HIGH ALTITUDE NOTES
— Bryce Brown, Alpine Ascents International Expedition Doctor and MountainZone.com Correspondent
As our team climbs towards the summit of Everest, we are exposed to decreasing barometric pressure. Barometric pressure (air pressure) falls with increasing altitude. Oxygen contributes about 21% to barometric pressure, therefore, as we ascend in elevation, our bodies are exposed to less oxygen. This is the main cause of altitude problems - hypoxia. For example, at Everest Base Camp (5300m), we are exposed to about half as much oxygen as at sea level. At the summit, each breath contains about one third the oxygen at sea level.
ACCLIMATIZATION
"I listened to his labored, sonorous breathing and knew it was time to get low as fast as possible...." — Alex Lowe, treating Andrew McLean, Shishapangma 1999
I'm sure many people have seen the film Vertical Limit. Although we would all love to fly to Base Camp in a helicopter, have a rocking BBQ and then go for the summit the next day, the truth is, our bodies would not allow us to do this. A rapid ascent to the summit of Everest would cause unconsciousness and death within several minutes. However, with a slow ascent from sea level, our bodies can adjust to the thin air and allow ascent even without oxygen.
We term this adjustment to altitude "acclimatization." Physiologic changes in respiration, circulation, blood, and tissues increase the oxygen delivery to our body and the body's ability to withstand less oxygen. Success of acclimatization depends on rate of ascent, severity of the stress and an individual's physiology.
Individual ability to acclimatize varies - some adjust easily and quickly, while others may take longer and develop symptoms of altitude illness. There are even an unfortunate few who cannot acclimatize at all! People who live at high altitude during childhood seem to get the maximum benefit from the changes of acclimatization, especially in terms of exercise performance. This certainly explains our Sherpa colleagues, who perform very well at high altitude.
Respiratory Changes
One of the first changes we notice at altitude is a faster breathing rate. This can start as low as 1500m. This is termed Hypoxic Ventilatory Response (HVR). The HVR varies from person to person and is also affected by stimulants (such as coca and caffeine), and depressants (such as alcohol and antihistamines). Physical fitness appears to have no effect on the HVR. A good HVR enhances acclimatization, while a poor HVR may predispose one to altitude illness.
"When I finally got home, I had an MRI and was pronounced to have had a small bit of damage upstairs.... The numbness lasted on and off for about four years..." — Eric Simonson, Expedition Leader Everest '99
As our breathing rate increases, we take in more oxygen, but we also breath out more carbon dioxide, which causes chemical changes in the blood. Within 24 to 48 hours, our kidneys try to counteract these chemical changes by excreting bicarbonate. Basically, what this means is that we pee lots while acclimatizing. This process of compensation is sped up by a drug called Acetazolimide (or Diamox), but more about that later.
Circulatory Changes
High altitude stresses the body. In response to this, stress hormones are released into the blood. This causes an initial mild increase in blood pressure and heart rate. With time at altitude, resting heart rate returns to that at sea level. However, our maximum heart rate actually decreases. As you can imagine, at some point, resting and maximum heart rates converge as the limits of acclimatization are approached.
The volume of plasma (blood minus the cells) also drops due to the increased amount of peeing (see above). Plasma volume actually drops about 15% in the first three days. Obviously it becomes important for us to stay well hydrated during acclimatization. It is not uncommon to drink five or six 6 liters a day!
The pulmonary vessels constrict with increase in altitude. This causes an increase in pulmonary artery pressure. This increases even more with exercise. This is one of the factors which contributes to pulmonary edema, which I will explain below.
Blood Changes
Erythropoietin (EPO) stimulates the bone marrow to produce more red blood cells (which are responsible for carrying oxygen). This hormone is secreted by the kidneys in response to low oxygen levels. Within four to five days, new red blood cells are in circulation. Over the weeks at altitude the body continues to produce more red blood cells to carry the sparse oxygen from the lungs to the tissues where it is needed. The blood also undergoes chemical changes, which helps oxygen bind in the lungs. This raises oxygen saturation, or the amount of oxygen carried by each red blood cell.
