AUTHOR=Fahlman Andreas , Cozzi Bruno , Manley Mercy , Jabas Sandra , Malik Marek , Blawas Ashley , Janik Vincent M. 

TITLE=Conditioned Variation in Heart Rate During Static Breath-Holds in the Bottlenose Dolphin (Tursiops truncatus)

JOURNAL=Frontiers in Physiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2020.604018

DOI=10.3389/fphys.2020.604018

ISSN=1664-042X

ABSTRACT=<p>Previous reports suggested the existence of direct somatic motor control over heart rate (<italic>f</italic><sub>H</sub>) responses during diving in some marine mammals, as the result of a cognitive and/or learning process rather than being a reflexive response. This would be beneficial for O<sub>2</sub> storage management, but would also allow ventilation-perfusion matching for selective gas exchange, where O<sub>2</sub> and CO<sub>2</sub> can be exchanged with minimal exchange of N<sub>2</sub>. Such a mechanism explains how air breathing marine vertebrates avoid diving related gas bubble formation during repeated dives, and how stress could interrupt this mechanism and cause excessive N<sub>2</sub> exchange. To investigate the conditioned response, we measured the <italic>f</italic><sub>H</sub>-response before and during static breath-holds in three bottlenose dolphins (<italic>Tursiops truncatus</italic>) when shown a visual symbol to perform either a long (LONG) or short (SHORT) breath-hold, or during a spontaneous breath-hold without a symbol (NS). The average <italic>f</italic><sub>H</sub> (i<italic>f</italic><sub>Hstart</sub>), and the rate of change in <italic>f</italic><sub>H</sub> (di<italic>f</italic><sub>H</sub>/dt) during the first 20 s of the breath-hold differed between breath-hold types. In addition, the minimum instantaneous <italic>f</italic><sub>H</sub> (i<italic>f</italic><sub>Hmin</sub>), and the average instantaneous <italic>f</italic><sub>H</sub> during the last 10 s (i<italic>f</italic><sub>Hend</sub>) also differed between breath-hold types. The di<italic>f</italic><sub>H</sub>/dt was greater, and the i<italic>f</italic><sub>Hstart</sub>, i<italic>f</italic><sub>Hmin</sub>, and i<italic>f</italic><sub>Hend</sub> were lower during a LONG as compared with either a SHORT, or an NS breath-hold (<italic>P</italic> &lt; 0.05). Even though the NS breath-hold dives were longer in duration as compared with SHORT breath-hold dives, the di<italic>f</italic><sub>H</sub>/dt was greater and the i<italic>f</italic><sub>Hstart</sub>, i<italic>f</italic><sub>Hmin</sub>, and i<italic>f</italic><sub>Hend</sub> were lower during the latter (<italic>P</italic> &lt; 0.05). In addition, when the dolphin determined the breath-hold duration (NS), the <italic>f</italic><sub>H</sub> was more variable within and between individuals and trials, suggesting a conditioned capacity to adjust the <italic>f</italic><sub>H</sub>-response. These results suggest that dolphins have the capacity to selectively alter the <italic>f</italic><sub>H</sub>-response during diving and provide evidence for significant cardiovascular plasticity in dolphins.</p>