Evaluating cardiac physiology through echocardiography in bottlenose dolphins: using stroke volume and cardiac output to estimate systolic left ventricular function during rest and following exercise

Abstract

Heart-rate ( f H ) changes during diving and exercise are well documented for marine mammals, but changes in stroke volume (SV) and cardiac output (CO) are much less known. We hypothesized that both SV and CO are also modified following intense exercise. Using transthoracic ultrasound Doppler at the level of the aortic valve, we compared blood flow velocities in the left ventricle and cardiac frequencies during rest and at 1, 3 and 4 min after a bout of exercise in 13 adult bottlenose dolphins (Tursiops truncatus, six male and seven female, body mass range 143-212 kg). Aortic cross-sectional area and ventricle blood velocity at the aortic valve were used to calculate SV, which together with f H provided estimates of left CO at rest and following exercise. f H and SV stabilized approximately 4-7 s following the post-respiratory tachycardia, so only data after the f H had stabilized were used for analysis and comparison. There were significant increases in f H , SV and CO associated with each breath. At rest, f H , SV and CO were uncorrelated with body mass, and averaged 41±9 beats min , respectively. One minute following high intensity exercise, the cardiac variables had increased by 104±43%, 63±11% and 234±84%, respectively. All variables remained significantly elevated in all animals for at least 4 min after the exercise. These baseline values provide the first data on SV and CO in awake and unrestrained cetaceans in water.

Echocardiographic Left Ventricular Structure and Function in Healthy, Non-Sedated Southern Sea Lions (Otaria flavescens)

“…These are the first published values for left ventricular structure and function in SSLs and are comparable with other marine mammals such as dolphins (Sklansky et al, 2006;Chetboul et al, 2012;Miedler et al, 2015) and manatees (Gerlach et al, 2013(Gerlach et al, , 2015, and similar to those reported in some terrestrial mammals such as dairy cattle (Hallowell et al, 2007), sheep (Locatelli et al, 2011), gorillas (Murphy et al, 2011), grizzly bears (Nelson et al, 2003), and humans (Lang et al, 2015).…”

“…Although we focused on measurements of the left heart chambers and aorta, other cardiac structures were correctly identified as pulmonary artery, right ventricle, and interatrial septum but without obtaining reliable quantitative measurements. The use of a cardiac ultrasound to evaluate non-sedated aquatic mammals has been limited by some anatomophysiological conditions to obtain an optimal acoustic window such as lung interposition, large sternum, and respiratory pattern (Sklansky et al, 2006;Chetboul et al, 2012;Miedler et al, 2015).…”

“…However, its use as a diagnostic tool requires knowledge of echocardiographic techniques and reference values for each species (Pereira & Pizzi, 2012). This information is not currently available for most marine mammals, the only exception at this time being trained bottlenose dolphins (Chetboul et al, 2012;Miedler et al, 2015).…”

Respiratory function and mechanics in pinnipeds and cetaceans

“…These models assume that the O 2 exchange ratio and V T remain constant during the surface interval. However, both change during recovery from exercise and diving, and accounting for these dynamic changes in physiology improves the estimated metabolic rate (Ridgway et al, 1969;Reed et al, 1994Reed et al, , 2000Miedler et al, 2015;. Thus, an improved knowledge of respiratory physiology may be useful to improve estimates of field metabolic rate using this method.…”

Ventilation and gas exchange before and after voluntary static surface breath-holds in clinically healthy bottlenose dolphins, Tursiops truncatus

“…The recovery time at the surface is reduced by increased cardiac output in bottlenose dolphins (Tursiops truncatus) (Miedler et al, 2015). Changes in ventilation following diving, in contrast, are not as obvious or not reported (Kooyman et al, 1971;Kooyman et al, 1973;Reed et al, 1994).…”