Preflight medical screening of patients.

Travel by commercial jet aircraft is a popular, expeditious, safe and generally affordable mode of transportation. Millions of passengers fly all over the world every year. A proportion of them are disabled, or have experienced recent injury or illness. Despite the comfort and convenience of modern commercial aircraft, there are environmental factors that may affect some persons, particularly those with limited physiological reserve. By far the most important one is reduced barometric pressure (PB), which may expose patients with altered pulmonary gas exchange to a poorly tolerated hypoxic stress. Altitude is associated with a decrease in PB. The cruising altitude of most commercial airliners is 9,000±12,000 m, which corresponds to a PB decrease from the sea-level 101 kPa (760 mmHg) to 30.7±19.3 kPa (231±145 mmHg). The inspired partial pressure of oxygen (PI,O2) at 9,000 m can be calculated from the equation: PI;O2 ˆ FI;O2…PBÿPair;H2O…378C†† ˆ 5:1 kPa …39 mmHg†; …1†