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So NIR: And yet so far

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Ezine

• Published: May 1, 2014
• Author: David Bradley
• Channels: Infrared Spectroscopy
• http://www.spectroscopynow.com/ir/details/ezine/145acab884e/So-NIR-And-yet-so-far.html

From NIR to eternity?

Because it is there, many people don their boots grab their crampons and head for the hills, but many of them suffer debilitating headaches while mountaineering which gives rise to safety issues as well as reducing their enjoyment. German researchers have now used near infrared spectroscopy (NIRS) to monitor blood flow in the brains of six climbers scaling Mount Kilimanjaro in north-east Tanzania, with a view to understanding and hopefully preventing such headaches, which are a well-known problem for those suffering from altitude sickness. Kilimanjaro is 5,895 metres at its peak.

Altitude sickness, acute mountain sickness or hypobaropathy, is a group of symptoms, headache, dizziness, fatigue and digestive problems, that arise when the body is deprived of oxygen, something that occurs when people ascend to above 2500 metres or so, at this altitude, the partial pressure of oxygen is much lower than at sea level. Below a certain altitude, most people gradually acclimatise as their body produces more red blood cells to extract more oxygen from each breath and the symptoms subside.

The reduced oxygen pressure at high altitude affects breathing patterns although this is not generally noticeable to mountaineers who regulate their breathing when climbing. However, when they sleep their breathing alternates between rapid, deep breathing (hyperventilation) and then much slower, shallower breathing (hypoventilation) and sometimes stopping briefly, (apnoea); the cycle can last half a minute or so as the body reacts to fluctuating carbon dioxide concentration in the blood.

Run to the hills

"The lack of oxygen at high altitude causes climbers to hyperventilate, which leads to a decline in carbon dioxide in the blood," explains Peter Stein of department of anaesthesiology, intensive care medicine and pain therapy at University Hospital Frankfurt, Germany. "This leads to episodes of hypoventilation or even apnoea when the conscious breathing control subsides during sleep. As a consequence the oxygen level drops, causing arousal and subsequent hyperventilation." This is referred to as a Cheyne–Stokes-like breathing pattern. Whether or not this disturbed breathing pattern during sleep was leading to a reduction on the flow of oxygen to the brain was up for debate. Obviously, this could have long-term health implications for climbers. Stein and colleagues Anne Lampe, Andreas Pape, Kai Zacharowski, Robert Hudek and Christian Friedrich Weber, have turned to near infrared spectroscopy to see if they could monitor changes in the concentration of haemoglobin, both oxygenated and deoxygenated, in the blood supply to the brain of climbers.

Head in the clouds, feet on the ground

They joined an expedition of six climbers as they scaled Mount Kilimanjaro, whose peaks are well beyond the threshold for the onset of altitude sickness. NIR electrodes attached to the climbers' foreheads while they slept were able to record haemoglobin concentrations. The most challenging part was to transport not only the NIR spectrometer to the base camp but also all the equipment necessary to provide electricity, Stein explains. They had to pack a lightweight generator and sufficient fuel to provide electricity each night of the six-day expedition.

What they discovered was that the abnormal breathing pattern caused periodic changes in the concentration of oxygenated haemoglobin and total haemoglobin, but not in the concentration of deoxygenated haemoglobin. This indicates that although the abnormal breathing pattern did alter the flow of blood into the climbers' brains, it did not reduce the amount of oxygen reaching their brain tissue; once again revealing the evolutionary power of the brain to cope with extreme conditions. The researchers also showed that those climbers experiencing the most extreme periodic changes in haemoglobin concentrations in the brain as they slept were also those that suffered most from headaches at high altitudes. This suggests that one simple approach to preventing these headaches is to find ways to stop the abnormal breathing that occurs when sleeping at high altitudes. Stein hopes that it might now be possible to develop a therapeutic approach to increase comfort and safety for climbers in the future.

At the time of writing, Stein was in the Italian Dolomite mountains, but he had this to say to SpectroscopyNOW from base camp: "Our experiments are fundamental research to reveal a pathomechanism contributing to the aetiology of the most common symptom of altitude sickness, headache," he told us. "I hope that based on our findings it will be possible to develop new therapeutic approaches that help to increase comfort and safety reserve for climbers in the future." "At the moment, we are analysing data from another field study at Mt. Aconcagua where we tried to improve haematopoiesis and thus oxygen supply by administering intravenous iron," he adds. "The cardiocirculatory effects of exposure to high altitude in real-life conditions and the differences in the two groups (iron- vs. control-group) were monitored with noninvasive, continuous hemodynamic Monitoring (NEXFIN)."