Ask Captain Lim

Hello Capt Lim,

I am 73 years old, active, healthy and have flown world-wide for many years. I have a family in the United Kingdom, Australia and elsewhere. I have fainted on three recent overseas flights when I got up to visit the toilet. However, each time I recovered almost immediately. Is there a foolproof method to prevent this problem?

My wife refuses to fly with me again until I am sure it will not recur. We have a new grandchild due next spring in Queensland and we want to fly again.
Many thanks for any advice.

Regards,

R E Marcus

Dear Marcus,
 
Dr JB Lim has replied to your query on fainting spells and the vasovagal episodes below. As I am not a doctor, I have to refer your question to him. He has been very generous to come up with a comprehensive response.  I believe, he has taken the trouble to explain to us more than what we need to know about postural hypotension. I hope the knowledge on the prevention of this problem would be useful to the other visitors of this website as well.
 
Regards,
 
KH Lim.

Black out while attempting to stand during a flight

Dear Capt Lim,  

Thank you very much for referring Mr Marcus case to me.

I think what Mr Marcus has, was just a simple case of what we call ‘postural hypotension’. It was just an indirect cause of what Mr Marcus described as a vasovagal attack or a vasovagal reaction, which is an autonomic cause of a faint. Vasovagal attack is a temporary loss of consciousness (faint) due to the sudden slowing of the heartbeat normally caused by severe pain, stress, shock or fear, caused by over stimulation of the vagus nerve which controls breathing and blood circulation. From the description given by Mr Marcus, his fainting experiences were probably not a ‘vasovagal attack’ in which the vagus (vagal) nerve was over stimulated (attacked), causing the heart to slow down (bradycardia), and a drop in blood pressure due to the blood vessels (vaso) opening up. Thus the name ‘vasovagal attack’ as he described. Mr Marcus problem was probably only a mechanical one due to a change in position from sitting to suddenly standing up. I shall explain that shortly. There is not much to worry about if Mr Marcus merely experienced it three times previously. He probably was sitting down for a long time in the cramped seat of his aircraft, and suddenly standing up, wanting to go to the toilet.

Blood not Reaching the Brain
 
This is merely due to the inability of the heart to pump sufficient blood to the brain. The brain is very sensitive to lack of oxygen carried by blood in circulation. Even a momentary loss of blood flow to the brain causes a black out or a faint (syncope). Reason this to ourselves, and we will feel comfortable that this fainting episode is quite normal. When we sit down for a long time, especially in a cramped condition with not much leg room, the blood tends to pool into the lower extremities (legs) of the body. Gravity pulls the blood towards the legs against the pull of the heart towards it, and upwards further towards the head. There is a decrease in what we call poor venous return in the legs. When a person suddenly stands up, there is an inability for the heart to cope by sending sufficient blood from the remaining blood volume in active circulation towards the head. This is due to the sudden increase in height against gravity triggered by abruptly standing up. A sudden drop in blood pressure results in a decline in blood (oxygen) perfusion to the tissues (brain). This causes a faint.

This is the same mechanism that causes a solider standing at attention for a long time in a parade. Although the solider in this case has not changed his position, the underlying cause is the same – insufficient blood going to the brain. The blood merely gravitates to the lower part of his body if he does not aid venous return by at least marching on the spot. The act of marching causes the muscles of the legs to contract and relax alternately. This acts like a pump. This promotes venous return, an increase in blood volume in other parts of the body, in turn increases hydrostatic pressure, and hence, the blood pressure. The flow of blood upwards towards the head and body is also increased. An occasional dizziness or a faint due to a sudden standing up from a lying down or sitting position is absolutely normal. A lot of people experience this before, including myself.

This occurs also especially in tall people, and who does not exercise to increase their cardiac efficiency, and pumping action. In occurs often particularly among young menstruating females who are tall and anemic. Females tend to faint more often than males. This is not because they are a weaker sex. An anemic individual has less oxygen-carrying capacity in her blood than an individual with normal haemoglobin levels. The incidence of females fainting in a crowd, or when they are standing still too long for an inspection in a parade, is very much higher than their males counterparts in the same age group, with the same weight and height, physical make-up, or even in the same ethnic group.

An Analogy in Haemodynamics

One of the best analogies to understand why the act of suddenly standing up will cause a drop of blood pressure and blood flow to the brain, is to imagine the body as a water hose with water (‘blood’) from the tap running out, but kept in a horizontal (lying down) or sitting down position. The water (‘blood’) pressure gushing out towards the outlet (the head) is horizontally the same throughout the horizontal column of the hose (the rest of the body). If we suddenly raise the hose upwards, there is a momentarily drop in the height of the water now directed upwards (the head). It will take a few seconds before the water can reestablish pressure again, and shoot out to a more stable height. The water pressure has little time to fight against gravity if you raise the hose suddenly. That explains the sudden drop in pressure and height of water. But if we raise the hose upwards slowly, we will see there is no drop in water pressure and water height. The same haemodynamics holds for the body if there is an abrupt change in position from lying or sitting down to standing up position.

