Saturday, June 30, 2012


Hyperventilation in Flying

When you breath too rapidly you blow off too much carbon dioxide. Basically, it affects the amount of free hydrogen ions (that determine acidity - too little pH above 7.0 (alkaline) - too much pH below 7.0 (Acidic).

The increased pH causes symptoms that alarms pilots when it occurs. When your frightened you breathe even faster and more deeply that increases the symptoms.

Hyperventilation can lead to unconsciousness when your respiratory system tries to regain control of your breathing.

Two instances where hyperventilation can occur is scuba diving and flying at higher altitudes. In both these situations a pilot may breathe faster than normal.

A little gruesome is the panic one feels when terminally ill with lung disease and breathing is difficult. You attempt to breathe faster and the pain becomes severe.

Many of these symptoms are similar to hypoxia. It is important to recognize the differences and diagnose what is really happening.

If you are using oxygen check the equipment and flow rate to ensure the symptoms are not hypoxia related.

Common symptoms of hyperventilation include:

• Visual impairment
• Unconsciousness
• Lightheaded or dizzy sensation
• Tingling sensations
• Hot and cold sensations
• Muscle spasms

Breathing normally is the best treatment for hyperventilation.
It restores the proper carbon dioxide level in the blood stream of your body. Sensors pick up on the lowered levels and restores normal breathing.

Another device is breathing into a paper bag (mixture begins to build up the amount of carbon dioxide which you inhale. This increases the concentration of carbon dioxide in your blood. (restores normal breathing). Talking aloud does the same thing. It prevents the release of carbon dioxide. Since, if you're still alive :):) , your cells continue to form carbon dioxide from normal respiration and the symptoms of hyperventilation disappear. The concentration of carbon dioxide rises in the blood. The pH of your blood lowers to the normal value of 7.42. (blood pH is slightly alkaline)

These methods of reversing the effects of hyperventilation will help after you recognize the symptoms.

Friday, June 29, 2012

Histotoxic Hypoxia

Histotoxic Hypoxia

In histotoxic hypoxia cells cannot use oxygen effectively. In this type of hypoxia the supply of oxygen is normal. Compromised is  the ability to use the oxygen.

Cellular respiration is the process where nutrients, after digestion into membrane selectable molecules, proceed into a series of chemical changes to produce ATP that provides the energy for the body to function.

There are both physical and chemical means to limit the ability of a cell's use of oxygen.

The beauty of the human body is the creation of energy at normal body temperature. (98.6 degrees Fahrenheit) Factors that may effect metabolism and cellular respiration is changes in the enzymes that catalyze the chemical reactions. Since these enzymes are located in a living human or lower animal they are called bio-enzymes. They need a perfect environment to operate and allow chemical reactions to proceed at body temperature. 

The practice of Medicine is the care of the body Systems that help, in normal conditions, to maintain this perfect environment for all the enzymes in the body. Oxygen is the final reactant, in this whole process that forms the ATP, that each and every cell in the body uses to produce its specific function.

Temperature changes, pH(Acidic Measurement), Concentrations of  liquid solutes, Trauma to the body (Shaking, automobile accident), Inorganic co-enzymes, and the concentration of enzymes themselves may change the enzyme or stop its production to prevent it from catalyzing its particular function. When that happens the entire reaction chain stops. Oxygen isn't utilized until the body can return itself to a perfect operating environment.

If this is serious the body may need a physician to help in the recovery.

There are substances that can affect the ability of an enzyme to attach to a chemical that is necessary for a reaction to take place. When the physical shape, of an enzyme changes, it is denatured and is no longer effective.
Chemicals that bring about change are drugs that can affect the perfect environment of the enzyme. Alcohol, poisons, narcotics, drinks that are too acidic or alkaline are a few examples.

Physical factors could be trauma, changes in membrane thickness (cellular) and, of course, the altitude which controls air pressure.

Histotoxic hypoxia is a very important form of hypoxia because substances that we eat, smell or absorb can interfere with the physiology of cells.

Thursday, June 28, 2012

Stagnant Hypoxia

Stagnant Hypoxia

Stagnant means “not flowing,” and stagnant hypoxia, or ischemia, results when the oxygen-rich blood in the lungs is not moving, for one reason or another, to the tissues that need it. 

