Ascending aortic impedance patterns in the kangaroo: their explanation and relation to pressure waveforms

Area of Science:

• Cardiovascular Physiology
• Comparative Anatomy
• Biomechanical Engineering

Background:

• The ascending aortic pressure waveform and impedance spectral pattern in kangaroos are atypical.
• Understanding these patterns is crucial for comprehending kangaroo cardiovascular function.

Purpose of the Study:

• To elucidate the mechanisms behind the peculiar ascending aortic pressure waveform and impedance spectral pattern in kangaroos.
• To investigate the role of wave reflections in shaping these hemodynamic characteristics.

Main Methods:

• Pulsatile pressure and blood flow velocity were measured in the ascending aorta, descending thoracic aorta, and brachiocephalic artery of 15 rock kangaroos.
• Input impedance was calculated from pressure and velocity data.
• An asymmetric uniform T-tube model of the systemic arterial tree was used for interpretation.

Main Results:

• A prominent secondary wave was observed in the ascending aortic pressure waveform, often exceeding peak systolic pressure during diastole.
• The impedance spectral pattern indicated a dominant wave reflection site in the lower body.
• Wave reflections from the upper body were minimal, being overshadowed by those from the lower body.

Conclusions:

• The unique waveform and impedance patterns are attributed to intense wave reflections from the large, muscular lower body of kangaroos.
• Body size, shape, and the eccentric heart location contribute significantly to these observed hemodynamic phenomena.
• The findings were supported by simulations using an asymmetric T-tube model.