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Storlund RL, Rosen DAS, Haulena M, Sanatani S, Vander Zaag J, Trites AW. Ultrasound images of the ascending aorta of anesthetized northern fur seals and Steller sea lions confirm that the aortic bulb maintains continuous blood flow. JOURNAL OF EXPERIMENTAL ZOOLOGY. PART A, ECOLOGICAL AND INTEGRATIVE PHYSIOLOGY 2024; 341:458-469. [PMID: 38409932 DOI: 10.1002/jez.2799] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Revised: 02/02/2024] [Accepted: 02/09/2024] [Indexed: 02/28/2024]
Abstract
The increased size and enhanced compliance of the aortic bulb-the enlargement of the ascending aorta-are believed to maintain blood flow in pinnipeds during extended periods of diastole induced by diving bradycardia. The aortic bulb has been described ex vivo in several species of pinnipeds, but in vivo measurements are needed to investigate the relationship between structure and function. We obtained ultrasound images using electrocardiogram-gated transesophageal echocardiography during anesthesia and after atropine administration to assess the relationship between aortic bulb anatomy and cardiac function (heart rate, stroke volume, cardiac output) in northern fur seals (Callorhinus ursinus) and Steller sea lions (Eumetopias jubatus). We observed that the aortic bulb in northern fur seals and Steller sea lions expands during systole and recoils over the entire diastolic period indicating that blood flow is maintained throughout the entire cardiac cycle as expected. The stroke volumes we measured in the fur seals and sea lions fit the values predicted based on body size in mammals and did not change with increased heart rates, suggesting that greater stroke volumes are not needed for aortic bulb function. Overall, our results suggest that peripheral vasoconstriction during diving is sufficient to modulate the volume of blood in the aortic bulb to ensure that flow lasts over the entire diastolic period. These results indicate that the shift of blood into the aortic bulb of pinnipeds is a fundamental mechanism caused by vasoconstriction while diving, highlighting the importance of this unique anatomical adaptation.
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Affiliation(s)
- Rhea L Storlund
- Marine Mammal Research Unit, Institute for the Oceans and Fisheries, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
| | - David A S Rosen
- Marine Mammal Research Unit, Institute for the Oceans and Fisheries, University of British Columbia, Vancouver, British Columbia, Canada
- Vancouver Aquarium, Vancouver, British Columbia, Canada
| | | | - Shubhayan Sanatani
- Division of Cardiology, British Columbia Children's Hospital, Vancouver, British Columbia, Canada
- Department of Pediatrics, University of British Columbia, Vancouver, British Columbia, Canada
| | - Jessica Vander Zaag
- Division of Cardiology, British Columbia Children's Hospital, Vancouver, British Columbia, Canada
| | - Andrew W Trites
- Marine Mammal Research Unit, Institute for the Oceans and Fisheries, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
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Doppler echocardiography in a healthy, non-sedated Southern Sea Lion (Otaria flavescens) - a preliminary approach about the feasibility and clinical utility. Vet Res Commun 2022; 47:953-961. [DOI: 10.1007/s11259-022-10019-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Accepted: 10/09/2022] [Indexed: 11/06/2022]
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Storlund RL, Rosen DAS, Trites AW. Electrocardiographic Scaling Reveals Differences in Electrocardiogram Interval Durations Between Marine and Terrestrial Mammals. Front Physiol 2021; 12:690029. [PMID: 34630134 PMCID: PMC8493095 DOI: 10.3389/fphys.2021.690029] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Accepted: 08/30/2021] [Indexed: 12/02/2022] Open
Abstract
Although the ability of marine mammals to lower heart rates for extended periods when diving is well documented, it is unclear whether marine mammals have electrophysiological adaptations that extend beyond overall bradycardia. We analyzed electrocardiographic data from 50 species of terrestrial mammals and 19 species of marine mammals to determine whether the electrical activity of the heart differs between these two groups of mammals. We also tested whether physiological state (i.e., anesthetized or conscious) affects electrocardiogram (ECG) parameters. Analyses of ECG waveform morphology (heart rate, P-wave duration, and PQ, PR, QRS, and QT intervals) revealed allometric relationships between body mass and all ECG intervals (as well as heart rate) for both groups of mammals and specific differences in ECG parameters between marine mammals and their terrestrial counterparts. Model outputs indicated that marine mammals had 19% longer P-waves, 24% longer QRS intervals, and 21% shorter QT intervals. In other words, marine mammals had slower atrial and ventricular depolarization, and faster ventricular repolarization than terrestrial mammals. Heart rates and PR intervals were not significantly different between marine and terrestrial mammals, and physiological state did not significantly affect any ECG parameter. On average, ECG interval durations of marine and terrestrial mammals scaled with body mass to the power of 0.21 (range: 0.19–0.23) rather than the expected 0.25—while heart rate scaled with body mass to the power of –0.22 and was greater than the widely accepted –0.25 derived from fractal geometry. Our findings show clear differences between the hearts of terrestrial and marine mammals in terms of cardiac timing that extend beyond diving bradycardia. They also highlight the importance of considering special adaptations (such as breath-hold diving) when analyzing allometric relationships.
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Affiliation(s)
- Rhea L Storlund
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada.,Marine Mammal Research Unit, Institute for the Oceans and Fisheries, University of British Columbia, Vancouver, BC, Canada
| | - David A S Rosen
- Marine Mammal Research Unit, Institute for the Oceans and Fisheries, University of British Columbia, Vancouver, BC, Canada.,Vancouver Aquarium, Vancouver, BC, Canada
| | - Andrew W Trites
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada.,Marine Mammal Research Unit, Institute for the Oceans and Fisheries, University of British Columbia, Vancouver, BC, Canada
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