Question

1. You receive a patient who has been admitted to the hospital after being trapped in the bitter winter cold without adequate warm clothing. Initially, his body vasodilated his peripheral capillary beds to try to keep his arms and legs warm, but ultimately, it shut down blood flow to his extremities to preserve the core temperature of his body. Begin with the increased venous return to his heart, and show me that you understand completely what happened to his heart rate as he lay exposed in the cold. Then explain to me the exact mechanism the body used to alter his heart rate. 20 points for a perfect answer.

Answer 1

The human body has multiple thermoregulatory mechanisms to counter the external extreme temperatures whose main objective is to keep temperature homeostasis within normal values. As exposure time to these stressful conditions increases and the external temperature becomes even more extreme, the body systems start adapting to its environment progressively. All of the adaptations, at the beginning of the exposure somewhat irrelevant, may become very important since they can affect all of the body systems in a negative manner and finally, compromise life. Clinically, all of these responses and adaptations are manifested through clinical signs and symptoms.

Thermoregulatory physiology main goal is to keep a Tc within a degree or two of 37 ℃ and it works because of a coordinated set of autonomic responses to maintain equilibrium between heat production (produced by metabolism primarily) and its dissipation.

Exposure to cold causes various physiological responses in the human body. It has been reported that cold exposure results in increased heart rate and systolic blood pressure.Cold-induced increase in heart rate may be associated with reduced vagal activation compared with sympathetic response to cold. In addition, exposure to cold causes peripheral vasoconstriction leading to increase in systemic vascular resistance and diastolic blood pressure.

In this case , as the patient lays exposed in the cold, heart rate increases leading to increased venous return to the heart, eventually causing increase in blood pressure. To enhance thermoregulatory mechanism, the blood vessels show profound vasodilatation causing decrease in venous return and eventual decrease in blood pressure.