Cardiac output and stroke volume in exercising ducks and pigeons.

The purpose of this study was to determine the relationship between oxygen consumption (VO2) and cardiac output, stroke volume, and arteriovenous O2 content differences in resting and exercising birds. Pigeons and ducks showed a linear relationship between oxygen consumption and cardiac output and appeared to have a greater cardiac output for a given oxygen consumption than do mammals of the same body mass. In these birds the arteriovenous O2 content difference was hyperbolically related to oxygen consumption. The cardiac output was relatively high, implying a smaller arteriovenous O2 content difference than found in mammals. Resting stroke volume, relative to body mass, was greater in these birds than in mammals. However, as birds have disproportionately larger hearts for their body mass, these birds showed almost the same stroke volume per gram of heart as do mammals.