Influence of peripheral chemodenervation on the complexity of respiratory patterns during early maturation.

Previous studies in humans have revealed that, during development, the fetus/neonate may be susceptible to environmental perturbations such as overheating, smoking, hypercapnia and hypoxia (LEWIS and BOSQUE, 1995; MASKERY, 1995). In particular, alterations in behavioural states during early development can result in permanent alterations in their organisational states and subsequent abnormalities in the regulation of the cardiovascular and respiratory systems. The influence of the peripheral chemoreceptor afferent input on the approximate entropy (complexity) of the phrenic neurogram in the piglet was investigated in three different age groups: 3-7 days (n = 7), 10-16 days (n = 6) and 25-31 days (n = 4). The phrenic neurogram was recorded from piglets during control (40% O2) and severe hypoxia (gasping) (5-10% O2), before and after peripheral chemodenervation, and was analysed using the approximate entropy (ApEn) method. The results show that the complexity values of the phrenic neurogram during eupnea and gasping did not change significantly before and after chemodenervation, regardless of postnatal age. The complexity values during gasping were not significantly influenced by the carotid chemodenervation for the 3-7 day-old group, but they were significantly decreased by the carotid chemodenervation for the 10-16 day-old age group (p < 0.01) and the 25-31 day-old age group (p < 0.05). However, the complexity values significantly decreased when the O2 concentration was shifted from eupnea to gasping (p < 0.001), both before and after the chemodenervation (p < 0.001), regardless of the postnatal age. These results suggest that the peripheral chemodenervation reduces the complexity of the phrenic neurograms during gasping only for the 10-16 day-old and 25-31 day-old age groups, and it has no significant influence on the 3-7 day-old age group. Therefore it is speculated that the peripheral chemoreceptors may be inactive for the first seven days of postnatal life and become more active after seven days.