THE INCIDENCE OF ACUTE MOUNTAIN SICKNESS
IN CHILDREN AT MODERATE ALTITUDE
Mary Kay Theis
B.A., University of Colorado, 1980
A thesis submitted to the
Faculty of the Graduate School of the
University of Colorado in partial fulfillment
of the requirements for the degree of
Master of Arts
Department of Anthropology
This thesis for the Master of Arts
Mary Kay Theis
has been approved for the
Department of Anthropology
Theis, Mary Kay (M.A. Anthropology)
The Incidence of Acute Mountain Sickness in Children at Moderate Altitude
Thesis directed by Professor Lorna Grindlay Moore
Acute Mountain Sickness (AMS) is generally a mild syndrome of altitude
illness marked by symptoms of headache, insomnia, and nausea. Understanding
its incidence in Colorado at moderate altitudes (8000-10,000 ft) is important
given the large number of visitors to these elevations and the rare but
sometimes fatal progression of AMS to High Altitude Pulmonary Edema
(HAPE). That a form of HAPE occurs principally in children (reascent HAPE)
suggests that children may be equally, if not more susceptible to AMS than
adults, yet little is known concerning the incidence of AMS in children. In order
to determine the incidence of AMS in children, a questionnaire specifically
designed to address symptoms of AMS in children was distributed to 558
Denver-Metro (average elevation 5280 ft) students between the ages of 9 and 13
who attended a field science school at Keystone, Colorado (9300 ft). All
children completed the questionnaire within 48-72 hours of arrival. As a sea-
level control group, 347 children, ages 10-14, who attended a field science
school in Sausalito, California completed identical questionnaires within 48-72
hours of arrival. The occurrence of three or more of the principal symptoms:
mild or severe headache, fatigue, insomnia, shortness of breath, loss of appetite,
dizziness, and vomiting, was used to define a case of sickness. Based on this
definition, more children who travelled to Keystone developed sickness (28%)
than children in California (21%, P <0.05). The difference (28% 21%,
relative risk 1.5) suggests that ascent from 5280 ft to 9300 ft increases the
occurrence of sickness. This increase represents the component due to altitude
and may be termed Acute Mountain Sickness. Symptoms of fatigue, headache
(mild and severe), and shortness of breath occurred more frequently in the
Keystone children and sea-level children reported more loss of appetite (P
<0.05). While this study shows that Acute Mountain Sickness occurs in
children, the overwhelming preponderance of symptoms reported at low
altitude implied that travel and disruption in daily activities was the principal
contributor to the symptoms.
The form and content of this abstract are approved. I recommend its
Acknowledgments ........................... vi
1. STUDY PURPOSE ................................... 1
2. PHYSIOLOGICAL EFFECTS OF HIGH ALTITUDE........... 3
3. HIGH ALTITUDE ILLNESS............................ 6
Acute Mountain Sickness .................... 7
High Altitude Pulmonary Edema.............. 10
4. STUDY APPROACH.................................. 14
Definition of AMS........................... 15
5. RESULTS ........................................ 17
6. DISCUSSION...................................... 24
Adaptation and the Environment.............. 26
Altitude Adaptation......................... 30
Summary and Conclusion...................... 33
A. QUESTIONNAIRE.................................. 34
A project as this one is in many senses a collective effort that represents
the time, support, and thought of many people. Friends, colleagues, and
professionals in many fields assisted me with their valuable criticism and advice
and to them I would like to express my gratitude and indebtedness.
Special thanks to Dr. Lorna Moore who showed me through wit,
hardwork, and insight the standards of excellence for committed scholars. Dr.
Charles Houston opened the doors of opportunity throughout this project, and
made valuable suggestions. Patti Pearce of CARI, Dr. Dan McBride of the
Keystone Science School, and Michael Carr of the Headlands Institute, handled
the often unexciting task of collecting the questionnaires. Pam Young, Dr.
Craig Janes, and Dr. Dwayne Quiatt kindly served as manuscript readers. Jane
Mclean and Dr. Ben Honigman of the University of Colorado Health Sciences
Center aided in the statistical analysis. Dr. Dick Nicholas, Dr. Ray Yip, and Dr.
Dick Hoffman gave of their time and information to answer my many questions.
High and remote mountains, once reserved for indigenous people and
the rare explorer, have witnessed an explosion of visitors within the last fifty
years. Skiers, backpackers, climbers, scientists, and "peak baggers" who possess
leisure time and money, ascend with relative ease and speed into the
Himalayas, the Andean Altiplano, and the Rocky Mountains. Today, nearly 40
million people are permanent residents at elevations above 8000 ft, and about
an equal number annually visit high altitudes (Moore 1987:966). Within
Colorado, Moore estimates that more than 14 million persons each year travel
to high altitude. Since many are arriving at these altitudes quickly and not
staying longer than one or two days they cannot be expected to have undergone
complete physiological adjustments. It is therefore possible that the
combination of increasing numbers of people travelling rapidly to altitude,
insufficient time for complete acclimatization, and physical exertion may
produce altitude-related illnesses in these visitors.
Acute Mountain Sickness (AMS) is generally a mild syndrome of altitude
illness which is marked by symptoms of headache, insomnia, and nausea.
Although not proven, there is likely an innate susceptibility in certain
individuals to AMS, but rapid ascent to altitude increases both the incidence
and severity of AMS. Other determinants include age, with younger being
slightly more susceptible, previous history of AMS, and the degree of physical
exertion (Hackett 1980:6).
The factor generally accepted as responsible for initiating AMS and the
array of other altitude-aggrevated illness is hypobaric hypoxia. Yet, the fact that
AMS develops hours to days after ascent, and is not always relieved by
supplemental oxygen, suggests that it is the response to hypoxia over time rather
than hypoxia perse that causes the illnesses (Hackett and Roach 1987:981).
