Examination of Witnesses (Questions 120-139)
Professor Michael Bagshaw, Dr Sarah MacKenzie Ross,
Professor Helen Muir and Dr William Toff
10 JULY 2007
Q120 Baroness Perry of Southwark: Who
is doing the publicity, letting the general public know what the
risks are and that they should be discussing with their physicians,
if they have any of the pre-conditions?
Dr Toff: The Department for Transport and the
Department of Health have done a very good job in reflecting the
background, the ongoing research and, very promptly, the findings
of that research on their websites. The difficulty, as I perceive
it, is that most travellers do not spend a lot of time looking
at those websites and, having recently booked long-haul flights,
there is no point in the process at which the risk is even raised
or mentioned until possibly they read the High Life magazine
during the flight and discover that there is some circulatory
risk.
Q121 Lord Colwyn: Of course you can identify
these high-risk passengers. Would it not be possible at the check-in
to take some of them aside and give them a slightly more comprehensive
tutorial on in-flight exercise?
Dr Toff: The horse has bolted to some extent
by that time. That would be a time at which the generic intervention,
in particular the advice to exercise the legs regularly, at least
hourly, could be given and subsequently reinforced. It is too
late by then to get a measured graduated compression stocking,
appropriately sized for the person. It is too late to discuss
the risks and benefits of other measures such as subcutaneous
heparin. The highest risk people will, in a sense, be too late
to have any useful intervention over and above the general measures,
the efficacy of which is unproven in this setting. We know that
increased venous flow in the deep veins of the leg is achieved
by dorsiflexing and plantarflexing at the ankle; we know that
is an effective manoeuvre to increase flow, but of course it can
only be done when you are awake, when you remember and if you
are physically able to do it. So for perhaps the frailer elderly
person, who is at the highest risk, there is nothing very much
that could be done at the check-in to reduce that risk.
Q122 Chairman: Could you explain to me,
as an engineer, why it is that a compression stocking helps the
flow of blood?
Dr Toff: The short answer is no, but I can tell
you what other people have told me in answer to the same question.
The general view is that the compression of the deep veins in
the leg reduces their diameter and thereby increases the rate
of flow. The physics of that, I suspect are well known to you,
but it is the reduction in calibre of the vessel that is thought
to be the main factor.
Q123 Chairman: It increases the speed
of the blood?
Dr Toff: Yes; the flow rate in the deep veins.
The other benefit of stockings, which goes beyond the pure issue
of venous thrombosis, is that they do undoubtedly reduce ankle
swelling which is beneficial in itself and helps you to get your
shoes back on at the end of the flight. They may also reduce the
risk of thrombosis secondarily.
Q124 Lord Colwyn: The WRIGHT report does
not mention the highest risk of all which is recent surgery.
Dr Toff: The WRIGHT report itself did not specifically
look at all risk groups across the board. It is a given and you
are absolutely right, that would be the highest risk; recent surgery
within the last three months would be regarded as an important
risk factor. There was no element of the WRIGHT study that specifically
looked at that group and in the epidemiological studies the number
of such subjects would have been very small, so they would not
have figured in any specific analysis.
Q125 Lord Howie of Troon: You mentioned
the danger in other modes of travel. Has comparable research been
done on a train journey from, say, London to Inverness?
Dr Toff: I am not aware of any specific studies
looking at train journeys. There are two or three studies which
have looked at long bus journeys, looking at clinical outcomes,
and blood clotting changes, and they are concordant with our findings
in that they found some pro-coagulant changes after prolonged
sitting on a bus but they were no different from prolonged sitting
in an aeroplane.
Q126 Lord Howie of Troon: Coming down
here this morning, I saw a bus travelling from London to Aberdeen.
Has research been done in that? A bus journey from London to Aberdeen
is fairly lengthy. I do not know quite how long it would take,
but I should not like to undergo it myself.
Dr Toff: It is important, not just at the airline
check-in, but it is important that the general public health message
is somehow also communicated. Whether you are sitting at your
computer for 12 hours, sitting on a bus from Aberdeen for 12 hours
or whatever, there is a risk from prolonged seated immobility,
particularly when you have hyperflexion at the knee, which impedes
the blood flow to some extent, and also at the hip. I was telephoned
last week by Motorcycle News because I believe that the
Institute of Advanced Motorists has recently issued a caution
for motorcyclists undertaking prolonged journeys where their leg
position is just such as would aggravate the thrombotic tendency.
Q127 Lord Sutherland of Houndwood: I
am interested in the length of the journey and you have specified
over four hours. To declare an interest, I do rail journeys four
hours each way, once a week, to be here. Is the frequency of travel
relevant? Is there any evidence on that?
Dr Toff: Yes. There is increased risk associated
with taking multiple long journeys in a short period. The exact
quantification of the risk is complex, but it is greater than
if you had just taken a single journey in your eight-week risk
period. If you take another journey, you will get an increment
in risk.
Q128 Lord Sutherland of Houndwood:
A related point. Would taking aspirin help me in these journeys?
