Cerebral blood flow regulation, exercise and pregnancy: why should we care?

Prenatal exercise and cardiovascular health (PEACH) study: impact of acute and chronic exercise on cerebrovascular hemodynamics and dynamic cerebral autoregulation

We performed a randomised controlled trial measuring dynamic cerebral autoregulation (dCA) using a sit-to-stand maneuver before (SS1) and following (SS2) an acute exercise test at 16-20 weeks gestation (trimester 2; TM2) and then again at 34-37 weeks gestation (third trimester; TM3). Following the first assessment, women were randomised into exercise training or control (standard care) groups; women in the exercise training group were prescribed moderate intensity aerobic exercise for 25-40 minutes on 3-4 days per week for 14±1weeks. Resting seated mean blood velocity in the middle cerebral artery (MCAv_mean) was lower in TM3 compared to TM2 but not impacted by exercise training intervention. dCA was not impacted by gestational age, or exercise training during SS1. During SS2, dCA was altered such that there were greater absolute and relative decreases in mean arterial blood pressure (MAP) and MCAv_mean, but this was not impacted by the intervention. There was also no difference in the relationship between the decrease in MCAv_mean compared to the decrease in MAP (%/%), or the onset of the regulatory response with respect to acute exercise, gestational age, or intervention; however, rate of regulation was faster in women in the exercise group following acute exercise (interaction effect, p=0.048). These data highlight the resilience of the cerebral circulation in that dCA was well maintained or improved in healthy pregnant women between TM2 and TM3. However, future work addressing the impact of acute and chronic exercise on dCA in women who are at risk for cardiovascular complications during pregnancy is needed.

The Nine Month Stress Test: Pregnancy and Exercise - Similarities and Interactions

Of all physiological systems, the cardiovascular system takes on the most profound adaptation in pregnancy to support fetal growth and development. The adaptations that arise are systemic and involve structural and functional changes that can be observed at the cerebral, central, peripheral, and microvascular beds. This includes, although is not limited to increased heart rate, stroke volume and cardiac output with negligible change to blood pressure, reductions in vascular resistance and cerebral blood flow velocity, systemic artery enlargement, enhanced endothelial function. All of this takes place to accommodate blood volume expansion and ensure adequate fetal and maternal oxygen delivery. In some instances, the demand placed on the vasculature can manifest as cardiovascular maladaptation and thus, cardiovascular complications can arise. Exercise is recommended in pregnancy because of its powerful ability to reduce the incidence and severity of cardiovascular complications in pregnancy. However, the mechanism by which it acts is poorly understood. The first aim of this review is to describe the systemic adaptations that take place in pregnancy. Secondly, this review aims to describe the influence of exercise on these systemic adaptations. It is anticipated that this review can comprehensively capture the extent of knowledge in this area while identifying areas that warrant further investigation.

Longitudinal study of cerebral blood flow regulation during exercise in pregnancy

Cerebrovascular adaptation to pregnancy is poorly understood. We sought to assess cerebrovascular regulation in response to visual stimulation, hypercapnia and exercise across the three trimesters of pregnancy. Using transcranial Doppler (TCD) ultrasound, middle and posterior cerebral artery mean blood velocities (MCAv_mean and PCAv_mean) were measured continuously at rest and in response to (1) visual stimulation to assess neurovascular coupling (NVC); (2) a modified Duffin hyperoxic CO₂ rebreathe test, and (3) an incremental cycling exercise test to volitional fatigue in non-pregnant (n = 26; NP) and pregnant women (first trimester [n = 13; TM1], second trimester [n = 21; TM2], and third trimester [n = 20; TM3]) in total 47 women. At rest, MCAv_mean and P_ETCO₂ were lower in TM2 compared to NP. PCAv_mean was lower in TM2 but not TM1 or TM3 compared to NP. Cerebrovascular reactivity in MCAv_mean and PCAv_mean during the hypercapnic rebreathing test was not different between pregnant and non-pregnant women. MCAv_mean continued to increase over the second half of the exercise test in TM2 and TM3, while it decreased in NP due to differences in ΔP_ETCO₂ between groups. Pregnant women experienced a delayed decrease in MCAv_mean in response to maximal exercise compared to non-pregnant controls which was explained by CO₂ reactivity and P_ETCO₂ level.

