Research Article: Cardiovascular autonomic modulation and baroreflex control in the second trimester of pregnancy: A cross sectional study

Date Published: May 14, 2019

Publisher: Public Library of Science

Author(s): Mikaela da Silva Corrêa, Aparecida Maria Catai, Juliana Cristina Milan-Mattos, Alberto Porta, Patricia Driusso, Antonio Palazón-Bru.


The aim is to evaluate and characterize cardiovascular autonomic control and baroreflex function and their response to an orthostatic stressor in the second trimester of pregnancy via time, frequency, information and symbolic analyses.

We evaluated 22 women at 18 weeks of pregnancy, labeled as pregnant group (PG) (30.8±4.4 years), and 22 non-pregnant women (29.8±5.4 years), labeled as control group (CG). Electrocardiogram, non-invasive photoplethysmographic arterial pressure (AP) and respiratory signals were recorded at rest at left lateral decubitus (REST) and during active standing (STAND) for 10 minutes. The heart period (HP) variability and systolic AP (SAP) variability were assessed in the frequency domain. High frequency (HF) and low frequency (LF) spectral indexes were computed. Nonlinear indexes such as symbolic markers (0V%, 1V%, 2LV% and 2UV% indexes), Shannon entropy (SE) and normalized complexity index (NCI) were calculated as well. Baroreflex control was assessed by cross-spectral HP-SAP analysis. We computed baroreflex sensitivity (BRS), HP-SAP squared coherence (K2) and phase in LF and HF bands.

At REST, the PG had lower mean, variance and HF power of HP series and lower K2(LF), BRS(LF) and BRS(HF) than the CG. During STAND, CG and PG decreased the mean, CI, NCI and 2UV% and increased 0V% of the HP series and augmented the SAP variance. LFabs of SAP series increased during STAND solely in CG. BRS(HF) was reduced during in both PG and CG, while HFabs of HP series did not diminish during STAND either in PG or CG. Complexity of the autonomic control was similar in PG and CG regardless of the experimental condition.

We conclude that the second trimester of pregnancy was characterized by a lower parasympathetic modulation and reduced BRS at REST, preserved complexity of cardiac and vascular controls, limited sympathetic response to STAND and general conservation of the baroreflex responses to posture changes.

Begistro Brasileiro de Ensaios clínicos, Number: RBR-9s8t88.

Partial Text

Pregnancy is a period of intense hemodynamic modifications, especially in the second trimester when cardiac output increases significantly reaching its maximum and remaining constantly elevated during the third trimester [1]. Hemodynamic changes require adjustment of mechanisms for allowing the maintenance of hemodynamic stability with the baroreflex system being the most important short-term mechanism involved in limiting the magnitude of arterial pressure (AP) oscillations [2]. The analyses of heart period (HP) variability, AP variability and baroreflex control have become powerful tools for the assessment of cardiovascular autonomic control [3–5].

The characterization of the two groups is presented in Table 1. None of the reported variables differ in two groups. Five pregnant and four control women presented a body mass index (BMI) can be classified as overweight, while the remaining ones are features a normal BMI. In the PG, 8 women were in their second gestation, while 14 were primigravidae. Respiratory rates were similar regardless of groups and experimental condition.

The main findings of the present study can be summarized as follows: 1) pregnancy led to a lower vagal modulation of the heart, while sympathetic modulation to the vessels remained unmodified; 2) the response of the cardiac parasympathetic control to postural challenge is preserved in pregnancy; 3) the response of the sympathetic control to the vessels to postural challenge is lower in pregnancy; 4) the complexity of HP and SAP controls is maintained in pregnancy and responds to postural maneuver similarly to the CG; 5) pregnancy leads to a decrease of amplitude of baroreflex gain and coupling; 6) the response of baroreflex gain and coupling to STAND is preserved in PG; 7) during pregnancy the phase of the HP-SAP relationship in LF band was more negative at REST than during STAND;

The lack of hemodynamic measurements such as cardiac output does not allow confirmation of the influence of blood volume and venous return among others in the variables studied. Moreover, the lack of full monitoring of respiration prevents the ability to investigate further the effect of breathing pattern on cardiovascular control above and beyond the sole influences of breathing rate. Because the study is cross-sectional, it is possible to only state the influence of the second trimester, while preventing to follow the evolution of gestation on the cardiovascular autonomic modulation. Since the sample size was decided according to the possibility of finding a significant difference between HP mean of the pregnant group and control group according to the scheme of our protocol (two factors, namely group and experimental condition) and, then, inclusion was stopped, we advocate studies with larger sample sizes adopting the same signal processing procedure to check whether some tendencies observed in this study might become significant.

In this study, we found that in the second trimester there is an attenuation of parasympathetic modulation, a reduced BRS and a lower coupling between HP and SAP series. These findings support a lower ability to maintain AP with changes in HP during pregnancy and a shift of the sympatho-vagal balance towards a sympathetic dominance. However, we also observed the conservation of complexity of the HP and SAP control and the preservation of the autonomic and baroreflex responses to the orthostatic challenge. This finding supports the strong resilience of the cardiac controls in pregnant women and its invariable functioning in response to a postural challenge. Only the response of sympathetic control directed to vessels with posture seems to be weaker. These findings can be helpful to better elucidate the responses of the autonomic control and baroreflex function in normal pregnancy and to detect impairment and pathological conditions in future studies.




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