An arm or leg “going to sleep” because the blood flow has accidentally been shut off is one form of stagnant hypoxia.

On a more serious note, this kind of hypoxia can also result from shock, the heart failing to pump blood effectively, or a constricted artery

A rapid pull up from a steep dive causes a Grey Out due to excessive g-forces that occur during the recovery. This is due to the inability to move oxygen-rich blood to the brain. A Black Out is more pronounced.

Cold temperatures also can reduce circulation and decrease the blood supplied to extremities.

The illustrations with stagnant hypoxia are important but the underlying physiology is simpler.

Hypemic Hypoxia

Hypemic Hypoxia

When blood cannot supply enough oxygen to all the cells in our body it is called hypemic hypoxia

The oxygen deficiency is not caused by a lack of inhaled oxygen from the atmosphere. Severe bleeding (reduced blood volume), certain blood diseases (anemias), smoking (carbon monoxide ), altitude and whole blood donations (lack of red blood cells in sufficient numbers) are conditions that may occur to cause the lack of oxygen for normal functioning. Carbon monoxide presence is the most common and affects a blood molecule called hemoglobin.

Hypemic hypoxia is the result of hemoglobin that can't  chemically bind oxygen molecules. Why can't they bind the oxygen?

Engines produce a colorless, odorless  gas named carbon monoxide (CO). It provides the competition for the oxygen binding sites on the hemoglobin molecule when it is present in the air you breath inside the cockpit. In automobiles, an additive is added to the gasoline they burn that warns the occupants that exhaust fumes exist inside the car that contains carbon monoxide molecules. If you ignore the warnings, and fail to open windows for proper ventilation, your blood hemoglobin binding sites are occupied by carbon monoxide rather than oxygen. Remember carbon monoxide has a much greater attraction for hemoglobin than oxygen.

The affinity of carbon monoxide for hemoglobin binding sites is twenty times that of oxygen. It creates an unfair disadvantage for oxygen. Oxygen loses the binding site competition and you can lose you life if you don't respond to the warnings that carbon monoxide is present in your car or planes passenger compartment.

Your plane engine, through the mixture control, is adjustable to eliminate most of the unburned fuel. When you back off on the mixture control by 25 to 50 degrees, the presence of carbon dioxide is there, but virtually undetectable by your sense of smell.

Since the carbon monoxide is twenty times more likely to bind to oxygen the net result of the exhaust leak into a planes interior is you become unconscious before you detect the exhaust leak. If you can't respond the plane will crash.

You may read stories, periodically, about young couples found dead in "Lovers Lanes" because of carbon monoxide poisoning. It is unmistakeable,  because the skin is bright red from carbon monoxide  when the couple is found.

There is a fix. There are carbon monoxide detectors, on the market, that provide visual indications or beep a loud, distinctive sound, or both, that carbon monoxide is present.

You respond by increasing the fresh air ventilation. You just prevented a life threatening event from happening by responding, with knowledge. The correct fix is fresh air immediately to refresh your body with the oxygen it requires. 

Hypoxia takes many forms and you just found a very important way to avoid hypoxia in aircraft.

Wednesday, June 27, 2012

Hypoxic Hypoxia

Hypoxic Hypoxia

Hypoxic hypoxia is the result of low oxygen levels available to the entire body. A blocked airway and drowning are  examples of how the lungs can be deprived of oxygen.

The reduction in partial pressure of oxygen at high altitude is an appropriate example for pilots.

Although the percentage of oxygen in the atmosphere is constant, its partial pressure decreases proportionately as atmospheric pressure decreases. 

As the airplane climbs during flight, the percentage of each gas in the atmosphere remains the same, but there are fewer molecules available. Why?

Daltons Law of Partial Pressure states that each gas exerts a unique pressure at STP. For oxygen, at STP, this is 20% of 760 mm Hg for an Atmosphere, or a partial pressure of 159 mm Hg. 

At 18,000 feet the atmospheric pressure is one half what it is at sea level. 360 mm Hg comes to mind. Take 20% of 360 and the drop in oxygen partial pressure goes to 72 mm Hg.

