This is a medical question of type : exams and tests 
 How to diagnose Obesity Hypoventilation Syndrome ? 
 Obesity hypoventilation syndrome (OHS) is diagnosed based on your medical history, signs and symptoms, and test results.
                
Specialists Involved
                
A critical care specialist, pulmonologist (lung specialist), and/or sleep specialist may diagnose and treat your condition.
                
A sleep specialist is a doctor who diagnoses and treats sleep problems. Examples of such doctors include lung and nerve specialists and ear, nose, and throat specialists. Other types of doctors also can be sleep specialists.
                
Your health care team also may include:
                
A registered dietitian or nutritionist to help you plan and follow a healthy diet. (Your primary care doctor also might oversee weight-loss treatment and progress.)
                
An exercise physiologist or trainer to assess your fitness level and help create a physical activity plan that's safe for you.
                
A bariatric surgeon if weight-loss surgery is an option for you.
                
Medical History and Physical Exam
                
Your doctor will ask about your signs and symptoms, such as loud snoring or daytime sleepiness. He or she also may ask about your use of alcohol and certain medicines, such as sedatives and narcotics. These substances can worsen OHS.
                
During the physical exam, your doctor will listen to your heart with a stethoscope. He or she also will check to see whether another disease or condition could be the cause of your poor breathing.
                
Diagnostic Tests
                
In OHS, poor breathing leads to too much carbon dioxide and too little oxygen in the blood. An arterial blood gas test can measure the levels of these gases in your blood.
                
For this test, a blood sample is taken from an artery, usually in your wrist. The sample is then sent to a laboratory, where the oxygen and carbon dioxide levels are measured.
                
Other tests also can measure the carbon dioxide level or oxygen level in your blood. These tests include a serum bicarbonate test and pulse oximetry.
                
A serum bicarbonate test measures the amount of carbon dioxide in the liquid part of your blood, called the serum. For this test, a blood sample is taken from a vein, usually in your wrist or hand.
                
Pulse oximetry measures the level of oxygen in your blood. For this test, a small sensor is attached to your finger or ear. The sensor uses light to estimate how much oxygen is in your blood.
                
Other Tests
                
Your doctor may recommend other tests to help check for conditions and problems related to OHS.
                
Polysomnogram
                
A polysomnogram (PSG) is a type of sleep study. You usually have to stay overnight at a sleep center for a PSG. The test records brain activity, eye movements, heart rate, and blood pressure.
                
A PSG also records the amount of oxygen in your blood, how much air is moving through your nose while you breathe, snoring, and chest movements. The chest movements show whether you're making an effort to breathe.
                
Your doctor might use the PSG results to help diagnose sleep-related breathing disorders, such as sleep apnea.
                
Lung Function Tests
                
Lung function tests, also called pulmonary function tests, measure how well your lungs work. For example, these tests show:
                
How much air you can take into your lungs. This amount is compared with that of other people your age, height, and sex. This allows your doctor to see whether you're in the normal range.
                
How much air you can blow out of your lungs and how fast you can do it.
                
How well your lungs deliver oxygen to your blood.
                
The strength of your breathing muscles.
                
Chest X Ray
                
A chest x ray is a test that creates pictures of the structures inside your chest, such as your heart, lungs, and blood vessels. This test can help rule out other conditions that might be causing your signs and symptoms.
                
EKG (Electrocardiogram)
                
An EKG is a test that detects and records the heart's electrical activity. The test shows how fast the heart is beating and its rhythm (steady or irregular). An EKG also records the strength and timing of electrical signals as they pass through your heart.
                
The results from an EKG might show whether OHS has affected your heart function.
                
Other Tests
                
A complete blood count (CBC) can show whether your body is making too many red blood cells as a result of OHS. A CBC measures many parts of your blood, including red blood cells.
                
A toxicology screen is a group of tests that shows which medicines and drugs you've taken and how much of them you've taken. A blood or urine sample usually is collected for a toxicology screen.