Cerebral blood flow is increased during controlled ovarian stimulation

Hormonal influences on cerebral aneurysms: unraveling the complex connections

INTRODUCTION

Intracranial aneurysms (IAs) occur in 3-5% of the general population and are characterized by localized structural deterioration of the arterial wall with loss of internal elastic lamina and disruption of the media. The risk of incidence and rupture of aneurysms depends on age, sex, ethnicity, and other different factors, indicating the influence of genetic and environmental factors. When an aneurysm ruptures, there is an estimated 20% mortality rate, along with an added 30-40% morbidity in survivors. The alterations in hormonal levels can influence IAs, while the rupture of an aneurysm can have various impacts on endocrine pathways and affect their outcome.

AREA COVERED

This review explores the reciprocal relationship between endocrinological changes (estrogen, growth hormone, and thyroid hormones) and IAs, as well as the effects of aneurysm ruptures on endocrine fluctuations.

EXPERT OPINION

Based on the data presented in this paper, we recommend further exploration into the influence of hormones on aneurysm formation and rupture. Additionally, we propose conducting endocrine assessments for patients who have experienced a rupture of IAs. Monitoring hormonal changes in patients with IAs could serve as a potential risk factor for rupture, leading to interventions in the approach to managing IAs.

Sex-Specific Cerebral Blood Flow Alterations in Youth Operated for Congenital Heart Disease

Background Lower cerebral blood flow (CBF) has previously been documented preoperatively in neonates with congenital heart disease (CHD). However, it remains unclear if these CBF deficits persist over the life span of CHD survivors following heart surgery. When exploring this question, it is critical to consider the sex differences in CBF that emerge during adolescence. Therefore, this study aimed to compare global and regional CBF between postpubertal youth with CHD and healthy peers and examine if such alterations are related to sex. Methods and Results Youth aged 16 to 24 years who underwent open heart surgery for complex CHD during infancy and age- and sex-matched controls completed brain magnetic resonance imaging, including T1-weighted and pseudo-continuous arterial spin labeling acquisitions. Global gray matter CBF and regional CBF in 9 bilateral gray matter regions were quantified for each participant. Compared with female controls (N=27), female participants with CHD (N=25) presented with lower global and regional CBF. In contrast, there were no differences in CBF between male controls (N=18) and males with CHD (N=17). Concurrently, female controls had higher global and regional CBF compared with male controls, with no differences in CBF between female and male participants with CHD. CBF was lower in individuals with a Fontan circulation. Conclusions This study provides evidence of altered CBF in postpubertal female participants with CHD despite undergoing surgical intervention during infancy. Alterations to CBF could have implications for later cognitive decline, neurodegeneration, and cerebrovascular disease in women with CHD.

Reproducibility and diurnal variation in middle cerebral artery blood velocity in healthy humans

NEW FINDINGS

What is the central question of this study? We sought to establish between-day reproducibility in estimates of middle cerebral artery blood velocity (MCAv) and cerebrovascular reactivity (CVR) in young, healthy male and female adults in tightly controlled experimental conditions. What is the main finding and its importance? Measures of MCAv assessed during morning, afternoon and evening hours are reproducible between days. There is diurnal variation in CVR, with values being highest during the evening compared with the morning. Greater diurnal variation in CVR is associated with more efficient sleep and greater nocturnal blood pressure dipping. These data enhance our understanding of modulators of MCAv and CVR.

ABSTRACT

Transcranial Doppler (TCD) is used to assess cerebral blood velocity (CBV) and cerebrovascular reactivity (CVR). Assessments of TCD reproducibility are limited, and few include multiple within-day measurements. We sought to establish reproducibility of CBV and CVR in healthy adults during three time periods (morning, afternoon and evening). We hypothesized that CBV and CVR measured at the same time of day are reproducible between days. We also hypothesized that CBV and CVR exhibit diurnal variation, with measurements being higher in the evening compared with morning/afternoon hours. Twelve adults [six male and six female, 27 years (95% CI, 22-31 years)] completed three measurements (morning, afternoon and evening) on two separate days in controlled conditions (e.g., meals, activity and sleep). Middle cerebral artery blood velocity (MCAv, TCD) was measured continuously at rest and during two CVR tests (end-expiratory apnoea and carbogen inhalation). Intraclass correlation coefficients for resting MCAv showed moderate to good reproducibility, which did not differ between morning, afternoon and evening (0.87, 0.56 and 0.67, respectively; P > 0.05). Intraclass correlation coefficients for peak MCAv during apnoea (0.80, 0.46 and 0.65, respectively; P > 0.05) and minute 2 of carbogen inhalation (0.81, 0.74 and 0.73, respectively; P > 0.05) were also not different from morning compared with afternoon/evening. Time of day had no effect on resting MCAv (F = 0.69, P = 0.51, ƞp 2  = 0.06) or the peak response to apnoea (F = 1.00, P = 0.39, ƞp 2  = 0.08); however, peak MCAv during carbogen breathing exhibited diurnal variation, with highest values in the evening (F = 3.41, P = 0.05, ƞp 2  = 0.24). Measures of CBV and CVR assessed via TCD during morning, afternoon and evening hours are reproducible between days. There is diurnal variation in the MCAv response to carbogen exposure, with CVR being highest during evening compared with morning hours.

