Delivery Mode Affects the Sympathetic Nervous System in Healthy Term Newborns
Pubblicato online: 20 ago 2023
Pagine: 68 - 73
Ricevuto: 24 giu 2023
Accettato: 07 lug 2023
DOI: https://doi.org/10.2478/acm-2023-0010
Parole chiave
© 2023 Marek Kozar et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
Spontaneous delivery (SD) is a natural way of human birth. From the physiological aspect, SD represents a crucial stress trigger, which is the substantial premise for a normal postnatal adaptation of a newborn. Several mechanisms participate on the triggering of perinatal stress – the onset of labor, change of environment (in utero to ex utero) with the mechanical (e.g. pressure of the birth canal) and temperature (and many other) stimuli affecting the neonatal organism during peripartal period (1). All these factors result into the activation of sympathetic nervous system (SNS) together with an increased production of catecholamine and cortisol in neonate (2). This is very important for the extrauterine adaptation of the respiratory and circulatory systems, thermogenesis, and energy metabolism (1). The labor without associated neonatal stress (i.e. elective caesarean section) is a potential factor which interferes in the process of postnatal adaptation (3).
The autonomic nervous system (ANS), consisting of SNS and parasympathetic nervous system (PNS), is extremely important for postnatal adaptation in newborns. More specifically, SNS enables brisk adaptation to postnatal life (2). From the developmental aspect, SNS is characterized by steady maturation during the pregnancy and requires at least 37 gestational weeks to reach accurate functioning (4). Maturation of ANS also continues after birth with PNS predominance in term neonates (5).
Electrodermal activity (EDA) also known as skin conductance (SC) represents a useful parameter reflecting the changes exclusively in SNS (6). The measurement of EDA reflects the changes of the skin electrical conductivity due to the activity of eccrine sweat glands. This phenomenon is under the pure control of sympathetic cholinergic nervous system (7). Peripheral SNS together with sweat glands located in the palms and plants are developed in the second trimester of pregnancy and continue to mature (8). In term newborns, fully developed functional emotional sweating was reported (9). From this perspective, EDA method represents an optimal tool for the assessment of SNS function in term newborns. In addition, EDA measurement is a safe, non – invasive, easy to handle method only little influenced by other factors (e.g. circulatory changes).
Understanding of normal early postnatal ANS function in full – term healthy newborns may provide a useful reference for studies of high – risk neonates and may have a prognostic value. Therefore, it is important to elucidate how different delivery modes influence the measures of ANS function in low – risk term newborns (10). To the best of our knowledge, there are no studies concerning the influence of delivery mode on SNS function and maturation measured by EDA within the first postnatal days in healthy term neonates. Therefore, we aimed to study potential changes in SNS indexed by EDA in early postnatal adaptation period in newborns depending on the delivery mode.
Our study was conducted from January 2019 to February 2020 at the Clinic of Neonatology of the University Hospital and Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava. The study included 50 healthy eutrophic full – term newborns with physiological immediate postnatal adaptation (Apgar score ≥ 8 points in the 1st minute and ≥ 9 in the 5th and 10th minute) who were divided into 2 groups according to the delivery mode: the spontaneous delivery (SD) group and the caesarean section (CS) group. All women who underwent caesarean section were in general anesthesia (a combination of intravenous thiopental and the inhaled sevofluran). Only newborns with indications of elective caesarean section were included (breech presentation, repeat caesarean section, primary maternal indication for caesarean section). SD group consisted of babies without the need for instrumental delivery (i.e., forceps and vacuum extractor).
Exclusion criteria involved all conditions that are proven or very likely associated with abnormal ANS function: pathological gravidity (preterm delivery, intrauterine growth restriction, etc.), maternal systemic disease (gestational or another types of diabetes), smoking during pregnancy, congenital anomaly of the neonate, signs of perinatal infection, metabolic disorders: hypoglycaemia and hyperbilirubinemia requiring phototherapy during hospitalization.
The examination was performed during the day (7 am – 12 am) and during sleep or quiet alert state in the supine position under standard conditions with the minimization of internal and external stimuli. Two silver – silver chloride bipolar electrodes with a sampling rate of 256 Hz placed on the sole of the neonate were used for the continuous EDA recording (FlexComp Infinity Biofeedback, Thought Technology Ltd., Canada) according to the recommendation of EDA biosignal measurements (11). The examination protocol included three EDA measurements that were performed 2 hours (measurement 1 – M1), 24 hours (measurement 2 – M2), and 72 hours (measurement 3 – M3) after birth. After the stabilization of the subjects (approximately 10 minutes – adaptation interval) the measurement of EDA was initiated (6 minutes records). EDA raw records were checked and the artefacts were removed for the final data analysis. The tonic EDA component was extracted by the 10th order low – pass finite impulse response filter (12). The following EDA parameters were analyzed: 1)
Jamovi version 1.6.9 (Sydney, Australia) was used for the statistical analysis and visualization of the measured data. The distribution and normality of the data was assessed using a violin plot and the Shapiro – Wilk normality test. Because of non – normal data distribution, the non – parametric ANOVA (Friedman test with post hoc Durbin – Conover test) was used. A value of p < 0.05 (two – tailed) was considered statistically significant.
This paper presents the preliminary data of our prospective observational study „Assessment of Autonomic Nervous Regulation During Postnatal Period in Newborns“ registered in Clinical Trials (ID NCT03830424). The clinical study was approved by the Ethics Committee of the Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava (EK 69/2018). All procedures performed in the study were in accordance with the 2000 Helsinki declaration of the World Medical Association. The subjects were included after meeting the inclusion criteria and with an approval by their parents after signing the informed consent.
