As almost always in medicine, it is not possible to say that we know everything. Although we know that patients with heart failure have elevated levels of BNP, it is not entirely clear whether monitoring the decrease in plasma levels can be used to monitor the effects of treatment.
Some observations have shown in people with overt heart failure that the pressure drop in the wedged branch of the lung is followed by a decrease in BNP levels, but these are observations in small groups of individuals that will require further verification.