Sure, There's A Lot To Learn; But IT Could Save Your Life

by Dean Stevenson, Aviation Lecturer

(This article, from the online journal "Aviation & Safety," looks like vital reading to us. We hope you agree. -- ed.)
 
Many of you know of the following conditions that could possibly occur in flight, typically in unpressurized aircraft. They normally do not affect persons below 10,000 feet (with the exception of night vision) and as a reminder I refresh your memories to:

Hypoxic Hypoxia which is a reduction in the amount of oxygen passing into the blood. It is caused by a reduction in oxygen pressure in the lungs, by a reduced gas exchange area, exposure to high altitude, or by lung disease. [This is the hypoxia that is a hazard to aviators.]

Hypemic Hypoxia (Anemic) is defined as a reduction in the oxygen carrying capacity of the blood. It is caused by a reduction in the amount of hemoglobin in the blood or a reduced number of red blood cells. A reduction in the oxygen transport capacity of the blood occurs through blood donation, hemorrhage, or anemia. A reduction in the oxygen carrying capacity of the blood occurs through drugs, chemicals, or carbon monoxide. [This hypoxia usually experienced by smokers.]

Stagnant Hypoxia is an oxygen deficiency due to poor circulation of the blood or poor blood flow. Examples of this condition are high "G" forces, prolonged sitting in one position or hanging in a harness, cold temperatures, and positive pressure breathing. [This hypoxia usually experienced when sitting for hours in a boring class or crunched up on a low altitude long haul flight.]

Histotoxic Hypoxia is defined as the inability of the tissues to use oxygen. Examples are carbon monoxide and cyanide poisoning. Certain narcotics, chewing tobacco, and alcohol will prevent oxygen use by the tissues. [This hypoxia usually experienced after drinking too much.] Of course this we know from basic PPL and CPL information when doing a ground school.

Ischemia is often a age related condition and if your reader smoked for a number of years, the long term effect of his smoking career would now manifest itself from a possible hardening of the arteries or some form of stenosis (chronic narrowing of a possible supply artery). In short, Ischemia is insufficient blood flow to provide adequate oxygenation. This, in turn, leads to tissue hypoxia (reduced oxygen) or anoxia (absence of oxygen). Ischemia always results in hypoxia; however, hypoxia can occur without ischemia if, for example, arterial hypoxia occurs. When the tissue is unable to extract adequate oxygen, the partial pressure of oxygen within the tissue falls (hypoxia) leading to a reduction in mitochondrial respiration and oxidative metabolism.

In a recent study in the states on this very subject, it was concluded that the Time of Useful Consciousness (TUC) made no apparent difference between smokers and non-smokers. In fact, the ability of smokers to perform tasks at certain altitudes sometimes bettered the non-smokers results.

In 1997 test results from a series of experiments showed that Increased levels of carboxyhemoglobin (COHb) in smokers are blamed for inducing pre-hypoxic tendencies classified as anemic hypoxia. So it was thought that if COHb can be simply converted to altitude, there should be significant differences between smokers and nonsmokers with respect to hypoxia tolerance. However, the studies of the effects of carbon monoxide and/or smoking habits on the physiological functions at altitude do not have consistent conclusions, and many pilots still have smoking habits. This study was designed to assess whether there was a definite significant difference for time of useful consciousness, subjective symptoms, or performance degradation between nonsmokers and smokers.

The method was, during the hypoxia experience of routine physiological training, TUC and 12 typical subjective symptoms were examined at the chamber altitude of 25,000 ft (7620 m) in 589 nonsmokers and 582 smokers in Study 1. The time until the deterioration of handwriting was assessed by 6 physiological training observers in 51 nonsmokers and 70 smokers in Study 2. The results were compared between the groups.

Smokers revealed significantly fewer subjective symptoms in 5 out of 12 symptoms. There were no significant differences in TUC and the rate of handwriting deterioration between the groups.

And this is the bit that makes you blink, paradoxically, smokers are slightly resistant to hypoxia with respect to emerging subjective symptoms. However, bluntness to hypoxia could postpone the detection of the possible hypoxic So there you have it, the smoking tendencies more likely "blanked" off the hypoxic awareness. Now that the reader has stopped his smoking, his body has become more aware of the symptoms associated with Hypoxia.

In summary, be thankful for two things, one you have stopped smoking and two, you can recognize the hypoxic symptoms.

FMI: www.aviationmedicine.com/smoking.htm