Anyone who flies, even as a passenger, can benefit from a basic knowledge of aviation physiology. It can be life-saving, as I hope to show.  A detailed topic, but I will try to keep it short, sweet and practical. For those who want more details, a simple Google or Wikipedia search on the specific topic will provide it.
Understand that the usual study of physiology concerns itself with abnormal physiology in a “normal” environment. Aviation physiology is about normal physiology in an “abnormal” environment. In order to understand it, we need to understand that environment, i.e. the atmosphere.

Most flight takes place in 3 layers or “strata” of the earth’s atmosphere. The Troposhere extends from the surface of the earth to about 35000 feet over the poles, and 65000 feet over the equator (i.e. it is not uniform). It is very important in aviation because weather happens here. It is characterized by decreasing temperature at a rate of about 2 degrees C for every thousand feet of altitude until it reaches a low of about  -55 degrees C. At the top is a thin layer called the Tropopause which traps water vapour in the lower level.  The Stratosphere extends upward from the tropopause about 22 miles. It is characterized by a constant temperature of – 55 degrees C and no moisture (water vapour).

The first BLOG in this series was titled "The Checklist". It discussed how pilots were the first to recognize the importance of checklists and develop them for aviation. Checklists were soon developed for all phases of flight as well as for mechanical and technical aircraft procedures. They have proven invaluable and have prevented countless accidents and deaths. They have also been adopted by many other disciplines (such as medicine) due to their utility and effectiveness in preventing errors and ensuring the best possible outcomes in almost any given situation or set of circumstances.

More recently, a checklist has been developed for a vital aircraft operating component...the pilot. This checklist is as important and valuable as any of the other checklists. It should be used by the pilot for each and every flight. It is referred to as the "I'M SAFE" checklist and is generally introduced in the early portion of most flight training programs. The mnemonic stands for:
I: Illness
M: Medication
S: Stress
A: Alcohol
F: Fatigue
E: Eating and Emotion (The FAA defines "E" as Eating - to include proper nutrition and hydration) Some other international aviation authorities define "E" as Emotion - referring to emotional and psychological state.

For further information check out the excellent article by Sarina Houston, aviation contributor for about.com, The I'm SAFE Checklist, Pilot Risk Management:There's a Checklist for That  click hiere    

 According to Transport Canada's Guide for Aviation Medical Examiners: "On any visit, a blood pressure level of 180 mmHG or more systolic or 105 mmHg or more diastolic, precludes medical certification". This is, without doubt, a dangerously high level of blood pressure. The guide also states that levels between 140 and 180 mmHg systolic and / or 90 and 105 mmHg diastolic require further evaluation.

"An applicant whose pressure does not exceed 155 mm mercury systolic and 95 mm mercury diastolic maximum pressure, who has not used antihypertensive medication for 30 days, and who is otherwise qualified should be issued a medical certificate by the Examiner."
Blood pressure readings in excess of these values will require the examiner to defer certification.

Regardless of what the agencies deem as acceptable blood pressure levels, the important point to be aware of is that hypertension is a thief and a killer. Over time, it will rob you of your health and then bring about a premature death. This knowledge had just begun to be realized when I was a medical student. Many slightly older physicians were not aware of this and did not believe it was necessary to treat high blood pressure. In their defense, it should be noted that the available antihypertensive medications of the day had many unpleasant side effects. Patients felt worse taking medication. In addition, there were no studies to prove that lowering the blood pressure with these medications was actually beneficial.

Since that time, many new medications have been developed and numerous high quality studies have shown unequivocally that lowering the blood pressure with these medications is extremely beneficial.

Perhaps just as important to the pilot or air traffic controller is the fact that many of these medications are acceptable to both Transport Canada and the FAA with no restriction to the medical certification.

The take home message: Adequately treated,  hypertension will not result in loss or restriction of your medical certificate. However, the complications of untreated hypertension very likely will.​

Fortunately, there are many things you can do to reduce high blood pressure if you are above the acceptable limits set out in the guidelines. These include lifestyle changes such as:

• weight loss
• exercise
• low salt and low fat diets
• quite smoking
• reduce caffeine

If necessary, there are many medications to control hypertension that are approved by both Transport Canada and the FAA.

The most important thing to remember is high blood pressure does not need to prevent you from being a pilot or air traffic controller. A single elevated reading is not enough for a diagnosis of hypertension. Anxiety, stress, fatigue, time of day may all affect a blood pressure reading, and if this occurs, several readings need to be done to obtain an average. Do not let fear prevent you from discussing this important issue with your doctor.
DO THE SMART THING!

