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Altitude and Pre-Existing Conditions

Preexisting Medical Conditions at Altitude

Many people with specific health issues can travel safely to altitude.
If you have a specific concern regarding a medical condition, read the section below and contact us if you need more information.

Pulmonary Problems

High Blood Pressure (HBP)

It is not uncommon for lowland visitors with a history of HBP to experience temporarily high blood pressure at high altitude. This occurs even if you are on blood pressure medication and have well controlled blood pressure at sea level. A small percentage of these people will have unusually labile (unstable) blood pressure. HBP at altitude usually returns to your baseline blood pressure after 1-2 weeks at altitude. One explanation for this is due to the higher levels of adrenaline or stress hormones in your body due to lower oxygen levels. Some persons with HBP, however, develop lower blood pressure on ascent to high altitude. You generally do not need to change your blood pressure medication dosage. Increasing your dosage could result in dangerously low blood pressure upon returning to low altitude. If you are having symptoms from your high blood pressure such as headache, dizziness, chest pain, or shortness of breath, you should seek medical treatment. Occasionally, HBP will need to be treated with medications. Further studies are needed to better understand blood pressure response at altitude and how best to treat it.

The following are things you can do that may help your high blood pressure:

Make sure your blood pressure is well controlled at sea level
Reduce salt in your diet
Stay on your medications
Check your blood pressure at high altitude
Seek medical care if symptoms develop or blood pressure is out of control

Persons with difficult-to-control blood pressure can use oxygen, especially at night, to avoid problems. Living at high altitude over long periods of time can result in lower blood pressure. The reason for this is also poorly understood and needs to be studied further.

Heart Disease (Coronary Artery Disease)

Altitude creates some stress on the heart, which is minimal at rest but can be significant during exercise. Cold in combination with the altitude and exertion may produce even more strain on the heart. Nevertheless, a few surveys done at moderate altitude showed that persons with underlying heart disease tolerated altitude quite well.

Patients with coronary artery disease will likely do well at moderate altitude of ski resorts if they follow a few guidelines:

Be accustomed to exercise at low altitude if you plan to exercise at high altitude
Reduce your exercise at high altitude to a bit less than you exercise at low altitude, especially the first few days
Stay on your regular medications
Bring a copy of a recent electrocardiogram with you
A negative stress test within the last year is helpful
Spend an extra 1-2 days acclimatizing and avoid altitude illness
Stay warm

Some evidence suggests that living at altitude may be protective for heart disease. One study showed an increase in blood vessels that grow in the heart in residents of high altitude compared to those at sea level. Further studies are needed to show conclusive evidence of the benefits of altitude on the heart.


PVCs or premature ventricular contractions occur frequently at altitude. The heart basically throws an extra beat every so often and while they are quite harmless they can be uncomfortable. Increasing levels of stress hormones in the body upon arrival to altitude are likely the cause for these additional beats. Avoidance of caffeine may help.

Many patients with irregular heart rhythms, such as supraventricular tachycardia (SVT), or atrial fibrillation (a-fib) travel safely to altitude every year. Whether these conditions are aggravated by high altitude is unknown. Irregular heart rhythms should be in good control before going to high altitude. You should discuss with your doctor if and which medications you should take if you have an arrhythmia, and discuss the safety of going to high altitude.

Congenital Heart Problems

Persons born with heart problems such as ventricular septal defect (VSD), atrial septal defect (ASD), patent ductus arteriosus (PDA), or tetralogy of Fallot which is partially corrected may experience increased symptoms at altitude. These conditions may predispose to HAPE. As the blood pressure in the lungs rises, normal blood flow through the heart may get pushed through these holes in the heart in what is called right to left shunting. This potentially contributes to altitude symptoms as there is less blood getting loaded with oxygen in the lungs. Little is known on how these people do at altitude after repair of these defects. Caution should be exercised when considering high altitude exposure in people with these issues. Use of oxygen at high altitude will prevent any problems.

