ABSTRACT
The autonomic nervous system plays a critical role in mediating many of the physiological adjustments to hypoxemia (1-4). The focus of this chapter will be on the autonomic nervous system responses to hypoxemia in humans, with emphasis, where data are available, on high altitude. Because the duration of exposure to altitude appears to influence the nature of the autonomic nervous system adjustments, the responses to both acute (minutes to hours) and sustained (days and longer) hypoxemia will be considered. Experimental data from sea level studies of humans (and animals) breathing low inspired O2 or in a hypobaric chamber to simulated altitude and field studies conducted at high altitude provide the substrate for this discussion. Because humans must perform the activities of daily life while at altitude, the influence of hypoxemia during exercise and orthostatic stress will also be discussed. Where information is available, we also will examine the mechanisms responsible for mediating autonomic nervous system adjustments to hypoxemia as well as their known or possible physiological significance. Finally, the potential modulatory effects of factors such as age, gender, and chronic physical activity status will be mentioned, although few data are available at present.
