03-05-2013
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Help PEEP (positive end Expiratory Pressure)

can anyone please help me to understand this PEEP!
According to Kaplan lecture notes it says, "it is the positive pressure which is applied at end of expiratory cycle to decrease alveolar collapse".

How the positive pressure can decrease the collapse! As it is the positive pressure in the expiratory cycle that causes the alveolar deflation . isn't it?

In video Lecture, giving the example of emphysema it is said that positive pressure helps the patient to empty his alveoli which he himself can not do.

what is the correct mechanism of this procedure?? and how does it leads to decreased cardiac output??

please help!!!!!!!!!!!!!!!!:sorry:: toosad:
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Old 03-06-2013
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Default Hi :)

It's just that PEEP is a therapeutic measure in which doctors force positive pressure air from a machine into the lungs just when the patient reaches the end of expiration. The other positive pressure that collapses the airways in emphysema is the patient's own normal intrathoracic pressure (outside lungs, inside chest cavity) generated by the relaxation of diaphragm and the upward movement of which kind of squeezes the respi system below-upwards and outside-inwards, leading to expiration. Now in emphysema, the elastic walls are pathologically compliant (i.e., give way in the direction of any +ve pressure). So, as the positive intrathoracic pressure is generated by the diaphragmatic relaxation, pressure is applied to the compliant airways which give way and are squeezed due to loss of elasticity, the basic pathology in emphysema.

Now imagine during expiration, when the +ve intrathoracic pressure tries to collapse the non-elastic emphysematous airway, we introduce a particular positive air pressure from a machine into the lungs and equalize the diaphragm generated +ve intrathoracic pressure, the airway won't collapse because now there's the machine generated opposing pressure from inside the airway which can be graduated to relieve hyperinflation in alveoli.

Now since we are applying +ve pressure from outside, it also increase the total pressure in chest cavity. But it's the -ve intrathoracic pressure which sucks in both air into the lungs and blood from veins in the Rt Atrium (=venous return which is equivalent to preload). And if we decrease preload, by Frank Starling curve, we are decreasing the CO!

Hope this helps.
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