A 56-year old woman has a mean systemic blood pressure of 100 mm Hg and a resting cardiac output of 4 L/min. What is the total peripheral resistance of this woman?

Total peripheral resistance (TPR) is equal to the pressure gradient across the circulation (mean aerial pressure - right atrial pressure) divided by the cardiac output. Right atrial pressure is assumed to equal 0 mm Hg. Thus, TPR = 100/4000 = 0.025 mm Hg/mL/min. The "ABC rule" is useful in remembering the relation between pressure (P), flow (Q), and resistance (R) because P=QR (P,Q and R in alphabetical order). Tip: Note that choices A, C, & D can be eliminated quickly because in each case the units are incorrect.