Cardiorespiratory coupling in cetaceans; a physiological strategy to improve gas exchange?

Area of Science:

• Marine Mammal Physiology
• Cardiovascular Physiology
• Comparative Physiology

Background:

• Understanding cetacean cardiovascular function is crucial for their conservation and welfare in managed care.
• Respiratory sinus arrhythmia (RSA) is a known phenomenon in mammals, but its extent and impact in cetaceans require further investigation.

Purpose of the Study:

• To measure cardiac output, heart rate, and stroke volume in cetaceans using echocardiography.
• To evaluate cardiorespiratory coupling and the impact of RSA on these parameters in various cetacean species.
• To compare cetacean cardiovascular responses with those of terrestrial mammals.

Main Methods:

• Transthoracic echocardiography was used to measure stroke volume (SV), heart rate (fH), and cardiac output (CO).
• Continuous electrocardiogram (ECG) was recorded in multiple cetacean species (beluga whale, bottlenose dolphin, false killer whale, killer whale, pilot whale).
• Measurements were taken during spontaneous breathing under voluntary control in managed care settings.

Main Results:

• Cetaceans exhibit a strong RSA, where fH and SV vary with breathing frequency (fR).
• RSA-corrected fH was lower in cetaceans than similarly sized terrestrial mammals.
• RSA-corrected SV and CO were comparable or lower in dolphins and false killer whales, but elevated in beluga whales compared to terrestrial mammals.
• Cetaceans showed a greater cardiac response to changes in fR compared to terrestrial mammals.

Conclusions:

• Cetacean cardiac function is strongly coupled with respiration, characterized by significant RSA.
• This cardiorespiratory coupling, particularly RSA, is vital for maximizing gas exchange during breath-hold periods at the surface.
• Findings suggest adaptations in cetacean cardiovascular physiology for efficient oxygen management during diving and surfacing cycles.