Final answer:
The denominator of the blood pressure ratio represents the diastolic pressure, indicating the minimal arterial pressure when the heart is at rest between beats.
Step-by-step explanation:
When measuring systemic arterial blood pressure, the reading is presented as a ratio of two numbers, the systolic pressure over the diastolic pressure. The denominator (lower number) of the blood pressure ratio, which represents the diastolic pressure, indicates the minimal value corresponding to the pressure in the arteries during the ventricular relaxation, or diastole, when the heart muscle is resting between beats and refilling with blood. The usual range for diastolic pressure is about 60 to 80 mm Hg, with an optimal reading being less than 80 mm Hg.