Cerebral autoregulation across the menstrual cycle in eumenorrheic women

There is emerging evidence that ovarian hormones play a significant role in the lower stroke incidence observed in pre‐menopausal women compared with men. However, the role of ovarian hormones in cerebrovascular regulation remains to be elucidated. We examined the blood pressure‐cerebral blood flow relationship (cerebral autoregulation) across the menstrual cycle in eumenorrheic women (n = 12; mean ± SD: age, 31 ± 7 years). Participants completed sit‐to‐stand and Valsalva maneuvers (VM, mouth pressure of 40 mmHg for 15 s) during the early follicular (EF), late follicular (LF), and mid‐luteal (ML) menstrual cycle phases, confirmed by serum measurement of progesterone and 17β‐estradiol. Middle cerebral artery blood velocity (MCAv), arterial blood pressure and partial pressure of end‐tidal carbon dioxide were measured. Cerebral autoregulation was assessed by transfer function analysis during spontaneous blood pressure oscillations, rate of regulation (RoR) during sit‐to‐stand maneuvers, and Tieck’s autoregulatory index during VM phases II and IV (AI‐II and AI‐IV, respectively). Resting mean MCAv (MCAv_mean), blood pressure, and cerebral autoregulation were unchanged across the menstrual cycle (all p > 0.12). RoR tended to be different (EF, 0.25 ± 0.06; LF; 0.19 ± 0.04; ML, 0.18 ± 0.12 sec⁻¹; p = 0.07) and demonstrated a negative relationship with 17β‐estradiol (R² = 0.26, p = 0.02). No changes in AI‐II (EF, 1.95 ± 1.20; LF, 1.67 ± 0.77 and ML, 1.20 ± 0.55) or AI‐IV (EF, 1.35 ± 0.21; LF, 1.27 ± 0.26 and ML, 1.20 ± 0.2) were observed (p = 0.25 and 0.37, respectively). Although, a significant interaction effect (p = 0.02) was observed for the VM MCAv_mean response. These data indicate that the menstrual cycle has limited impact on cerebrovascular autoregulation, but individual differences should be considered.

The regional effect of serum hormone levels on cerebral blood flow in healthy nonpregnant women

Sex hormones estrogen (EST) and progesterone (PROG) have received increased attention for their important physiological action outside of reproduction. While studies have shown that EST and PROG have significant impacts on brain function, their impact on the cerebrovascular system in humans remains largely unknown. To address this, we used a multi-modal magnetic resonance imaging (MRI) approach to investigate the link between serum hormones in the follicular phase and luteal phase of the menstrual cycle (MC) with measures of cerebrovascular function (cerebral blood flow [CBF]) and structure (intracranial artery diameter). Fourteen naturally cycling women were recruited and assessed at two-time points of their MC. CBF was derived from pseudo-continuous arterial spin labeling while diameters of the internal carotid and basilar artery was assessed using time of flight magnetic resonance angiography, blood samples were performed after the MRI. Results show that PROG and EST had opposing and spatially distinct effects on CBF: PROG correlated negatively with CBF in anterior brain regions (r = -.86, p < .01), while EST correlations were positive, yet weak and most prominent in posterior areas (r = .78, p < .01). No significant correlations between either hormone or intracranial artery diameter were observed. These results show that EST and PROG have opposing and regionally distinct effects on CBF and that this relationship is likely not due to interactions with large intracranial arteries. Considering that CBF in healthy women appears tightly linked to their current hormonal state, future studies should consider assessing MC-related hormone fluctuations in the design of functional MRI studies in this population.

Sex moderations in the relationship between aortic stiffness, cognition, and cerebrovascular reactivity in healthy older adults

It is well established that sex differences exist in the manifestation of vascular diseases. Arterial stiffness (AS) has been associated with changes in cerebrovascular reactivity (CVR) and cognitive decline in aging. Specifically, older adults with increased AS show a decline on executive function (EF) tasks. Interestingly, the relationship between AS and CVR is more complex, where some studies show decreased CVR with increased AS, and others demonstrate preserved CVR despite higher AS. Here, we investigated the possible role of sex on these hemodynamic relationships. Acquisitions were completed in 48 older adults. Pseudo-continuous arterial spin labeling (pCASL) data were collected during a hypercapnia challenge. Aortic pulse wave velocity (PWV) data was acquired using cine phase contrast velocity series. Cognitive function was assessed with a comprehensive neuropsychological battery, and a composite score for EF was calculated using four cognitive tests from the neuropsychological battery. A moderation model test revealed that sex moderated the relationship between PWV and CVR and PWV and EF, but not between CVR and EF. Together, our results indicate that the relationships between central stiffness, cerebral hemodynamics and cognition are in part mediated by sex.

Cerebrovascular Function in Hormonal Migraine: An Exploratory Study

Background: Migraineurs, particularly young premenopausal women, are at increased risk of cerebrovascular disease; however, there is currently limited evidence as to whether hormonal migraine is associated with poor cerebrovascular function.

Objectives: The objectives of this study were to: (1) investigate the potential association of cerebrovascular function with hormonal migraine and (2) determine whether abnormalities of cerebrovascular function in hormonal migraineurs are associated with migraine-related disability and/or quality of life.

Method: A cross-sectional study was undertaken in 50 hormonal migraineurs (mean age: 38.7 ± 1.2 years) and 29 controls (mean age: 35.6 ± 1.8 years). Data were collected at a single point in time from all participants during the inter-ictal period when they were free from migraine and not menstruating. Transcranial Doppler ultrasound was used to measure resting blood flow velocity and cerebrovascular responsiveness (CVR) to hypercapnia and cognitive stimulation (neurovascular coupling) in the left and right middle cerebral artery (MCA). Additionally, hormonal migraineurs completed three questionnaires to assess migraine-related disability and quality of life as well as migraine frequency and intensity: Headache Impact Test-6™, Migraine-Specific Quality of Life and Migraine Disability Assessment.

Results: Hormonal migraineurs had lower resting mean blood flow velocity (MBFV) (P = 0.009) and neurovascular coupling during cognitive stimulation (P = 0.010) in the left MCA than controls. No such differences were found in the right MCA. Additionally, heart rate (P = 0.004) was higher in hormonal migraineurs than controls. However, no differences in CVR to hypercapnia were found between hormonal migraineurs and controls. Multi-variate analysis revealed age to be a significant (P = 0.012) predictor of MBFV in the left MCA. Negative correlations between headache frequency and CVR to hypercapnia in the left (P = 0.026) and right MCA (P = 0.044) were found. Additionally, negative correlations between neurovascular coupling during the 2-Back 1.5 s task in the right MCA and the MSQoL emotional (P = 0.013) and role-function restrictive (P = 0.039) domains were found.

