A new study from University College London and the University of Warwick suggests that critically ill patients could benefit from drugs or procedures that promote the body's production of nitric oxide.

Researchers studied 198 trekkers and 24 mountain climbers, to gauge the body's response to low oxygen levels, since critically ill patients often suffer from a shortage of oxygen (hypoxia), which can be life-threatening. NO is produced by virtually every cell and organ in the body and serves several important functions, including the regulation of blood pressure, learning and memory formation and offering protection from infectious diseases.

The research was conducted by using blood samples and results collected during the 2007 Caudwell Xtreme Everest expedition. The results show that NO production and activity are elevated in people who live near sea level when they ascend to higher altitudes, leading to changes in the blood flow in the smallest blood vessels.

"Climbing to extreme altitudes puts the body in an environment with very low oxygen availability, similar to the experience of patients in intensive care with diseases affecting the heart, lungs or vascular system," said Denny Levett, researcher and joint-lead author of the study.

"By taking blood samples from hypoxic, but otherwise healthy, individuals we have been able to show that the body's natural response to low oxygen availability is to increase the production of nitric oxide. Thus, elevated NO occurs not just in those who live at high altitudes permanently, but also in lowlanders who are trying to adapt to high altitude conditions," added Levett.

The CXE team made the first-ever measurement of the oxygen level in the blood of a human being 8,400 m above surface level. This was the centrepiece of an extensive and continuing programme of research into hypoxia and human performance at extreme altitude, aimed at improving care of critically ill and other patients for whom hypoxia is a fundamental problem.

"In the years ahead, this research may herald a change in emergency treatment and intensive care. It suggests there is an alternative way of alleviating the consequences of low oxygen levels by creating a more sustained tolerance to those low levels through treatments which boost NO production," said Martin Feelisch, a senior author of the research team, in a statement.

The research also shows a difference between individuals in terms of the level of their NO response at altitude. The sample size, however, is too small to draw concrete observations in this regard. But individuals with greater experiences of climbing at altitude had a greater NO response early in the expedition, suggesting their bodily constitution with respect to NO was different from climbers with less experience of ascent to high altitude. Similar factors may explain the differences in disease outcome between patients on the intensive care unit, the reasons of which are not well understood.