Tissue Changes:
To increase needed oxygen delivery, the amount of small blood vessels (capillaries) in the muscles increase. The muscles also decrease significantly in size (due to atrophy). This is actually a benefit as the oxygen has less distance to travel in a smaller muscle.
Sleep Changes
It is very common to have sleeping difficulties at altitude. Breathing is normally controlled by carbon dioxide levels in the blood; when carbon dioxide levels rise, our brain tells us to breath. The backup system is oxygen levels in the blood. If oxygen levels drop, again our brain says breath. When we breath rapidly at altitude, we blow off carbon dioxide - our brain senses low levels - we stop breathing. When the oxygen level drops from not breathing, our brain signals to breath. Then we breath quickly again and blow off carbon dioxide... It is a vicious cycle of rapid breathing and no breathing.
Oxygen System
The non-breathing phases can last 30 seconds or more. This is termed periodic breathing and is very common while acclimatizing. As you can imagine, it can be quite disruptive to normal sleep. It is common to wake suddenly with a feeling of suffocation, and be gasping for breath. As acclimatization continues, this phenomenon decreases, but does not disappear totally. The drug Acetazolimide (Diamox) decreases periodic breathing substantially, and is commonly used as a sleep aid while acclimatizing.
Deterioration
Altitudes of approximately 5800m are the limit of long-term habitation (of course this varies by individual). Problems of weight loss, increasing lethargy, poor sleep, and weakness become realities of living at high altitude. The higher the elevation, the quicker the deterioration. Above 8000m (known affectionately as "The Death Zone"), this deterioration is so rapid that death can occur in just a few days. Most climbers on Everest use supplemental oxygen, which greatly improves performance in The Death Zone.
Weight loss is a big concern on long expeditions to altitude. Two problems contribute to this: poor appetite and problems with absorption of nutrients. The appetite decreases with altitude, to the point that on summit day climbers have only been able to stomach a few Pringles or a candy bar. Also, the body only absorbs about half as much fat and three quarters as many carbohydrates as at sea level. It is not uncommon to lose 10% of one's body weight on an Everest climb! We are thinking of starting the "Everest Weight Loss Program" - a sure success!
HIGH ALTITUDE ILLNESS
Rapid ascent to altitude, without allowing the body time to acclimatize, can cause several illnesses. They all occur within the first few days of ascent and respond to descent. Prevention, with a slow-graded ascent is the key. Current guidelines suggest avoiding abrupt ascent to sleeping elevation of more than 3000m. Spend two to three nights at 3000m and then allow an extra night for acclimatization every 600 to 900m. Avoid abrupt increases of more than a 600m in sleeping elevation per day. The old climber saying "climb high, sleep low" is good advice - day climb to a higher elevation and then return lower for sleep.
Mild exercise will help the body adjust to higher altitude. However, keep in mind that overexertion will contribute to altitude illness. This idea of slow ascent is why we took almost two weeks to trek from Namche (3400m) to Everest Base Camp (5300m). On the trek up, no one had any more than mild altitude problems.
Acute Mountain Sickness (AMS)
"The air is extremely thin up there, and we had no supplemental bottled oxygen, so at that altitude every step is a painful and oxygen-starved, brain-numbed decision...." — Dan Mazur Expedition Leader Cho Oyu, 2000
The severity of AMS depends on altitude, rate of ascent, length of exposure, exertion and individual physiology. AMS is generally not all that significant, but it can progress to more serious forms of altitude illness. AMS produces headache, dizziness, fatigue, loss of appetite, and nausea. These symptoms are often described as similar to a hangover. This problem is usually seen with a rapid ascent of more than 1000m, although it can occur with less elevation gain.