Understanding the incidence of AMS in Colorado at moderate altitudes
(8000-10,000 ft) is important given the large number of visitors to these
elevations and the rare but sometimes fatal progression to High Pulmonary
Edema (HAPE). That a form of HAPE occurs principally in children (reascent
HAPE) suggests that children may be equally, if not more susceptible to AMS
in adults, yet little is known concerning the incidence of AMS in children. The
purpose of this study was to determine the incidence of AMS in Denver-Metro
children who ascend to, and stay for 48 72 hours at 9300 ft.
PHYSIOLOGICAL EFFECTS OF HIGH ALTITUDE
At all altitudes, barometric pressure is due to the weight of the blanket
of air pressing on the earth: at sea level this is equivalent to 15 psi or 760 Torr
(or mm Hg). Barometric pressure decreases as altitude increases. Thus at 5000
ft barometric pressure is 632 torr; 10,000 ft, 523 torr; and at 18,000 ft the
barometric pressure is half that of sea level or 380 torr. However, within these
altitudinal limits it must be remembered that atmospheric pressure also varies
slightly with temperature, weather, and latitude. Above 20,000 ft most people
cannot physiologically tolerate low barometric pressure. The upper limit of
tolerance for both the trained mountaineer and the indigenous native resident is
The composition of air is constant throughout the atmosphere: 20.93%
oxygen with most of the remainder being nitrogen. By Daltons law, the partial
pressure of individual gases also falls as altitude increases. The partial pressure
of oxygen at sea-level is 160 torr (21% x 760 torr) and 80 torr at 18,000 ft. The
lower atmospheric pressure at this altitude, and the associated reduction in the
partial pressure of oxygen in the inspired air produces hypobaric hypoxia which
in turn is an important causal variable in the numerous physiological
adjustments to high altitude.
Living cells require an uninterrupted supply of oxygen to sustain life and
function. Oxygens primary role is to act as the terminal electron acceptor in
the process of oxidative phosphorylation which occurs in the mitochondria. In
anaerobic conditions, formation of adenosine triphosphate (or ATP, the
currency of energy conversion in the cell) ceases in the mitochondria and the
overall production of energy rapidly declines. Without ATP the cell ultimately
Human beings are too large to permit every cell to exchange gases
directly with the external environmental air. Instead, our cells rely on an
integrated cardiovascular-pulmonary system for acquisition, transport, and
delivery services. Ambient air is pumped into the lungs via the action of
breathing where oxygen diffuses across the alveoli into the capillary bed.
Oxygen enters the red blood cell, and is actively bound to hemoglobin; one
molecule of hemoglobin is capable of carrying four oxygen molecules. The red
blood cells are pumped by the heart via the blood vessels to the tissues where
oxygen diffuses across the capillary and tissue membranes to reach the
At each stage in the transport system, oxygen readily diffuses "down" its
pressure gradient. At sea level the partial pressure of ambient oxygen is 160
torr. As the oxygen enters the lungs it becomes saturated with water vapor thus
reducing the partial pressure of oxygen to 149 torr. In the alveoli of the lungs,
oxygen is diluted by carbon dioxide, and its partial pressure (Pa02) t0
approximately 104 torr. The second step of the oxygen transport cascade occurs
from the alveoli to the capillary bed which has a partial PO2 of 40 torr. This 64
torr (104 -40 torr) pressure gradient permits oxygen to diffuse rapidly into
capillaries. The partial pressure of oxygen in arterial blood (Pa02) is
approximately 96 torr. As the blood circulates throughout the body, oxygen
diffuses from the blood into the tissues and eventually to the mitochondria
At sea level, the hemoglobin in the arterial blood is nearly fully
saturated with oxygen. As inspired oxygen tension (PjC>2) diminishes in direct
proportion to the reduction in barometric pressure, the blood becomes less
saturated with oxygen. The higher the altitude the lower the percentage of
arterial oxygen saturation; thus, at high altitudes arterial hypoxemia occurs
(Fogiel 1978:495). If an arterial oxygen saturation of 90% is used to define the
onset of high altitude, "high" altitude may be said to begin at 8000 ft. However,
the altitude at which arterial oxygen saturation falls below 90% can vary among
people such that for persons with impaired oxygen transport systems, "high"
altitude may be as low as 5800 ft (Moore 1987:966).
Under conditions of reduced oxygen availability, a series of physiological
changes take place in the cardiovascular and pulmonary systems as the body
attempts to maintain a balance between oxygen supply and oxygen demand.
Depending on the speed of ascent and the altitude reached, the body responds
to the decrease of oxygen by increasing ventilation, dilating blood vessels,
raising cardiac output, as well as a host of other responses. For many,
adjustment to hypoxia occurs naturally but for others there is an adverse effect
on their performance, health, and well-being. The physiological consequence of
this hypoxia gives rise to various forms of altitude illness.
HIGH ALTITUDE ILLNESS
Possibly one of the earliest description of acute mountain sickness is
contained in Plutarchs account of Alexanders troop crossing into India in 326
B.C. He writes:
"Many then were the dangers he (Alexander) underwent in those encounters
and serious the wounds he received; but the greatest harm to his expedition
came from their lack of necessary supplies and from the unsteadiness of the
atmosphere" (alternative translation, "severity of weather") (Ward 1975:1).
Between 37 and 32 B.C., the high Chinese official Too-Kin, reported to
the Prime Minister of the difficulties encountered by an armed escort in a
region that is probably the Kilik Pass (15,837 ft) of Afghanistan. He describes
"the Great Headache Mountain" and "the Little Headache Mountain" where
"mens bodies become feverish, they lose color, and are attacked with headache
and vomiting" (Gilbert 1983:316).
