Cardiovascular adjustments to laboratory diving in beavers and nutria

Area of Science:

• Comparative physiology
• Mammalian diving response
• Cardiovascular and respiratory regulation

Background:

• Beavers (Castor canadensis) and nutria (Myocastor coypus) are semi-aquatic mammals with unique physiological adaptations for diving.
• Understanding their cardiovascular and metabolic responses to aquatic immersion is crucial for elucidating mammalian diving physiology.

Purpose of the Study:

• To investigate the physiological responses of beavers and nutria to simulated diving conditions.
• To quantify changes in cardiac output, regional blood flow, oxygen consumption, and blood gas parameters during simulated dives.

Main Methods:

• Anesthesia and catheterization of beavers and nutria for hemodynamic and blood gas measurements.
• Simulated diving by immersing animals in cold water (15-20°C) for controlled durations.
• Measurement of regional blood flow distribution, cardiac output, oxygen consumption, arterial/venous blood gases, and pH before and during simulated dives.

Main Results:

• Heart rate and cardiac output decreased significantly (75-80%) during simulated dives.
• Arterial and venous oxygen partial pressure, content, and pH decreased, while carbon dioxide pressure increased.
• Oxygen consumption at rest exceeded predicted values; however, the rate of decline in oxygen stores during diving was substantially reduced (89-93%).
• Regional blood flow was redirected from most organs to the adrenals, heart, lungs, and brain, with brain blood flow increasing.

Conclusions:

• Beavers and nutria display profound cardiovascular adjustments during diving, including bradycardia and reduced cardiac output, indicative of a strong diving response.
• These mammals exhibit remarkable metabolic efficiency and oxygen conservation strategies during aquatic immersion.
• The observed blood flow redistribution prioritizes oxygen supply to critical organs like the brain, essential for survival during prolonged dives.