Successful treatment is based on early detection. The most basic treatment is to stop ascent. This allows time for the body to acclimatize, and may take several days. If symptoms continue to worsen, then DESCEND. Acetazolimide (Diamox) can help speed acclimatization and therefore can improve symptoms if given early. The most accepted dose is 125mg twice a day. Symptomatic treatment with over-the-counter medications for headache or nausea are okay, as long as you don't go higher. Also, sedatives, such as alcohol, antihistamines or sleep aids, should be avoided. The best treatment is descent. The general rule is descend until the symptoms are gone, usually about 500 to 1000m. Another possible treatment is with a portable hyperbaric chamber (commonly known as GAMOW or PAC bags). These inflatable chambers simulate descent by increasing the air pressure inside.
High Altitude Cerebral Edema (HACE)
It is probably easiest to think of altitude illness as a spectrum, with AMS on the mild side and progressing to HACE on the serious side. HACE is basically extreme AMS. It is caused by swelling of the brain. The main signs of HACE are ataxia (walking like a drunk) and altered consciousness (drowsy, confused, stupor or coma). Headache and vomiting are also often present. The progression from mild AMS to coma can be as fast as 12 hours, but usually takes several days.
Treatment again depends on early recognition. At the first signs of ataxia, or altered consciousness, DESCEND, DESCEND, DESCEND! The drug Dexamethasone (Decadron) should also be started with an 8mg injection, or orally, then 4mg every six hours. Oxygen is also helpful if available.
High Altitude Pulmonary Edema (HAPE)
This is the illness made famous recently in Vertical Limit (although they didn't get it quite right)!
This is the most common cause of death due to altitude. Again, this is easily treatable if recognized early. Basically, HAPE is caused by the blood vessels in the lungs leaking fluid into the air spaces and the lungs filling with fluid. This obviously causes problems with breathing!
The earliest signs are decreased exercise tolerance and increased recovery time. Signs of AMS are often present as well. Initially, a persistent dry cough often develops, and nailbeds and lips become a blue/gray color (known as cyanosis). As the illness progresses, shortness of breath at rest and audible crackles in the lungs develop. This is serious. Often, if the patient lies down they become more short of breath. Frothy sputum, often blood tinged, is a very late finding and very bad. The illness may then progress to mental changes, ataxia and coma (HACE). More than half of the victims with HAPE also develop HACE.
Successful treatment, as always, depends on early recognition, and on DESCENT. However, because exertion worsens the condition, exercise must be minimized. Oxygen immediately improves the situation. If descent is not possible, oxygen may be lifesaving and should be the highest priority. Drugs are of limited value in treating HAPE. The drug Nifedipine (Adalat XL) has proven effective - 30 mg every 12 hours orally. However, improvement is much better with descent and oxygen than with any drug.
The treatment given "Dex" in Vertical Limit was not medically correct. Neither was the discoloration of the victim's chest wall. To the filmmaker's defense, HAPE did make for a very dramatic and time-dependent problem. Plus, injections and needles are always much more dramatic than swallowing a pill. Ah, Hollywood.
OTHER HIGH ALTITUDE SYNDROMES
High Altitude Bronchitis
This is most commonly known as the "Khumbu Cough." Sore throat and chronic cough afflict almost all of us who spend more than two weeks at Base Camp or above. This problem is not necessarily a sign of infection or HAPE (although I keep a close eye). The big problem is the increase in breathing, often through the mouth, which means air is not being moisturized in the nose. The cold, dry air irritates the throat and breathing passages and causes a dry, hacking cough. Exertion makes this problem worse, which is a problem when you're trying to climb the highest mountain in the world. This can actually become severe enough to crack ribs due to coughing and this is not rare. Basically, the only cure is descent, although we try all sorts of tricks, from codeine to cough candies, to sleeping with masks.
High Altitude Flatus Expulsion (HAFE)
This is the bane of all tentmates! It is a serious syndrome, listed in any good altitude textbook... I am not making this up! This problem is caused by the expansion of bowel gas as one increases in altitude (Boyle's Law explains this. Remember high school physics?). This results in the unwelcome passage of colonic gas (translation - you fart lots). Many a tentmate have been put off by this affliction!
