Definition of Obesity hypoventilation syndrome (OHS):

Obesity hypoventilation syndrome (OHS) is a condition that occurs in obese people, in which poor breathing leads to lower oxygen levels and higher carbon dioxide levels in the blood.

Causes, incidence, and risk factors:

The exact cause of OHS in unknown. Most (but not all) patients with the syndrome have a form of sleep apnea.

OHS is believed to result from both a defect in the brain's control over breathing, and excessive weight (due to obesity) against the chest wall, which makes it hard for a person to take a deep breath. As a result, the blood has too much carbon dioxide and not enough oxygen. People with OHS are often tired due to sleep loss, poor sleep quality, and chronic hypoxia.

Excess (morbid) obesity is the main risk factor.

See also: Respiratory acidosis