Muscle sympathetic nerve activity during pregnancy: A systematic review and meta-analysis

Blood pressure responses to handgrip exercise but not apnea or mental stress are enhanced in women with a recent history of preeclampsia

Preeclampsia is a risk factor for future cardiovascular diseases. However, the mechanisms underlying this association remain unclear, limiting effective prevention strategies. Blood pressure responses to acute stimuli may reveal cardiovascular dysfunction not apparent at rest, identifying individuals at elevated cardiovascular risk. Therefore, we compared blood pressure responsiveness with acute stimuli between previously preeclamptic (PPE) women (34 ± 5 yr old, 13 ± 6 mo postpartum) and women following healthy pregnancies (Ctrl; 29 ± 3 yr old, 15 ± 4 mo postpartum). Blood pressure (finger photoplethysmography calibrated to manual sphygmomanometry-derived values; PPE: n = 12, Ctrl: n = 12) was assessed during end-expiratory apnea, mental stress, and isometric handgrip exercise protocols. Integrated muscle sympathetic nerve activity (MSNA) was assessed in a subset of participants (peroneal nerve microneurography; PPE: n = 6, Ctrl: n = 8). Across all protocols, systolic blood pressure (SBP) was higher in PPE than Ctrl (main effects of group all P < 0.05). Peak changes in SBP were stressor specific: peak increases in SBP were not different between PPE and Ctrl during apnea (8 ± 6 vs. 6 ± 5 mmHg, P = 0.32) or mental stress (9 ± 5 vs. 4 ± 7 mmHg, P = 0.06). However, peak exercise-induced increases in SBP were greater in PPE than Ctrl (11 ± 5 vs. 7 ± 7 mmHg, P = 0.04). MSNA was higher in PPE than Ctrl across all protocols (main effects of group all P < 0.05), and increases in peak MSNA were greater in PPE than Ctrl during apnea (44 ± 6 vs. 27 ± 14 burst/100 hb, P = 0.04) and exercise (25 ± 8 vs. 13 ± 11 burst/100 hb, P = 0.01) but not different between groups during mental stress (2 ± 3 vs. 0 ± 5 burst/100 hb, P = 0.41). Exaggerated pressor and sympathetic responses to certain stimuli may contribute to the elevated long-term risk for cardiovascular disease in PPE.NEW & NOTEWORTHY Women with recent histories of preeclampsia demonstrated higher systolic blood pressures across sympathoexcitatory stressors relative to controls. Peak systolic blood pressure reactivity was exacerbated in previously preeclamptic women during small muscle-mass exercises, although not during apneic or mental stress stimuli. These findings underscore the importance of assessing blood pressure control during a variety of experimental conditions in previously preeclamptic women to elucidate mechanisms that may contribute to their elevated cardiovascular disease risk.

Impact of maternal obesity on resting muscle sympathetic nerve activity during uncomplicated pregnancy: a longitudinal assessment

Maternal obesity increases the risk of adverse pregnancy outcomes. The mechanisms that contribute to this elevated risk are unclear but may be related to greater activity of the sympathetic nervous system, which is associated with hypertensive disorders of pregnancy. We hypothesized that resting muscle sympathetic nerve activity (MSNA) would be greater in women with obesity during pregnancy when compared with normal-weight women. Blood pressure, heart rate, and MSNA were recorded during 5 min of supine rest in 14 normal-weight women [body mass index (BMI) 22.1 ± 2.1 (SD) kg/m2] and 14 women with obesity (BMI 33.9 ± 3.5 kg/m2) during (early and late) pregnancy and postpartum. All women had uncomplicated pregnancies. Resting MSNA burst frequency was not different between groups during early (normal weight 17 ± 10 vs. obesity 22 ± 15 bursts/min, P = 0.35) but was significantly greater in the obesity group during late pregnancy (23 ± 13 vs. 35 ± 15 bursts/min, P = 0.031) and not different postpartum (10 ± 6 vs. 9 ± 7 bursts/min, P = 0.74). These findings were also apparent when comparing burst incidence and total activity. Although still within the normotensive range, systolic blood pressure was greater in the obesity group across all time points (P = 0.002). Diastolic blood pressure was lower during pregnancy compared with postpartum (P < 0.001) and not different between groups (P = 0.488). Heart rate increased throughout pregnancy in both groups (P < 0.001). Our findings suggest that maternal obesity is associated with greater increases in sympathetic activity even during uncomplicated pregnancy. Future research is needed to determine if this is linked with an increased risk of adverse outcomes or is required to maintain homeostasis in pregnancy.NEW & NOTEWORTHY The impact of maternal obesity on resting muscle sympathetic nerve activity was examined during (early and late) and after uncomplicated pregnancy. Resting muscle sympathetic nerve activity is not different during early pregnancy or postpartum but is significantly elevated in women with obesity during late pregnancy when compared with normal-weight women. Future research is needed to determine if this is linked with an increased risk of adverse outcomes or is required to maintain homeostasis in pregnancy.

Commentary on: Increased stiffness of omental arteries from late pregnant women at advanced maternal age

Worldwide, pregnancy at age 35 or older, termed 'advanced maternal age (AMA)', is increasing exponentially. As the incidence of pregnancy at AMA has increased, a growing body of evidence has suggested that AMA is also associated with increased risk for adverse maternal and fetal outcomes outside of genetic anomalies. Importantly, despite the mounting evidence and the increased global risk of adverse perinatal outcomes observed, few studies have examined the potential mechanisms underlying this elevated risk in pregnant people ≥35 years of age. Wooldridge and colleagues begin to address this gap in the literature. In their recent report, they examine vessel stiffness in omental resistance vessels obtained from pregnant individuals ≥35 years of age compared with pregnant individuals <35 years of age. Omental arteries were isolated and assessed via pressure myography (mechanical properties) and histological analysis for collagen and elastin content. Overall, the findings from this investigation report that maternal resistance arteries collected from women of AMA were less compliant and had less elastin than arteries obtained from women <35 years of age, suggesting that maternal resistance vessel stiffening in AMA may contribute to increased risk of adverse pregnancy outcomes. The authors should be commended for completing these studies in human resistance vessels, which now open new avenues for investigation and provoke a cascade of questions related to maternal cardiovascular adaptations to pregnancy in women ≥35 years of age.