Heart Failure

Heart failure (HF) has not been studied extensively at altitude. Persons with HF have increased sensitivity to fluid retention. Since retaining fluid at altitude occurs frequently with or without AMS, this could potentially cause a worsening of heart function. Patients with HF, if they are careful, can likely travel to moderate altitudes safely. Below are suggested recommendations:

See your doctor on a regular basis
Know your dry weight and weigh yourself daily at altitude
Take your medications regularly and discuss with your doctor if you need to increase the dosage of your water pill (Lasix® [furosemide] or others)
Consider taking Diamox® to speed up acclimatization, prevent AMS and help prevent fluid retention
Seek medical help early if getting worse

Pulmonary Hypertension

This condition of high blood pressure in the lungs can occur from many causes. Since high blood pressure in the pulmonary vessels is a main mechanism that leads to HAPE, persons with pulmonary hypertension have a much higher risk of developing HAPE and need to consider this risk before coming to altitude. The risk should be discussed with the physician. One approach is to use supplemental oxygen during the altitude stay, which will alleviate concern for any problems.


Lung Diseases


Persons with asthma do better at high altitude, contrary to some opinions. Pollution is less and dust mites, a very common allergen, don't live at high altitude. Overall there is evidence that those plagued with asthma, in particular allergic asthma, do better at altitude than at sea level. One study done on children with exercise-induced asthma concluded that there is no increased risk for asthma exacerbation at altitude vs sea level. As always, any asthmatic should continue their asthma medications and carry a relief inhaler with them at altitude just as they would at sea level.


Patients with chronic lung disease have difficulty transporting oxygen from their lungs to their blood stream. Unfortunately, these people tend to do worse living at altitude. A study done in New Mexico and Utah showed increased death rates in people with emphysema living at high altitude compared with those living at low altitude. It is safe to say those with chronic lung disease will do better living at low altitude.

Visiting moderate altitude for those with emphysema may be feasible. One study suggests that low-landers with moderate, well controlled COPD tolerated a trip to altitude reasonably well. The possible explanation for this is that they already tolerate lower oxygen levels and therefore have some functional acclimatization. Testing blood oxygen levels at rest at low altitude in these people may help give us a better picture of who will do okay at altitude. Those with emphysema who wish to visit high altitude should visit their doctor to optimize their condition and may want to consider additional oxygen while visiting high altitude.

Oxygen at high altitude will help anyone with lung disease and is easily available. Have your doctor write a prescription for oxygen or call us at the Institute for Altitude Medicine.

Cystic Fibrosis

Children and young adults with cystic fibrosis tend to do poorly at altitude. They generally should avoid altitude. However, some may be able to visit moderate altitude safely if given supplemental oxygen and aggressive care with other medications for CF including antibiotics. One report exists of a young person with mild CF who was able to hike to over 16,500 feet safely.

Neurologic Conditions


Persons with migraine headaches are not at increased risk of altitude illness. If a migraine develops at high altitude, however, it might be difficult to distinguish this from an altitude headache, although altitude headache does not have an aura and is not unilateral. A recent study suggests that low oxygen levels can trigger migraines. If you suffer from migraines, you should use your regular migraine medication at altitude if your headache seems like your typical migraine. If your medication is not effective, then you may need oxygen in addition to other treatments, as your headache may be due to AMS.


Incidence of cerebrovascular disease in those living at altitude appears to be lower, according to surveys from Asia and South America. Whether this incidence is lower at higher altitudes in the US is unknown. For tourists to high altitude, no evidence suggests that the risk of stroke is increased, except in soldiers at extremely high altitude in the Himalaya. Occasionally, stroke-like symptoms such as weakness on one side of the body or partial blindness have been reported in otherwise young healthy persons climbing at very high altitude. These symptoms resolve with oxygen or returning to lower altitude. If you or someone you know experiences these symptoms you should seek medical treatment immediately. If you have had a prior stroke and you decide to go to altitude you should continue to take all your medications as directed by your doctor and consider limiting your activity at high altitude. Persons taking a blood thinner such as Coumadin or Plavix need to be careful to avoid trauma, because of the risk of increased bleeding when on the medications.

Brain Tumors

Tumors or cysts that take up additional space in the brain can produce more symptoms at altitude. Individuals with brain tumors have less room for expansion inside the skull. Headaches and other symptoms of AMS may be more common. Several individuals, previously undiagnosed, traveled to altitude, developed symptoms and were subsequently diagnosed with brain tumor. Avoidance of altitude is the best advice for those with tumors. Those with brain cysts or benign brain tumors such as a Meningioma should consult their doctor.