Conclusions: This is the first study to show that hormonal migraineurs have poorer cerebrovascular function, as represented by lower resting MBFV and impaired neurovascular coupling in the left MCA. Future studies should investigate whether improving cerebrovascular function can prevent hormonal migraine and improve quality of life.

Clinical Trial Registration: ACTRN12618001230246.

A Systematic Review and Meta-Analysis Examining Whether Changing Ovarian Sex Steroid Hormone Levels Influence Cerebrovascular Function

Sex differences in cerebrovascular disease rates indicate a possible role for ovarian sex steroid hormones in cerebrovascular function. To synthesise and identify knowledge gaps, a systematic review and meta-analysis was conducted to assess how ovarian sex steroid hormone changes across the lifespan affect cerebrovascular function in women. Three databases (EMBASE, MEDLINE and Web of Science) were systematically searched for studies on adult cerebrovascular function and ovarian sex steroid hormones. Forty-five studies met pre-defined inclusion criteria. Studied hormone groups included hormone replacement therapy (HRT; n = 17), pregnancy (n = 12), menstrual cycle (n = 7), menopause (n = 5), oral contraception (n = 2), and ovarian hyperstimulation (n = 2). Outcome measures included pulsatility index (PI), cerebral blood flow/velocity (CBF), resistance index (RI), cerebral autoregulation, and cerebrovascular reactivity. Meta-analysis was carried out on HRT studies. PI significantly decreased [−0.05, 95% CI: (−0.10, −0.01); p = 0.01] in post-menopausal women undergoing HRT compared to post-menopausal women who were not, though there was considerable heterogeneity (I² = 96.8%). No effects of HRT were seen in CBF (p = 0.24) or RI (p = 0.77). This review indicates that HRT improves PI in post-menopausal women. However, there remains insufficient evidence to determine how changing ovarian sex steroid hormone levels affects cerebrovascular function in women during other hormonal phases (e.g., pregnancy, oral contraception).

Cerebral blood flow, cerebrovascular reactivity and their influence on ventilatory sensitivity

NEW FINDINGS

What is the topic of this review? Cerebrovascular reactivity to CO₂ , which is a principal factor in determining ventilatory responses to CO₂ through the role reactivity plays in determining cerebral extra- and intracellular pH. What advances does it highlight? Recent animal evidence suggests central chemoreceptor vasculature may demonstrate regionally heterogeneous cerebrovascular reactivity to CO₂ , potentially as a protective mechanism against excessive CO₂ washout from the central chemoreceptors, thereby allowing ventilation to reflect the systemic acid-base balance needs (respiratory changes in P aC O 2 ) rather than solely the cerebral needs. Ventilation per se does not influence cerebrovascular reactivity independent of changes in P aC O 2 .

ABSTRACT

Alveolar ventilation and cerebral blood flow are both predominantly regulated by arterial blood gases, especially arterial P C O 2 , and so are intricately entwined. In this review, the fundamental mechanisms underlying cerebrovascular reactivity and central chemoreceptor control of breathing are covered. We discuss the interaction of cerebral blood flow and its reactivity with the control of ventilation and ventilatory responsiveness to changes in P C O 2 , as well as the lack of influence of ventilation itself on cerebrovascular reactivity. We briefly summarize the effects of arterial hypoxaemia on the relationship between ventilatory and cerebrovascular response to both P C O 2 and P O 2 . We then highlight key methodological considerations regarding the interaction of reactivity and ventilatory sensitivity, including the following: regional heterogeneity of cerebrovascular reactivity; a pharmacological approach for the reduction of cerebral blood flow; reactivity assessment techniques; the influence of mean arterial blood pressure; and sex-related differences. Finally, we discuss ventilatory and cerebrovascular control in the context of high altitude and congestive heart failure. Future research directions and pertinent questions of interest are highlighted throughout.

Profiling cerebrovascular function in migraine: A systematic review and meta-analysis

Previous studies have investigated whether migraine is a circulatory disorder, as migraineurs are at heightened risk of cerebrovascular disease. However, in most cases, systemic vascular function was evaluated, which may not reflect abnormalities in the cerebral circulation. Therefore, we aimed to determine whether cerebrovascular function differs between migraineurs and controls. A systematic literature search was conducted across three electronic databases to search for studies that compared cerebrovascular function in migraineurs to controls. Where applicable, meta-analyses were used to determine standardised mean differences (SMD) between migraineurs and controls. Seventy articles were identified, 40 of which contained quantitative data. Meta-analyses showed pulsatility index (PI) was higher (SMD = 0.23; 95%CI = 0.05 to 0.42, P = 0.01) and cerebrovascular responsiveness (CVR) to hypercapnia was lower (SMD=-0.34; 95%CI=-0.67 to -0.01, P = 0.04) in the posterior circulation of migraineurs, particularly those without aura. The meta-analyses also indicated that migraineurs have higher resting mean blood flow velocity in both anterior (SMD = 0.14; 95%CI = 0.05 to 0.23, P = 0.003) and posterior circulations (SMD = 0.20; 95%CI = 0.05 to 0.34, P = 0.007). Compared to healthy controls, migraineurs have altered cerebrovascular function, evidenced by elevated PI (representing arterial stiffness) and impaired CVR to hypercapnia (representing cerebral vasodilator function). Future studies should investigate whether improvement of cerebrovascular function is able to alleviate migraine.

Awake endovascular coiling of a dissected intracranial aneurysm in a third-trimester twin pregnancy: A case report

RATIONALE

Subarachnoid hemorrhages (SAHs) from ruptured intracranial aneurysms are very rare during pregnancy. Management of ruptured intracranial aneurysms with SAH in pregnancy is often challenging because of the risks to the fetus and the mother. We present the first successful awake endovascular coiling of a dissected intracranial aneurysm in a third trimester twin pregnancy.

PATIENT CONCERNS

A 28 years' old pregnant woman was admitted at the obstetric department of our hospital on account of very severe headaches associated with nausea and vomiting.

