Respiratory physiology & neurobiology
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Respir Physiol Neurobiol · Nov 2006
Flying high: a theoretical analysis of the factors limiting exercise performance in birds at altitude.
The ability of some bird species to fly at extreme altitude has fascinated comparative respiratory physiologists for decades, yet there is still no consensus about what adaptations enable high altitude flight. Using a theoretical model of O(2) transport, we performed a sensitivity analysis of the factors that might limit exercise performance in birds. We found that the influence of individual physiological traits on oxygen consumption (Vo2) during exercise differed between sea level, moderate altitude, and extreme altitude. ⋯ Increases in the temperature effect on P(50) could also be beneficial for high flying birds, provided that cold inspired air at extreme altitude causes a substantial difference in temperature between blood in the lungs and in the tissues. Changes in lung diffusion capacity for O(2), cardiac output, blood Hb concentration, the Bohr coefficient, or the Hill coefficient likely have less adaptive significance at high altitude. Our sensitivity analysis provides theoretical suggestions of the adaptations most likely to promote high altitude flight in birds and provides direction for future in vivo studies.