Jeremy S. Windsor

Arterial Blood Gases and Oxygen Content in Climbers on Mount Everest

BACKGROUND The level of environmental hypobaric hypoxia that affects climbers at the summit of Mount Everest (8848 m [29,029 ft]) is close to the limit of tolerance by humans. We performed direct field measurements of arterial blood gases in climbers breathing ambient air on Mount Everest. METHODS We obtained samples of arterial blood from 10 climbers during their ascent to and descent from the summit of Mount Everest. The partial pressures of arterial oxygen (PaO(2)) and carbon dioxide (PaCO(2)), pH, and hemoglobin and lactate concentrations were measured. The arterial oxygen saturation (SaO(2)), bicarbonate concentration, base excess, and alveolar-arterial oxygen difference were calculated. RESULTS PaO(2) fell with increasing altitude, whereas SaO(2) was relatively stable. The hemoglobin concentration increased such that the oxygen content of arterial blood was maintained at or above sea-level values until the climbers reached an elevation of 7100 m (23,294 ft). In four samples taken at 8400 m (27,559 ft)--at which altitude the barometric pressure was 272 mm Hg (36.3 kPa)--the mean PaO(2) in subjects breathing ambient air was 24.6 mm Hg (3.28 kPa), with a range of 19.1 to 29.5 mm Hg (2.55 to 3.93 kPa). The mean PaCO(2) was 13.3 mm Hg (1.77 kPa), with a range of 10.3 to 15.7 mm Hg (1.37 to 2.09 kPa). At 8400 m, the mean arterial oxygen content was 26% lower than it was at 7100 m (145.8 ml per liter as compared with 197.1 ml per liter). The mean calculated alveolar-arterial oxygen difference was 5.4 mm Hg (0.72 kPa). CONCLUSIONS The elevated alveolar-arterial oxygen difference that is seen in subjects who are in conditions of extreme hypoxia may represent a degree of subclinical high-altitude pulmonary edema or a functional limitation in pulmonary diffusion.

Heights and haematology: the story of haemoglobin at altitude

In order to compensate for the low partial pressure of oxygen at altitude, the human body undergoes a number of physiological changes. A vital component in this process is the increase in the concentration of circulating haemoglobin. The role of HIF-1α, erythropoietin and red blood cells in this acclimatisation process is described, together with the fall in plasma volume that increases the concentration of haemoglobin in the early stages of hypoxic exposure.

A Review of Electrocardiography in the High Altitude Environment

An ascent to altitude places considerable demands on the cardiovascular system. Changes in the rate, rhythm, and morphology of the electrocardiogram reflect the fall in the partial pressure of inspired oxygen (PiO2) and the adaptive responses that the human body makes. The effect of hypoxia on the autonomic nervous system results in changes to the heart rate during rest and exercise. Although this is raised during rest and submaximal exercise, maximal heart rate at altitude is reduced as a result of changes in parasympathetic activity. Hypoxic pulmonary vasoconstriction leads to a rise in pulmonary artery pressure and morphological changes on the electrocardiogram. Right axis deviation, right bundle branch block, and changes to P and T wave amplitudes are commonly found on ascent and resolve only after a return to low altitude. Although atrial and ventricular ectopic activity is also common, tachyarrhythmias are rare in healthy individuals. However, in those with significant cardiac disease, the hypoxic environment can be hazardous, exposing individuals to ischemia and the risk of sudden cardiac death.

Wilderness Medical Society Practice Guidelines for the Treatment of Acute Pain in Remote Environments: 2014 Update

The Wilderness Medical Society convened an expert panel to develop evidence-based guidelines for the management of pain in austere environments. Recommendations are graded on the basis of the quality of supporting evidence as defined by criteria put forth by the American College of Chest Physicians. This is an updated version of the original WMS Practice Guidelines for the Treatment of Acute Pain in Remote Environments published in Wilderness & Environmental Medicine 2014;25(1):41-49.