The first detailed description of mountain sickness is that of the Jesuit
missionary, Father Jose dAcosta, who lived in Peru from 1572 to 1587. His
published account The Natural and Moral History of the Indies (1590) is full of
lively descriptions of life in the high sierra. In his graphic account of his
experience in crossing an Andean pass (15,750 ft) he writes:
"...when I came to mount the degrees, as they call them, which is top of this
mountaine I was suddenly surprised with so mortall and strange a pang, that I
was ready to fall from the top to the ground... I was surprised with such
pangs of straining and casting as I thought to cast up my heart too; for having
cast up meate fleugme, and choller, both yellow and greene; in the end I cast
up blood with the straining of my stomacke. To conclude, if this had
continued, I should undoubtedly have died...
...I therefore perswade myselfe that the element of air is there so subtile and
delicate, as it is not proportionable with the breathing of man, which requires
a more gross and temperate aire, and I beleeve it is the cause that doth so
much alter the stomacke, & trouble all the disposition (Gilbert 1983:329).
Although the effects of altitude have been recognized for a long time,
only recently have they been examined in sufficient detail to permit
classification into four categories: Acute Mountain Sickness (AMS), High-
Altitude Pulmonary Edema (HAPE), High-Altitude Cerebral Edema (HACE),
and Chronic Mountain Sickness (CMS). These are not separate entities but
parts of a continuum with a common underlying pathogenesis ranging from
benign, self-limiting AMS to the more serious, life threatening HACE (Houston
threatening HACE (Houston 1980:126). The incidence, duration, and severity
of these maladies (except for possibly CMS) depend on the rate of ascent,
altitude reached, and individual susceptibility. Because HACE and CMS occurs
rarely in children they will not be discussed in this paper.
Acute Mountain Sickness
Acute Mountain Sickness (AMS) is a well documented and preventable
syndrome developing in individuals who ascend rapidly to altitudes above 8000
ft. Characterized by a variety of symptoms headache, decreased appetite,
lassitude, insomnia, and vomiting AMS generally occurs within six to 48 hours
after ascent. Other symptoms include irritability, dyspnea on exertion, reduced
capacity for sustained mental work, malaise, and dull pain or discomfort in the
chest wall (Jacobson 1988:137). The disorder affects both sexes equally and is
not related to the degree of physical fitness. Although the symptoms vary
widely among individuals, most people who ascend rapidly develop symptoms
above 10,000 ft.
In the majority of cases AMS is mildly annoying, requires no treatment
and disappears in a few days. If the symptoms become severely disabling,
descent is the treatment of choice. A number of measures have been
recommended to prevent or ameliorate AMS symptoms. These include: gradual
ascent, moderate exertion in the first few days at altitude, the use of
acetazolamide (Diamox), an inhibitor of the enzyme carbonic anhydrase, and
increasing carbohydrate and water intake (Houston 1980:140; Malconian and
For convenience, we consider altitude moderate from 8000 to 10,000 ft,
high from 10,000 to 18,000 ft, and extreme above 18,000 ft. AMS rarely
develops below 6000 ft although predisposing conditions such as
hemoglobinopathies (e.g., sickle cell, thalassemia), respiratory illness, sedative
medications, alcohol, and anemia may reduce the functioning of the oxygen
transport system. Thus, physiologic altitude can exceed absolute altitude
producing tissue oxygen deficit at lower elevations (Baird and Mcaninch
Considerable literature on the subject of altitude-related illnesses has
appeared in the last 30 years. In 1969, Singh and colleagues published clinical
observations of 1,925 soldiers who had suffered various forms of altitude illness
during the Sino-Indian conflict in the Himalayas when thousands of Indian
troops were hastily transported from near sea level to altitudes of 14,000-18,000
ft. At the time this was the largest collection of altitude illness cases yet
reported. The incidence of acute mountain sickness varied from 0.1% to 8.3%
and depended on how quickly the men arrived at altitude with the worse
symptoms occurring after air travel (Singh et al. 1969:175).
At the aid post on the trail to Mount Everest base camp, Hackett and
Rennie examined 200 trekkers arriving at 13,600 ft. Among the subjects who
first flew to an airstrip at 9187 ft and then walked up (four to six days), 49% had
AMS. The trekkers who began at 4300 ft in Kathmandu and hiked for two
weeks showed an AMS frequency of 31% (Hackett and Rennie 1979:214).
Most studies that examine the frequency and/or health effects of high
altitude have been conducted on select samples of healthy, young men at high
elevations (> 12,000 ft). Only recently has research examined the incidence of
AMS at moderate altitude (8000 -10,000 ft). In a survey of 3906 winter visitors
to six Colorado mountain resorts (elevation between 8000 and 9500 feet),
Houston (1985:162) found that 17% had symptoms at the time of the interview
and of these 12% were experiencing three or more symptoms considered
characteristic of Acute Mountain Sickness.
A recent survey by Montgomery, Mills, and Luce (1989:73) of 454 health
professionals attending meetings at Steamboat Springs, Colorado (6890 ft) and
Park City, Utah (6860 ft), found that 25% had symptoms suggesting AMS; since
only 56% of the attendees responded, the adjusted incidence would be closer to
12%. A control group of 96 health professionals attending similar programs in
San Francisco reported 5% incidence of similar symptoms. Study subjects were
classified as having AMS when they reported three or more of the five possible
symptoms: headache, insomnia, dyspnea, anorexia, and fatigue.
Dean, Yip, and Hoffman (1990) surveyed 96% of 105 attendees at a four
day meeting of epidemiologists in a Colorado hotel (altitude 9800 ft). Overall,
90% of the respondents reported at least one symptom and 42% had mild AMS
as defined by three or more of five possible symptoms. The symptom frequency
ranked from headache, 59%; shortness of breath, 59%; difficulty in sleeping,
45%; weakness or dizziness, 40%; and nausea, 12%. None of the eight persons
who normally live at above 5000 ft met the case definition of AMS.
