COLD
COMFORT
The Snowbikers guide to the dangers of breathing cold air
Winter is great! When else are you able to justify having spent the national debt of a small South American country on that pile of fleece and Gore-tex you've been tripping over all year. Winter riding is fun too. The hills are much quieter, and there are a whole set of different conditions to tackle. Of course, you need to plan a little more tightly, what with unpredictable weather and short daylight hours, but with the right equipment and plenty of contingency plans, the runs can be more enjoyable than summer.
On the downside, the major risks associated with winter cycling, with the possible exception of getting lost in fog and heading off a cliff, stem directly or indirectly from the cold. Exposure, and to a lesser extent frostbite, are the big problems, even in the comparatively mild UK, but suitable clothing provides an obvious solution. However, there is a large surface area of the body which, although exposed directly to the air, is often not considered at all: the lungs. Think back to a long hard climb on a frosty day and you will remember the burning sensation as the cold air is drawn deep down. Just what are the consequences of hard aerobic activity in a cold environment?
Extremes
Sometimes the best approach to such a question is to examine what happens
when humans are subjected to the harshest of conditions, and then work
backwards. On the face of it, things look good! Studies looking at the
Inuit peoples inhabiting the Canadian Arctic found that a traditional
lifestyle was generally associated with healthy lung function (1). This
is not too surprising since the human animal is very good at adapting
behaviour to suit it’s particular environment. In hot countries,
a good example of this social acclimatization is the "siesta"
taken at the hottest part of the day. Indigenous peoples also have the
benefit of time-proven clothing developed for the conditions in which
they live. The hood of the traditional Inuit parka, for example, normally
maintains a cushion of warmer air infront of the face which "conditions"
incoming air before it is inhaled, and therefore lessens the cold-shock
to the lungs. Of course, such adaptive changes do not arise overnight,
but have often been fine-tuned over many generations. Sadly, they can
be lost in one lifetime. Over the space of the last 30 years, cultural
changes within the Inuit community have been accompanied by a marked
decline in chest health, particularly amongst men, and the inhalation
of cold air has been cited as a potential risk factor (2). During the
now-common operation of high-speed snow-mobiles, cold air is actively
forced into the parka hood. This may disrupt or, at worst, completely
remove the protective effects of the warm air cushion (2).
A high rate of breathing in a cold environment may also accentuate the risk of sustaining permanent lung damage. Hunters of both Inuit and European descent, who trapped fur in the high arctic earlier this century, and whose physically demanding work would lead to the deep inhalation of extremely cold air, were subsequently found to exhibit signs of premature lung aging (3).
So it seems that at the extremes of the scale at least, prolonged exposure to cold air, particularly whilst undertaking hard aerobic activities, may well have the potential to damage the lungs. This suggestion is supported by several studies of Scandinavian elite cross-country skiers, which found a high incidence of asthma amongst such athletes when compared to the population as a whole (4, 5, 6, 7). This is a highly aerobic sport which may take place in temperatures colder than -15 C. In a two-centre study, the location with the coldest climate had the highest incidence of asthma (7). Perhaps more worrying from a UK perspective are the reports of similar findings amongst a figure-skating population (8) where rink air temperatures are above freezing point. However, pollutants often present in the rink environment may also make a significant contribution to this problem (9).
Take
a breather
During normal breathing, the air passes down the windpipe (trachea),
which divides into two large tubes (bronchi), one for each lung. Each
bronchus then subdivides into many bronchioles which terminate in sac-like
alveoli. It is here that the blood absorbs oxygen and releases carbon
dioxide. In healthy subjects exposed to cold air, some of the normal
physical responses, such as a runny nose, are very apparent, but changes
in airway physiology have also been detected. These include constriction
of the airways (10) and an increased sensitivity to irritants (11).
Such changes are subtle and often unnoticed by the patient, but some
subjects react much more strongly than others (12, 13). It seems that
symptom-free people who suffered from asthma as children are particularly
sensitive to this challenge (13, 14).
Asthma
In subjects with asthma, the airways of the lungs (mainly the bronchi
and bronchioles) can become temporarily narrowed or completely blocked
by increased mucus production, by inflammation, or by constriction of
the surrounding muscles, and as a consequence breathing becomes laboured
and inefficient. This occurs following an encounter with a trigger-stimulus,
the nature of which can vary from patient to patient. Common triggers
include viral respiratory infections, exercise, allergies and environmental
irritants. Whilst healthy airways can respond to inhaled irritants,
(e.g. acrid smoke), the asthmatic's airways are oversensitive and so
need less stimulus to trigger them.
Chill
out
It is well known that cold air can trigger breathing problems in those
already susceptible, and in fact is used as a challenge for assessing
exercise-induced asthma (13, 14, 15). There is however, still some debate
as to why this occurs. Cooling of the airways may directly initiate
broncho-constriction (16), although chilling of the nasal cavity (10)
or the face (17) may play a part. Think of how a splash of cold water
in the face takes your breath away, and it isn't too hard to believe
that there is a link between skin temperature and breathing. A further
complication in the understanding of this effect is that cold air is
generally quite dry. On a frosty bright day, visibility is often very
good for just this reason. Since dry air has also been shown to trigger
asthmatic attacks, some researchers have attributed the effect of cold
air to its low humidity (18).