DIAGNOSIS

Emergency obstetric ultrasound scan done confirmed 32 weeks' twin gestation, whereas magnetic resonance imaging established hemorrhage in the suprasellar cistern and the subarachnoid space. Magnetic resonance angiography revealed a dissected aneurysm in the ophthalmic segment of the left internal carotid artery.

INTERVENTIONS

Awake cerebral angiography as well as embolization of the aneurysm with coils was done via the transarterial route and the twins were delivered via caesarean section at 37 weeks' gestation.

OUTCOMES

Two years' follow-up indicated no complications and children as well as their mother are healthy.

LESIONS

Awake endovascular coiling was very beneficial in our case because we avoided general anesthesia and the use of osmotic diuretics which are potentially hazardous during pregnancy.

Cardiorespiratory fitness is associated with increased middle cerebral arterial compliance and decreased cerebral blood flow in young healthy adults: A pulsed ASL MRI study

Cardiorespiratory fitness is thought to have beneficial effects on systemic vascular health, in part, by decreasing arterial stiffness. However, in the absence of non-invasive methods, it remains unknown whether this effect extends to the cerebrovasculature. The present study uses a novel pulsed arterial spin labelling (pASL) technique to explore the relationship between cardiorespiratory fitness and arterial compliance of the middle cerebral arteries (MCAC). Other markers of cerebrovascular health, including resting cerebral blood flow (CBF) and cerebrovascular reactivity to CO2 (CVRCO2) were also investigated. Eleven healthy males aged 21 ± 2 years with varying levels of cardiorespiratory fitness (maximal oxygen uptake (V · O2MAX) 38-76 ml/min/kg) underwent MRI scanning at 3 Tesla. Higher V · O2MAX was associated with greater MCAC (R2 = 0.64, p < 0.01) and lower resting grey matter CBF (R2 = 0.75, p < 0.01). However, V · O2MAX was not predictive of global grey matter BOLD-based CVR (R2 = 0.47, p = 0.17) or CBF-based CVR (R2 = 0.19, p = 0.21). The current experiment builds upon the established benefits of exercise on arterial compliance in the systemic vasculature, by showing that increased cardiorespiratory fitness is associated with greater cerebral arterial compliance in early adulthood.

A Systematic Review of Intracranial Aneurysms in the Pregnant Patient - A Clinical Conundrum

Hemodynamic and hormonal changes during pregnancy can increase rates of formation, growth, and rupture of intracranial aneurysms (IA), and the increased incidence of subarachnoid hemorrhage (SA) in pregnant patients represents a risk to both mother and fetus. Despite this, management and treatment guidelines have not been defined for this patient population. In most instances, treatment decisions are made on a case-by-case basis with varying degrees of input from subspecialists. Important considerations, such as aneurysm location, morphology, size, growth pattern, and patient characteristics have not been presented in a management algorithm in the context of the pregnant patient. Given limited and controversial literature describing management of IAs in pregnant patients, we performed a systematic literature review. We then describe our multidisciplinary team approach and provide analysis of existing literature to provide guidelines for the management of the pregnant patient with an IA. A systematic review was undertaken to identify studies describing the management of IAs in the pregnant patient using the PubMed database. Overall maternal and fetal morbidity and mortality rates were determined. Data was analyzed for 1537 patients, including 1115 (73%) pregnant with ruptured intracranial aneurysms. In most cases, these aneurysms were managed conservatively (77%; 781/1013); however, when treatment was provided, surgical clipping was the most common modality (15%; 149/1013). Overall maternal outcomes were reported for 934 cases with morbidity and mortality rates of 5% (42/934) and 21% (194/934), respectively. Overall fetal outcomes were reported for 114 cases with morbidity and mortality rates of 10% (12/119) and 8% (9/119), respectively. Pregnancy-associated physiological changes likely elevate the risk of intracranial aneurysm formation, growth, and rupture. Treatment for aneurysms and SAs is safe and effective during pregnancy when risks are properly mitigated. Due to the complexity of care, such patients should be treated using a collaborative, interdisciplinary approach by a multidisciplinary team.

Role of pregnancy and female sex steroids on aneurysm formation, growth, and rupture: a systematic review of the literature

OBJECTIVE

Women have been shown to have a higher risk of cerebral aneurysm formation, growth, and rupture than men. The authors present a review of the recently published neurosurgical literature that studies the role of pregnancy and female sex steroids, to provide a conceptual framework with which to understand the various risk factors associated with cerebral aneurysms in women at different stages in their lives.

METHODS

The PubMed database was searched for "("intracranial" OR "cerebral") AND "aneurysm" AND ("pregnancy" OR "estrogen" OR "progesterone")" between January 1980 and February 2019. A total of 392 articles were initially identified, and after applying inclusion and exclusion criteria, 20 papers were selected for review and analysis. These papers were then divided into two categories: 1) epidemiological studies about the formation, growth, rupture, and management of cerebral aneurysms in pregnancy; and 2) investigations on female sex steroids and cerebral aneurysms (animal studies and epidemiological studies).

RESULTS

The 20 articles presented in this study include 7 epidemiological articles on pregnancy and cerebral aneurysms, 3 articles reporting case series of cerebral aneurysms treated by endovascular therapies in pregnancy, 3 epidemiological articles reporting the relationship between female sex steroids and cerebral aneurysms through retrospective case-control studies, and 7 experimental studies using animal and/or cell models to understand the relationship between female sex steroids and cerebral aneurysms. The studies in this review report similar risk of aneurysm rupture in pregnant women compared to the general population. Most ruptured aneurysms in pregnancy occur during the 3rd trimester, and most pregnant women who present with cerebral aneurysm have caesarean section deliveries. Endovascular treatment of cerebral aneurysms in pregnancy is shown to provide a new and safe form of therapy for these cases. Epidemiological studies of postmenopausal women show that estrogen hormone therapy and later age at menopause are associated with a lower risk of cerebral aneurysm than in matched controls. Experimental studies in animal models corroborate this epidemiological finding; estrogen deficiency causes endothelial dysfunction and inflammation, which may predispose to the formation and rupture of cerebral aneurysms, while exogenous estrogen treatment in this population may lower this risk.

