Carbon Monoxide

Carbon monoxide is produced by incomplete combustion of carbon. Jet exhausts contain less than 1% carbon monoxide whereas exhaust gases from reciprocating engines can consist of as much as 9%. It may be introduced into the air from leaking exhausts and heater fumes.

The dangers of a presence of carbon monoxide cannot be emphasized too strongly.

Haemoglobin has a much greater affinity for carbon monoxide molecules than for oxygen (up to 210-50 times) and will transport them in preference to oxygen. Carbon monoxide combines with haemoglobin to form carboxyhaemoglobin which gives the blood a bright pink colour. Carbon monoxide is odourless which adds significantly to its dangers.

The first symptom of carbon monoxide poisoning is a headache (or tightness across the forehead) nausea and dizziness. Thus the peril will probably not be immediately recognized by an individual thereby increasing the danger. As a precaution, fresh air should always be used in conjunction with cabin heat to minimize the effects of possible carbon monoxide poisoning.

The mild hypoxia associated with flying at cabin altitudes of 8 to 10 thousand feet accentuates the effects of carbon monoxide.

Finally it is an important fact that the effects of carbon monoxide are cumulative. Thus a pilot who flies several times in the same day or on successive days in an aircraft with carbon monoxide concentrations, can eventually suffer serious effects.

Symptoms of Carbon Monoxide Poisoning

•Headache, tightness across the forehead, dizziness and nausea.

•Impaired vision.

•General feeling of lethargy or weakness.

•Impaired judgement.

•Personality change.

•Impaired memory.

•Slower breathing rate and weakening pulse rate.

•Loss of muscular power.

•Flushed cheeks and cherry-red lips.

•Convulsions.

•Death.

Treatment of Carbon Monoxide Poisoning

•Turn off cabin heat.

•Stop all smoking.

•If oxygen available, it should be inhaled by those effected.

•Increase the supply of fresh air through vents and windows.

•Land as soon as possible.

Susceptibility to Carbon Monoxide Poisoning

•Altitude.

•Smoking.

•Age.

•Obesity.

•General state of health.

The Circulation System 2

System Circulation The 2

Many aircraft are equipped with carbon monoxide detectors. They should be checked regularly by the pilot in flight and correctly maintained by engineering.

Smoking

Apart from the addictive properties of nicotine which are thought to increase the risk of cardiovascular disease and tar which is carcinogenic (known to increase the risk of cancer), smoking tobacco produces carbon monoxide which links with the haemoglobin in the blood to deny oxygen carriage. A person smoking 20 cigarettes a day will have a raised carboxyhaemoglobin level by about 7%. This equates to a reduction in oxygen carrying capacity of 4000 to 5000 ft. Add this to a cockpit altitude of 6000 to 8000 ft and the smoker would react as if at an altitude up to 12 000 ft with resulting anaemic hypoxia leading to reduced performance and slower reactions.

Individuals suffering from ‘passive’ smoking will also be affected and there is a tendency for modern airlines to move more and more towards a non-smoking policy on board aircraft.

Smoking also leads to:

•Lung cancer.

•Breathing problems.

•Circulatory problems.

•Reduced tolerance to g-forces.

•Increased risk of heart attack.

•A stimulation of the secretion of adrenaline and an increase of vigilance caused by the nicotine - but as stated above, this substance is the one which causes addiction.

•Degradation of night vision.

Some airlines may not accept into their training programmes pilots who smoke. So:

IF YOU SMOKE - STOP

IF YOU DON’T SMOKE - DON’T START

Blood Pressure

As part of any medical examination the doctor will measure your blood pressure. The result will be given as two numbers e.g. 120/80. The higher figure is the systolic pressure, that is the pressure exerted by the heart when it contracts to send blood around the body. The lower figure is the diastolic pressure which is the permanent pressure within the arterial system. The pressures are measured in mm of mercury.

System Circulation The 2

Low blood pressure (hypotension) normally does not constitute a danger. However if the pressure decreases too much, leading to a shortage of oxygen to the tissues, it can lead to:

•Lethargy/tiredness.

•Reduced resistance to the effects of shock (faints or collapse).

•Congestion of the respiratory system.

•Stagnation in the blood supply.

•Reduced capability to withstand positive g-forces.

The normal range of blood pressure varies with age, but a healthy young adult will typically have a systolic pressure of about 120 mm Hg and a diastolic pressure of about 80 mm Hg

(120/80).

Both hypertension and hypotension may disqualify a pilot from obtaining a medical clearance to fly.

Pressoreceptors and their Function Maintaining Blood Pressure

General

Pressoreceptors are located in the wall of the carotid sinus in the neck and upstream of the brain. They are part of the pressure regulating system of the blood supply to the brain.

Function

Hypertension

Should the Pressoreceptors detect an increase of blood pressure, impulses are sent to the brain which will cause a reduction of the heart rate and a relaxation of the blood vessels effecting a reduction of blood pressure.

Hypotension

Should the Pressoreceptors detect a decrease of blood pressure, impulses are sent to the brain which will cause an increase of the heart rate and a tightening of the blood vessels effecting an increase of blood pressure.

It can be seen from the above that the primary function of the pressoreceptors is that of maintaining homeostasis.

The Effect of G-forces and Blood Pressure

Should a pilot experience positive g, the blood pressure will decrease in the area of the brain and the pressoreceptors will attempt to protect the brain by increasing the pressure. At high g-forces the pressoreceptors can no longer cope and the pilot may suffer from grey or blackout. In the case of negative g, the reverse process will take place except that the pilot will experience redout - negative g (see Chapter 6).

Not only can the blood vessels in the eye and face burst with large negative g-forces but the lower eyelids are pushed upwards obscuring vision.

Positive g-forces will also increase the hydrostatic variation of the circulatory blood system. This is explained in detail in Chapter 6 (Flying and Health).