The widespread among estimated incidence rates (from 8.3% to 49%)
and the wide range of altitudes (6900 to 18,000 ft) demonstrates the need for
further studies especially in a well-defined population group. In addition,
excluded from all of these studies is the incidence and risk of AMS among
children and elderly adults who travel to moderate altitude. Although AMS is
not life-threatening, current knowledge indicates that AMS may progress to the
more serious HAPE and/or HACE, which indeed are life threatening. This
makes it highly desirable to obtain accurate incidence figures in order to better
define preventive and therapeutic measures.
High Altitude Pulmonary Edema
High altitude pulmonary edema (HAPE) is an unusual form of
noncardiogenic pulmonary edema that occurs in trekkers who ascend too
rapidly and sleep at elevations above 9,000 ft. Onset is usually gradual, taking
24 to 72 hours after arrival to develop. This serious and sometimes fatal illness
is characterized by shortness of breath, irritative cough, great fatigue, vomiting,
headache, and audible rales. HAPE patients may progress to symptoms of
cyanosis, and tachycardia, production of a white or pink frothy sputum, and
possibly coma and death (Houston 1983:126; Sutton 1983:130). Early HAPE
responds best to descent, supplemental oxygen, rest, and liquid replacement
whereas the only effective treatment for severe HAPE is descent (Hackett
1978:49; Houston 1976:2193). Nevertheless, the first and easiest step to
management of this illness is prevention, by way of slow ascent, gradual
acclimatization and sleeping at lower elevations.
In two separate studies, spanning seven years, Sophocles examined the
frequency of HAPE in Summit and Eagle Counties, Colorado (elevation 9000
and 8200 ft, respectively) and found men comprised 96% of the cases. All were
visitors who lived at elevations below 5000 ft, with majority residing below 3000
ft. Ascent for nearly all the cases was rapid, usually taking less than 12 hours.
Comparison of age for the two counties were similar with the Summit County
group ranging from 22 to 63 years (mean age 37.8), and the slightly younger
Eagle County group, ranging from 12 to 55 (mean age 35.6).
That HAPE is rare in healthy, premenopausal women at moderate
altitude suggests that women may be protected by a mechanism related to the
presence of one or more female hormones (Sophocles 1986:573; Sophocles and
Bachman 1983: 1015).
Most studies of HAPE have focused on lowlanders who temporarily visit
high altitudes. However, altitude natives and long-term residents of altitude
have been reported to be prone to developing HAPE upon their return to high
altitude after a sojourn to lower altitudes (Gray 1983:142). Physicians in the
mining and tourist town of Leadville, Colorado (elevation 10,152 ft), the highest
permanent community in North America, have noticed acute pulmonary edema
in Leadville and the surrounding Lake County residents (total population: 8300)
who returned after a visit to low altitude (Scoggin, et al. 1977:1269). Termed
re-entry or reascent HAPE, this phenomenon appears to be a disorder primarily
of childhood and adolescence that affects the sexes equally (Sophocles
In their 1970 to 1977 study of HAPE in Lake County residents, Scoggin
et al. examined the hospital records of 32 patients (14 female and 18 male) who
met the diagnostic criteria for HAPE. Their ages ranged from three to 41 years,
with 18 of the 21 being less than 21 years old. Average age was 11.9 years and
19 of the 21 patients were residents of high altitude. Of the 30 Lake County
residents, one patient suffered HAPE after an appendectomy in Leadville
without prior descent to low altitude. The other 29 developed HAPE after
returning to Lake County from visits to low-altitudes. Half the patients were at
low altitude less than a week, three for only one day. Of the twenty residents
Scoggin was able to question personally only two had not been to lower altitude
in the previous year. None of the 18 patients with prior trips to low altitude had
experienced an illness requiring hospitalization on their return in Leadville.
However, many residents believed they had symptoms of respiratory dysfunction
similar to HAPE that resolved spontaneously and did not require medical
Scoggin calculated a yearly incidence of HAPE in the county for people
15 years and older as 50 per 100,000 residents, and for those one to 14 years of
age, as 140 per 100,000 residents (Scoggin et al. 1977:1270).
These findings suggest that reascent HAPE in Colorado residents of
high altitudes occurs predominantly in children. Specifically, children appear to
be susceptible to HAPE upon their return to altitude after descending, even for
one day, to low altitudes. Yet the evidence is far from conclusive. Although the
number of HAPE cases in residents outnumbered that in visitors, what is
unknown is the total number of altitude children who reascended without
developing HAPE. Thus the relative risk cannot be estimated (Gray 1983:142).
Houston points out that many thousands of people who live at high altitude
routinely descend to lower elevation for visits. If reascent HAPE were common
under such conditions we would have heard much more about it (Houston
1980:167). Also it is not known how long the children resided in Lake County,
or if they were life-long residents.
Scoggins study makes no mention of whether or not any of the HAPE
patients had upper respiratory infections such as a common cold or bronchitis.
This omission is a weak point in this study since viral infections in the
respiratory tract are recognized as increasing the likelihood of HAPE.
Nevertheless, the relatively young age of those affected by HAPE is striking and
raises some intriguing questions. Why are children seemingly at risk than
adults? Are the reasons hormonal or behavioral, and is there a genetic
determination of individual susceptibility to HAPE (Moore and Regensteiner
This study was carried out from August 1989 to April 1990 at Keystone
Science School and the Headlands Institute with the assistance of the Colorado
Altitude Research Institute (CARI), a division of the Snake River Health
Service (aka the Clinic). Subjects were obtained through the generous
collaboration of the Keystone Science School and the Headlands Institute. The
Keystone Science School is part of the Keystone Center, a non-profit facility,
located at Keystone (elevation 9300 ft), Colorado, 75 miles west of Denver.