Your body needs approximately 100 mm Hg partial pressure at the alveolar sacs to replenish to adequate levels of oxygen in the blood. Why the drop from 159 mm Hg to 100 mm Hg at sea level.

When the air mixes with carbon dioxide and water vapor, in the physical respiratory system track, before it gets to the alveoli, the partial pressure of oxygen is too low to keep you awake for flying. You will pass out in approximately thirty minutes without supplemental oxygen.

The decrease in the partial pressure of oxygen prevents an adequate number of oxygen molecules reaching the alveoli.

This is hypoxic hypoxia.

Hypoxia - Symptoms

Hypoxia Symptoms

There are several types of hypoxia but each causes the brain to receive less oxygen than normal. This is hypoxia and, as you receive less oxygen, each of us that experience hypoxia don't realize the symptoms that warn us we are impaired.

A general feeling that "all is well" and we think nothing is wrong because we feel so good. If the lack of available oxygen decreases more your arms and legs don't seem as responsive and coordinated flying starts to disappear.

Most folks may or may not share the following symptoms that reflect you are hypoxic.
  • Cyanosis - (blue fingernails and lips)
  • Headache
  • You don't react well
  • Your judgement is impaired
  • Feeling of "all is well"
  • Vision begins to deteriorate
  • You become sleepy
  • You become lightheaded
  • You experience dizziness
  • You have tingling sensations in your hands and feet
  • Numbness
If the hypoxia worsens the field of vision narrows. (it is like looking through a tube - peripheral vision disappears). Your ability to interpret what the instruments show dissolves. You have a false sense of security and are deceived into thinking everything is normal.

The treatment for hypoxia, while flying, includes flying at lower altitudes or using supplemental oxygen.

All pilots are susceptible to hypoxia regardless of physical endurance or acclimatization. If you plan to fly at high altitudes you must use supplemental oxygen to avoid the symptoms of hypoxia.

The term "time of useful consciousness" describes the maximum time the pilot has to make rational life-saving decisions and  carry them out at a given altitude without supplemental oxygen. As your altitude increases above 10,000 feet the symptoms of hypoxia increase rapidly. The time of useful consciousness rapidly decreases.

Since symptoms of hypoxia can be different for each individual, the ability to recognize hypoxia can be greatly improved by experiencing and witnessing the effects of it during an altitude chamber “flight.” (hyporbaric chamber)

The Federal Aviation Administration (FAA) provides this opportunity through aviation physiology training, which is conducted at the FAA CAMI and at many military facilities across the United States. For information about the FAA’s one-day physiological training course with altitude chamber and vertigo demonstrations, visit the FAA web site above. 

Landing Errors due to Optical Illusions

Landing Illusions

Illusions created in flying an airplane can kill. This post provides pilots with information to recognize conditions that lead to optical illusions and how to cope while flying.

  • You can anticipate the possibility of visual illusions when you fly into a new airport destination.  Especially at night and/or when adverse weather conditions exist. Make sure you consult Jepp Charts on runway slope, terrain and lighting.
  • Increase your scan of the altimeter during all approaches in day or night conditions.
  • If possible, consult with a pilot that actually landed at the new airport destination. He may provide important information. If not, try and inspect the the airport yourself before flying there.
  • Use Visual Approach Slope Indicators (VASI) or Precision Approach Path Indicators (PAPI).These systems help visual reference in adverse conditions where the horizon is obscured or visually missing. Another source is an electronic glideslope, if available.
  • Use a visual descent point (VDP) found on many non-precision instrument approach procedure charts. These help protect you from beginning your approach too soon or too late.
  • If emergency or other activity distracts you from your usual approach procedures the chance of an accident  increases.
  • Maintain, by practice, proficiency in landing procedures.

In addition to the sensory illusions due to misleading inputs to the inner ear vestibular system, a pilot may also encounter various visual illusions during flight.

Illusions rank among the most common factors cited as contributing to fatal aviation accidents. That is one of the safety factors stressed in my posts.

Sloping cloud formations, an obscured horizon, a dark scene spread with ground lights and stars and certain geometric patterns of ground light can create illusions of not being aligned correctly with the actual horizon. these may cause you to approach too high or too low. Serious matters depending on obstructions before the runway or running out of runway if too high.