CONCLUSIONS

The aim of this work is to equip the neurosurgical and obstetrical/gynecological readership with the tools to better understand, critique, and apply findings from research on sex differences in cerebral aneurysms.

Pubertal Hormonal Changes and the Autonomic Nervous System: Potential Role in Pediatric Orthostatic Intolerance

Puberty is initiated by hormonal changes in the adolescent body that trigger physical and behavioral changes to reach adult maturation. As these changes occur, some adolescents experience concerning pubertal symptoms that are associated with dysfunction of the autonomic nervous system (ANS). Vasovagal syncope (VVS) and Postural Orthostatic Tachycardia Syndrome (POTS) are common disorders of the ANS associated with puberty that are related to orthostatic intolerance and share similar symptoms. Compared to young males, young females have decreased orthostatic tolerance and a higher incidence of VVS and POTS. As puberty is linked to changes in specific sex and non-sex hormones, and hormonal therapy sometimes improves orthostatic symptoms in female VVS patients, it is possible that pubertal hormones play a role in the increased susceptibility of young females to autonomic dysfunction. The purpose of this paper is to review the key hormonal changes associated with female puberty, their effects on the ANS, and their potential role in predisposing some adolescent females to cardiovascular autonomic dysfunctions such as VVS and POTS. Increases in pubertal hormones such as estrogen, thyroid hormones, growth hormone, insulin, and insulin-like growth factor-1 promote vasodilatation and decrease blood volume. This may be exacerbated by higher levels of progesterone, which suppresses catecholamine secretion and sympathetic outflow. Abnormal heart rate increases in POTS patients may be exacerbated by pubertal increases in leptin, insulin, and thyroid hormones acting to increase sympathetic nervous system activity and/or catecholamine levels. Given the coincidental timing of female pubertal hormone surges and adolescent onset of VVS and POTS in young women, coupled with the known roles of these hormones in modulating cardiovascular homeostasis, it is likely that female pubertal hormones play a role in predisposing females to VVS and POTS during puberty. Further research is necessary to confirm the effects of female pubertal hormones on autonomic function, and their role in pubertal autonomic disorders such as VVS and POTS, in order to inform the treatment and management of these debilitating disorders.

Evidence the U.S. autism epidemic initiated by acetaminophen (Tylenol) is aggravated by oral antibiotic amoxicillin/clavulanate (Augmentin) and now exponentially by herbicide glyphosate (Roundup)

Because certain hereditary diseases show autistic behavior, and autism often runs in families, researchers seek genes underlying the pathophysiology of autism, thus core behaviors. Other researchers argue environmental factors are decisive, citing compelling evidence of an autism epidemic in the United States beginning about 1980. Recognition that environmental factors influence gene expression led to synthesis of these views - an 'epigenetic epidemic' provoked by pervasive environmental agents altering expression of vulnerable genes, inducing characteristic autistic biochemistries in many mothers and infants. Two toxins most implicated in the U.S. autism epidemic are analgesic/antipyretic acetaminophen (Tylenol) and oral antibiotic amoxicillin/clavulanate (Augmentin). Recently herbicide glyphosate (Roundup) was exponentially implicated. What do these toxins have in common? Acetaminophen depletes sulfate and glutathione required to detoxify it. Oral antibiotics kill and glyphosate inhibits intestinal bacteria that synthesize methionine (precursor of sulfate and glutathione, and required to methylate DNA), bacteria that synthesize tryptophan (sole precursor of neuroinhibitor serotonin), and bacteria that restrain ammonia-generating anaerobes. Sulfate plus glutathione normally sulfate fetal adrenal androgen dehydroepiandrosterone to DHEAS - major precursor of placental/postnatal estrogens. Glyphosate (and heavy metals) also inhibit aromatase that turns androgens to estrogens. Placental/postnatal estrogens dehydrate/mature brain myelin sheaths, mature corpus callosum and left hemisphere preferentially, dilate brain blood vessels, and elevate brain serotonin and oxytocin. Stress-induced weak androgens and estrogen depletion coherently explain white matter asymmetry and dysconnection in autism, extreme male brain, low brain blood flow, hyperexcitability, social anxiety, and insufficient maternal oxytocin at birth to limit fetal brain chloride/water and mature GABA.

Elevated Amygdala Perfusion Mediates Developmental Sex Differences in Trait Anxiety

BACKGROUND

Adolescence is a critical period for emotional maturation and is a time when clinically significant symptoms of anxiety and depression increase, particularly in females. However, few studies relate developmental differences in symptoms of anxiety and depression to brain development. Cerebral blood flow is one brain phenotype that is known to have marked developmental sex differences.

METHODS

We investigated whether developmental sex differences in cerebral blood flow mediated sex differences in anxiety and depression symptoms by capitalizing on a large sample of 875 youths who completed cross-sectional imaging as part of the Philadelphia Neurodevelopmental Cohort. Perfusion was quantified on a voxelwise basis using arterial spin-labeled magnetic resonance imaging at 3T. Perfusion images were related to trait and state anxiety using general additive models with penalized splines, while controlling for gray matter density on a voxelwise basis. Clusters found to be related to anxiety were evaluated for interactions with age, sex, and puberty.

RESULTS

Trait anxiety was associated with elevated perfusion in a network of regions including the amygdala, anterior insula, and fusiform cortex, even after accounting for prescan state anxiety. Notably, these relationships strengthened with age and the transition through puberty. Moreover, higher trait anxiety in postpubertal females was mediated by elevated perfusion of the left amygdala.

CONCLUSIONS

Taken together, these results demonstrate that differences in the evolution of cerebral perfusion during adolescence may be a critical element of the affective neurobiological characteristics underlying sex differences in anxiety and mood symptoms.

