USN T-45 Grounded After Pilots Strike

[SpazSinbad]

Way back when A-4 pilots sucked pure oxygen under pressure from their masks (one had to get used to opening the mouth with outward pressure to resist the inward pressure of the LOX coming down). Valsalva Maneuver anyone? Buehler? Anyone? Best let medicos explain:

Physiology of Flight
"...Another oxygen effect which may be loosely grouped under the general heading of oxygen toxicity is atelectasis while breathing 100 percent oxygen during + Gz acceleration, although the term “oxygen toxicity” in this context is a misnomer. Acceleration atelectasis is included in this section only because it occurs when an aviator is breathing 100 percent oxygen. The primary factor responsible for the atelectasis is probably the complete cessation of basilar alveolar ventilation under acceleration. There is also markedly increased blood flow to the basilar alveoli as opposed to the apical ones, along with a reduction in basilar alveolar volumes as the weight of the lung under acceleration compresses the bases against the diaphragm. With these factors acting in concert, and when the alveoli in question contain only oxygen, water vapor, and carbon dioxide, oxygen absorption (the main cause of acceleration atelectasis) leads to alveolar collapse, and atelectasis can occur very rapidly.

If nitrogen is present in the inspired gas, the gas absorption and consequent alveolar collapse are greatly slowed. The time required for complete absorption of gas contained in the lower quarter of the unventilated lung, with normal blood flow distribution, is increased from five minutes on 100 percent oxygen to about 25 minutes on 50 percent oxygen, 50 percent nitrogen. In addition, there is evidence that nitrogen in the lung acts as a “spring” by preventing alveolar collapse when all the oxygen is absorbed.

Pulmonary atelectasis during flight may result in several performance-degrading effects, including distracting or perhaps even incapacitating cough and chest pain and arterial hypoxia due to the shunt of venous blood through the nonaerated alveoli. The Flight Surgeon should remain aware that coughing, substernal pain, and decreased altitude tolerance may indicate the development of this condition. In any event, acceleration atelectasis usually resolves itself in a few days with little or no treatment...." http://www.operationalmedicine.org/T...eonsManual.pdf

AP Impact: Air Force insiders foresaw F-22 woes 27 Sep 2012

“...The group [RAW-G] was founded by members of the F-22 community who were concerned about how the unique demands of the aircraft could affect pilots. The fighter can evade radar and fly faster than sound without using afterburners, capabilities unmatched by any other country. It also flies higher than its predecessors and has a self-contained oxygen generation system to protect pilots from chemical or biological attack....

...By the time RAW-G got going, some pilots were already experiencing a problem called "Raptor cough" — fits of chest pain and coughing dating back to 2000 that stem from the collapse of overworked air sacs in the lungs.

The group concluded that the F-22's On-Board Oxygen Generation System — or OBOGS — was giving pilots too much oxygen, causing the coughing. The more often and higher the pilots flew after being oxygen-saturated, group members believed, the more vulnerable pilots affected by the condition would be to other physiological incidents.

RAW-G recommended more tests and that the F-22's oxygen delivery system be adjusted through a digital controller and a software upgrade.

"The schedule would provide less oxygen at lower altitudes than the current schedule, which has been known to cause problems with delayed ear blocks and acceleration atelectasis," the technical term for the condition that leads to the coughing, according to the minutes from RAW-G's final meeting....” http://www.rdmag.com/news/2012/09/ap...saw-f-22-woes/