Leaving the scientific debate to one side, what are the impacts for the average winter cyclist? Although some cyclists may experience no discomfort, for others there is the potential for anything from a mild tightening of the chest to a full blown asthmatic attack. Breathing problems should be assessed and managed by your doctor, but they do not necessarily mean that you should hang up the bike until spring. Simple precautions may help those susceptible to cold-induced breathing problems to keep riding all winter. For example, a simple face-mask has been shown to greatly reduce the irritant effect of cold air, whether by insulating the face, or by moistening and warming incoming air (19). A colleague wears a commercially available smog-mask in winter for this very reason. Although less effective than a mask, a scarf around the face still provides a significant benefit (19). A survey of contributors to a winter-cycling mailing list found a fair number of asthmatics (most with onset before they started serious winter cycling) who, with only minor precautions, happily tackled quite harsh winter conditions. These people found that a good warm-up period helped deflect some of the problems, whilst concentrating on nose breathing wherever possible, and maintaining a modest pace gave the incoming air the greatest chance to become "conditioned" before hitting the sensitive airways (20 ).
Then of course, there is the common sense "don’t run with knives" stuff that hardly needs mentioning. If you are on medication for breathing problems, make sure the dosage is kept up to date, and if inhalers are used, carry a spare one in your bag. Try to avoid riding alone, incase it all goes pear-shaped, and make sure that your buddies are aware of potential problems and what to do should they arise. As ever, listen and learn how your body responds to different conditions, and don't bite off more than you can chew.
Like the Inuit, we have to learn to adapt our behaviour to suit the environment, and if this means sticking to a slower pace, wearing a face mask or indeed doing something else when the conditions dictate, then so be it. One thing is for sure, we have to get along with the elements, because we certainly won't beat them!
References
1) Shephard RJ 1988. Modern civilisation and the Eskimo in a cold climate: lessons for the sports physician. Australian J Sci Med Sport. 20, 11-15.
2) Rode A, Shephard RJ 1994. The aging of lung function: Cross-sectional and longitudinal studies of an Inuit community. Eur Respir J 7,1653-1659.
3) Schaefer O, Eaton RDP, Timmermans FJW, Hildes JA 1980. Respiratory function impairment and cardiopulmonary consequences in long-time residents of the Canadian Arctic. Can Med Association J 123, 997-1004.
4) Larsson K, Ohlsen
P, Larsson L, Malmberg P, Rydstrom P-O, Ulriksen H 1993. High
prevalence of asthma in cross country skiers. BMJ 307, 1326-1329.
5) Larsson L, Hemmingsson P, Boethius G 1994. Self reported obstructive airway symptoms are common in young cross-country skiers. Scand J Med Sci Sport 4, 124-127.
6) Heir T, Oseid S Self reported asthma and exercise induced asthma symptoms in high level competitive cross country skiers. Scand J Med Sci Sport 1994, 4, 128-133.
7) SueChu M, Larsson L, Biermer L 1996. Prevalence of asthma in young cross-country skiers in central Scandinavia: Differences between Norway and Sweden. Respir Med 90, 99-105.
8) Mannix ET, Farber MO, Palange P, Galassetti P, Manfredi F 1996. Exercise-induced asthma in figure skaters. Chest 109, 312-315.
9) Andre D, Kosatsky T, Bonnier J-G 1988. Problems and intervention schemes for carbon monoxide intoxication in arenas. Canadian Journal of Public Health. 79, 124-129.
10) Fontanari P, Burnet H, Zattara-Hartmann MC, Jammes Y 1996. Changes in airway resistance induced by nasal inhalation of cold dry, dry, or moist air in normal individuals. J Applied Physiol: Respiratory, Environmental & Exercise Physiology. 81, 1739-1743.
11) Amirav I, Plit M 1989. Temperature and humidity modify airway response to inhaled histamine in normal subjects. Am Rev Respir Dis 140, 1416-1420.
12) Schaanning J, Finsen H, Lereim I, Saeterhaug A 1986. Effects of cold air inhalation combined with prolonged submaximal exercise on airway function in healthy young males. Eur J Respir Dis 68(sup143), 74-77.
13) Sinclair DG, Sims MM, Hoad NA, Winfield CR 1995. Exercise-induced airway narrowing in army recruits with a history of childhood asthma. Eur Respir J 8, 1314-1317.
14) Steinbrugger B, Zach M 1990. Nonspecific bronchial reactivity in symptom-free adolescent asthma patients. Monatsschrift fur Kinderheilkunde. 138, 389-391.
15) Nicolai T, Mutius EV, Reitmeir P, Wjst M 1993. Reactivity to cold-air hyperventilation in normal and in asthmatic children in a survey of 5,697 schoolchildren in southern Bavaria. Am Rev Respir Dis 147, 565-572.
16) Kaminsky DA, Irvin CG, Gurka DA, Feldsien DC, Wagner EM, Liu MC, Wenzel SE 1995. Peripheral airways responsiveness to cool, dry air in normal and asthmatic individuals. American Journal of Respiratory & Critical Care Medicine. 152,1784-1790.
17) Koskela H, Tukiainen H 1995. Facial cooling, but not nasal breathing of cold air, induces bronchoconstriction: A study in asthmatic and healthy subjects. Eur Respir J 8, 2088-2093.
18) Anderson SD, Schoeffel RE, Black JL, Daviskas E 1985. Airway cooling as the stimulus to exercise-induced asthma - a re-evaluation. Eur J Respir Dis 67, 20-30.
19) Millqvist E, Bake B, Bengtsson U, Lowhagen O 1995. Prevention of asthma induced by cold air by cellulose-fabric face mask. Allergy. 50, 221-224.
20) O'Hanlon GM Survey of breathing complaints amongst the "IceBike" mailing list: winter '96-'97 (unpublished).
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