I had a conversation with a very well respected hematologist this morning and, as a joke, asked him to prescribe a pill that will put me asleep for at least 10 hours of an upcoming 13 hour flight.

He got very serious and told me that would be the worst thing possible. He said I should avoid FC where I am liable to go to sleep, not drink any alcohol, drink a lot of water during the flight, and get out of my seat at least once every two hours and walk around.

Anyone over 60 facing a flight of 8 or more hours should do this, he said, to reduce the risk of thrombosis.

Personally, I never drink while flying and very rarely can afford Biz or FC across the pond but would never dream of turning down an upgrade if it were offered. I also enjoy sleeping away as much of the flight as I can.

Do any of you (especially hematologists) have any input on this?

I thought thrombosis was more related to sitting in a chair for extended periods without moving your muscles to push the blood back. Lying down and sleeping seems a bit excessive. What happens when you sleep at night are the wanting older people to wake up every couple of hours and walk around the house? Otherwise just wear a pair of those hospital socks that prevent thrombosis.

Out of curiousity, what is the difference between sleeping at home and sleeping in a first class suite? Although I have a king sized bed, I rarely use more than the width of a FC sleeper. Unless cabin pressure has something to do with it, I dont get it!

I believe (and, in fact, have heard before) that the problem is, indeed, cabin pressure.

I know that people have been advised for several years to get some exercise while seated but I have never heard anyone say to avoid sleeping more than two hours.

I really would be interested in hearing what other doctors, especially hematologists, think about this.

But the cabin pressure is equivalent to 6000ft give or take....which is not excessivley high.

I am certainly neither an MD, DO, or PA-C. As such, my opinion on this matter should be taken with a grain of salt. Although I usually don't sleep on flights, the few times I have been in a cabin with a lie flat (or semi lie flat) bed, I have probably dozed a few times.

I know alcohol dehydrates the body, and that coupled with lower cabin pressure and low humidity in the air may serve to dry the body or more substantially than usual. That said, I usually have a drink or two on a long flight, or where it is free. I've never had any problems, but I'm not 60 either.

I'm going to go ahead and keep trying to sleep on flights. If I die up there due to sleeping, c'est la vie (actually c'est la mort). At least I'll go painlessly. All in all, though, I'm not too worried about it.

There have been cases of DVT in young people even teenagers as well as older people. It occurs when you are sitting in a cramped area for a long periods of time and the blood is not circulating well in your legs. This is especially important for long trips. I personally do the exercises and do get up and walk around.

I'm sure I remember reading recently that DVT is more about the quality of air in the aircraft than the air pressure. I've recently heard rumours that some airlines have been reducing the quality of air in cabin to save energy (by reducing the number of times it gets recycled). I can well believe this because recently, I can't do a long haul flight without turning into the "snot monster" (usually corrected with a few Whiskeys)!

The hospital socks do not prevent thrombosis; they help to minimize edema.

Thrombosis is caused when blood flow ceases to be laminar, i.e. smooth and fluid, through the blood vessels. This is especially pertinent in the larger veins of the legs (i.e. femoral), where regular muscle movement is the primary means to ensure blood returns towards the heart. When blood does not move properly, such as when a person is immobile for extended periods of time, there is a risk that clots will begin to form (thrombosis) because platelets (a clotting factor) contact vessel walls.

This can happen from sitting too long without moving from time to time, as well as laying in a bed for too long without moving either. Hospital patients are at high risk for thrombosis, as are the elderly who remain in bed for extended periods.

Regarding sleep, most people move when they sleep, so thrombosis is not a problem. There are few people who lay perfectly and absolutely still while sleeping. Maybe the very elderly, but even they wake up enough to move their legs a little bit.

DVT has often been associated with sitting in economy class, but simply sitting in economy is not a factor in thrombis formation. One could be on a private jet, and still be at risk of thrombosis if the passenger remains immobile for too long. The risk of economy class is that, such as when sitting in the window seat, the oppurtunity to move around is limited. But in first class, a person may be immobile by simply sitting too long.

The big risk of thrombosis is embolism: when a person "throws a clot" that then becomes lodged in the lungs, for example.

I am not a doctor (just in training), but I think simply sleeping is not a risk factor. Most people cannot sleep so deeply on airplanes that they would never move once, anyway.

My impression from the accounts I've heard is that death from flight-induced DVT rarely (if ever) occurs while in flight, but instead usually occurs some time (hours, I think) after the passenger disembarks and begins moving around, thus dislodging the blood clot that has formed. I'm not sure, but assume that death is usually the result of a heart attack, which is not necessarily painless.

I am fairly certain that neither cabin pressure nor air quality have anything to do with thrombosis, not as far as I know. People living at higher altitudes are not at greater risk for thrombosis, and neither are people who live in polluted cities such as Hosuton, Los Angeles or Johannesburg.

It has everything to do with lack of mobility, blood clotting and some other predisposing factors such as use of oral contraceptives, obescity and smoking.

One has to remember that simply developing a pathologic blood clot (thrombis) will not in itself lead to death or severe morbidity. It also will not happen in a healthy person within the span of one long-haul flight. There are predisposing factors (see above), and the formation of a clot severe enough to cause complications will develop over time. The complications only occur when the thrombis blocks a blood vessel or, more seriously, leads to pulmonary embolism. It is certainly is possible that an embolism can form during flight or periods of inactivity, but people should not overexaggerate the connection between flying and thrombosis/embolism.

Smokers and overweight people should think about those issues before whether choosing between first or economy class.

I'm a 64-year-old guy.

I generally sleep through the night without getting up.

I had no bad aftereffects from sleeping in Santa Fe, N.M. (elevation 7000') for several nights last summer.

If somebody upgrades me to a sleeper seat on my next trip over the Pacific, I'll take it. (Memo to the world's airlines: you'll probably have a few chances to do this in 2007. PM me if you want to take advantage of this valuable opportunity.)

Are you sure the good doctor wasn't just trying to keep F a little emptier to increase his own chances for an upgrade?

I guess I'd have an easier time believing this second-hand story if I saw heaps of dead old people inside the first class door every time an international flight landed.

In the grand scheme of risks, this one doesn't seem terribly high.

Look out for bees, too.

For me, the story is not second hand. I also know that many doctors have advised me not to smoke but I have never seen heaps of dead people inside the smoking lounges at airports.

I still smoke (although I acknowledge the risks) and I am certainly not in a position to debate this with a hematologist -- although I would not hesitate for a second to take the upgrade.