Which do you prefer?
A: Your blood pressure is 140/80 mmHg.
B: Your blood pressure is 120/70 mm Hg.
I am not talking about the blood pressure but the unit of blood pressure (i.e., mmHg versus mm Hg). The two ways to describe the unit of blood pressure may be minimal; the former has no space between mm and Hg, whereas there is a space in the latter.
I believe that most doctors consider mmHg common, but let me explain the basis of the unit, mmHg. As you know, mm means millimeter and Hg is a symbol of a chemical material, mercury. I am still wondering if the combination of two different staffs makes any sense? Don't you think they look more academic when separated?
Actually, in the New England Journal of Medicine, which is the top journal in the field of clinical medicine, "mm Hg" is adopted instead of "mmHg", although almost all other medical journal use a unit of mmHg when it comes to blood pressure.