Clinical investigation of the autonomic nervous system: Application in the premature neonate and study of the influence of chronic intrauterine hypoxia.

摘要

In this thesis work our findings are presented on the function of the autonomic nervous system as estimated from clinical tests, in premature neonates who suffered from conditions assumed to be associated with chronic intrauterine hypoxia, i.e maternal hypertension, intrauterine growth retardation and maternal smoking.;In a first part, the prenatal and postnatal development and function of the autonomic nervous system which includes the sympathetic, parasympathetic, opioid and the non-adrenergic non-cholinergic system, is reviewed. It is concluded that there are no firm indications to when exactly the parasympathetic and the sympathetic system start showing their preponderance or how these systems interact which each other at different gestational ages. Characteristics in the neonate of vital functions which are under the influence of the developing autonomic nervous system, are then discussed (Chapter II, parts 1 and 2). As in our patients the diagnosis of CIUHX was based on clinical situations during pregnancy; these situations are discussed in more detail as is their probable pathophysiology (Chapter II, part 3). Clinical investigation of the autonomic nervous system has mainly been carried out in adults or older children and literature data in the neonatal population is scarce. Furthermore, the neonates that were studied are heterogenous in pathology and the tests have mostly not been standardised. A survey of the tests available in the adult and the older child and their application in the neonate is discussed. As to the latter, a cautionary note on their interpretation is made (Chapter II, part 4).;The third chapter relates to our personal work. The aim of the study is explained and the study population described. The methodology of the different tests, which are standardisations of methods used in other studies, is explained in more detail. Six clinical tests were carried out 3 times. Heart rate, respiratory frequency, systolic, diastolic and mean blood pressure were recorded at short time intervals as was sleep state for the entire test.;Much attention is given to the pilot study, the statistical methods which have been used and to the limitations which are inherent to the type of study material (Chapter III, parts 1, 2, 3, 4 and 5).;In the next part, the results of the different tests are given in detail. As is explained in the discussion, no great differences in response could be observed between the hypoxia group and the comparison-group. In the cold test and in the odor test, the hypoxia group showed a less pronounced parasympathetic effect than the comparison group. In the pain test and the postural change test the sympathetic effect seemed more accentuated in the HX-group. On the whole, our results suggest that neonates who were exposed to chronic intrauterine hypoxia, have a deregulated autonomic nervous system, and more specifically have a preponderant sympathetic activity, possibly due to enhanced maturation. Other possibilities, however, have to be taken into account and, more specifically, these reflexes should be studied in full-term neonates to see whether the increased sympathetic activity may not be due to prematurity itself. (Chapter III, parts 6 and 7). Our study has shown that these tests can be performed in a standardised way in newborns.