Pulsation in internal fluid simulation

First, make sure you have it set as a time-dependent problem under  the General Settings.  When you define your boundary condition, pressure  or flowrate, simply click on the "f(x)" button next to the input.  A  new dialog opens where you can change the dependency from constant to a  formula dependent on time or tablular data.  In your case, a formula is  best.

Make sure your pressure units are in mmHg before you define the formula.  Define the formula in terms of A*sin(omega*t)+C.  Using the values you gave, pressure would be: 170*sin(70/(2*pi)*t)+280.  Now you may have to consider that Flow Sim only uses absolute pressure so if the numbers you provided are gage pressures then change the formula to add roughly 760 mmHg (or 14.7 psi) to the constant 280.