Hyperdynamic circulation

My son's echocardiogram results state, " Left aortic arch - high great arterial laminar flow velocities are consistent with a hyperdynamic circulation." When I google this phrase, I get, "abnormally increased circulatory volume with low vascular resistance and often tachycardia, a condition sometimes accompanying septic shock, preeclampsia, and other conditions."  

My son's doctors said this echo was normal, but that he does have some sort of autonomic nervous system dysfunction - maybe POTS, maybe Vasovagal.  These same cardiologist said his resting bp 5 mins after the end of his treadmill stress test of 240/60 (do not know what it was at the very end of the test, as the techs could not get a reading) was normal!

Any translations, ideas, input?

Thanks.