Persons with seizure disorder well controlled on medications do well at high altitude, and it is generally considered safe to travel to altitude with epilepsy that is controlled with seizure medications. High altitude may unmask a seizure disorder in someone who has never had a previous seizure. In addition, the stress of altitude, usually in combination with other factors such as cold, overexertion, alcohol or lack of sleep, may cause a single seizure in persons without any type of seizure disorder. Persons who have been on seizure medication in the past but who have discontinued it might want to consider taking it again for a high-altitude trip, especially a longer trip or if going to a very high altitude.


High Altitude Resident Mothers

Infants born to women of high altitude residence have lower birth weights on average than those born to low altitude mothers. This is due to slower growth rate in the uterus during late pregnancy, after 33 weeks. With that being said, high altitude babies do not have negative health consequences and risks because of their lower weight, unlike low weight babies born to smoking mothers. Recent data in Colorado shows no increase in infant death rates of babies born at high altitude compared with those born at low altitude. Pregnancy-associated hypertension and preeclampsia are slightly more common in high altitude pregnancies.

Low Altitude Resident Mothers Visiting High Altitude

Many women in all stages of pregnancy safely visit moderate altitude every year. In fact, elevated hormone levels (progesterone) increase the breathing rate, raise blood oxygen and may protect against AMS.

The safety of travel to altitude during pregnancy has not been thoroughly studied. However, many pregnant tourists visit high altitude destinations such as Colorado every year and report no complications. One study found no difference in fetal heart changes and circulating stress hormones between mothers exercising at sea level and at 6000ft. This suggests that the exposure to this altitude does not produce additional stress on pregnant women. Women with complications of pregnancy, such as hypertension, preeclampsia, placental insufficiency, or any other complication, should avoid unnecessary exposure to high altitude. The pregnant woman can take Diamox, but only if truly necessary; slow ascent is preferred to medications.

Recommendations for pregnant tourists visiting high altitude:

Have a check-up with your doctor to assure your pregnancy is low-risk; this might include an ultrasound
Avoid trauma if skiing, cycling, climbing, etc.
Avoid over-exertion; exercise a bit less than at you do at home
Stay well hydrated
Avoid altitude illness; see above
Seek medical care early if any problems

Peter Hackett, MD and Linda Keyes, MD

Pregnancy and Travel to Altitude FAQ

Most pregnant women can safely travel to high altitude destinations during pregnancy without any complications or problems. Here are some commonly asked questions about travel to altitude during pregnancy.

How high can I go when I am pregnant?
Sleeping altitude is the important factor, not maximum altitude reached during the day. As long as your pregnancy is not considered "high-risk", travel to sleeping altitudes up to 9-10,000 ft in Colorado or elsewhere should not pose a risk to you or your fetus. Information on higher sleeping altitudes is too limited to provide quality guidelines.

What precautions should I take before traveling to altitude?
We recommend a check up by your obstetrician and an ultrasound to make sure the pregnancy is normal so far. If possible, spend a night at a medium altitude, between 5-7,000 ft before sleeping above 8500 ft to help your body adjust.
Identify how and where you will get medical care at your destination if any problems were to develop.

Who should not travel to high altitude during pregnancy?
Any woman with a high-risk pregnancy condition such as pregnancy-induced hypertension, preecclampsia or intrauterine growth retardation should not travel to high altitude. Ask your obstetrician if you are not sure if your pregnancy is high risk. Women with certain underlying medical problems are also at risk of complications and should probably avoid travel to high altitude. These diseases include certain congenital heart diseases, some restrictive lung diseases like sarcoidosis or pulmonary fibrosis, or significant anemia. Discuss with your doctor if you have any of these problems before going to high altitude while pregnant. Finally, women who smoke should not travel to high altitude while pregnant.

Will going to high altitude increase my risk of miscarriage or birth defects?
There is no risk of increased miscarriage or birth defects in lowland women traveling to high altitude.

