Allometric relations of cardiovascular function in birds

Area of Science:

• Comparative physiology
• Avian biology
• Cardiovascular research

Background:

• Birds exhibit distinct cardiovascular traits compared to mammals, including larger hearts and lower heart rates relative to body size.
• Understanding the scaling of cardiovascular function with body mass is crucial for avian physiology.

Purpose of the Study:

• To investigate the relationship between body size and cardiovascular parameters in nine bird species across a 1,000-fold mass range.
• To compare avian cardiovascular function, including cardiac output and stroke volume, with that of mammals.

Main Methods:

• Collected data on heart mass, body mass, heart rate, cardiac output, oxygen consumption, and stroke volume from nine bird species.
• Utilized allometric equations to describe the scaling relationships between these cardiovascular variables and body mass.

Main Results:

• Established equations for heart mass (HM = 8.76 M^0.92), heart rate (HR = 178.5 M^-0.282), and cardiac output (Q = 290.7 M^0.69) in relation to body mass (M).
• Demonstrated that birds possess greater cardiac output for a given body mass and oxygen consumption rate compared to mammals.
• Found that stroke volume scales with body mass in birds (SV = 1.72 M^0.97) but results in a lower stroke volume per gram of heart tissue than in mammals.

Conclusions:

• Bird cardiovascular systems are adapted for high metabolic demands, characterized by efficient cardiac output scaling with body size.
• Despite larger relative heart size, birds have a lower stroke volume per unit of heart mass, suggesting a different cardiac efficiency strategy compared to mammals.