Cerebral blood flow regulation in women across menstrual phase: differential contribution of cyclooxygenase to basal, hypoxic, and hypercapnic vascular tone

In healthy young women, basal cerebral blood flow (CBF) and cerebrovascular reactivity may change across the menstrual cycle, but mechanisms remain untested. When compared with the early follicular phase of the menstrual cycle, we hypothesized women in late follicular phase would exhibit: 1) greater basal CBF, 2) greater hypercapnic increases in CBF, 3) greater hypoxic increases in CBF, and 4) increased cyclooxygenase (COX) signaling. We measured middle cerebral artery velocity (MCAv, transcranial Doppler ultrasound) in 11 healthy women (23 ± 1 yr) during rest, hypoxia, and hypercapnia. Subjects completed four visits: two during the early follicular (∼day 3) and two during the late follicular (∼day 14) phases of the menstrual cycle, with and without COX inhibition (oral indomethacin). Isocapnic hypoxia elicited an SPO2 = 90% and SPO2 = 80% for 5 min each. Separately, hypercapnia increased end-tidal CO2 10 mmHg above baseline. Cerebral vascular conductance index (CVCi = MCAv/MABP·100, where MABP is mean arterial blood pressure) was calculated and a positive change reflected vasodilation (ΔCVCi). Basal CVCi was greater in the late follicular phase (P < 0.001). Indomethacin decreased basal CVCi (∼37%) and abolished the phase difference (P < 0.001). Hypoxic ΔCVCi was similar between phases and unaffected by indomethacin. Hypercapnic ΔCVCi was similar between phases, and indomethacin decreased hypercapnic ΔCVCi (∼68%; P < 0.001) similarly between phases. In summary, while neither hypercapnic nor hypoxic vasodilation is altered by menstrual phase, increased basal CBF in the late follicular phase is fully explained by a greater contribution of COX. These data provide new mechanistic insight into anterior CBF regulation across menstrual phases and contribute to our understanding of CBF regulation in women.

Effects of Steroid Hormones on Sex Differences in Cerebral Perfusion

Sex differences in the brain appear to play an important role in the prevalence and progression of various neuropsychiatric disorders, but to date little is known about the cerebral mechanisms underlying these differences. One widely reported finding is that women demonstrate higher cerebral perfusion than men, but the underlying cause of this difference in perfusion is not known. This study investigated the putative role of steroid hormones such as oestradiol, testosterone, and dehydroepiandrosterone sulphate (DHEAS) as underlying factors influencing cerebral perfusion. We acquired arterial spin labelling perfusion images of 36 healthy adult subjects (16 men, 20 women). Analyses on average whole brain perfusion levels included a multiple regression analysis to test for the relative impact of each hormone on the global perfusion. Additionally, voxel-based analyses were performed to investigate the sex difference in regional perfusion as well as the correlations between local perfusion and serum oestradiol, testosterone, and DHEAS concentrations. Our results replicated the known sex difference in perfusion, with women showing significantly higher global and regional perfusion. For the global perfusion, DHEAS was the only significant predictor amongst the steroid hormones, showing a strong negative correlation with cerebral perfusion. The voxel-based analyses revealed modest sex-dependent correlations between local perfusion and testosterone, in addition to a strong modulatory effect of DHEAS in cortical, subcortical, and cerebellar regions. We conclude that DHEAS in particular may play an important role as an underlying factor driving the difference in cerebral perfusion between men and women.

Cerebrovascular regulation in men and women: stimulus-specific role of cyclooxygenase

Greater cerebral artery vasodilation mediated by cyclooxygenase (COX) in female animals is unexplored in humans. We hypothesized that young, healthy women would exhibit greater basal cerebral blood flow (CBF) and greater vasodilation during hypoxia or hypercapnia compared to men, mediated by a larger contribution of COX. We measured middle cerebral artery velocity (MCAv, transcranial Doppler ultrasound) in 42 adults (24 women, 18 men; 24 ± 1 years) during two visits, in a double-blind, placebo-controlled design (COX inhibition, 100 mg oral indomethacin, Indo). Women were studied early in the follicular phase of the menstrual cycle (days 1–5). Two levels of isocapnic hypoxia (S_PO₂ = 90% and 80%) were induced for 5-min each. Separately, hypercapnia was induced by increasing end-tidal carbon dioxide (PET_CO2) 10 mmHg above baseline. A positive change in MCAv (ΔMCAv) reflected vasodilation. Basal MCAv was greater in women compared to men (P < 0.01) across all conditions. Indo decreased baseline MCAv (P < 0.01) similarly between sexes. Hypoxia increased MCAv (P < 0.01), but ΔMCAv was not different between sexes. Indo did not alter hypoxic vasodilation in either sex. Hypercapnia increased MCAv (P < 0.01), but ΔMCAv was not different between sexes. Indo elicited a large decrease in hypercapnic vasodilation (P < 0.01) that was similar between sexes. During the early follicular phase, women exhibit greater basal CBF than men, but similar vasodilatory responses to hypoxia and hypercapnia. Moreover, COX is not obligatory for hypoxic vasodilation, but plays a vital and similar role in the regulation of basal CBF (∼30%) and hypercapnic response (∼55%) between sexes.

Impact of puberty on the evolution of cerebral perfusion during adolescence

Puberty is the defining biological process of adolescent development, yet its effects on fundamental properties of brain physiology such as cerebral blood flow (CBF) have never been investigated. Capitalizing on a sample of 922 youths ages 8-22 y imaged using arterial spin labeled MRI as part of the Philadelphia Neurodevelopmental Cohort, we studied normative developmental differences in cerebral perfusion in males and females, as well as specific associations between puberty and CBF. Males and females had conspicuously divergent nonlinear trajectories in CBF evolution with development as modeled by penalized splines. Seventeen brain regions, including hubs of the executive and default mode networks, showed a robust nonlinear age-by-sex interaction that surpassed Bonferroni correction. Notably, within these regions the decline in CBF was similar between males and females in early puberty and only diverged in midpuberty, with CBF actually increasing in females. Taken together, these results delineate sex-specific growth curves for CBF during youth and for the first time to our knowledge link such differential patterns of development to the effects of puberty.