The school provides environmental field science programs year-round to
students of all ages.
The Headlands Institute is located across the bay from San Francisco,
California in the Golden Gate National Recreation Area (elevation 100 ft). As
a member of the Yosemite National Institutes, a private educational system, the
school focuses on student exploration of various ecosystems including marine,
coastal and forest ecologies.
The moderate altitude children, ages 9 to 13, came to the Keystone
Science School from Denver-Metro public schools (average elevation 5280 ft).
They traveled for two hours by bus, and spent 48 to 72 hours at 9300 ft with day
excursions up to 14,000 ft. At the end of their visit, and shortly before their
departure for home, 558 children completed a one page questionnaire which
was administered by the director of the Keystone Science School.
The sea-level control group consisted of 347 children of the same age
cohort who came to Headlands overland and whose travel time varied between
20 minutes and 2 hours. The children came from surrounding schools and lived
at altitudes ranging from sea level to 2000 ft. These students were surveyed
using the same questionnaire administered in Keystone after they had been at
Headlands for 48 to 72 hours. The program director administered the
The questionnaire was designed to obtain the following data: age, sex,
weight, height, symptoms present, effect of symptoms on routine activities, and
if the subjects have ever experienced similar problems at altitude. In addition,
the children were asked if they took any medications for their symptoms,
whether they had asthma, diabetes, or any other preexisting health problems.
Questionnaires that had more than 40 percent of the symptom data missing
were rejected for analysis.
Information on each child was entered in a microcomputer with the use
of Epi Info questionnaire processing program (Centers for Disease Control) to
determine: a) the age and sex distribution; b) incidence of AMS; c) occurrence
of underlying health conditions; and e) the relationship between signs and
symptoms of AMS with underlying health conditions. The data were
subsequently processed using statistical capabilities in Epi Info and SAS.
Statistical analysis was examined by chi-square test and odds ratio. The
accepted of P value was less than 0.05.
Definition of AMS
Although a precise definition of AMS and its relation to the
physiological alteration in the oxygen transport system at high altitude remains
elusive, the presence of selected symptoms after ascent to high altitude has
frequently been used as a basis for classification for AMS. These symptoms, in
order of frequency are, headache, insomnia, lassitude, anorexia, nausea,
dizziness, excessive breathlessness, peripheral edema, vomiting, and
incoordination (Hackett and Rennie 1983:132). In this study AMS was defined
as the presence, at altitude of three or more symptoms of the following
symptoms: mild headache, severe headache, loss of appetite, vomiting, fatigue,
insomnia, shortness of breath, and dizziness.
Peripheral edema, and incoordination were rejected as components of
the case definition because of difficulty in accurately assessing these conditions
and because, in addition, these symptoms are usually not present in mild AMS
cases. Nausea was also excluded from the case definition because it was found
that children would not know or understand the term; the term vomiting was
This study was approved by the Committee on Human Research,
University of Colorado, Denver.
During the eight month period of study 558 questionnaires from
Keystone, Colorado, and 352 questionnaires from Sausalito, California, were
collected and analyzed. Five questionnaires from California, were rejected
because of missing symptom data; thus the total analyzed was 347. No
Colorado questionnaires were rejected.
The 274 girls and 266 boys of the Keystone group had a mean age of
11.06 years (range, 9 to 13 years). The 168 girls and 174 boys in the sea-level
control group were slightly older than the altitude group with a mean age of
11.41 years (range, 10 to 14 years) (Table 1 and 2).
In declining frequency, the symptoms the Keystone children reported
were mild headache (39%); fatigue (37%); insomnia (22%); shortness of breath
(21%); loss of appetite (19%); dizziness (17%); severe headache (13%); and
vomiting (4%). The California children reported a similar frequency of
symptoms which consisted of mild headache (33%); fatigue (31%); loss of
appetite (25%); insomnia (20%); shortness of breath (11%); dizziness (10%);
severe headache (9%); and vomiting (4%) (Graph 1).
California children clearly experienced more anorexia while Colorado
children more commonly experienced headache, shortness of breath and fatigue
(P <0.05). There was no difference in the frequency of fatigue, vomiting, or
insomnia between the two groups.
As Table 3 illustrates, girls complained of symptoms more frequently
than boys. For only two symptoms, vomiting and loss of appetite, were there no
statistical differences between the sexes.
Twenty-one percent of the sea-level, California group and 28% of the
Colorado group reported three or more symptoms. The difference between
these two groups was statistically significant (P < 0.05, Graph 2).
The number of Colorado children who reported three or more of the
seven possible symptoms and took medication for their complaints was similar
in frequency to the children who reported two or less symptoms (53% vs 47%).
California children displayed a similar frequency range; the children with two or
less symptoms took more medications than the group who reported three or
more symptoms (52% vs 48%). Overall, the California group consumed more
medicines than the Keystone group (19% vs 13%).