What precautions should I take when I arrive at altitude?
Take it easy the first several days at altitude, and do not exert yourself at a level greater than you would do at sea-level (e.g. no major hike to the top of a big peak if that's not something you're used to doing). Avoid trauma and don't take unnecessary risks. If you ski, hike or climb, do so carefully and stay well within your abilities. Staying hydrated is important, as is taking some time to let your body adjust to the altitude before exerting yourself. Acetaminophen (brand name: Tylenol) is safe to take if you develop a headache.

Can I exercise at altitude while I am pregnant?
In general, exercise is safe and beneficial during pregnancy. We know that exercise up to 8000ft is safe for non-smoking women. At higher altitudes, take extra time to acclimatize before exercising and avoid heavy exertion or very strenuous exercise. Keep the exertion level lower than you would do at home and include more frequent rests.

Am I at increased risk of altitude sickness because I am pregnant?
Being pregnant will not increase your risk of developing altitude illness. In fact, the increased progesterone of pregnancy makes you breathe more at altitude. This keeps your oxygen level higher than non-pregnant women, and thus helps to prevent altitude sickness. We very rarely see pregnant women with altitude sickness.

Can I take medicine to prevent mountain sickness while pregnant?
Most pregnant women are naturally protected against altitude sickness due to the increased respiratory drive of pregnancy and preventive medications are not necessary. Acetazolamide (brand name: Diamox) is the best medicine for altitude sickness prevention, but this medicine is not recommended during pregnancy unless truly necessary. The safety and effectiveness of herbal medications like Ginkgo Biloba are unclear during pregnancy and are not recommended. It is OK to treat a headache with over-the-counter medicine like acetaminophen (brand name: Tylenol).

What if I live at high altitude and I'm pregnant?
Women who live at high altitude (>8000 ft) throughout their pregnancy may be at risk for certain pregnancy-related complications such as high blood pressure or preecclampsia. Babies born at high altitude tend to be smaller than their sea-level counterparts, but healthy. It is important that you receive ongoing pre-natal care and monitoring throughout your pregnancy. Your doctor can tell you if you are at risk, or are developing any problems.

Other pre existing conditions


Lower red blood cell levels, as occurs in anemia, would seem to affect acclimatization. These cells contain hemoglobin which is responsible for carrying oxygen from the lungs to the tissues. Indeed, anemia does affect exercise performance at altitude, but there is no evidence that it increases susceptibility to altitude illnesses. Women with regular menstrual cycles are more prone to lower iron levels and anemia. Red blood cell production increases around the third week at altitude and improves oxygen carrying capability of the blood. This response maybe impaired if iron stores are low. If you have a history of anemia you should:

  • Make sure the source of your anemia is diagnosed by your doctor
  • Have your red blood cell and hemoglobin levels checked prior to going to altitude
  • Take additional iron supplements if you plan to be at high altitude for more than a few weeks


Experts debate on whether or not the blood clots more easily at altitude. No study has shown that climbers or visitors to high altitude have an increased risk of blood clots in their lungs (pulmonary embolus or PE) or legs (deep venous thrombosis or DVT). For those that already have Protein C deficiency, antiphospholipid syndrome, or some other disorder where the blood clots easily, they may want to take a baby aspirin daily at altitude. Others who have previously had PEs or DVTs, who smoke, or women on birth control or hormone therapy may consider taking an aspirin a day as well.


Carbon monoxide or CO, released as a byproduct of combustion, binds to the hemoglobin (oxygen-carrying molecule in red blood cells) so tightly that it will not release oxygen to the tissues. CO poisoning at altitude is far more serious due to lower oxygen levels. Poor ventilation in cabins, cooking in closed tents, and failure to ventilate snow shelters contribute to CO poisoning. The importance of investing in a carbon monoxide detector for your home at altitude cannot be overemphasized and could be life-saving. Each year, several deaths at altitude can be attributed to CO poisoning. Symptoms include headache, dizziness, nausea, weakness. CO can mimic altitude illness or even bring on altitude illness much more readily due to lower tissue oxygen. If you suspect CO poisoning, remove yourself and/or the victim and force hyperventilation (fast deep breathing) to increase oxygen intake. CO poisoning can be rapidly reversed by breathing oxygen. 


