What effect does decreased carbon dioxide have on blood vessels during hyperventilation?

During hyperventilation, an individual breathes excessively fast and deep, which leads to a significant decrease in carbon dioxide (CO2) levels in the blood. This drop in CO2, known as hypocapnia, triggers a physiological response that affects blood vessels.

The correct answer indicates that decreased carbon dioxide results in constriction of blood vessels. When CO2 levels decrease, it leads to an increase in blood pH, making the blood more alkaline. This higher pH level causes smooth muscle in the blood vessel walls to contract, resulting in vasoconstriction. This response is part of the body's attempt to regulate blood flow and pressure, which can sometimes lead to a range of symptoms including lightheadedness or tingling.

The other options describe effects that are not aligned with the physiological response to low CO2 levels during hyperventilation. For instance, dilation would typically occur with increased CO2, not decreased, and expansion and relaxation may suggest a widening or loosening effect which does not occur with vasoconstriction induced by hypocapnia. Understanding this relationship is crucial for recognizing how changes in gas levels in the body can influence vascular dynamics.