As a physician who travels quite a lot, I spend a lot of time on planes listening for that dreaded 'Is there a doctor on board?' announcement. I've been【C1】______only once--for a woman who had merely fainted. But the【C2】______made me quite curious about how【C3】______this kind of thing happens. I wondered what I would do if【C4】______with a real midair medical emergency--without access【C5】______a hospital staff and the usual emergency equipment. So【C6】______the New England Journal of Medicine. last week【C7】______a study about in-flight medical events, I read it【C8】______interest. The study estimated that there are a(n)【C9】______of 30 in-flight medical emergencies on U. S. flights every day. Most of them are not【C10】______ fainting and dizziness are the most frequent complaints.【C11】______13% of them--roughly four a day--are serious enough to【C12】______a pilot to change course. The most common of the serious emergencies【C13】______heart trouble strokes, and difficulty breathing. Let's face it: plane rides are【C14】______For starters, cabin pressures at high altitudes are set at roughly【C15】______they would be if you lived at 5,000 to 8,000 feet above sea level. Most people can tolerate these pressures pretty【C16】______, but passengers with heart disease【C17】______experience chest pains as a result of the reduced amount of oxygen flowing through their blood.【C18】______common in-flight problem is deep venous thrombosis--the so-called economy class syndrome(综合症).【C19】______happens, don't panic. Things are getting better on the in-flight-emergency front. Thanks to more recent legislation, flights with at【C20】______one attendant are starting to install emergency medical kits to treat heart attacks. 【C1】