In this video, from our Pulmonary Function Testing Essentials course, you'll learn about the physiological basis for (and interpretation of) high altitude simulation tests that are used when assessing patients who are planning for commercial air travel.
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[00:00:00] Commercial airline flight exposes patients and crew to atmospheric conditions similar to ascending to an altitude of 1,800 to 2,400 meters. Under the hypobaric conditions of air travel, arterial PO2 falls. For people with normal lung function and normal resting arterial oxygen levels at sea level,
[00:00:30] the fall still translates into an acceptable arterial PO2. However, for patients with lung disease like obstructive airways disease or interstitial lung disease, the fall in arterial PO2 during flight may be a problem. Two approaches have been taken in evaluating such patients for air travel. One, use of a nomogram and two, use of the high altitude
[00:01:00] simulation test or HAST. The first approach uses regression equations and a nomogram to predict the resulting arterial PO2 in flight. Using the patient's arterial PO2 at sea level, along with the FEV1% predicted, arterial PO2 at an altitude equivalent to 2,400 meters can be estimated and if necessary supplemental
[00:01:30] oxygen can be prescribed. The other approach, now offered in many pulmonary function laboratories, is the high altitude simulation test or HAST, also known as the hypoxia inhalation test. The patient breathes a hypoxic gas mixture, which contains 15.1% oxygen. This percentage of oxygen mimics the oxygen concentration in an airplane cabin
[00:02:00] pressurized to about 2,400 meters above sea level. The electrocardiogram is monitored following a period of equilibration, which generally is about 20 minutes. An arterial blood gas analysis is performed and arterial PO2 measurement obtained. Supplemental oxygen can then be titrated to mitigate the drop in oxygen saturation or PO2 [00:02:30] and a prescription for supplemental oxygen use during flight created.