||e. In patients with chronic bronchitis, emphysema, bronchiectasis, and cor pulmonale, where oxygenation is already compromised, exposure to altitude may result in severe tissue hypoxia. Most of these patients may be transported satisfactorily provided that supplementary oxygen is available during the flight. A ground level PO2 of 50 mmHg is a good indication that supplementary oxygen should be used. The use of 100% oxygen may, however, worsen some cases, since it may remove the hypoxic drive to ventilation, with consequent hypoventilation and carbon dioxide retention. In general, dyspnea at rest is a contraindication to flight, and patients with poor exercise tolerance (dyspnea after walking 50 m on level ground) require further assessment with full pulmonary function tests and a trial of 100% oxygen. Although a low pre-flight arterial PO2 level provides a useful pointer to likely in-flight problems, the additional use of pulmonary function tests, and particularly the FEV1, is even more valuable.
Fitness to Travel by Air. In: Harding RM, Mills FJ, eds. Aviation Medicine, 3rd ed. London: British Medical Journal, 1993:58-72.