Estrogen and cerebrovascular regulation in menopause

Estrogen (E2), classically viewed as a reproductive steroid hormone, has non-reproductive functions throughout the body including in the brain and vasculature. Studies report diminished neuroprotection with declining E2 levels, corresponding with higher incidence of cerebrovascular and neurological disease. However, the effects of menopausal hormone therapy (MHT) on the cerebral vasculature and brain function remain controversial. This review will focus on evidence of 17β-estradiol actions in the cerebral vasculature, with a particular emphasis on the vasoactive, anti-inflammatory, anti-oxidant, metabolic and molecular properties. Controversies surrounding MHT in relation to cerebrovascular disease and stroke risk will be discussed, particularly the emerging evidence from clinical trials supporting the critical period hypothesis of estrogen protection.

Early, but not late onset estrogen replacement therapy prevents oxidative stress and metabolic alterations caused by ovariectomy

AIMS

The usefulness of estrogen replacement therapy (ERT) in preventing oxidative stress associated with menopause is controversial. We aimed to study if there is a critical time window for effective treatment of the effects of ovariectomy with estrogens at the molecular, metabolic, and cellular level.

RESULTS

Our main finding is that early, but not late onset of ERT prevents an ovariectomy-associated increase in mitochondrial hydrogen peroxide levels, oxidative damage to lipids and proteins, and a decrease in glutathione peroxidase and catalase activity in rats. This may be due to a change in the estrogen receptor (ER) expression profile: ovariectomy increases the ER α/β ratio and immediate estrogen replacement prevents it. Positron emission tomography analysis shows that ovariectomy decreases the brain glucose uptake in vivo and that estrogen administration is beneficial, but only if administered immediately after deprivation. Ovariectomy decreases GLUT-1 and 3 glucose transporters in the brain, and only early onset estrogen administration prevents it. Plasma from rats treated with estrogens immediately after ovariectomy show similar metabolomics profiles as controls.

INNOVATION

We provide molecular basis for the recommendation of early onset ERT and explain its lack of effectiveness if a significant time period elapses after ovariectomy and probably after the onset of menopause.

CONCLUSION

Only early, but not late onset administration of estrogens after ovariectomy has beneficial effects at molecular levels on oxidative stress, brain glucose uptake, and metabolomic profiles.

Changes in maternal posterior and anterior cerebral artery flow velocity during pregnancy and postpartum--a longitudinal study

BACKGROUND

To evaluate the normal range of blood flow velocity in the maternal anterior (ACA) and posterior cerebral arteries (PCA) along the normal pregnancy and postpartum period.

METHODS

Transcranial Doppler ultrasound was used to measure the systolic, diastolic, and mean blood velocities in the ACA and PCA during normal gestation. The resistance and pulsatility indices were calculated. Data were analyzed using multilevel modeling, incorporating random effects models, to construct mean and percentile curves.

RESULTS

We performed 355 measurements on 59 patients, which showed that systolic and mean velocity in the ACA decreased, whereas diastolic velocity increased in the PCA during normal pregnancy. Resistance and pulsatility indices in both vessels increased to a maximum in the second trimester, decreased during the third trimester, and increased during the postpartum period.

CONCLUSIONS

This study provides normative data for ACA and PCA velocity and indices during pregnancy and postpartum, demonstrating changes in velocity that suggest a shift of cerebral blood flow from the anterior to the posterior cerebral circulation.

Elevated aerobic fitness sustained throughout the adult lifespan is associated with improved cerebral hemodynamics

BACKGROUND AND PURPOSE

Age-related impairments in cerebral blood flow and cerebrovascular reactivity to carbon dioxide (CVRCO2) are established risk factors for stroke that respond favorably to aerobic training. The present study examined to what extent cerebral hemodynamics are improved when training is sustained throughout the adult lifespan.

METHODS

Eighty-one healthy males were prospectively assigned to 1 of 4 groups based on their age (young, ≤30 years versus old, ≥60 years) and lifetime physical activity levels (trained, ≥150 minutes recreational aerobic activity/week versus sedentary, no activity). Middle cerebral artery blood velocity (MCAv, transcranial Doppler ultrasound), mean arterial pressure (MAP, finger photoplethysmography), and end-tidal partial pressure of carbon dioxide (PETCO2, capnography) were recorded during normocapnia and 3 mins of iso-oxic hypercapnea (5% CO2). Cerebrovascular resistance/conductance indices (CVRi/CVCi) were calculated as MAP/MCAv and MCAv/MAP, respectively, and CVRCO2 as the percentage increase in MCAv from baseline per millimeter of mercury (mm Hg) increase in PETCO2. Maximal oxygen consumption ( O2MAX, online respiratory gas analysis) was determined during cycling ergometry.

RESULTS

By design, older participants were active for longer (49±5 versus 6±4 years, P<0.05). Physical activity attenuated the age-related declines in O2MAX, MCAv, CVCi, and CVRCO2 and increase in CVRi (P<0.05 versus sedentary). Linear relationships were observed between O2MAX and both MCAv and CVRCO2 (r=0.58-0.77, P<0.05).

CONCLUSIONS

These findings highlight the importance of maintaining aerobic fitness throughout the lifespan given its capacity to improve cerebral hemodynamics in later-life.