Sleep disturbance at altitude

Purpose of review The aim is to describe the impact of altitude upon sleep, the physiology that underpins these changes and the therapeutic solutions that are currently in place. Recent findings On ascending to altitude, lowland residents commonly experience some degree of sleep disturbance. Occasionally, this can prove very uncomfortable and impact upon daytime activities. Historically, the underlying cause of sleep disturbance was thought to be due to the effect of periodic breathing. However, recent research has shown that the link between periodic breathing, lighter stages of sleep and arousals is far from convincing. Instead, it appears that hypoxia has a far wider effect upon sleep at altitude than was previously thought. A number of new approaches to the treatment of sleep disturbance at altitude have recently been identified. Whereas some treat the underlying hypoxia through pharmacological or technological means, others seek to address the symptoms of sleep disturbance more directly. Summary Many of the current approaches to treating sleep disturbance at altitude have been shown to be well tolerated and successful, although few comparisons have been made. Future research is likely to focus upon matching the safest and most successful approach to the individual and their environment.

Are UK commercial expeditions complying with wilderness medical society guidelines on ascent rates to altitude

The incidence of acute mountain sickness can be reduced by ascending slowly to altitude. We compared a recommended ascent rate with those offered by commercial companies to three of the most popular high-altitude destinations in the world. While the majority complied with the recommended ascent rate, ascents on Kilimanjaro did not.

A Comparison of the Incidence and Understanding of Altitude Illness Between Porters and Trekkers in the Solu Khumbu Region of Nepal

OBJECTIVE Altitude illness can occur in anyone who ascends to high altitude. Better understanding of altitude illness is associated with a lower incidence of acute mountain sickness (AMS). The purpose of this study is to compare, for the first time, the incidence and understanding of altitude illness between foreign trekkers and indigenous porters in Nepal. METHODS Interviews and questionnaires were completed at the International Porter Protection Group Rescue Post at Machermo (4470 m). Participants completed the Lake Louise acute mountain sickness self-assessment questionnaire. They were also asked about their actions in response to high altitude illness scenarios as well as their perception of the vulnerability of porters vs trekkers to altitude illness. Ascent profile, age, gender, ethnic origin, and altitude of home residence were also obtained. RESULTS Trekkers (n=131) had a significantly higher incidence of AMS (21% vs 8%) than porters (n=92; P < .02). Lowland porters (whose home villages were below 3050 m, n=61) had a numerically higher, though not significantly different, incidence of AMS (10% vs 3%) compared to highland porters (n=31). The majority of trekkers and porters recognized the symptoms of altitude illness and the most appropriate action to be taken. Despite the lower incidence of AMS in porters, around half felt that they were at greater risk than trekkers. CONCLUSIONS Porters had a lower incidence of AMS, which may be attributable to repeated ascents through the trekking season, or differences in reporting symptoms. Both trekkers and porters demonstrated appropriate knowledge of actions to be taken in response to altitude illness.

Airway Mucociliary Function at High Altitude

Abstract Despite the presence of a number of anecdotal reports in the mountaineering literature, mucociliary dysfunction at high altitude has received little scientific attention. However, the dry, cold, thin air at high altitude has the potential to undermine normal mucociliary function. This seems increasingly likely in mountaineers who also experience dehydration, nasal obstruction, and extremes of aerobic respiration when climbing in such environments. These factors may result in a number of clinical conditions that range from sore throats and coughs commonly seen at altitude to rarer cases of bronchiolar collapse and lung atelectasis. The purpose of this review is to discuss the etiology of mucociliary dysfunction at altitude and outline a number of potential solutions to the problems this phenomenon presents.

Wilderness Medical Society Practice Guidelines for the Treatment of Acute Pain in Remote Environments

The Wilderness Medical Society convened an expert panel to develop evidence-based guidelines for the management of pain in austere environments. Recommendations are graded based on the quality of supporting evidence as defined by criteria put forth by the American College of Chest Physicians.

Using ultrasound lung comets in the diagnosis of high altitude pulmonary edema: fact or fiction?

High altitude pulmonary edema is a life-threatening condition that remains a concern for climbers and clinicians alike. Within the last decade, studies have shown ultrasonography to be valuable in the accurate diagnosis of a variety of lung pathologies, including cardiogenic pulmonary edema, pleural effusion, pneumothorax, and lung consolidation. Recently, studies conducted in remote areas have demonstrated that ultrasound lung comets can be used as a measure of subacute pulmonary edema and high altitude pulmonary edema in climbers ascending to altitude. This clinical review article provides an overview of lung ultrasonography and its relevance as a diagnostic aid to respiratory pathology. In addition, we describe a standardized technique for identifying ultrasound lung comets and its utility in recognizing the presence of extravascular lung water, as well as the results of studies that have used this approach at sea level and high altitude.