In fact, scar tissue can restrict many layers of muscle and connective tissue, which can cause varying degrees of pain or discomfort. Scar tissue is weaker, less elastic and more prone to re-injury than normal, healthy tissue, and can lead to chronic pain if it affects the functioning of other structures--especially nerves and blood vessels.
Negative pressure means the pressure in the pipe/duct/room is less so flow would go into the room. These are all gauge pressures, which can be positive or negative since they are merely measuring a relative pressure compared against some constant pressure, typically atmospheric which is about 14.7 psi.
Negative means focused on what is bad or lacking. A negative ad tells you bad things about the competition. A negative person loves to complain. In math, a negative number is less than zero. People who see the glass half empty have a negative outlook. Ask your mom for ice cream and receive an answer in the negative? Don't be too negative back to her, or it'll be a while before you have another chance at ice cream. Thesaurus