Various surface features and atmospheric conditions encountered in landing can create illusions of being on the wrong approach path. Landing errors due to these illusions can be prevented by anticipating them during approaches, inspecting unfamiliar airports before landing, using electronic glideslope or VASI systems when available, and maintaining proficiency in landing procedures.

Tuesday, June 26, 2012

Like a Sinking Plane - Does it Create Lift

Sinking Planes - Do they create Lift?

Lets exaggerate a possible situation how an airplane in flight adjusts its own lift to its own weight.

First have the airplane flying straight and level at cruising speed. The airplanes lift and weight are in equilibrium. More lift than weight it would balloon upward. More weight than lift it would sink. Since it is flying straight and level it is "in balance."

Keeping the planes attitude exactly as it was in straight and level flight reduce the speed by twenty miles per hour. Using the controls keep the nose of the aircraft, relative to the horizon, exactly where it was in straight and level flight.

To see what happens, in just a fraction of time, let these events seem like they take minutes to occur.

If everything remains the same (attitude, relative wind, angle of attack) the wings move through the air at a slower speed and develop less lift. 

If you have a 3,500 pound SeaBee and it is only developing 3,000 pounds of lift force it does what a stone does - it drops.

It doesn't drop nose down because you, the pilot, are maintaining the attitude exactly as it was in straight and level flight. You are not allowing the attitude to change with respect to the horizon. The plane does not descend, it falls.

A plane, like a falling stone, falls slowly at first, then falls faster and faster because of gravity. If nothing else happens gravity acts on the 500 pound difference between the weight of the SeaBee and the 3000 pounds of lift force until the airplane crashes into the ground.

Something does happen to stop its falling like a rock. Remember, the SeaBee is sometimes referred to as "The Flying Rock" for it tendency to enter a steep glide angle after you cut power for a landing.

All of the above happens so fast (remember we delayed the events) the plane falls only a few inches. It finds a cushion of new lift and what creates this cushion is the aircraft's sinking. How does this happen?

As the airplane moves downward through the air as well as forward the relative wind now blows at the wings as well from in front. The Angle of Attack becomes greater even when the attitude of the plane hasn't changed. Angle of Attack is the angle at which the wing meets the air. The greater the Angle of Attack means that more lift is created. As the plane reaches a sinking speed at which the Angle of Attack is so high that lift forces are now equal to its weight and the plane acts like an aircraft again.

If the power is maintained at the level you reduced it to the aircraft recovered its equilibrium in descent and it will stay in descent. It is a steady descent.

This is a "Power Descent" much like a modern commercial jet that cuts power many miles from the airport as it begins it approach.

You see, a sinking plane does create lift!

Monday, June 25, 2012

A New Look at Dalton's Law of the Partial Pressures of Gases

Dalton's Law of Partial Pressures - New Look

Why do we seem "winded" on a hot, humid Summer day? Why can't we cool down? Good questions. At Standard Temperature and Pressure, at Sea Level, one Atmosphere consists of nitrogen, oxygen, carbon dioxide, water vapor and trace gases. If you took the partial pressures of each gas they would exert their pressures independently of each other but, in total, would add up to 760 mm Hg at STP.

Each of these gases make up a  specific percentage of the whole atmosphere. This doesn't change. Nitrogen 79% , oxygen 20% and all the rest 1%. If water vapor partial pressure increases the partial pressures of the other gases is reduced to reflect the presence of water vapor in the atmosphere. The slight reduction in oxygen's partial pressure is enough to "tire" us a bit.

In dry climates the humidity is low. In sunny South Carolina the humidity is quite high. The "Comfort Index" indicates conditions are very uncomfortable. Why is that?

Upon evaporation of water (changing from a liquid state to a gaseous state) the evaporation could use up 580 +- calories per gram of water evaporated. In total, that is a "cooling effect" that makes you feel good and normal body temperature is a good thing to control. Think heat prostration and heat stroke.

If the water vapor content is high, evaporation ceases or decreases. You can't convert water to water vapor to create the cooling effect.

Notice, all of these changes are taking place at sea level, with slight adjustments for the elevation.