Dec 8, '07
You seem to have an adequate understanding of the process. The heart gets its blood flow to the coronary arteries during diastole. The balloon inflating pushes blood forcefully back toward the heart providing maximal filling of the coronary arteries. Yes, it is as simple as the sudden drop in pressure as the balloon deflates that reduces afterload. 80% of the hearts workload is in the initial 1/3 of ejection; opening the aortic valve and overcoming the resistance of forcing blood through the aorta. By deflating the balloon just before myocardial contraction you form a relative negative pressure in the decending aorta greatly reducing the work in opening the a valve and starting blood flow. Timing is critical. If the blood has a chance of refilling the aorta by backflow from the dista aorta before the heart contracts you have lost the benifit of the IABP for afterload reduction. If the balloon is still inflated when contraction starts you make afterload MUCH MUCH higher and can cause harm. Most IABPs now have an "R wave deflate" safety to reduce the chance of this. Since contraction is delayed from the electrical "Rwave" event when the balloon sees what may be an R wave it will automaticaly deflate to get out of the way of the comming contraction.
Last edit by suanna on Dec 10, '07