Final answer:
Carpopedal spasms from hyperventilation syndrome are caused by relative hypocalcemia due to more calcium binding to albumin in the blood, a condition induced by respiratory alkalosis leading to an increase in bound calcium.
Step-by-step explanation:
The carpopedal spasms that occur due to hyperventilation syndrome are a result of a relative hypocalcemia, secondary to an increase in bound calcium. Hyperventilation leads to respiratory alkalosis, which occurs when there is too much CO2 exhaled from the lungs, resulting in abnormally low blood carbon dioxide levels and high (alkaline) blood pH. This alkalosis causes calcium to become more bound to albumin in the blood, which reduces the concentration of free ionized calcium. Since it is the ionized calcium that is physiologically active, when its levels decrease, symptoms such as muscle cramps or spasms can occur, which is termed as hypocalcemia.
In conclusion, the carpopedal spasms in hyperventilation syndrome are due to a relative hypocalcemia caused by an increase in bound calcium, and not due to a decrease in total calcium -- which would be considered true hypocalcemia. Thus, the correct choice is A) Hypocalcemia, decrease in unbound calcium.