Dr Toff: That is a very interesting and controversial
area. The evidence from a meta-analysis and post-surgical studies
in orthopaedic surgery suggests that aspirin might reduce the
risk of thrombosis by something in the order of 25%. Where you
are dealing with an issue such as travellers' thrombosis, where
the absolute event rate is very low, you have to treat a lot of
people to prevent one thrombosis and the estimate would be something
in the region of treating 24,000 people to prevent one thrombosis.
On the other hand, the number that you need to treat for harm
from aspirin is in the region of one in 17,000; that is by way
of bleeding or allergic reaction or whatever. In this particular
instance, where the risk is very low, say for the average traveller,
the use of aspirin is a relatively ineffective intervention. It
does have some benefit but it is relatively ineffective and the
prospect of harm may outweigh the prospect of benefit. In public
health terms, we would not advocate aspirin as an intervention
for any group and it is not in fact advocated as prophylaxis in
any setting for venous thrombosis.
Q129 Baroness Finlay of Llandaff: Could
you just tell us a little bit about the implications of ultra-long-haul
flights for passengers' health, perhaps building on what you said,
Dr Toff, and then to others?
Dr Toff: I do not come forearmed with the specific
figures, but for the longer flights it has been consistently observed
that there is a much greater increase in risk. Flights in excess
of 12 hours and certainly flights in excess of 16 hours would
be associated with a substantially increased risk of venous thrombosis
compared with the shorter flights.
Q130 Baroness Finlay of Llandaff: You
gave us a figure before of flights more than four hours giving
a doubling of risk. Do you have further figures on travelling
that goes on for longer than eight hours or 12 hours?
Dr Toff: There are figures from a number of
sources, but, to give an example, in a study of pulmonary embolism
occurring after long-haul travel in people returning to a Paris
airport, the particular study showed that overall the risk of
pulmonary embolism was less than one in a million person flights,
but if you had travelled in excess of 12 hours, I believe the
figure was four to five per million.
Q131 Baroness Finlay of Llandaff: If
we broadened that from thrombosis to other risks to health, I
wonder whether anyone else would like to comment.
Professor Bagshaw: I have looked specifically
at the risk from cosmic radiation and I am pleased to advise you
that the increase in risk is of no significance. Even for the
longest flights that are currently planned, there is no risk of
exceeding the limits recommended by the International Commission
on Radiological Protection. The other thing to consider is the
dry cabin air. The research on the effects of very low humidity
has looked at simulated flights of eight hours; no work has yet
been done to look at the zero humidity environment in excess of
eight hours. Looking at the data from that study at Farnborough,
there is no sense of concern in the extrapolation, but we will
not know until we do the flights. As far as cabin air quality
is concerned, there is good evidence and good data to show that
the cabin air quality is bacteriologically clean because of the
use of high efficiency particulate filters, and there is no suggestion
that that will degrade over a long flight. The biggest concern
is probably boredom and what to do with yourself during such a
long period of time. We examined the effects of ultra long haul
flights at the IATA Cabin Health Conference last year held in
Geneva where Emirate Airlines and I presented data which was reassuring,
with the exception of the increased risk of deep venous thrombosis.
Q132 Baroness Finlay of Llandaff: I just
wondered whether Professor Muir would like to talk about the psychological
impacts of an ultra-long-haul flight.
Professor Muir: Some of these psychological
factors are not well understood but one thing that is relevant
is that the public expectation of being able to travel when one
is considerably older is changing and the demographics of the
population travelling on these ultra-long-haul flights will increasingly
involve elderly people, people who perhaps do not have such good
general health. I am nervous about using that word in the company
of the medical profession but there is the issue of people who
are perhaps in their 90s going to take a flight with a journey
time of 23 hours and then you get into the issues of fatigue.
I would not have thought there would be psychological difficulties.
Q133 Baroness Finlay of Llandaff: There
are posture issues certainly for people who are older, back pain
and so on. I just wonder whether the one-size-fits-all seat of
an airline is appropriate in this day and age with the very broad
range of passengers, not only in age, but in size and shape.
Professor Muir: There is quite a lot of evidence
that one-size-fits-all is not the ideal scenario. The problem
is, if we started designing seats for different sizes of people
and putting them on aircraft, there would be a quite complex check-in
problem. The practicalities of that may make it almost impossible
to achieve.
Q134 Baroness Finlay of Llandaff: Should
we have minimum stopover times on these very long flights? Would
it make any difference?
Dr Toff: As a consumer, I suspect choice is
the watchword. The option to stop over is undoubtedly a useful
thing for the people who, for whatever reason, do not enjoy the
long flights. From the point of view of prophylaxis of venous
thrombosis, if you take two consecutive flights within a relatively
short period, the risk will not be much different unless you use
the intervening period specifically to exercise. Even then, the
components need to be broken up by periods of exercise as well.
It probably does not make a great deal of difference from the
thrombosis point of view. It is possible that, if anything, it
might actually prolong the journey time by sitting around in an
intervening airport for an extra hour or two.
