Marine Mammal Cardiology

Question 1

Describe the cardiothoracic anatomy of marine mammals generally?

What adaptations exist for deep diving?

How does venous structure differ from terrestrial mammals?

Answer 1

• Cardiothoracic
  
  • Hearts are flattened dorsoventrally with a rounded apex
  • Terminal airways in all marine mammals are reinforced with cartilage or muscle – prevents collapse during diving
  • Venous sinuses line upper airways in diving species, engorge to help prevent collapse of airways during dives
  • Allometrically, deeper diving animals have smaller lungs than shallow divers which have larger than expected lungs
  • Fully aquatic animals: lack femoral arteries
  • Seals, cetaceans, sirenians: few or no valves in veins

Question 2

Describe the relationship between the air sacs and venous sinuses in the cetacean skull.

How does this affect you clinically?

What is unique about cetacean lung anatomy?

What is the aortic bulb?

Answer 2

• Cardiothoracic
  
  • Odontocetes: extensive venous structures in ventral air sacs – keep in mind when intraoral/pharyngeal procedures conducted
  • Accessory sinus system of air sacs present along ventral aspect of skull, connected to nasal passages via Eustachian tube, juxtaposed to venous plexuses and/or venous lakes that can accommodate diving-related pressure changes
  • Stranded cetaceans have cardiac myofiber degeneration and contraction bands, likely secondary to catecholamine release
  • Vascular access: superficial veins in flukes, peduncle, dorsal fin; interpret with caution because of AV mixing
  • Cetacean lungs are unlobed
    
    • Cranial aspect of right lung lobe has tracheal/accessory bronchus that branches prior to main bifurcation
  • Some cetaceans: dilation of aortic arch = aortic bulb; helps maintain diastolic pressure during deep diving

Question 3

What is the function of the aortic bulb in pinnipeds?

What about the caval sphincter?

Answer 3

• Cardiothoracic
  
  • Pinnipeds + some cetaceans: dilation of aortic arch = aortic bulb; helps maintain diastolic pressure during deep diving
  • Caval sphincter: muscular sphincter controlled by phrenic nerve, regulates flow of oxygenated blood in the large venous hepatic sinus to the heart during dives; found in cranial aspect of diaphragm

Question 4

Sirenians have unique cardiothoracic anatomy.

What is unique about their pericardium?

Describe the vasculature to their extremeties. How does this differ from cetaceans?

Describe their lung anatomy.

Where is the diaphragm? What is the transverse septum?

Where is the mediastinum and what is in it?

Answer 4

• Cardiothoracic
  
  • Manatee pericardium has more fluid than found in other mammals/marine mammals
  • Vascular bundles instead of retia, supply extremities, lips, pectoral flippers, fluke, intercostal spaces
  • Lungs: extend length of body cavity, remain dorsal to heart, unlobed
  • Diaphragm occupies horizontal plane along entire length of body cavity; transverse septum occupies “normal” diaphragm position
    
    • Unique location of diaphragm helps with buoyancy
  • Mediastinum (dorsal to pericardial attachment to heart, ventral to diaphragm, cranial to transverse septum: thyroid, thymus, tracheobronchial LN, tracheobronchial bifurcation