Characteristics of Colorado and California Subjects
Number 558 347
Age (years) 11.06 (S.D. 0.72) 11.41 (S.D. 0.82)
Sex 49% Female 51% Female
51% Male 49% Male
% Asthmatic 9.5% 10.7%
% Diabetic 0% 0.3%
Altitude of residence 5000 6000 ft 0 2000 ft
Table 2. Age Distribution
Years No. % No. %
9 2 0.4 - -
10 46 8.3 36 10.4
11 401 72.2 177 51.4
12 103 18.5 107 31.1
13 3 0.5 15 4.3
14 9 2.6
Comparison of Gender Response to Specific Symptoms
Symptom TOT Female Male TOT Female : Male
Mild Headache 212 61% 39% 112 66% 34%
Severe Headache 70 54% 46% 32 59% 41%
Loss of Appetite 106 53% 47% 82 59% 41%
Vomiting 24 38% 62% 15 33% 67%
Fatigue 201 59% 41% 102 60% 40%
Insomnia 115 63% 37% 66 53% 47%
Dizziness 93 62% 38% 33 73% 27%
Shortness of Breath 113 61% 39% 38 66% 34%
Table 4. Number of Colorado Children Reporting Symptoms
Svmotoms Total Percent Female Male
0 147 26.3 50 90
1 135 24.2 69 63
2 120 21.5 55 61
3 81 14.5 50 29
4 49 8.8 34 14
5 16 2.9 12 3
6 9 1.6 4 5
7 1 0.2 0 1
TOTAL 558 100.0% 274 266
Note: 18 (3%) of the children did not report their gender
Number of California Children Reporting Symptoms
Symptoms Total Percent Female Male
0 119 34.3 40 79
1 92 26.5 43 48
2 63 18.2 40 21
3 42 12.1 25 16
4 14 4.0 10 3
5 11 3.2 7 4
6 5 1.4 3 2
7 1 0.3 0 1
TOTAL 347 100 168 174
Note: 5 (2%] 1 of the children did not report their gender
Comparison of Gender to Symptom Responses
Number of FEMALE MALE
Symptoms Colorado California Colorado California
0 18% 24% 34% 46%
1 25% 26% 24% 28%
2 20% 23% 23% 12%
3 18% 15% 11% 9%
4 13% 6% 5% 2%
5 4% 4% 1% 2%
6 2% 2% 2% 1%
7 0 0 <1% <1%
TOTAL 100% 100% 100% 100%
GRAPH 1. Frequency of Symptoms
g High Altitude ^ Low Altitude
Fatigue Insomnia Shortness Loss of Dizziness
of Breath Appetite
GRAPH 2, Comparison of symptom response. AMS is defined as the
presence, at high altitude, of three or more symptoms.
gHigh Altitude ^ Low Altitude
The purpose of this study was to determine the incidence of Acute
Mountain Sickness (AMS) in Denver-Metro children at an elevation of 9300 ft.
AMS is defined as a complex of many symptoms headache, fatigue, shortness
of breath, to list a few which occur, usually simultaneously, 6 to 48 hours after
ascent, at elevations above 8000 ft. A precise, clinical definition for AMS
remains elusive. Following the precedent set by other studies AMS was defined
as the occurrence of three or more of the following symptoms: headache (severe
or mild), shortness of breath, fatigue, vomiting, loss of appetite, insomnia, and
dizziness. The results showed a slight but significant increase in the incidence of
sickness at 9300 ft compared to sea level (28% vs 21%, P <0.05). Colorado
children also reported headache (mild and severe), shortness of breath and
fatigue more frequently than sea-level children.
The preponderance of symptoms reported even at sealevel implies travel
and disruption in daily activities contribute substantially to the occurrence of
symptoms at both altitudes. Altitude is probably not a major contributing factor
to the high frequency of reported symptoms here. These children may have
been away from home for the first time. Their diet, sleep schedule, and physical
activity may have been altered. Emotions and feelings such as excitement, fear,
loneliness, embarrassment may have been intensified. The questionnaire did
not ask the children their level of exertion, the amount of water consumed, if
they have ever been away from home, if they had any coexistent illness, or
menstrual symptoms, factors which many have delimitated the effects of altitude
from the disruption of daily events.
It must be emphasized that the Colorado study group lived at an
altitude ranging from 5000 to 6000 ft and many traveled throughout the nearby
mountains. These children, on average, were healthy and should be expected to
be acclimatized to altitudes between 8000 and 10,000 ft. The 7% difference
(28% -21%) between the Keystone, Colorado and Sausalito, California groups
was identical to Montgomery, Mills, and Luces findings (adjusted AMS rate
12% -5%). Although they surveyed at a relatively low altitude (6900 ft), 96% of
these respondents resided at altitudes below 5000 ft. Symptoms of AMS
occurred primarily in this group. Because of the low incidence of symptoms in
the sea-level group, Montgomery and colleagues eliminated travel as a
Dean, Yip, and Hoffman (1990) asserted that an epidemic of AMS
occurred at a four day meeting held in Colorado at an altitude of 9800 ft. The
42% incidence rate was considerably higher than Houstons 1982 survey in
which 12% of the visitors to six Colorado ski resorts (elevations 8000 9500 ft)
reported AMS. This 42% incidence rate was similar to AMS rates observed at
altitudes above 14,000 ft. As in Montgomery et al. s study, the majority of the
attendees came from altitudes below 5000 ft and also reported a higher
frequency of symptoms. One major drawback of this study was the lack of a sea
level control group to account for other possible causal factors.
The Colorado Tourism Board estimates that 75% of the nearly 30 million
people who traveled throughout Colorado in 1989 were from out-of-state. This
means, in all likelihood, that they were residents of low altitudes. The majority
visit for vacation purposes in which the mountains was often a destination point.
If 7 25% of these tourists refrained from spending money because they are
feeling miserable, then resort owners and the state of Colorado may be losing
tens of millions of dollars annually. Clearly AMS is more than a medical
nuisance; it also has large human and financial impact (Houston 1980:135).
Adaptation and the Environment
The history of human life on earth has been a history of interaction
between our genetic, behavioral and cultural traits with a range of
environmental conditions. No one disputes our biological success as a species,
however tenacious and temporary it may be. For humans, as for all species,
there is a totality of adaptations which enable us to occupy a certain habitat.
However, unlike most species, the extent to which we dominate and control our
surroundings, our adaptability, and lack of biological specialization have
permitted us colonize most of the earth.