Our set of subjects consists of 50 newborns (28 girls, mean gestational age 39 ± 0.21 weeks, mean birthweight 3362 ± 79 grams). Baseline characteristics of subject groups according to delivery mode is presented in Table 1.
Baseline characteristics of subject groups
| DELIVERY MODE | |||
|---|---|---|---|
| SD | CS | p | |
| N (girls) | 27 (17) | 23 (12) | – |
| GA (weeks) | 39.4 ± 0.23 | 38.4 ± 0.34 | |
| BW (g) | 3383 ± 113 | 3335 ± 110 | 0.685 |
BW = birthweight, CS = caesarean section, GA = gestational age, N = number of subjects, SD = spontaneous delivery
Non – parametric Friedman test showed a significant effect of delivery mode for the parameters NS.SCRs (F[1]=6.66; p=0.01) and a mixed effect of mode of delivery and phase for the parameters SCL (F[5]=42.0; p <0.001), NS.SCRs (F[5]=25.9; p<0.001). Post – hoc analysis revealed a significantly higher SCL in M1 vs M2 (SD: p<0.001; CS: p<0.001) and M1 vs M3 (SD: p=0.003; CS: p=0.028) in both groups. However, a significant difference in NS.SCRs was observed only in CS: significantly lower values in M1 vs M2 (p=0.001) and M1 vs M3 (p=0.005) (Fig 1). There was no difference in the remaining parameters.
Fig. 1
Changes of EDA parameters within first three postnatal days according to the delivery mode.
A) SCL – skin conductance level; B) NS.SCRs – nonspecific skin conductance responses. CS = caesarean section; SD = spontaneous delivery, μS = microsiemens. Values are present as a mean ± standard error of the mean (SEM). Symbols: * = significant difference between the measurements in SD group; # = significant difference between the measurements in CS group; symbols above „24 hours“ represent the difference between M1 and M2; symbols above „72 hours“ represent the difference between M1 and M3; *, # p < 0.05; **, ## p < 0.01; ***, ### p < 0.001.
The statistical analysis revealed a significantly lower NS.SCRs in neonates born by CS vs SD in M1 (p=0.01). (Table 2). No significant differences were revealed in the remaining parameters.
Comparison of EDA parameters between groups
| M1 a | M2 b | M3 c | p a | p b | p c | ||||
|---|---|---|---|---|---|---|---|---|---|
| SD (n=27) | CS (n=23) | SD (n=27) | CS (n=23) | SD (n=27) | CS (n=23) | ||||
| SCL (μS) | 3.74±0.68 | 2.96±0.62 | 0.49±0.15 | 0.33±0.12 | 1.40±0.30 | 0.87±0.30 | 0.461 | 0.54 | 0.964 |
| NS.SCRs(/min) | 3.58±1.35 | 1.46±0.74 | 5.54±0.79 | 5.26±1.13 | 5.00±1.33 | 4.96±1.35 | 0.457 | 0.597 | |
SCL – skin conductance level; NS.SCRs – nonspecific skin conductance responses. CS = caesarean section; SD = spontaneous delivery; μS = microsiemens; p = statistical significance; n = number of subjects; M1 = 1st measurement; M2 = 2nd measurement; M1 = 3rd measurement
Our study investigated the potential effect of delivery mode on SNS activity and maturation during early postnatal life in healthy term neonates evaluated by EDA analysis. The major findings of this study are following: 1) significantly higher values of SCL were observed early after birth (M1) in all newborns followed by a significant decrease during the following measurements (M2 and M3) reflecting a post – delivery stress – related sympathetic withdrawal after postnatal adaptation; 2) NS.SCRs representing the
During the peripartal period, the SNS outflow from central ANS structures increases and together with neuroendocrine support (e.g. catecholamines) enables brisk postnatal adaptation (2). After birth, SNS constantly continues to develop. Regarding the development and normal functioning of palmar and plantar sweat glands, Harpin and Rutter (9) reported functional emotional sweating in term neonates. Our study showed the highest values of SCL in all newborns 2 hours after birth supporting the functionality of eccrine sweat glands in term neonates immediately after delivery. According to our results, SNS activity decreased within the first 24 hours of life in both groups reflecting the depression of acute stress adaptation process triggered by the delivery. Therefore, EDA is a sensitive marker which is able to detect these subtle changes in sympathetic regulatory mechanisms.
Further, the elevation of NS.SCRs within the first postnatal day in all newborns indicates a physiological excitation of central nervous system. NS.SCRs as a discrete fluctuation of skin conductance around the baseline arise spontaneously, without the influence of an external stimuli and reflect states of increased “arousal” (14). The increase of NS.SCRs within the first postnatal day may reflect changes related to an increased processing of perceptions and the activation of receptors in the context of adaptation to the extrauterine environment.
Lower NS.SCRs values in CS group during the immediate postnatal adaptation could be explained by the absence of physiological delivery mechanisms associated with stress response represented by the activation of SNS and stress hormones (10). Another importnant factor contributing to the lower SNS activity is the general anesthesia of the mother during CS – an sympatholytic effect was described for sevoflurane and thiopental (15, 16) – both drugs were used in our study. However, this effect seems to be temporary.
The precise understanding of SNS development in the earliest postnatal life is limited – there are no studies in the literature focusing on EDA measurements with regard to the mode of delivery in newborns so far. Therefore, our findings can provide novel insights into the SNS regulatory mechanisms immediately after birth and during the earliest postnatal life.
Our study evaluated the effect of delivery mode on SNS measured by EDA in healthy term newborns within the first three postnatal days. The results revealed a lower