Hyperventilation refers to a higher-than-normal rate and depth of breathing, often associated with anxiety attacks. This excessive breathing surpasses the body's need to expel CO2, leading to a condition known as hypocapnia – an unusually low level of carbon dioxide in the blood. Hypocapnia can constrict cerebral blood vessels, reducing blood flow to the brain, which may result in dizziness or fainting. Early signs include tingling and muscle spasms in the hands and face, caused by falling blood calcium levels as blood pH rises. A simple remedy involves breathing into a paper bag, allowing re-inhalation of expired air rich in CO2 and as a result, retaining it in the blood.
On the other hand, hyperpnea is an increased ventilation response to meet metabolic needs commonly observed during physical exertion that heightens oxygen demand in active muscles. The onset of hyperpnea as exercise begins is thought to be influenced by psychological anticipation of exercise, cortical motor activation of muscles and respiratory centers, and excitatory impulses from moving muscles, tendons, and joints reaching the respiratory centers. The medulla oblongata's ventral respiratory center coordinates this process, activating accessory muscles for breathing. In extreme cases of forced breathing, abdominal muscles participate in exhalation, compressing against the diaphragm and reducing the thoracic cavity's volume.