Heart Action

Under normal circumstances, a number of reflexes become operative to stabilize blood pressure. There are within the blood vessels, pressure sensors (baro-receptors) that act via the involuntary (autonomic) nervous pathways that respond to changes in the blood volume and blood pressures. First, the nervous feedback mechanisms will cause the heart to beat faster, and more forcefully to increase the blood flow. The muscles in the arteries constrict, and the veins in the lower part of the body contract to increase blood pressure. This will send more blood towards the heart and head.

These circulatory reflexes when they function well, will adjust the blood pressure, and stabilize it, giving hardly any symptoms felt from lying and sitting to standing up positions. If the heart is efficient, as in athletes, and where the volume of blood discharge per minute (cardiac output) is normal (between 2.5 and 4.5 litres per minute at rest, to as much as 30 litres per minute after vigorous exercise), faints are less likely to occur. In elderly people, this pumping action may be a little lower, especially those with cardiac disease. If the heart is smaller, or the myocardium (heart muscles) are damaged or are weak, and the cardiac output is lower, or the heart rate lower (bradycardia). In such events, dizziness, faints and blackouts are more likely to happen.

If an individual already suffers from low blood pressure (hypotension), he is likely to faint even more if he suddenly stands up. That makes his blood pressure drops even more. But it is very normal if faints due to postural changes are only occasional, as experienced by Mr Marcus or anybody else. There is just nothing to worry about. Nevertheless, I suggest Mr Marcus have his blood pressure check to be more certain, as well as for other conditions which I shall describe a little later. If an individual experiences many episodes of syncope very often, he needs a throughout medical examination to look at other underlying causes.

Diseases Associated with Postural Syncope

Frequent dizziness and faints associated with postural hypotension may be the result of certain medication, such as antihypertensive drugs, notably the alpha and beta-blocking agents – drugs that are used in treating high blood pressure by lowering the pressure. They act by blocking the transmission of pressure changes from the autonomic (involuntary) nervous system to the heart and blood vessels. In short, they block circulatory reflexes that increase and stabilize blood pressure. Postural hypotension may also result from certain disease and nutritional disorders. Diabetes mellitus is one, and alcoholism is another. In diabetes, nerve damage disrupt the reflexes that controls blood pressure.Other causes of postural hypotension is the result of some injury, such as an injury to the spinal cord, notably at the level of T-6 (6th thoracic vertebrae) and above. In spinal cord injury, the blood vessels fail to constrict in response to sudden drop in blood pressure due to malfunction of the autonomic nervous system.

The * vagus nerve - the 10th cranial nerve, and the longest nerve that controls the heart rate and other systems in the thoracic region is normally involved. The blood remains pooled in the pelvic cavity and legs, whether sitting or standing. Other causative factors are the result of serious burns and trauma that leads to a fluid loss and a reduction in blood volume (hypovolaemia) , such as in shock. Sudden and acute hypotension may also develop in events such as AMI (Acute Myocardial Infraction – heart attack) or in adrenal failure which all lead to hypovolaemia and shock. However all these triggers for postural faints do not apply in Mr Marcus case, from the description and history given by him. Mr Marcus case is very clear cut. It was a simple and uncomplicated cause. His dizziness and syncope were merely due to sitting too long, and suddenly trying to get up.

Comparative Physiology

A giraffe with a long neck does not faint even if the animal suddenly raise its head from the ground to the tree tops, because of the valves in its neck blood vessels that stop the blood from slipping back from its head. Because of its long neck, the valves are specially created or evolved that way to prevent a giraffe from fainting. Human veins too have valves to prevent regurgitation of blood (blood flowing backwards), but our body and neck are just not long and tall enough to merit this sort of physiological function. We depend on other haemostatic and feedback mechanisms such as baro-sensors in the arteries, constriction of blood vessels, and an increase in the cardiac output to overcome these physical and physiological variations.

More Serious Medical Threats

Sitting too long in an aircraft in a cramped seat with hardly any leg-room to move about, as in an economy class, has far more serious medical consequences than simple dizziness and syncope experienced when passengers suddenly stand up. The more serious health threat is a relatively recent development called “Deep Vein Thrombosis” (DVT), erroneously named as ‘Economy Class Syndrome’. This is a much more serious medical problem that can be fatal due to an intravascular blood clot (thrombus) in the leg vein, which can break away, and travel to block a blood vessel in the lungs to cause life-threatening pulmonary embolism (PE), especially if the blood originates in the knees or above the knees. DVT can occur in many, many other situations, and not merely sitting in the economy class seat of a long-haul aircraft. It can occur whether sitting in an economy class, or a first or business class seat. DVT can also occur sitting in a car, bus, train, or even sitting too long watching TV at home. It can occur if we are not moving about, not exercising, lying in bed for a long time due to an illness, after surgery, and other causes. It is not caused by sitting in the economy class of a plane. But that is another story.

