So do you or do you not agree with the idea that the prior post of blood pressure is valid
Logically, it's invalid as far as the LSAT goes. Correlation is one thing, a valid principle. But conditional logic (lsat wise) doesn't account for this. For example, write a paradox question with that same stimulus.
Blood pressure goes up then heart attack goes up, but blood pressure going low, doesn't reduce the chance of heart attack
Which of the following resolves the apparent paradox:
As blood pressure falls too low, the heart works harder to move blood, and initiates a heart attack
As blood pressure falls, veins constrict causing heart attack
If you could see this principle in this form, you might see what I'm saying.
As far as conditional logic goes, you can't chart anything but the contrapositive of one rule. If the rule or a contrapositive of a rule should tie in with another rule, then you might be able to expand on the concept...but with what you gave, the only thing to be said is
A up -> B up
~B up -> ~A up