Patients who have had carotid surgery are likely to have a decreased ability to acclimatize because of damage to the carotid body, which senses low oxygen in the blood and causes increased breathing at high altitude. These persons should be aware of their impaired ability to acclimatize and somewhat increased risk of AMS.


Individuals who travel to altitude may have noticed that even the smallest cut or wound takes longer to heal the higher the altitude. Reasons for this are increasing stress hormones and lower overall oxygen delivery to the tissues. Wounds tend to get infected more easily as well. Keeping your wounds clean and covered will prevent infection. Often applying a triple antibiotic ointment regularly will keep the wound from overly drying and aid in healing. Wound healing becomes an issue only at very high altitudes, over 14,000 ft or so.

Diabetes Mellitus

Little is known about how altitude affects diabetes. There may be an increased insulin requirement. Those monitoring their blood sugar with a self-monitoring device (glucometer), need to make sure that it is functioning properly. A study done in Colorado showed that these devices are accurate at high altitude. If you are diabetic you should check your blood sugar more often at altitude is to see if your insulin needs change. Only diabetics experienced with exercise and in good control should attempt vigorous exercise at high altitude.


Retinal hemorrhages at altitude, increased cerebral edema, brain swelling, increase brain pressure, snow blindness, corneal edema.

Snow blindness is a risk at altitude. This condition is painful sunburn of the eyes that causes pitting and swelling of the cornea (the outer layer of the eye) that can temporarily blind. Eye protection is important to prevent this. The atmosphere is thinner at altitude, allowing more harmful UV rays through. Full coverage sunglasses are necessary as rays from the sun can reflect underneath and on the sides of sunglasses especially if skiing or traveling on the snow.

The cornea swells mildly in response to low oxygen. The swelling is uniform in a normal cornea, but in someone who has undergone radial keratotomy, a surgical procedure for corrective vision, irregular swelling results in potentially severe visual problems. LASIK, a laser procedure for correcting vision, is far preferred for those traveling to altitude. It allows for uniform swelling and much less visual change at altitude. Those that have already undergone radial keratotomy should carry glasses with them of increasing plus power when traveling to altitude.

Retinal hemorrhages or bleeding in the back of the eye occur at higher altitudes. They usually do not affect vision and resolve on their own in days to weeks. Occasionally, they will produce a dark patch in the vision, which again will resolve on its own.


Climbers and mountaineers have noticed for some time that infections are a common occurrence at high altitudes. Indeed, there is some impairment of certain immune cells. However, a person’s active immunity remains intact. Most of these infections are more of a nuisance such as small skin and wound infections or coughs and runny noses that last a long time. Serious life threatening infections in healthy people secondary to the altitude have not been reported. Care to use proper hygiene, hand washing, and avoidance of others will illness will help improve chances of staying healthy.


Some evidence shows a slightly increased risk for altitude sickness in obese individuals. Although unclear, one reason for this may be heavy snoring with less oxygen passing into the lungs during sleep leading to overall lower oxygen levels. These individuals may not breathe as deeply due to the weight compressing their chests. Overall, obese individuals will likely do okay at altitude if they follow the same acclimatization rules. Some may find loss of body fat after a stay of several weeks at altitude.


Persons with SCD are extremely sensitive to lower oxygen levels. With less oxygen, the shape of their red blood cells changes from a disc to a sickle shape. These sickle cells get stuck in certain areas of the body, cutting off blood supply and causing a pain crises. It is generally recommended that SCD patients avoid altitude. Persons with the sickle cell trait (but not the full disease) traveling to altitude are susceptible to splenic infarction due to obstructing cells. This is an uncommon occurrence in those with the trait and these people may otherwise travel to altitude unaffected.


Sleep disturbances such as Obstructive Sleep Apnea (OSA) have the potential to drop oxygen levels lower during sleep at altitude. However, a little evidence exists that OSA may do better at altitude, whereas those with Central Sleep Apnea may not. CPAP (continuous positive airway pressure) machines used for heavy snorers need to have a pressure compensating feature to allow them to work properly at altitude. For other certain sleep-disordered breathing problems a little bit of oxygen at night can really help.