Rest Assured

Rest assured Mr Marcus, your ‘problem’ is really not a medical concern at all. It is a very normal physiological phenomena, and a simple one too. It all has to do with haemodynamics (the physics of blood circulation). If you understand it, you will feel as safe as flying in an aircraft as Captain Lim has repeatedly pointed out. From the description of your history, the 2-3 episodes you had, and always in an aircraft, and the very short spell of your faints, it was none involving  the more complicated causes of postural hypertension I merely described for general discussion.

What to do to Avoid a Faint

The next time you go on a long haul journey in a plane, and you have been sitting down for a long time, and wanting to get up to go to the toilet, do this:
Move your legs, and toes as much as possible. The muscles in the legs when exercised, will act like a pump to force the stagnant blood in your legs to move upwards towards the heart and head. Press your toes in your shoes, relax them upwards, press again many times over. Press both your legs onto the floor, whatever leg room you can get. The best way to do this is to raise your buttocks from your seat as if attempting to stand up. Sit down again, repeat this action many times. Step up and down with both your feet, as if marching-on-the-spot. Than raise your buttocks again, supporting your body with your arms on the arm rest, and sit down again. Do all these maneuvers say for about 5 minutes. This act itself will clear all the remaining pool of blood in the legs, and get them all going. You may also recline your seat as horizontal as possible, and raise the legs to almost as horizontal a position as your seat and body allow.

Like the analogy of the water hose I have earlier described, this will allow blood to flow horizontally, unaffected by gravity, and also easier for your heart to pump at level (horizontally) rather than upwards towards the head against the force of gravity. Lie down this way for a few minutes. Now upright your seat – loh ! try to stand up very slowly. Be kind to your heart by giving it time to adjust to changes in position and blood pressure. If you feel a bit dizzy, or about to black out, even if you try to get up slowly, quickly sit down again, and this time lower your head between your knees to allow more blood to flow towards your brain. Keep it there for just a minute or two. Now raise your head again, and try to stand up slowly. If you feel like fainting, quickly sit down again. Then attempt to slowly stand up again.

Now Continue Enjoying Your Flight:

There you are Mr Marcus. You will be perfectly normal now. Stand up now, and enjoy your toilet visit. You will not faint. After your toilet visit, walk up and down the isle for a few minutes before sitting down into your seat. This will solve not only your faints, but prevent you from the potentially fatal DVT. All travelers on long haul flights should try to do this, especially exercising their legs, and walking about occasionally to prevent the risk of DVT. Enjoy the rest of your journey.

Over to You Captain

Now I shall hand back your passenger to you, Captain Lim.
Also congratulations to Mr & Mrs Marcus, whose new grandchild will be due this coming Spring in Queensland. Do enjoy flying there and remember to institute the prophylactic (preventive) exercises I have suggested. Mr Marcus should land in Queensland without much problem the next time round.

JB Lim, 
MD, PhD, FRSH, FRSMed
Principal Medical & Scientific Advisor.

Foot Note : The Action of the Vagus Nerve.

For those not familiar with the meaning of autonomic nervous system, very briefly, the autonomic nervous system is part of the central nervous system, and is made up of ganglia and fibers. It is divided into two major components – the sympathetic and the parasympathetic nervous systems. The functions of both systems are to control involuntary activities involving the smooth muscles, such as those responsible for respiration, heart beat, digestion, pupil size, etc. The sympathetic and parasympathetic nervous systems work in opposite action to one another. One stimulates, and the other inhibit the action. For example, the sympathetic nerve accelerates the heart beat, while the parasympathetic slows it down. The 10th cranial nerve is the vagus nerve, and is a parasympathetic nerve that controls and slows down the heart-rate. The nerve that accelerates the heart is called the accelerator or augmenter sympathetic nerve. If the vagus nerve is stimulated, it will slow down the heart rate to the extent of inducing a cardiac arrest (similar to giving excessive potassium). But if the stimulus is continuously applied, the heart will escape this vagal restraint, and commence to beat again (‘vagal escape of the heart’), with the first few ventricular contractions being exceptionally forceful. I must say nature is very kind to us to ensure we continue to survive. If the vagus nerve is cut, or temporary paralyzed by a full dose of atropine (a drug with parasympatholytic action), the heart rate will be doubled (150 –180 beats per minute). Just for information sake, the vagus nerve is not there just to control the heart. After it emerges from the medulla oblongata (part of the brain stem), this longest cranial nerve starts to supply branches to the larynx, pharynx, trachea, heart, lungs, and most of the digestive system, and controls all of them.