To this point, the information presented suggests that a brisk hypoxic ventilatory response may be advantageous with respect to adaptation to hypoxia, as illustrated by the association of a vigorous hypoxic ventilatory response with better performance and fewer symptoms following ascent to high altitude and better maintenance of ventilation in patients with COPD. However, this view, if it is correct, may apply only to individuals accustomed primarily to normal oxygenation and in whom hypoxia is an accident of nature occasioned by ascent to high altitude or by disease. However, in contrast to these amateurs with the hypoxic experience, true professionals—species uniquely adapted to high altitude—seem to play by a different set of rules. The best-studied examples are the llama and bar-headed goose. The latter, less well known than the llama, has a truly remarkable tolerance to hypoxia, manifested by its migratory path over the summit of Mt. Everest (9,000 m). Both the bar-headed goose and llama seem to rely relatively less on ventilation when confronted by hypoxia than do low-altitude species because, although the ventilatory response may ultimately become quite vigorous, it is left-shifted so that pronounced responses require Po2 levels roughly 20 mm Hg less than those producing comparable stimulation in low altitude species. buy ortho tri-cyclen online