Answer: Physiologist
Explanation:
A physiology is the study of function and organization of the body of a living being. It focuses over how cells, tissues, organs and organ system together work to perform a function in an organism.
A physiologist is a medical practisioner who studies physiology. He/ she studies the cardiac, respiratory, digestive system functioning in the body.
He/she can study the change in heart rythm or heart rate with external and internal conditions of the body like change in temperature of the body.
