FIGURE 4.

The cardiorespiratory and metabolic responses to hypoxia at rest are enhanced in bar-headed geese compared with lowland waterfowl

Total ventilation (V̇_Tot) and cardiac output (Q̇) increase in hypoxia below the arterial O₂ tension at which the blood begins to desaturate, but this increase is much greater in bar-headed geese than in greylag geese. Associated with this heightened cardiorespiratory response to hypoxia in bar-headed geese is a much larger increase in O₂ consumption rate (V̇o₂), which is reflected by the area of the bars in the right panels for each species in normoxia and in 5% inspired O₂ fraction. Data are from Ref. 41, with the exception of cardiac output, which was calculated by the Fick equation (V̇o₂= Q̇ [Ca_O2 − Cv_V̄o2]) from data in Ref. 41. Ca_O2, arterial O₂ content; Cv_V̄o2, mixed venous O₂ content; a, arterial; V̄, mixed venous.