Formal criteria for diagnosis of<unk>  are: * Body mass index over 30 kg/m2 (a measure of<unk> , obtained by taking one's weight in kilograms and dividing it by one's height in meters squared) * Arterial carbon dioxide level over 45 mmHg or 6.0 kPa as determined by arterial blood gas measurement * No alternative explanation for<unk> , such as use of narcotics, severe obstructive or interstitial lung disease, severe chest wall disorders such as kyphoscoliosis, severe hypothyroidism (underactive thyroid), neuromuscular disease or congenital central<unk>  syndrome If<unk>  is suspected, various tests are required for its confirmation. The most important initial test is the demonstration of elevated carbon dioxide in the blood. This requires an arterial blood gas determination, which involves taking a blood sample from an artery, usually the radial artery. Given that it would be complicated to perform this test on every patient with sleep-related breathing problems, some suggest that measuring bicarbonate levels in normal (venous) blood would be a reasonable screening test. If this is elevated (27 mmol/l or higher), blood gasses should be measured. To distinguish various subtypes, polysomnography is required. This usually requires brief admission to a hospital with a specialized sleep medicine department where a number of different measurements are conducted while the subject is asleep; this includes electroencephalography (electronic registration of electrical activity in the brain), electrocardiography (same for electrical activity in the heart), pulse oximetry (measurement of oxygen levels) and often other modalities. Blood tests are also recommended for the identification of hypothyroidism and polycythemia. To distinguish between<unk>  and various other lung diseases that can cause similar symptoms, medical imaging of the lungs (such as a chest X-ray or CT/CAT scan), spirometry, electrocardiography and echocardiography may be performed. Echo- and electrocardiography may also show strain on the right side of the heart caused by<unk> , and spirometry may show a restrictive pattern related to<unk> . Classification<unk>  is a form of sleep disordered breathing. Two subtypes are recognized, depending on the nature of disordered breathing detected on further investigations. The first is<unk>  in the context of obstructive sleep apnea; this is confirmed by the occurrence of 5 or more episodes of apnea, hypopnea or respiratory-related arousals per hour (high apnea-hypopnea index) during sleep. The second is<unk>  primarily due to "sleep<unk>  syndrome"; this requires a rise of CO2 levels by 10 mmHg (1.3 kPa) after sleep compared to awake measurements and overnight drops in oxygen levels without simultaneous apnea or hypopnea. Overall, 90% of all people with<unk>  fall into the first category, and 10% in the second.
Obesity hypoventilation syndrome
Central hypoventilation syndrome
Hyperventilation syndrome
Upper airway resistance syndrome
Reactive airway disease
Sleep apnea
Cardiac asthma
Central sleep apnea