Understanding human biological adaptation is of interest to the
biologist and anthropologist trying to ascertain evolutionary processes and
historical relationships. The most direct evidence of our past comes from the
fossil record but the material is insufficient to trace the emergence of modern
Homo sapiens in any detail. That leaves living populations as a source from
which, by careful and statistical comparisons, to infer something of our ancestral
roots. As animals, human populations are influenced by biological factors that
determine our development and behavior. Yet, an added element, culture,
influences our biological selves, possibly changing selective pressures and other
factors operating in evolution. Thus, to function and reproduce successfully in
our environment, we rely on a mutual interaction of biological and cultural
traits which, if effective, permit the population to adapt.
Adaptation, as a term, is inextricably interwoven in the concepts of
biological and social sciences. However, it has slightly different connotations in
these respective fields which often leads to considerable misunderstanding. To
add to the confusion, adaptation can define a "state" of being and a "process" of
achieving such a state.
Adaptation, from modern evolutionary theory, is defined as a process by
which an organism becomes fitted to its environment as a result of natural
selection acting upon heritable variation (Fisher 1985:121). Few will disagree
that adaptation through natural selection is a key process in the history of life.
Critics of the "adaptationist programme" have raised issues concerning the role
natural selection plays in organic evolution and the phenomenon of adaptation
itself. Targeted by this criticism has been the tendency for evolutionary
biologists, sociobiologists and nature television shows, in an attempt to develop
adaptive explanations, to indulge in adaptive scenarios. The speculative
storytelling in the adaptationist mode to explain how giraffes attained their long
necks or why Redstart Warblers permit cuckoo nestlings to live parasitically in
their nests. Adaptation is a powerful force which has been trivialized by a
variety of adaptive proposals that run from the absurdly ad hoc to the plausible
Physiologists define adaptation as any property of an organism,
environmentally or genetically determined, which favors survival and
reproduction in a specific environment, particularly a stressful one (Prosser
1964:11). Stress, the environmental force that stimulates the need to change,
produces a deviation in homeostasis, or precise biological regulation.
Organisms respond to stress by either removing the stress directly, employing
feedback mechanisms to return to a state of homeostasis, or by accommodating
to the physiological deviation by maintaining a new homeostatic level.
Response may be considered adaptive if it is successful and maladaptive if it is a
failure, or if the environment changes and the organism cannot cope. For
example, people who possess the heterozygous gene for sickle cell trait have
greater resistance to malaria in areas where the disease is endemic. Outside of
malarial regions this genetic peculiarity no longer is an asset and may, instead,
become a handicap for survival.
Acclimatization refers to any of the numerous, gradual adjustments of an
organism to environmental change. Such responses last for a season or a
relatively extended period of time and are more or less reversible should
environmental conditions revert to previous conditions (Poirier 1977:401).
However, not all acclimatization is reversible. If exposure to environmental
stress occurs during prenatal and early postnatal periods, developmental
acclimatization, which is irreversible, takes place. The barrel-shaped chests of
the Andean Quechua Indians is induced during childhood by exposure to high
altitude and does not appear to represent a genetic difference between them
and their lowland relatives (Vander 1976:2). In contrast to adaptation,
acclimatization does not involve an alteration in the genetic structure or
mechanisms of the organism. Human acclimatization, although limited by genes
and thus limited to a certain range, characterizes our remarkable phenotypic
The anthropological definition of adaptation is diffuse and generally
lacking in consensus. Cultural ecologists, biological, cultural, and psychological
anthropologists employ the concept of adaptation within their theoretical fields
but each represent it as quite different phenomena. Thus currently, there is no
unified theory of human cultural and biological adaptation to permit an
integrated approach to understanding human populations. Despite these
problems, it can be said that anthropologists take a holistic approach to human
adaptation compared to the limited and costly, one-stress-one-response
laboratory studies of physiologists. Overall, adaptation is defined in human
populations as a dynamic, systemic, life-serving, biocultural set of processes
(Laughlin and Brady 1978:282). Anthropologists, through multidiscipline
strategies, attempt to understand these complex genetic, physiological and
cultural interactions which characterize human adaptation.
Clarifying the effects of environment on human populations and judging
the efficacy of adaptation is problematic for several reasons. First,
demonstrating that a biological trait is of benefit to a selected individual, and
thus adaptive, is complicated by the role socioculture (behavior, technology,
subsistence patterns, etc.) plays in reducing or intensifying environmental stress.
If a benefit can be demonstrated, it is unknown whether the response is due to
short-term physiological responses, modification during growth and
development, or the product of natural selection. Next, simply extrapolating
individual responses to the assessment of population adaptation may spread
into the sphere of speculative storytelling in the adaptationist mode. A
particular individual "benefit" may be temporally and spatially specific,
dependent upon nutritional, health or growth factors and not representative of
the whole population.
Second, comprehensively analyzing human populations, is restricted by
political, fiscal, social and ethical constraints. Working usually alone for a
relatively short period of time in the field and unable to "experiment" because of
ethical reasons, the researcher is expected to reach scientific explanations
representative of thousands of people (Laughlin and Brady 1978:x). Also,
genetic adaptive processes may occur over generations, far too long for one
research career to sufficiently study.
Recognizing these problems, it is possible to operationalize
anthropological studies of human adaptation in two ways. First, by examining
all phases of the human life cycle, (conception, birth, maturation, and death)
and then piecing the parts together into a picture, a process of adaptation from
one generation to the next can be patched together (Moore and Regensteiner
1983:288). In addition, because populations are comprised of people of both
sexes, of all ages, and health conditions, studying populations generationally can
help determine if environmental stressors are the same for all people or
whether gender, age, health status, and other conditions influence physiologic
responses (Moore 1990:50).
