Rhea Storlund

PhD Student

Tel: 604.822.8181

Fax: 604.822.8180


Supervisor: Dr. Andrew Trites

Education: BSc Biology, University of British Columbia, Canada (2015)

Research Interests: Marine mammal cardiovascular physiology, diving ability, and conservation

Research Location: The Vancouver Aquarium

Is the aortic bulb an adaptation for diving? Relating aortic bulb size and compliance to cardiovascular physiology, hemodynamics, and diving ability in pinnipeds.


It has long been known that marine mammals have an enlarged ascending aorta compared to terrestrial mammals. This adaptation, termed the aortic bulb, is suggested to be beneficial for diving as it can maintain continuous blood flow during diving bradycardia and reduce the amount of work performed by the heart. However, the link between aortic bulb properties and diving ability has not been established. My research will explore how aortic bulb size and compliance relate to cardiovascular physiology, hemodynamics, and diving ability.


Using echocardiography on anaesthetized Steller sea lions and northern fur seals, I will measure the size of their aortic bulb, the thickness of their left ventricular walls, and the velocity of blood as it travels through the aortic valve. From these measurements I will calculate stroke volume and blood flow. I predict that stroke volume and left ventricular wall thickness will positively correlate to aortic bulb radius. These measurements directly relate to the proposed functions of the aortic bulb as a larger stroke volume will allow for a longer duration of continuous blood flow during diastole and left ventricular wall thickness is inversely proportional to cardiac work. Thus, a larger aortic bulb will result in the ability for lower heart rates to be achieved while diving and for reduced oxygen consumption by the heart. With these in vivo measurements, we will be able to revisit the proposed functions of the aortic bulb and explain the importance of aortic bulb size.

Anatomical examinations

Using excised aortas collected opportunistically from dead pinnipeds, I will measure aortic bulb size and compliance. I will use inflation testing to measure compliance. My goal will be to sample from both good and poor divers according to values from the literature of average dive duration, depth, and diving heart rate. After standardizing aortic bulb size to body mass I will compare across species to see if size and compliance are related to diving ability. This comparative study will add evidence to support or refute the claim that marine mammals with a larger aortic bulb are better divers, while also showing that compliance may be as important as size.


Knowing how the aortic bulb constrains diving ability will allow us to assess which species are diving at their cardiovascular limits and the impact of cardiovascular characteristics on the foraging ecology of pinnipeds.