Altitude-related cough

THE INFLUENCE OF CO2 ON SPATIOTEMPORAL FEATURES OF MECHANICALLY INDUCED COUGH IN ANESTHETIZED CATS

Effective cough requires a significant increase in lung volume used to produce the shear forces on the airway to clear aspirated material. This increase in tidal volume during cough, along with an increase in tidal frequency during bouts of paroxysmal cough produces profound hyperventilation and thus reduces arterial CO₂. While there are several reports in the literature regarding the effects of hypercapnia, hyperoxia, and hypoxia on cough, there is little research quantifying the effects of hypocapnia on the cough reflex. We hypothesized that decreased CO₂ would enhance coughing. In 12 spontaneously breathing adult male cats, we compared bouts of prolonged mechanically stimulated cough, in which cough induced hyperventilation (CHV) was allowed to occur, with isocapnic cough trials where we maintained eupneic end-tidal CO₂ by adding CO₂ to the inspired gas. Isocapnia slightly increased cough number and decreased esophageal pressures with no change in EMG magnitudes or phase durations. The cough-to-eupnea transition was also analyzed between CHV, isocapnia, and a third group of animals that were mechanically hyperventilated to apnea. The transition to eupnea was highly sensitive to added CO₂, and CHV apneas were much shorter than those produced by mechanical hyperventilation. We suggest that the cough pattern generator is relatively insensitive to CHV. In the immediate post-cough period, the appearance of breathing while CO₂ is very low suggests a transient reduction in apneic threshold following a paroxysmal cough bout.

High-altitude mountaineering made safer

Mountains all over the world are attracting a steadily growing number of visitors due to the increasing number of cheap flights; the construction of new roads, railways, and cable cars; and commercial offers of trekking tours and expeditions to attempt even the world's highest peaks. However, one must not forget that mountains are typically inhospitable areas characterised by cold and hypoxic environments and rapidly changing weather and track conditions associated with a relatively high risk of accidents and emergencies. Beside the objective hazards, subjective hazards, for example physical fitness and health status, mountaineering skills, and equipment, contribute substantially to the risk. Whereas in some regions, for example the Alps, rescue operations and medical emergency interventions can be performed rapidly and effectively, this is absolutely not the case in most of the very remote areas and on very high mountains. Therefore, the understanding of the risk associated with the various modes of mountaineering as well as knowledge about how to optimise prevention is of the utmost importance. Ultimately, it is the informed mountaineer who has to decide whether the risks are acceptable or not. Continuing joint efforts of scientists, medical and alpine institutions, expedition organisers, and mountaineers will help to make high-altitude mountaineering safer.

Australian senior adventure travellers to Peru: Maximising older tourists' travel health experience

Financially comfortable, with ample spare time and much better health, older people travel more than ever and to more adventurous destinations. Taking Australian senior adventure travellers to Peru as an example, travel health preparations need to take into account the phenomenon 'senior traveller', the destination with its attractions and challenges, and age-related changes and restrictions. The need for routine travel health advice, vaccinations and prophylaxis remains unchanged. However, more emphasis should be placed on locality-specific issues so that age-appropriate advice and preparations maximize the chances for a safe and memorable travel experience.

Desensitization of the cough reflex by exercise and voluntary isocapnic hyperpnea

Little is known about the effects of exercise on the sensory and cognitive aspects of coughing evoked by inhalation of tussigenic agents. The threshold for the cough reflex induced by inhalation of increasing nebulizer outputs of ultrasonically nebulized distilled water (fog), an index of cough reflex sensitivity, was assessed in twelve healthy humans in control conditions, during exercise and during voluntary isocapnic hyperpnea (VIH) at the same ventilatory level as the exercise. The intensity of the urge to cough (UTC), a cognitive component of coughing, was recorded throughout the trials on a linear scale. The relationships between inhaled fog nebulizer outputs and the correspondingly evoked UTC values, an index of the perceptual magnitude of the UTC sensitivity, were also calculated. Cough appearance was always assessed audiovisually. At an exercise level of 80% of anaerobic threshold, the median cough threshold was increased from a control value of 0.73 to 2.22 ml/min ( P < 0.01), i.e., cough sensitivity was downregulated. With VIH, the threshold increased from 0.73 to 2.22 ml/min ( P < 0.01), a similar downregulation. With exercise and VIH compared with control, mean UTC values at cough threshold were unchanged, i.e., control, 3.83 cm; exercise, 3.12 cm; VIH, 4.08 cm. The relationship of the fog nebulizer output/UTC value was linear in control conditions and logarithmic during both exercise and VIH. The perception of the magnitude of the UTC seems to be influenced by signals or sensations arising from exercising limb and thoracic muscles and/or by higher nervous (cortical) mechanisms. The results indicate that the adjustments brought into action by exercise-induced or voluntary hyperpnea exert inhibitory influences on the sensory and cognitive components of fog-induced cough.

Ear, nose, and throat effects of high altitude

High altitude changes human physiology and can result in illnesses such as acute mountain sickness, high-altitude cerebral edema, and high-altitude pulmonary edema. The physiological impacts of high-altitude illnesses occur secondary to extravasation of fluid from the intravascular space into the extravascular space during a rapid ascent. Headache, hearing disturbances, vestibular disturbances, epistaxis, sleep apnea, coughing, respiratory tract infections, and nasal obstruction are main ear, nose, and throat complaints of individuals travelling to high altitude. These complaints can cause delays or cancelations in a person's climbing plans. In this article, we review the ear, nose, and throat effects of high altitude based on the relevant literature.

Who should not go high: chronic disease and work at altitude during construction of the Qinghai-Tibet railroad

From 2001 to 2005, a new railroad linking Beijing with Lhasa was built by more than 100,000 workers, of whom 80% traveled from their lowland habitat to altitudes up to 5000 m to work on the railroad. We report on the medical conditions of 14,050 of these altitude workers, specifically with regard to preexisting illness. All subjects were seen at low and high altitude. Average age was 29.5 +/- 7.4 (SD) yr, range 20 to 62 yr; 98.8% of the subjects were men and 1.2% were women. Overall incidence of AMS upon first-time exposure was 51%, that of HACE 0.28%, and that of HAPE 0.49%. About 1% of the subjects were hypertensive before altitude exposure. Those with blood pressure >or=160/95 were excluded from employment at altitude. Altitude exposure led to a greater increase of blood pressure in hypertensives compared to normotensives. On prealtitude screening prevalence of cardiac arrhythmias was 0.33%. Since the majority of these were rather benign and occurring in young and otherwise healthy subjects, we allowed altitude employment. Follow-up at altitude was uneventful. Subjects with coronary heart disease and diabetes were excluded from altitude employment. Obesity was a risk factor for acute mountain sickness and for reduced work performance at altitude. Overweight subjects lost more weight during their altitude stay than subjects with normal weight. Altitude exposure was a risk factor for upper gastrointestinal tract bleeding, especially in combination with alcohol, aspirin, and dexamethasone intake. Asthmatic subjects generally did better at altitude compared to low altitude, with the exception of one subject who experienced an asthma episode from pollen exposure. In conclusion, careful evaluation of preexisting chronic illness and risk factors allowed prevention of altitude deterioration of a preexisting health condition, all the while allowing subjects with some specific conditions to work and live at altitude without problems.