Second, populations living in environments in which existing stresses
cannot be readily removed or diminished by technology, provide "natural
laboratories" to delineate biological adaptations from sociocultural responses.
At high altitudes, hypobaric hypoxia, or the decrease in partial pressure
of inspired oxygen, is the primary challenge to human life. Other environmental
stressors such as cold, dryness, increased ultraviolet radiation are also
important; however, only hypoxia cannot easily be modified by human
inventions. Permanent high altitude residents, specifically descendents of
multiple generations of high altitude residents, are believed to be adapted,
although possibly precariously, to hypobaric hypoxia. It is unknown whether the
enlarged chests and lung dimensions, smaller body size and growth retardation
of permanent high altitude residence result from genetic, or developmental
adaptations or acclimatization. To date, there is no clear evidence of specific
human genetic adaptation to altitude. The adaptation of a population to a
specific environment may be measured in a variety of ways. The prime
indicators, many will agree, of a populations success is the general health of a
group, and their survival and continuity (Baker 1978:317). Studies of high
altitude residents, native and recent migrants, have indicated that altitude
produces a different disease pattern from the one found in surrounding low-
altitudes. The health problems of long-term residents of high altitudes
associated principally with the oxygen transport system include a small increase
in the incidence of congenital malformations, problems of increased incidence
of pre-clampsia, low infant birth weight, and hyperbilirubinrmia, growth
retardation from infancy through adolescence, reascent HAPE, chronic
mountain sickness, and increased emphysema mortality. Yet it is not know
whether the physiological effects of chronic hypoxia are problems or solutions
for adaptation to high altitude (Moore and Regensteiner 1983:301).
Lowlanders who ascend rapidly to high altitude react physiologically to
hypoxia with a series of cardiovascular adjustments. Hypoxia must be
considered to be the common denominator for altitude induced illnesses;
however, the events that trigger these disorders are incompletely understood, as
well as why some people are susceptible and others not. If the visit is extended
over six to eight days, acclimatization, or gradual biological adjustment occurs.
An individualistic series of interrelated, integrated, and dynamic events takes
place within the systems of the body, that, in the case of hypobaric hypoxia, tend
to restore oxygen pressure in the tissues toward normal.
Virtually all studies on altitude-aggrevated illness has been conducted on
adults. This study indicates that children from an average elevation of 5280 ft
experience AMS at 9300 ft. Yet the high frequency of reported symptoms at
both sea-level and Colorado altitudes suggest a number of factors may be
Stress and pain, in a very basic sense, are universal human experiences.
Although we all possess nerve endings sensitive to pressure, heat, and pain, it is
the influence of our sociocultural and psychological components which shapes
our response to stress. Both groups of children reported high frequency of
symptoms. Are these children unquestionably stressed and thus, is stress poorly
tolerated by 9 -14 year old children? Or, are children more open about their
feelings? Young children go through a stage when they respond to every
question with a NO! In their preadolescent years they desire to please, and are
more inclined to answer YES! The children in this study were away from home,
and probably were not sure how to respond. The high frequency of yes
responses may be more of a factor of "saying what you want to hear" rather than
a lack of tolerance for stress.
Some individuals, for reasons not completely understood, are at risk for
having high-altitude illness. Within this unknown, is the health effects of
altitude on children, and the whole human spectrum. This study raises a number
of avenues for further systematic study such as whether high altitude aggravates
pre-existing health conditions, and what cultural and biological attributes
further our adaptation to high altitude.
Summary and Conclusion
Twenty-eight percent of Denver-Metro children, ages 9 13, who
sojourned at 9300 ft for 48 to 72 hours developed three or more of the following
symptoms: headache (mild or severe), fatigue, insomnia, shortness of breath,
loss of appetite, dizziness, and vomiting. Twenty-one percent of a sea-level
control group, ages 10 -14, also reported three or more symptoms. The
difference (28% 21%) in rates suggest that ascent from 5280 ft to 9300 ft
increases the occurrence of sickness. This increase represents the component
due to altitude and may be termed Acute Mountain Sickness (AMS), While this
study shows that AMS occurs in children, the preponderance of symptoms
exhibited by the sea-level control group suggests travel, or disruption of normal
routine, rather than altitude may be responsible for the symptoms observed.
COLORADO ALTITUDE RESEARCH INSTITUTE
A Division of the Snake River Health Services Inc.
Box 38 Keystone Colorado 80435
1. How old are you _______? Are you a boy or a girl (circle one)?
2. How much do you weigh?________________pounds
3. How tall are you?______feet and_______inches
4. Where do you live? City__________________State____________________
5. Do you go to see the doctor regularly for any health problems?_Yes __No
If Yes, do you have asthma? Yes____ No_______
Do you have diabetes? Yes______No_____
Do you have anything else? (write the name of it as best you can)________________
11. During the time that you have been in Headlands, have you had any of the problems listed below?
Headache: No________ a little headache_________ a big headache______________
Feeling nor hungry at meal time: No_____ Yes-------
Vomiting (throwing up, puking): Yes______ No________
Feeling unusually tired: Yes______ No______
Waking up alot at night and not being able to get back to sleep: Yes- No--------
Feeling dizzy or like you were going to faint: Yes______ No______
Feeling as though you couldnt get enough air to breathe while resting: Yes_ No-----
12. If you had any of these problems, did you (circle one)
Go to bed Stop and rest Ignore it and hope
for a while it would go away
13. Did you take any medicines for these problems?
No_________ Tylenol_________________ Aspirin________
Advil______ Other (give name of the medicine)____________________
15. Have you ever been to the mountains before? Yes________ No__________
Did you have any of the problems listed above? Yes______ No__________
Group #_______________ID #_________________ Date of Survey________mo/________da/_________yr
THANK YOU FOR YOUR HELP
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