Andrews, Katharine Ann; (1997) The development of the cutaneous flexion reflex in human infants: The effects of noxious stimuli and tissue damage in the newborn. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The aim was to investigate the development of spinal sensory processing in the human neonate using the cutaneous flexion reflex, and to measure changes in the reflex resulting from repeated tissue damage. A further aim was to quantify flexion reflex responses elicited by different intensities of mechanical and electrical stimuli using EMG recordings. Experiments were performed with ethical approval and informed parental consent on a group of preterm and full-term infants aged between 27 and 42 weeks postconceptional age. Mechanical stimuli were applied to the sole of the foot using calibrated von Frey hairs mounted on a piezo transducer which triggered the sweep of an EMG unit. These were delivered at threshold intensities, and at 2.8, 7.6, and 21 x threshold. Heel lance stimuli were delivered with a modified 'Autolet' device which also triggered the EMG sweep. Electrical stimuli were applied to the skin overlying the sural nerve using a neonatal bipolar stimulator at threshold intensities, and in steps of 0.5mA to 1.85 x threshold. Single surface EMG responses were recorded ipsilaterally from lower limb flexor muscles, and the latency, amplitude, duration and area of the response were recorded. There was variability between neonates and between successive responses in all reflex parameters. Nevertheless, a clear correlation was found between stimulus intensity and the latency, amplitude, duration and area of the mechanically-evoked reflex. The latency of the response decreased with increasing stimulus intensity from threshold to heel lance. The amplitude, duration and area of the response increased with stronger stimuli across all PC ages. Repeated suprathreshold mechanical stimulation clearly affected the duration and area of the response. Onset latencies of electrically-evoked reflexes were more constant, but the relationship between stimulus intensity and response parameters was less clear. Finally, the flexion reflex threshold was clearly lowered by tissue damage.

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