Effects of positive pressure on the pulmonary circulation and the left cardiac chambers

The effects of positive pressure on the pulmonary circulation and the left cardiac chambers can be summarized by an increased LV preload, a decreased LV afterload, and a decreased LV wall tension.

[merelymaterial]

Fantastic and efficient explanation. Thank you all the way from New Zealand!

[domenicdigioia]

Could you help explain this one concept: Wall stress is proportional to chamber radius and transmural pressure and inverse to wall thickness. When you use PPV, you create a positive intrathoracic pressure, which affects the transmural pressure --> Like in your example, if the LV is at 90 mmHg, and the IP pressure is +10, then Ptm = 80. According to the statement above, that would reduce wall stress and thus after load.

Now from a visual perspective, am I wrong to envision the transmural pressure across the LV like a vacuum? For instance, if someone has increased WOB from atelectasis or pulmonary edema and takes a huge inhale creating a large negative IT pressure, that will increase the transmural pressure, which based on the above will increase wall stress and after load. How I visualize this is that the ventricle now has to contract to overcome aortic pressure and the outward radial force from the negative intrathoracic pressure, increasing the wall stress.

Is that thought process completely incorrect?

[parth]

So decrease in blood pressure with PEEP during mechanical ventilation is due to decrease in venous return to right chambers of heart not the left chambers Right?