Terrestrial apnoeas and the development of cardiac control in Australian fur seal (Arctocephalus pusillus doriferus) pups

Abstract

The development of cardiac control in association with terrestrial respiration patterns was examined throughout the period of maternal dependence in Australian fur seal pups. Resting eupnoic heart rate and respiration rate were significantly correlated (r (2) = 0.49) and both decreased with age (P < 0.05 in both cases). From an early age (1 month), pups displayed terrestrial apnoeas (18.1 +/- 0.5 s) accompanied by substantial bradycardia (127 beats min(-1), a 13% decrease from eupnoic HR). Terrestrial apnoea duration increased significantly with age reaching a mean of 41 s just prior to weaning, slightly lower than the mean dive duration (52 s) previously recorded for pups of the same age. Correspondingly, mean apnoic heart rate decreased with age to 74 beats min(-1) just prior to weaning, representing a 25% decrease on eupnoic heart rate. Importantly, concomitant with the decrease in mean apnoic heart rate with age, an increase in the control of bradycardia was evident with the variability in instantaneous apnoic heart decreasing such that older pups were able to maintain a low steady heart rate for the duration of the apnoea. The changes seen in these parameters are similar to those reported during postnatal development in elephant seals (Mirounga spp.) and harbour seals (Phoca vitulina), and are considered indicative of the development of cardiac control. These findings suggest a common strategy for the development of bradycardia control in both otariid and phocid seals.

Variations in heart rate and rhythm of harbor seal pups during rehabilitation

“…, Bertelsen et al . , Deacon and Arnould ). It is possible that the activation of the sympathetic nervous system during ECG recordings triggered an exaggerated compensatory parasympathetic response (Katz ), which would further support the presence of an immature nervous system.…”

“…Other studies report a significant correlation of heart and respiratory rate and a reduction of respiration rate with age (Lapierre et al . , Deacon and Arnould ). In the present study only a weak correlation was observed and highest respiratory rates were present at day 14 with a median of 26 breaths/min.…”

“…, ; Lapierre et al . ; Deacon and Arnould ). Sinus tachycardia was still recorded in some animals at later time points, suggesting individual differences and seal pups potentially more sensitive to stress factors (Porges , Oldehinkel et al .…”

“…, ; Lapierre et al . ; Deacon and Arnould ). Free‐ranging harbor seals can drastically reduce their heart rate during terrestrial apneas from birth onwards, although at first this is highly erratic (Greaves et al .…”

“…, ; Lapierre et al . ; Deacon and Arnould ). Recently, an iPhone ECG device was developed that allows a noninvasive ECG recording by placing the phone with its adapter at the lateral thoracic wall.…”