Thanks for your thoughts, Bob.
You are touching on a subject that is more complex than it may seem at first blush.
BP is indeed a biomarker with considerable variability. In research we typically differentiate between beat-to-beat, diurnal, day-to-day, visit-to-visit, and seasonal variability. Any single measurement is only a snapshot of BP that does not carry any information about BP variability. The latter, however, is a strong predictor of health and disease outcomes. There are many studies on the subject of BPv and its correlation with various risks and morphological changes of the vasculature. In an overly simplified way, one could says that the higher the variability, the greater the risk for the undesirable outcome (e.g. stroke).
The problem is, that the different BPv that I mentioned in the beginning are not created equal as predictors. B2B variability better correlates with risk and with morphology than ambulatory BPv. But B2B is not practical to measure in a routine clinical setting.
What your nurse mentioned is an oversimplification. Yes, repeated application of suprasystolic pressure with the cuff of her BP device might affect the brachial artery at the measurement location. But these effects are opposed to each other: temporary occlusion may cause reactive hyperemia, that is, following the release of the pressure the artery may dilate (leading to a slight decrease in BP), to accommodate a larger compensatory blood flow (leading to slight increase in pressure). However, reactive hyperemia is a biomarker that we always assess after at least a 5-minute occlusion. BP measurement in the office should not trigger a RH response large enough to appreciably affect the BP in a repeat measurement.
My own experience in the lab: we have developed an oscillometric BP measurement device that we use for the derivation of PWV. The routine I typically use is BP measurement in triplicate, following a 5-minute rest (in supine position), and with breaks of 1 minute between measurements (at the same location). The repeatability, or the variability, of these BP measurements is within what we typically expect to see, and with a slight negative trend from first to third measurement.
