Final answer:
Normothermia is the state of a normal body temperature, while deviations such as hyperthermia and hypothermia can affect heart function. Controlled hypothermia reduces metabolic demands and is used in medical procedures like open-heart surgery. Extreme temperature changes can be fatal due to disruptions in enzyme function and central nervous system operations.
Step-by-step explanation:
Normothermia refers to the maintenance of normal body temperature, which is critically important for proper physiological and enzymatic function. In the context of myocardial temperatures, changes from normothermia such as hyperthermia (elevated body temperature) and hypothermia (suppressed body temperature) can significantly affect heart function. Slight hyperthermia can lead to an increase in heart rate (HR) and strength of contraction, whereas hypothermia induces a decrease in the rate and strength of heart contractions as part of the diving reflex to conserve oxygen for essential organs.
In surgical settings, especially during open-heart surgeries, controlled hypothermia is used to lower metabolic demands on the brain, heart, and other organs to reduce the risk of injury. It involves cooling the body to temperatures between 25-32°C (79-89°F) and may involve stopping the heart and using a heart-lung machine to maintain the body's blood supply and gas exchange. Outside of clinical settings, extreme hyperthermia or hypothermia can be fatal as they disrupt normal enzyme function and the central nervous system.