Short Latency Mechanically Evoked Peripheral Nerve and Somatosensory Potentials in Newborn Infants

Abstract

Summarya 36-wk ~estational ape infant who was studied 4 days after birth.Mechanically evoked short-latency potentials were recorded from ten newborn infants ranging in gestational age from 36 to 42 wk and from a 3-month-old infant during natural sleep. Potentials were recorded from four electrode configurations: (1) over the peripheral nerve at the wrist: distal-proximal; (2) over the peripheral nerve at the axilla-deltoid insertion; (3) over the cervical spinal cord and cerebrum: Cn-F,,; and (4) over the cerebrum: C4-F,.. All subjects produced clear potentials from configurations 1, 2 and 3. Configuration 4 produced reliable potentials only in one newborn who was large for gestational age (42 wk) and the 3-month-old infant. ~v e r a~e peripheral nerve conduction velocities were 26 m/sec from wrist to axilla and 29 m/sec from axilla to neck. N o significant correlation was found between conceptional age and nerve conduction velocity. The application of this technique could allow lesion localization in peripheral as well as central portions of the somatosensory pathway of newborns.The &hod for kechanical stimulation and recordings has been described previously (21). and a number of modifications were made to accommodate the newborn population tested. In brief, subjects were tested immediately after feeding during spontaneous sleep. No monitoring of sleep stage was attempted because short latency components are independent of sleep stage (9). They were lying on a flat, padded surface, and the hand stimulated was supported by one examiner with the fingers taped to a flat board. Because of the subjects' small size. precautions against stimulusgenerated electrode movement artifacts were taken. Thus, care was taken that no other part of the hand was in touch with the supporting board. The surface on which subjects lay. the fingersupporting board, and the mechanical stimulator were placed on three separate stands. The stimulus was a 50-msec duration square electric pulse transduced by a moving coil vibrator. The vibrating tip had a 2 mm diameter hemispheric surface which. in the resting state. was ~e r~e n d i c u l a r to and iust in contact with the nail of the middle fi&e; Stimuli were delivered at a rate of 4/sec. The skin Sensory evoked potentials recorded by surface electrodes using temperature of the proximal Part of the fingers was measured and computer averaging have been utilized in the newborn nurseries. maintained at approximately 35°C throughout the recording sesAuditory ( I , 2, 18, 23, 25. 26, 28. 31) and visual evoked potentials sion. which lasted approximately 20 min. (14, 15, 30) have been well described and found to reflect periphTin disc electrodes, 6 mm in diameter. were placed over the eral (auditory) and central (auditory and visual) maturation in median nerve at the wrist and near the axilla, over the insertion of addition to indicating pathologic changes. Somatosensory evoked the deltoid muscle, over the second cervical vertebra (CII). over potentials in newborn infants have so far only been ob...