What causes increased heart rate in response to hypoxemia?

Increased heart rate in response to hypoxemia is primarily caused by the release of adrenaline, also known as epinephrine. When the body experiences low levels of oxygen (hypoxemia), it activates the sympathetic nervous system as part of the body's overall response to stress and an attempt to maintain adequate oxygen delivery to vital tissues.

The release of adrenaline stimulates the heart to beat faster (increased heart rate) and stronger (increased contractility), which helps to augment blood flow and enhance oxygen transport to organs and tissues. This physiological response is critical during times of oxygen deprivation, as it helps to improve oxygenation and maintain metabolic functions.

In contrast, while cerebral responses and electrolyte imbalances can influence heart rate under different circumstances, they are not the direct cause of the increased heart rate when hypoxemia occurs. Hydration levels, while important for overall cardiovascular function, do not directly trigger the compensatory mechanism of increased heart rate due to hypoxemia.