Q135 Lord Haskel: Just coming back to
the question of cosmic risk, which Professor Bagshaw raised, we
are told that modern aircraft are now being built of carbon fibre
composites and all kinds of new materials. Can we be sure that,
with these new materials, there will be no risk of cosmic risk?
Professor Bagshaw: Yes, the aircraft structure
does not act as a shield. Whatever the material it makes no difference.
Q136 Lord Sutherland of Houndwood:
Dr MacKenzie Ross, you carried out a study of 27 pilots who reported
some ill health. Can you summarise very briefly the outcomes and
what your findings were?
Dr MacKenzie Ross: It is important to state
that it was not a research study. In addition to being a researcher,
I am also a clinician and basically over the last two years around
40 pilots have come to see me reporting ill health which they
attribute to exposure to hydraulic fluids and jet engine oils
in the cockpit. Last year I was approached by a government committee,
the Committee on Toxicity, and asked to present some interim findings;
at that time I had seen 27 pilots. These pilots came to see me
either as a medical referral or they referred themselves because
they were concerned about their health, but were very anxious
about notifying the authorities in case they lost their licence.
They came to see me for an assessment both of cognitive function
and also of what we call adult mental health and mood state. What
we found was that all bar one of the pilots that came to UCL had
basically reported and complained of chronic health problems,
including fatigue, sleep difficulties, fluctuating gastro-intestinal
problems, numbness in fingers and toes and of interest to me was
memory and other intellectual impairment. What we did was to put
them through a very thorough examination process that took an
entire day for each pilot and the results confirmed on psychometric
testing that they did indeed show evidence of cognitive impairment
but in very specific areas. They were not globally impaired but
they did have very specific deficits in that they were slower
to process information, they had fluctuating attention and they
had some difficulties with high-level functions like multi-tasking.
How this translates in terms of their job in the aircraft was
that they said that when working they were missing instructions
from air traffic controllers, getting numbers regarding heading
and altitude and speed the wrong way round, completing tasks in
the incorrect sequence, forgetting whether or not they had done
certain things like lowering the undercarriage and that kind of
stuff; so quite alarming deficits were reported and deficits were
confirmed on testing. They also had some evidence of abnormalities
from other medical specialists; so it was not just me finding
abnormalities, they were found elsewhere too. The main issue was
that they believed this was due to exposure to contaminated air
in the aircraft. When they came to see me there was no particular
evidence of exposure that they could present me. Apparently, there
is not monitoring on aircraft, so they were not able to come with
a printout of what was coming into the aircraft. What we did was
to look at whether there were alternative explanations that we
could identify to see whether perhaps they had made an attribution
error and it was not contaminated air at all. We basically looked
for common causes of cognitive impairment and the sorts of symptoms
they report. We looked at all their medical notes to see whether
they had a history of any medical problems, we looked at whether
they might have another disease process, a neurological injury
of some sort and we looked at whether they might have a mood disorder,
whether they might be malingering. We did all of that and basically
we were able to exclude those explanations in at least 18 pilots.
We had 18 pilots who were impaired and ill and we could find no
explanation for why that was the case and, as I said earlier,
they were reporting it was contaminated air. Given that there
is not aircraft monitoring as standard to know whether or not
contaminants are coming in and if they are, on what level, my
personal feeling is that it is very important that some further
research is undertaken. These people are definitely ill; that
is beyond a doubt. The question is: why? They think it is contaminated
air and, as yet, there does not appear to be any data that would
allow us to prove or disprove that hypothesis. It is absolutely
imperative that further research is done.
Q137 Lord Sutherland of Houndwood:
Thank you very much. That was very, very clear and very helpful.
Is there yet a unified view amongst experts about reported fume
events as we might call them or is there still much uncertainty?
Dr MacKenzie Ross: As far as I understand it,
it is accepted in the industry that fume events definitely occur.
They are reported in many cases, but there is also apparently
a degree of under-reporting, so it is unclear how often they happen,
what it is that is coming into the aircraft and what quantities
and what effects it might have on people, if any.
Q138 Lord Sutherland of Houndwood:
For example, one issue that is bound to occur to one is if you
have 27 pilots out of a profession of however many thousands,
could you find a similar group amongst lawyers or doctors or members
of the House of Lords even?
Dr MacKenzie Ross: Obviously this is what we
call a self-selected sample and it is small in comparison to the
pool that it is coming from. They are ill, but it is unclear how
representative they are of their group. However, we did compare
the performance of these pilots with what we class as healthy
controls; these were people randomly pulled off the street. The
profile of deficits in the pilots is not the same; there are not
deficits in people you pull off the street generally speaking,
so the profile is different.
Q139 Lord Howie of Troon: Did the ages
of these play any part? I have noticed a deterioration in some
of my colleagues.
Dr MacKenzie Ross: The tests that we use allow
us to do what we call age corrections; so age is removed as a
factor that could explain this.
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