For further reading from Hypertension Canada click here and from The American Heart Organization click here

Sleep apnea refers to a condition in which a sleeping individual stops breathing. Eventually, due to physiologic factors such as a drop in the oxygen saturation of the blood, the brain rouses the individual (usually only partially) and breathing resumes. The severity of the sleep apnea is gauged by how often these episodes occur, how long each one lasts, how much the blood oxygen level drops and other factors. In severe cases, this may occur hundreds of times per night leading to extremely fragmented and abnormal, non-restorative sleep. This results in a state of chronic fatigue along with all the medical issues described in part 1.

There are 3 types of sleep apnea: OBSTRUCTIVE, CENTRAL AND COMPLEX.

OBSTRUCTIVE SLEEP APNEA (OSA) is the most common type of sleep apnea.  It describes the obstruction of the airway by the tongue and soft palate during the deeper stages of sleep in susceptible individuals.

CENTRAL SLEEP APNEA is due to the brain failing to signal breathing, even though the airway is open.

COMPLEX SLEEP APNEA is a combination of the above types.

The following signs and symptoms may be related to non-restorative sleep due to sleep apnea. Anyone displaying one or more to any significant degree should have a sleep study.

Although being overweight or obese (BMI over 35), or having a large neck circumference (16” or more in females and 17” or more in males) do not predict sleep apnea in and of themselves, they are often associated with sleep apnea particularly in individuals with any of the above listed signs or symptoms.

There are several methods available to successfully treat sleep apnea. Not all are effective in every individual. These include oral appliances, CPAP (continuous positive airway pressure) machines, Surgery and others. In all cases, weight loss is important if the individual is overweight. In many cases, no other treatment is required.

Any individual who has suffered significant sleep apnea and been successfully treated will describe how good it was to once again feel “normal” and energetic. In addition, many medical problems such as high blood pressure resolve with no further need for medication.

All of us want to sleep well, feel well, and function at our best. Individuals who have safety-sensitive occupations upon which the welfare of others depends (such as pilots, air traffic controllers, etc.) have a moral, ethical and legal obligation to ensure they are fit to perform their duties. This concept is often referred to as "Self-assessment". I would urge any individual who believes they may suffer from sleep apnea to seek the advice of a sleep specialist.

For further information click here.

Sleep well, be well.

E.A. Mastrangelo, M.D.

We need to sleep. Everyone knows this instinctively. It is important to everyone and is critical for people in safety sensitive occupations....such as pilots.

It has been relatively recent that medical science has begun to study sleep in an in-depth fashion. This may be in part due to the fact that few adequate research tools were available to do this type of research. Most studies were of an observational nature or studied changes in blood chemistry. New tools are now available (such as neuro-imaging) and hold promise with respect to enhancing our knowledge in this area.

Numerous questions still exist. Why is sleep important? What function(s) does sleep serve? What ill effects will occur as a result of sleep deprivation? Why do some individuals tolerate sleep deprivation better than others? How do medications and what we eat and drink affect sleep architecture? And many more.

I suppose the place to start is with the basic question "Why do we need to sleep"? The following is taken from an article of the same title found in the MedSleep newsletter,  "Sleep Matters" (Volume 4.1) 

The multiple Hypotheses proposed to explain the function of sleep reflect our incomplete understanding. It is likely that sleep evolved to fulfill some sort of primitive function and has taken on multiple functions over time. Animals are most vulnerable when they are asleep. Evolution moves to minimize vulnerability. This would argue that sleep remains an essential physiologic process across all species.

 These hypotheses include:

GROWTH AND RESTORATION (bodily growth and development in children, and tissue repair and restoration in adults) 
ONTOGENESIS (development of an organism from the earliest stage to maturity)
MEMORY PROCESSING (allows solidification of knowledge and memory)
WASTE CLEARANCE (clearance of metabolic waste products produced by neural activity of the awake brain).

For further reading and information about MedSleep click here 

Normal sleep is divided into 2 main stages--NREM (non rapid eye movement) and REM (rapid eye movement) sleep. NREM sleep is further divided into 4 stages--stages 1 through 4, each being a progressively deeper state of sleep such that progressively stronger stimuli is needed to wake someone from each stage. The stages are defined based primarily on the appearance of the EEG (electroencephalogram) in each stage.

