In November I made a presentation at the AHA about the incidence and magnitude of leaning. ("leaning" is what some people call "not getting to full recoil")
The short form is that in a study where the cohort's age distribution approximated that of cardiac arrest victims, sixty percent of those tested exhibited enough residual force at the top of the recoil stroke to negatively impact a victim's probability of survival.
The reason for using a cohort with the same age distribution as the victims is that more than two-thirds of all SCAs occur at home, and if there is another person present who is capable of performing CPR, that person is usually about the same age as the victim.
What is wrong with leaning? More than 1.3 pounds of residual force on the sternum of an adult with average chest stiffness has three effects: (a) it decreases cardiac index - and five pounds of stiffness is enough to get the cardiac index into a range frequently associated with cardiogenic shock; (b) it increases left atrial blood pressure at diastole, which makes it more difficult for the blood returning to the heart to get in; and (c) it decreases myocardial blood flow. None of this s good.
We ran this study in preparation for a presentation at the AHA Resuscitation Science Symposium in November. We were shocked to find that sixty percent of the cohort leaned enough to negatively influence survival probability. For the sixty percent who failed to achieve full recoil, we explained the problem and retested them. Here's the shocker: only eighty percent of the re-tested subjects passed on the second trial.
for more information on leaning check www.slicc.org/ReSS_2014_028.pdf