What is the name of the instrument used to measure blood pressure?

Blood pressure is the force of blood against the blood vessels i.e. arteries and veins. It is measured using a device known as sphygmomanometer. 

A pulse oximeter helps in checking the oxygen saturation levels in the blood.

An electrocardiograph is used to record the electrical activity of the heart. 

A spirometer is used to measure lung volumes and capacities.