— Bryce Brown, Alpine Ascents International Expedition Doctor and MountainZone.com Correspondent
As our team climbs towards the summit of Everest, we are exposed to decreasing barometric pressure. Barometric pressure (air pressure) falls with increasing altitude. Oxygen contributes about 21% to barometric pressure, therefore, as we ascend in elevation, our bodies are exposed to less oxygen. This is the main cause of altitude problems - hypoxia. For example, at Everest Base Camp (5300m), we are exposed to about half as much oxygen as at sea level. At the summit, each breath contains about one third the oxygen at sea level.
ACCLIMATIZATION
"I listened to his labored, sonorous breathing and knew it was time to get low as fast as possible...." — Alex Lowe, treating Andrew McLean, Shishapangma 1999
I'm sure many people have seen the film Vertical Limit. Although we would all love to fly to Base Camp in a helicopter, have a rocking BBQ and then go for the summit the next day, the truth is, our bodies would not allow us to do this. A rapid ascent to the summit of Everest would cause unconsciousness and death within several minutes. However, with a slow ascent from sea level, our bodies can adjust to the thin air and allow ascent even without oxygen.
We term this adjustment to altitude "acclimatization." Physiologic changes in respiration, circulation, blood, and tissues increase the oxygen delivery to our body and the body's ability to withstand less oxygen. Success of acclimatization depends on rate of ascent, severity of the stress and an individual's physiology.
Individual ability to acclimatize varies - some adjust easily and quickly, while others may take longer and develop symptoms of altitude illness. There are even an unfortunate few who cannot acclimatize at all! People who live at high altitude during childhood seem to get the maximum benefit from the changes of acclimatization, especially in terms of exercise performance. This certainly explains our Sherpa colleagues, who perform very well at high altitude.
Respiratory Changes
One of the first changes we notice at altitude is a faster breathing rate. This can start as low as 1500m. This is termed Hypoxic Ventilatory Response (HVR). The HVR varies from person to person and is also affected by stimulants (such as coca and caffeine), and depressants (such as alcohol and antihistamines). Physical fitness appears to have no effect on the HVR. A good HVR enhances acclimatization, while a poor HVR may predispose one to altitude illness.
"When I finally got home, I had an MRI and was pronounced to have had a small bit of damage upstairs.... The numbness lasted on and off for about four years..." — Eric Simonson, Expedition Leader Everest '99
As our breathing rate increases, we take in more oxygen, but we also breath out more carbon dioxide, which causes chemical changes in the blood. Within 24 to 48 hours, our kidneys try to counteract these chemical changes by excreting bicarbonate. Basically, what this means is that we pee lots while acclimatizing. This process of compensation is sped up by a drug called Acetazolimide (or Diamox), but more about that later.
Circulatory Changes
High altitude stresses the body. In response to this, stress hormones are released into the blood. This causes an initial mild increase in blood pressure and heart rate. With time at altitude, resting heart rate returns to that at sea level. However, our maximum heart rate actually decreases. As you can imagine, at some point, resting and maximum heart rates converge as the limits of acclimatization are approached.
The volume of plasma (blood minus the cells) also drops due to the increased amount of peeing (see above). Plasma volume actually drops about 15% in the first three days. Obviously it becomes important for us to stay well hydrated during acclimatization. It is not uncommon to drink five or six 6 liters a day!
The pulmonary vessels constrict with increase in altitude. This causes an increase in pulmonary artery pressure. This increases even more with exercise. This is one of the factors which contributes to pulmonary edema, which I will explain below.
Blood Changes
Erythropoietin (EPO) stimulates the bone marrow to produce more red blood cells (which are responsible for carrying oxygen). This hormone is secreted by the kidneys in response to low oxygen levels. Within four to five days, new red blood cells are in circulation. Over the weeks at altitude the body continues to produce more red blood cells to carry the sparse oxygen from the lungs to the tissues where it is needed. The blood also undergoes chemical changes, which helps oxygen bind in the lungs. This raises oxygen saturation, or the amount of oxygen carried by each red blood cell.
