Mystery peak of altitude sickness

A hiker looks back from Ladakh's capital of Leh to the summit of Stok Kangri, 6153m up the Himalayas. Photo / Supplied

For trekkers and mountaineers, scientists have issued a mysterious warning. The worst place in the world for altitude sickness is Ladakh, the stark, beautiful region on India's northern border with China and Tibet - and nobody knows exactly why.

Ladakh, "the land of high passes", lies between the Himalayas and the Kunlun mountain range at a height of more than 3000m. The high-altitude desert has become popular with adventure travellers in the past decade, drawn by its remote culture and extraordinary panoramas.

Jean-Paul Richalet, professor of physiology at the University of Paris North, who led the study published in the American Journal of Respiratory and Critical Care Medicine, said: "When adjusted for all other risk factors, especially rate of ascent, one location - Ladakh - remained associated with a higher risk of severe high-altitude illness."

But the researchers were unable to identify why the region had the greatest impact. "No clear explanation linked to the climate or the difficulty of the terrain is available, although many informal reports mention the higher risk of this location," Richalat said.

The researchers assessed more than 1300 people who planned excursions to mountainous areas which involved at least three days above 4000m and sleeping overnight above 3500m.

Before they left they were given a series of tests to measure their breathing and heart rate at low-oxygen levels - to mimic the effects of high altitude - and the results were compared with their actual experience after their trip.

Almost one in four (318) suffered a severe altitude illness with symptoms of headache, nausea, fatigue and dizziness, associated in the some cases with swelling of tissue in the lungs and brain.

The study is the first to suggest an association between the geographical location of ascent and altitude sickness. The drug acetazolamide (Diamox) cut the risk of developing the condition among the participants by 44 per cent, the study found. Nevertheless, among the 318 who developed altitude sickness, a third (105) had used Diamox.

Participants who experienced a significant reduction in the amount of oxygen in the blood when exercising in a low-oxygen environment were more likely to develop symptoms.

A common experience at altitude is how breathing fails to keep pace with the demands of the body which triggers involuntary gasps for air and a feeling of suffocation. The study found that those who took most exercise to prepare for their trip were at increased risk from the condition.

Slow ascent is the key

Altitude sickness crept up on me without warning. Four years ago a friend and I trekked through the Karakoram, the jagged western-most edge of the Himalaya that begins on Pakistan's Afghan border and sweeps into Kashmir.

Our first stop was the Shandur Pass (3738m) which once a year is the venue for the world's highest polo match. Keen to get to the match as fast as possible, we hired a Jeep from the nearby town of Chitral (1100m) and drove to the top of the pass to camp for the night.

The next day I could barely move without breaking into a sweat. My head felt filled with lead and my stomach was battered by nausea.

It was like being hungover and seasick simultaneously. The only way I was going to get better was to drive back down the valley. We missed the polo match.

Slow ascents are vital. The next week we hit 4200m without problem because we trekked on foot.

This year, the same friend and I climbed Ethiopia's Mount Bwahit (4430m) and felt fine.

- Jerome Taylor

- INDEPENDENT