Normally, NREM sleep occurs first, progressing through stages 1 to 4, and REM sleep follows. This cycle repeats itself 4 or 5 times during an 8-hour sleep period. With each cycle, the amount of time spent in REM sleep increases from perhaps 10 minutes or so in the first cycle to 60 minutes or more in the last cycle.

Sleep is a state of unconsciousness in which the brain is relatively more responsive to internal than external stimuli. It was once thought to be a passive state, but we now know (thanks to neuro-imaging technology) that it is a very active and vital state, absolutely necessary for the maintenance of health in every sense of the word.

This is an area of intense clinical research with numerous published studies. Sleep deprivation is not only detrimental to health, it can be fatal. Studies with rats have shown that total sleep deprivation resulted in death in a matter of weeks or months. The rats also lost weight despite eating more than the control group. They developed sores on their tails and paws indicating a failure of the immune system. (Sleep 1989 Feb:12(1):13-21). True, people are not rats. But numerous human studies have demonstrated a plethora of adverse effects associated with sleep deprivation in all areas: physical, mental and emotional.

In Part 2, I will discuss sleep apnea. In recent years this condition has received much attention in both the medical literature and the lay press....with good reason. It has been linked to all the adverse health conditions associated with sleep deprivation mentioned above. In addition, it has been implicated as the cause of numerous accidents...in the air, on the road, and in the workplace.

Sleep well.....Be well.
Armando

As a medical student I was taught many "facts" which have since proven to be false. Among them was the "fact" that "a calorie is a calorie is a calorie". Which is to say that, if a body consumes more calories than required, irrespective of the source of those calories (i.e. fat, protein, or carbohydrate), that body will accumulate fat. We know now that this is not exactly true.

The preferred energy source for the human body is glucose. Sugar. Other substances can be converted to energy, but not as efficiently. Glucose is readily obtained from all carbohydrate sources. These include most types of sugar (i.e. granulated sugar, fruit sugar (fructose), milk sugar (lactose) etc.) and all grains, root vegetables and other sources. Carbohydrate will not be wasted. Any excess is stored, first in the form of glycogen in liver and muscle cells, and then as fat.

The storage capacity for glycogen in liver and muscle is fixed and only enough to last a few days. The fat "tank", on the other hand, is remarkable in that its capacity to expand is almost limitless. The fat cell is called an adipocyte. Its precursor is called a pre-adipocyte. Pre-adipocytes have the ability to multiply and make more fat cells. When the fat cells are full, pre-adipocytes multiply and make more. So the storage facility continues to enlarge. In order for storage to occur, the hormone insulin must be present. In general, the more insulin present, the greater the amount of storage (fat).

For most of humankind's evolutionary history, the ability to store fat conferred a survival benefit during periods of famine. In modern times, however, with the availability of carbohydrate dense food 24/7, 365 days a year, this benefit is lost. Instead, it has created the so called "obesity epidemic" with all its associated medical conditions, morbidity and mortality.

Limiting the carbohydrate intake to below the individual's daily energy requirements forces the body to use its energy stores. First the glycogen in liver and muscle is used. This lasts only a few days. Less if the individual exercises. When the glycogen is used up, fat stores are utilized. Fat will continue to be burned 24/7 as long as the carbohydrate intake is below daily requirements.

Replacing the carbohydrate with non carbohydrate food does not significantly affect the fat loss. Animal fat, saturated fat (bad fat) intake is discouraged since it can adversely affect lipid levels, insulin sensitivity and cause other problems. Intake of "good fats" such as omega-3, omega-6 and olive oil, in moderate amounts is beneficial. 

Protein intake does not result in blood sugar elevation or accumulation of fat. If an individual alters their diet in such a manner that carbohydrate is reduced to below daily requirements and replaced by pure protein, weight (fat) loss will occur. This is true even if the total calories in the protein is greater than the carbohydrate calories would have been. It appears, therefore, that when it comes to how the human body utilizes energy sources, a calorie does NOT equal a calorie.

There are many low carbohydrate diets on the market. Each has its own biases, but carbohydrate reduction is key in all of them.

No diet should be undertaken unless your physician approves and monitors it. All diets, including low carbohydrate diets can be dangerous if an individual has certain medical conditions. For example, a low carbohydrate diet may be dangerous for diabetics on oral medication and/or insulin. It would require very close monitoring by a physician, and may be totally inappropriate in some cases. Other medical conditions must also be excluded before an individual is started on a low carbohydrate or any other type of diet.

Stay well. Stay safe.

Armando

E. A. Mastrangelo M.D. CAME, AME