Tissue Changes:
To increase needed oxygen delivery, the amount of small blood vessels (capillaries) in the muscles increase. The muscles also decrease significantly in size (due to atrophy). This is actually a benefit as the oxygen has less distance to travel in a smaller muscle.
Sleep Changes
It is very common to have sleeping difficulties at altitude. Breathing is normally controlled by carbon dioxide levels in the blood; when carbon dioxide levels rise, our brain tells us to breath. The backup system is oxygen levels in the blood. If oxygen levels drop, again our brain says breath. When we breath rapidly at altitude, we blow off carbon dioxide - our brain senses low levels - we stop breathing. When the oxygen level drops from not breathing, our brain signals to breath. Then we breath quickly again and blow off carbon dioxide... It is a vicious cycle of rapid breathing and no breathing.
Oxygen System
The non-breathing phases can last 30 seconds or more. This is termed periodic breathing and is very common while acclimatizing. As you can imagine, it can be quite disruptive to normal sleep. It is common to wake suddenly with a feeling of suffocation, and be gasping for breath. As acclimatization continues, this phenomenon decreases, but does not disappear totally. The drug Acetazolimide (Diamox) decreases periodic breathing substantially, and is commonly used as a sleep aid while acclimatizing.
Deterioration
Altitudes of approximately 5800m are the limit of long-term habitation (of course this varies by individual). Problems of weight loss, increasing lethargy, poor sleep, and weakness become realities of living at high altitude. The higher the elevation, the quicker the deterioration. Above 8000m (known affectionately as "The Death Zone"), this deterioration is so rapid that death can occur in just a few days. Most climbers on Everest use supplemental oxygen, which greatly improves performance in The Death Zone.
Weight loss is a big concern on long expeditions to altitude. Two problems contribute to this: poor appetite and problems with absorption of nutrients. The appetite decreases with altitude, to the point that on summit day climbers have only been able to stomach a few Pringles or a candy bar. Also, the body only absorbs about half as much fat and three quarters as many carbohydrates as at sea level. It is not uncommon to lose 10% of one's body weight on an Everest climb! We are thinking of starting the "Everest Weight Loss Program" - a sure success!
HIGH ALTITUDE ILLNESS
Rapid ascent to altitude, without allowing the body time to acclimatize, can cause several illnesses. They all occur within the first few days of ascent and respond to descent. Prevention, with a slow-graded ascent is the key. Current guidelines suggest avoiding abrupt ascent to sleeping elevation of more than 3000m. Spend two to three nights at 3000m and then allow an extra night for acclimatization every 600 to 900m. Avoid abrupt increases of more than a 600m in sleeping elevation per day. The old climber saying "climb high, sleep low" is good advice - day climb to a higher elevation and then return lower for sleep.
Mild exercise will help the body adjust to higher altitude. However, keep in mind that overexertion will contribute to altitude illness. This idea of slow ascent is why we took almost two weeks to trek from Namche (3400m) to Everest Base Camp (5300m). On the trek up, no one had any more than mild altitude problems.
Acute Mountain Sickness (AMS)
"The air is extremely thin up there, and we had no supplemental bottled oxygen, so at that altitude every step is a painful and oxygen-starved, brain-numbed decision...." — Dan Mazur Expedition Leader Cho Oyu, 2000
The severity of AMS depends on altitude, rate of ascent, length of exposure, exertion and individual physiology. AMS is generally not all that significant, but it can progress to more serious forms of altitude illness. AMS produces headache, dizziness, fatigue, loss of appetite, and nausea. These symptoms are often described as similar to a hangover. This problem is usually seen with a rapid ascent of more than 1000m, although it can occur with less elevation gain.
