Final answer:
A sphygmomanometer is used to measure the pressure blood exerts against the artery walls, with readings given in systolic and diastolic pressures.
Step-by-step explanation:
The instrument used for measuring the pressure the blood exerts against the walls of the artery is called a sphygmomanometer. This device includes an inflatable cuff that is placed around the upper arm, above the systolic pressure to halt blood flow through the brachial artery. Listening with a stethoscope, the clinician can hear the return of blood flow, identifying the systolic pressure when a tapping sound is first heard, and the diastolic pressure when the sound disappears. The blood pressure reading is expressed in millimeters of mercury (mm Hg) and reported as two numbers, representing the systolic and diastolic pressures.