Porter F L, Porges S W, Marshall R E
Washington University School of Medicine.
Child Dev. 1988 Apr;59(2):495-505.
Clinical studies have demonstrated that the cries of chronically stressed, medically compromised infants are characteristically higher and more variable in pitch than those of healthy infants. Other studies have indicated that the vagal tone of chronically stressed infants is significantly reduced in comparison to that of normal infants. A neural model of cry production has been proposed which suggests that decreased vagal tone among infants at risk may, in fact, be related to these increases in cry pitch. Using routine, unanesthetized circumcision as a model of stress, we were able to examine the relation between cry acoustics and vagal tone in normal, healthy newborns undergoing an acutely stressful event. Vocalizations, heart, and respiratory waveforms were continuously recorded from 49 (32 experimental; 17 control) 1-2-day-old, full-term infants during preoperative, surgical, and postoperative periods. Vagal tone, as measured by the amplitude of respiratory sinus arrhythmia extracted from heart period data, was significantly reduced during the severe stress of circumcision, and these reductions were paralleled by significant increases in the pitch of the infants' cries. In addition, individual differences in vagal tone measured prior to circumcision surgery were predictive of physiological and acoustic reactivity to subsequent stress. These results emphasize the potential role of vagal control of the autonomic nervous system during stress.
临床研究表明，长期处于压力之下、身体有恙的婴儿的哭声，其特征在于音高比健康婴儿更高且变化更大。其他研究表明，与正常婴儿相比，长期处于压力之下的婴儿迷走神经张力显著降低。有人提出了一个哭声产生的神经模型，该模型表明，处于风险中的婴儿迷走神经张力降低，实际上可能与哭声音高的这些增加有关。我们以常规的、未麻醉的包皮环切术作为压力模型，得以研究正常、健康的新生儿在经历急性应激事件时哭声声学与迷走神经张力之间的关系。在术前、手术期间和术后，对49名（32名实验组；17名对照组）1 - 2日龄的足月儿的发声、心脏和呼吸波形进行了连续记录。通过从心动周期数据中提取的呼吸性窦性心律不齐的幅度来测量迷走神经张力，在包皮环切术的严重应激期间，迷走神经张力显著降低，并且这些降低与婴儿哭声音高的显著增加同时出现。此外，包皮环切术前测量的迷走神经张力的个体差异可预测对随后应激的生理和声学反应。这些结果强调了迷走神经在应激期间对自主神经系统控制的潜在作用。