Successful treatment is based on early detection. The most basic treatment is to stop ascent. This allows time for the body to acclimatize, and may take several days. If symptoms continue to worsen, then DESCEND. Acetazolimide (Diamox) can help speed acclimatization and therefore can improve symptoms if given early. The most accepted dose is 125mg twice a day. Symptomatic treatment with over-the-counter medications for headache or nausea are okay, as long as you don't go higher. Also, sedatives, such as alcohol, antihistamines or sleep aids, should be avoided. The best treatment is descent. The general rule is descend until the symptoms are gone, usually about 500 to 1000m. Another possible treatment is with a portable hyperbaric chamber (commonly known as GAMOW or PAC bags). These inflatable chambers simulate descent by increasing the air pressure inside.
High Altitude Cerebral Edema (HACE)
It is probably easiest to think of altitude illness as a spectrum, with AMS on the mild side and progressing to HACE on the serious side. HACE is basically extreme AMS. It is caused by swelling of the brain. The main signs of HACE are ataxia (walking like a drunk) and altered consciousness (drowsy, confused, stupor or coma). Headache and vomiting are also often present. The progression from mild AMS to coma can be as fast as 12 hours, but usually takes several days.
Treatment again depends on early recognition. At the first signs of ataxia, or altered consciousness, DESCEND, DESCEND, DESCEND! The drug Dexamethasone (Decadron) should also be started with an 8mg injection, or orally, then 4mg every six hours. Oxygen is also helpful if available.
High Altitude Pulmonary Edema (HAPE)
This is the illness made famous recently in Vertical Limit (although they didn't get it quite right)!
This is the most common cause of death due to altitude. Again, this is easily treatable if recognized early. Basically, HAPE is caused by the blood vessels in the lungs leaking fluid into the air spaces and the lungs filling with fluid. This obviously causes problems with breathing!
The earliest signs are decreased exercise tolerance and increased recovery time. Signs of AMS are often present as well. Initially, a persistent dry cough often develops, and nailbeds and lips become a blue/gray color (known as cyanosis). As the illness progresses, shortness of breath at rest and audible crackles in the lungs develop. This is serious. Often, if the patient lies down they become more short of breath. Frothy sputum, often blood tinged, is a very late finding and very bad. The illness may then progress to mental changes, ataxia and coma (HACE). More than half of the victims with HAPE also develop HACE.
Successful treatment, as always, depends on early recognition, and on DESCENT. However, because exertion worsens the condition, exercise must be minimized. Oxygen immediately improves the situation. If descent is not possible, oxygen may be lifesaving and should be the highest priority. Drugs are of limited value in treating HAPE. The drug Nifedipine (Adalat XL) has proven effective - 30 mg every 12 hours orally. However, improvement is much better with descent and oxygen than with any drug.
The treatment given "Dex" in Vertical Limit was not medically correct. Neither was the discoloration of the victim's chest wall. To the filmmaker's defense, HAPE did make for a very dramatic and time-dependent problem. Plus, injections and needles are always much more dramatic than swallowing a pill. Ah, Hollywood.
OTHER HIGH ALTITUDE SYNDROMES
High Altitude Bronchitis
This is most commonly known as the "Khumbu Cough." Sore throat and chronic cough afflict almost all of us who spend more than two weeks at Base Camp or above. This problem is not necessarily a sign of infection or HAPE (although I keep a close eye). The big problem is the increase in breathing, often through the mouth, which means air is not being moisturized in the nose. The cold, dry air irritates the throat and breathing passages and causes a dry, hacking cough. Exertion makes this problem worse, which is a problem when you're trying to climb the highest mountain in the world. This can actually become severe enough to crack ribs due to coughing and this is not rare. Basically, the only cure is descent, although we try all sorts of tricks, from codeine to cough candies, to sleeping with masks.
High Altitude Flatus Expulsion (HAFE)
This is the bane of all tentmates! It is a serious syndrome, listed in any good altitude textbook... I am not making this up! This problem is caused by the expansion of bowel gas as one increases in altitude (Boyle's Law explains this. Remember high school physics?). This results in the unwelcome passage of colonic gas (translation - you fart lots). Many a tentmate have been put off by this affliction!
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