Deacon N L, Arnould J P Y
School of Life and Environmental Sciences, Deakin University, Burwood, VIC, Australia.
J Comp Physiol B. 2009 Apr;179(3):287-95. doi: 10.1007/s00360-008-0313-5. Epub 2008 Nov 5.
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.
在澳大利亚海狗幼崽依赖母体的整个时期，研究了与陆地呼吸模式相关的心脏控制发育情况。静息时的平静呼吸心率和呼吸频率显著相关（r² = 0.49），且两者均随年龄增长而下降（两种情况P均< 0.05）。幼崽从早期（1个月）开始就表现出陆地呼吸暂停（18.1 ± 0.5秒），同时伴有明显的心动过缓（127次/分钟，比平静呼吸心率降低13%）。陆地呼吸暂停持续时间随年龄显著增加，在断奶前达到平均41秒，略低于先前记录的同年龄幼崽的平均潜水持续时间（52秒）。相应地，平均呼吸暂停心率随年龄下降，在断奶前降至74次/分钟，比平静呼吸心率降低25%。重要的是，随着年龄增长平均呼吸暂停心率下降的同时，心动过缓控制能力增强明显可见，即瞬时呼吸暂停心率的变异性降低，使得年龄较大的幼崽能够在呼吸暂停期间维持较低且稳定的心率。这些参数的变化与在海象（髯海豹属）和斑海豹（港海豹）出生后发育过程中所报道的变化相似，被认为是心脏控制发育的指标。这些发现表明在海狮科和海豹科海豹中，心动过缓控制的发育存在共同策略。
