Final answer:
Blood pressure readings comprise two phases: systolic pressure, the higher number during heart contraction, and diastolic pressure, the lower number during heart relaxation. Measurements are made using a sphygmomanometer, and common values are 120/80 mm Hg, known as 'one twenty over eighty.'
Step-by-step explanation:
The two phases measured in a blood pressure reading are the systolic and diastolic pressures. Systolic pressure is the higher value and represents the peak arterial pressure during the contraction of the heart's ventricles, or systole. Meanwhile, diastolic pressure is the lower value and reflects the arterial pressure during the relaxation phase of the heart, or diastole. Blood pressure is commonly written as systolic/diastolic, for example, 120/80 mm Hg, which is spoken as "one twenty over eighty."
When measuring blood pressure, a sphygmomanometer is used. This device consists of an inflatable cuff to cut off blood flow, a manometer to measure pressure, and either a stethoscope or electronic sensor to listen for when blood flow begins and becomes impeded as the cuff pressure is adjusted. The first audible sound of blood flow corresponds to the systolic pressure, while the point where the sound disappears correlates to the diastolic pressure. Throughout a day, these measures can vary due to factors like exercise, emotions, stress, and other physiological conditions.