One thing to keep in mind from the echo is that most of the measurements are derived from just a few physical statistics. It is all done from sound waves captured through the skin, muscle, etc. of the abdomen. I don't remember the exact calculations but I believe that the valve area calculation is in part based upon the velocity calculation, which in turn is based upon something else. In other words, it is possible for one measurement to change and cause changes in other calculations used to derive other measures. Maybe that's why they say that if any one of them gets out of range, then they want to act.