Aerobic Exercise Preconception and During Pregnancy Enhances Oxidative Capacity in the Hindlimb Muscles of Mice Offspring

Liu, J, Lee, I, Feng, H-Z, Galen, SS, Hüttemann, PP, Perkins, GA, Jin, J-P, Hüttemann, M, and Malek, MH. Aerobic exercise preconception and during pregnancy enhances oxidative capacity in the hindlimb muscles of mice offspring. J Strength Cond Res 32(5): 1391-1403, 2018-Little is known about the effect of maternal exercise on offspring skeletal muscle health. The purpose of this study, therefore, was to determine whether maternal exercise (preconception and during pregnancy) alters offspring skeletal muscle capillarity and mitochondrial biogenesis. We hypothesized that offspring from exercised dams would have higher capillarity and mitochondrial density in the hindlimb muscles compared with offspring from sedentary dams. Female mice in the exercise condition had access to a running wheel in their individual cage 30 days before mating and throughout pregnancy, whereas the sedentary group did not have access to the running wheel before mating and during pregnancy. Male offspring from both groups were killed when they were 2 months old, and their tissues were analyzed. The results indicated no significant (p > 0.05) mean differences for capillarity density, capillarity-to-fiber ratio, or regulators of angiogenesis such as VEGF-A and TSP-1. Compared with offspring from sedentary dams, however, offspring from exercised dams had an increase in protein expression of myosin heavy chain type I (MHC I) (∼134%; p = 0.009), but no change in MHC II. For mitochondrial morphology, we found significant (all p-values ≤ 0.0124) increases in mitochondrial volume density (∼55%) and length (∼18%) as well as mitochondria per unit area (∼19%). For mitochondrial enzymes, there were also significant (all p-values ≤ 0.0058) increases in basal citrate synthase (∼79%) and cytochrome c oxidase activity (∼67%) in the nonoxidative muscle fibers as well as increases in basal (ATP) (∼52%). Last, there were also significant mean differences in protein expression for regulators (FIS1, Lon protease, and TFAM) of mitochondrial biogenesis. These findings suggest that maternal exercise before and during pregnancy enhances offspring skeletal muscle mitochondria functionality, but not capillarity.

Assessment of maternal cerebral blood flow velocity by transcranial Doppler ultrasound before delivery and in the early postpartum period

OBJECTIVE

This prospective observational study aimed to identify the effects of labor on cerebral hemodynamics by measuring the middle cerebral artery (MCA) blood flow velocity by transcranial Doppler ultrasound (TCD), and the related factors just before delivery and within the 24 h after delivery.

METHODS

The study included 35 healthy pregnant women with a gestational age of >37 weeks who were in labor and a control group including healthy, age-matched, nonpregnant women (n = 24). Demographic characteristics and significant clinical information of pregnant women were recorded. The MCA blood flow velocity was assessed by TCD just before and within 24 h after delivery. The parameters assessed by TCD were mean cerebral blood flow velocity (MCBFV), peak systolic velocity (PSV), pulsatility index (PI), resistance index (RI), and systolic/diastolic ratio.

RESULTS

There was no significant difference between the pregnant and nonpregnant women regarding age (27 ± 5 years versus 28 ± 7 years; p = .751). The MCBFV, PSV, PI, and RI showed a significant increase within the 24 h after delivery as compared with those before delivery. Comparison of the pregnant women with the control group in terms of the values of all parameters related to the MCA blood flow velocity revealed that the values that were significantly low before delivery reached to the level of the control group after delivery Conclusion: The findings of this study demonstrated that the blood flow velocity of the MCA decreased during the late pregnancy period and increased in the early postpartum period to the level similar to that of the nonpregnant group.

The influence of prenatal exercise and pre-eclampsia on maternal vascular function

During healthy pregnancy, the cardiovascular system undergoes diverse adaptations to support adequate transfer of oxygen and nutrients from mother to fetus. In order to accommodate the large expansion of blood volume and associated cardiac output, the structure, mechanics, and function of the arteries are altered. Specifically, in healthy pregnancy there is a remodeling of arteries (increased angiogenesis and vasodilation), a generalized reduction in arterial stiffness (increased compliance), and an enhanced endothelial function. The development of pregnancy complications, specifically pre-eclampsia, is associated with poor placentation (decreased angiogenesis), increased arterial stiffness, and vascular dysfunction (reduced endothelial function). Many of the positive adaptations that occur in healthy pregnancy are enhanced in response to chronic exercise. Specifically, placental angiogenesis and endothelial function have been shown to improve to a greater extent in women who are active during their pregnancy compared with those who are not. Prenatal exercise may be important in helping to reduce the risk of vascular dysfunction in pregnancy. However, our knowledge of the vascular adaptations resulting from maternal exercise is limited. This review highlights maternal vascular adaptations occurring during healthy pregnancy, and contrasts the vascular maladaptation associated with pre-eclampsia. Finally, we discuss the role of prenatal exercise on vascular function in the potential prevention of vascular complications associated with pre-eclampsia.