In respiratory movements, the volume of air is measured by:

Explanation:

• The instrument that helps in the clinical assessment of pulmonary function (breathing) is Spirometer. 
• A spirometer is an equipment that is used to measure the volume of air inspired and expired by the lungs. The spirometer measures ventilation, the movement of air into and out of the lungs. 
• Working of a spirometer:
• A clip is placed over the patient's nose and he or she is asked to take a deep breath and blows air (as hard as possible) into the spirometer tube.
• The machine records the test data, which is then displayed in the monitor screen.

Additional Information

• Sphygmomanometer: It is an instrument that is used to measure blood pressure, typically it consists of an inflatable rubber cuff that is applied over the arm and connected to a mercury column next to a graduated scale, this determines the systolic and diastolic blood pressure by increasing and gradually releasing the pressure in the cuff.