Some forums threads suggest another solution to fix the gray out iPhone 4S Wifi issue: placing the iPhone 4S in a refrigerator or freezer for several minutes, for they considered the 4S WiFi issue after iOS 7 update is caused by the heating issues.
An ABG test uses blood drawn from an artery, where the oxygen and carbon dioxide levels can be measured before they enter body tissues. Partial pressure of oxygen (PaO2). This measures the pressure of oxygen dissolved in the blood and how well oxygen is able to move from the airspace of the lungs into the blood.
This is a blood test that may be ordered with your PFTs to give your doctor even more information about your lung health. ABGs can show how well your lungs are getting oxygen into your blood and carbon dioxide out of your blood. For this test, a sample of blood is drawn from your artery, from your wrist or elbow area.