Showing papers on "Altitude Hypoxia published in 2003"

Oxygen transport in blood at high altitude: role of the hemoglobin-oxygen affinity and impact of the phenomena related to hemoglobin allosterism and red cell function.

Abstract: Altitude hypoxia is a major challenge to the blood O2 transport system, and adjustments of the blood–O2 affinity might contribute significantly to hypoxia adaptation. In principle, lowering the blood–O2 affinity is advantageous because it lowers the circulatory load required to assure adequate tissue oxygenation up to a threshold corresponding to about 5,000 m altitude, whereas at higher altitudes an increased blood–O2 affinity appears more advantageous. However, the rather contradictory experimental evidence raises the question whether other factors superimpose on the apparent changes of the blood–O2 affinity. The most important of these are as follows: (1) absolute temperature and temperature gradients within the body; (2) the intracapillary Bohr effect; (3) the red cell population heterogeneity in terms of O2 affinity; (4) control of altitude alkalosis; (5) the possible role of hemoglobin as a carrier of the vasodilator nitric oxide; (6) the effect of varied red cell transit times through the capillaries.

Altitude-related hypoxia: risk assessment and management for passengers on commerical aircraft.

Abstract: Background: Individuals with pulmonary and cardiac disorders tare particularly at risk of developing hypoxemia at altitudes Or objective is to describe the normal and maladaptive physiological responses to altitude-related hypoxia, to review existing methods and guidelines for preflight assessment of air travelers, and to provide recommendations for treatment of hypoxia at altitude. Data synthesis: Falling partial pressure of oxygen with attitude results in a number of physiologic adaptalions including hyperventilation, pulmonary vasuccinstriction, altered ventilation/perfusion matching, and increased sympathetic tone. According to three guideline statements, the arterial pressure oi oxygen (PaO 2 ) should be maintained above 50 to 55 mm Hg at all altitudes. General indicators such as oxygen saturation and sea level blood gases may be useful in predicting altitude hypoxia. More specialized techniques for estimation of altitude PaO 2 , such as regression equations, hypoxia challenge testing. and hypobaric chamber exposure have also been examined. A regression equation using sea level PaO 2 and spirometric parameters can be used to estimate PoO 2 at altitude. Hypoxia challenge testing, performed by exposing subjects to lower inspired FnO 2 at sea level may be more precise. Hypobaric chamber exposure, the gold standard, mimics lower barometric pressure, but is mainly used in research. Conclusion : Oxygen supplementation during air travel is needed for individuals with an estimated PaO 2 (8000 ft) below 50 mmHg. There are a number of guidelines for the pre-flight assessment of patients with pulmonary and/or cardiac diseases. However, these data are based on small studies in patients with a limited group of diseases.