Influence of estradiol on functional brain organization for working memory

Working memory is a cognitive function that is affected by aging and disease. To better understand the neural substrates for working memory, the present study examined the influence of estradiol on working memory using functional magnetic resonance imaging. Pre-menopausal women were tested on a verbal n-back task during the early (EF) and late follicular (LF) phases of the menstrual cycle. Although brain activation patterns were similar across the two phases, the most striking pattern that emerged was that estradiol had different associations with the two hemispheres. Increased activation in left frontal circuitry in the LF phase was associated with increased estradiol levels and decrements in working memory performance. In contrast, increased activation in right hemisphere regions in the LF phase was associated with improved task performance. The present study showed that better performance in the LF than the EF phase was associated with a pattern of reduced recruitment of the left-hemisphere and increased recruitment of the right-hemisphere in the LF compared to EF phase. We speculate that estradiol interferes with left-hemisphere working-memory processing in the LF phase, but that recruitment of the right hemisphere can compensate for left-hemisphere interference. This may be related to the proposal that estradiol can reduce cerebral asymmetries by modulating transcallosal communication (Hausmann, 2005).

Elderly women regulate brain blood flow better than men do

BACKGROUND AND PURPOSE

Orthostatic intolerance and falls differ between sexes and change with age. However, it remains unclear what role cerebral autoregulation may play in this response. This study was designed to determine whether cerebral autoregulation, assessed using transcranial Doppler ultrasound, is more effective in elderly females than in males.

METHODS

We used transcranial Doppler ultrasound to evaluate cerebral autoregulation in 544 (236 male) subjects older than age 70 years recruited as part of the MOBILIZE Boston study. The MOBILIZE Boston study is a prospective cohort study of a unique set of risk factors for falls in seniors in the Boston area. We assessed CO2 reactivity and transfer function gain, phase, and coherence during 5 minutes of quiet sitting and autoregulatory index during sit-to-stand tests.

RESULTS

Male subjects had significantly lower CO2 reactivity (males, 1.10 ± 0.03; females, 1.32 ± 0.43 (cm/s)/%CO2; P<0.001) and autoregulatory indices (males, 4.41 ± 2.44; female, 5.32 ± 2.47; P<0.001), higher transfer function gain (males, 1.34 ± 0.49; females, 1.19 ± 0.43; P=0.002), and lower phase (males, 42.7 ± 23.6; females, 49.4 ± 24.9; P=0.002) in the autoregulatory band, implying less effective cerebral autoregulation. However, reduced autoregulation in males was not below the normal range, indicating autoregulation was intact but less effective.

CONCLUSIONS

Female subjects were better able to maintain cerebral flow velocities during postural changes and demonstrated better cerebral autoregulation. The mechanisms of sex-based differences in autoregulation remain unclear but may partially explain the higher rates of orthostatic hypotension-related hospitalizations in elderly men.

Maternal cerebral blood flow during normal pregnancy: a cross-sectional study

OBJECTIVE

Pregnancy is associated with substantial changes in the maternal circulatory physiology. Our aim was to investigate maternal cerebral blood flow (CBF) during normal pregnancies.

STUDY DESIGN

We prospectively measured maternal CBF in 210 low-risk pregnant women at different gestational ages, and in 15 nonpregnant women. CBF was assessed by measuring blood flow volume in the internal carotid artery (ICA) by dual-beam angle-independent digital Doppler ultrasound.

RESULTS

ICA blood flow volume increased during pregnancy from 318 mL/min ± 40.6 mL/min in the first trimester to 382.1 mL/min ± 50.0 mL/min during the third trimester, corresponding to CBF values of 44.4 and 51.8 mL/min(-1)/100 g(-1), respectively (P < .0001). CBF changes were associated with progressive decrease in cerebral vascular resistance and moderate increase in ICA diameter.

CONCLUSION

Maternal CBF is gradually increasing during normal pregnancy. Vasorelaxing impact of estrogens and other factors on cerebral vessels may explain the changes in CBF during pregnancy.

Reversible cerebral vasoconstriction syndrome associated with hormone therapy for intrauterine insemination

Introduction: Reversible cerebral vasoconstriction syndrome (RCVS) comprises a heterogeneous group of acute neurological diseases which are characterized by thunderclap headache and evidence of reversible multifocal constriction of cerebral arteries. A number of precipitating factors have been described in the literature, including recent childbirth and use of vasoactive substances.

Case description: Here we present the case of a female patient with RCVS which occurred in the setting of hormonal ovarian stimulation for intrauterine insemination.

Discussion: This case possibly contributes to the understanding of the pathophysiological mechanisms underlying reversible cerebral vasoconstriction.

Age-related changes in dorsal root ganglia, circulating and vascular calcitonin gene-related peptide (CGRP) concentrations in female rats: effect of female sex steroid hormones

The aim of the present study is to investigate whether immunoreactive (I) calcitonin gene-related peptide (CGRP) content is decreased in plasma and mesenteric arteries (resistance arteries) in middle-aged rats and if so, whether sex steroid hormones enhance I-CGRP in middle-aged female rats. We also examined whether vascular CGRP receptor components, calcitonin receptor like receptor (CRLR) and receptor activity modifying protein 1 (RAMP1) are elevated by sex steroid hormones treatment in middle-aged female rats. Young adult (3 months old) and middle-aged (10-12 months old) ovariectomized rats were treated subcutaneously with estradiol-17beta (E2; 2 mg), progesterone (P4; 5 mg), E2+P4 (2 mg+20 mg) or placebo (control). Radioimmunoassay and Western blot analysis were performed to measure I-CGRP content and CGRP receptor components in dorsal root ganglia (DRG), in resistance arteries and in plasma. Immunofluorescent staining methods were employed to determine cellular localization of CRLR, RAMP1 in resistance arteries. Our data demonstrated that I-CGRP content was significantly (p<0.05) lower in the plasma and resistance arteries of middle-aged female rats compared to young controls. Both RAMP1 and CRLR were concentrated in vascular endothelium and the underlying smooth muscle cells. RAMP1 but not CRLR appeared to be decreased in middle-aged rat vasculature. Chronic perfusion of sex steroid hormones to ovariectomized rats: 1 significantly (p<0.05) elevated I-CGRP in the DRG and in the plasma, and (2) significantly elevated RAMP1 (p<0.05) but did not alter CRLR in resistance arteries. These data suggest that female sex steroid treatment enhances I-CGRP and its receptors, and thus regulate the blood pressure in aged female rats.