I'd suggest fitting the data to an appropriate distribution (there's many standard available software that can do this) and using this distribution to estimate the probability that the blood pressure will lie in a given range. (again, the software would do that for you).
However, I'm not a trained statistician. You should take what I say with a grain of salt. If you're affiliated with a hospital, you should see if there's a statistician on the payroll that can give you professional advice.