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 【B1】 only once—for a woman who had merely feinted. But the 【B2】 made me quite curious about how 【B3】 this kind of thing happens. I wondered what I would do if 【B4】 with a real midair medical emergency—without access 【B5】 a hospital staff and the usual emergency equipment So 【B6】 the New England Journal of Medicine last week 【B7】 a study about in-flight medical events, I read it 【B8】 interest The study estimated that there are a(n) 【B9】 of 30 in-flight medical emergencies on U.S. flights every day. Most of them are not 【B10】; fainting and dizziness are the most frequent complaints. 【B11】 13% of them— roughly four a day—are serious enough to 【B12】 a pilot to change course. The most common of the serious emergencies 【B13】 heart trouble, strokes, and difficulty breathing. Let’’s face it plane rides are 【B14】. For starters, cabin pressures at high altitudes are set at roughly 【B15】 they would be if you lived at 5,000 to 8,000 feet above sea level. Most people can tolerate these pressures pretty 【B16】, but passengers with heart disease 【B17】 experience chest pains as result of the reduced amount of oxygen flowing through their blood. 【B18】 common in-flight problem is deep venous thrombosis—the so-called economy class syndrome (综合症). 【B19】 happens, don’’t panic. Things are getting better on the in-flight-emergency front. Thanks to more recent legislation, flights with at 【B20】 one attendant are starting to install emergency medical kits to treat heart attacks.