The influence of sex hormones on cerebrovascular function

The disproportionate rise in cerebrovascular disease risk for females in the first 10 years post-menopause indicates a role for ovarian sex hormones (i.e., oestrogen and progesterone) in healthy cerebrovascular function and regulation. However, the exact influence of changing sex hormones across the lifespan on the cerebrovasculature is yet to be elucidated. The primary aim of this thesis was to determine the influence of sex hormones on cerebrovascular function. A systematic review and meta-analysis established that hormone replacement therapy in post-menopausal females has the potential to improve cerebrovascular function, as reflected by a significant reduction in pulsatility index. Further, the effects of changing sex hormones in other hormone groups (e.g., menstrual cycle, menopause) remains unclear due to the substantial heterogeneity and limited evidence in the literature. Subsequently, three experimental studies examined measures of cerebrovascular function across the menstrual cycle, between males and females, and between pre- and post-menopausal females. Firstly, cerebrovascular responsiveness (indexed via measures of middle/posterior cerebral blood flow velocity (MCAv/PCAv) responses to altered arterial partial pressure of carbon dioxide (CO2)) across the menstrual cycle revealed a greater MCAv-CO2 responsiveness to hypocapnia during ovulation (O) when compared to the early follicular (EF) phase. Assessment of sex differences showed cerebrovascular-CO2 responsiveness to hypo- and hypo-to-hypercapnia was greater in females during EF in the PCA, and females during O in the MCA, when compared to males. Use of passive heat stress as an additional perturbation did not change cerebrovascular-CO2 responsiveness across the menstrual cycle, while a diminished PCA responsiveness to hypercapnia during heat stress was only evident in males. Finally, pre-menopausal females were shown to have an improved MCAv-CO2 responsiveness to hypercapnia compared to post-menopausal females, irrespective of menstrual phase. Preliminary data indicates possible differences between pre- and post-menopausal females in internal carotid artery (ICA) responsiveness to hypercapnia, and in cerebral autoregulation (indexed via MCAv responses to repeated squat-to-stand-induced changes in blood pressure). Collectively, these findings indicate that 1) acute fluctuations in oestrogen across the menstrual cycle can alter the vasoconstrictive capacity of the MCA, while progesterone appears to counteract the effects of oestrogen. 2) Sex differences in cerebrovascular-CO2 responsiveness are dependent on menstrual phase and the insonated vessel, and differences are present even when females are early follicular phase of the menstrual cycle. Further, cerebrovascular responses to passive heating are sex specific. Finally, 3) post-menopausal females have a blunted MCAv responsiveness to hypercapnia compared to pre-menopausal females. Overall, the findings that pre-menopausal females exhibit improved intracranial cerebrovascular-CO2 responsiveness compared to both young males and post-menopausal females supports the premise that sex hormones play a protective role in cerebrovascular function

The effect of social media interventions on physical activity and dietary behaviours in young people and adults:a systematic review

BACKGROUND: The objectives of this systematic review were to update the evidence base on social media interventions for physical activity and diet since 2014, analyse the characteristics of interventions that resulted in changes to physical activity and diet-related behaviours, and assess differences in outcomes across different population groups. METHODS: A systematic search of the literature was conducted across 5 databases (Medline, Embase, EBSCO Education, Wiley and Scopus) using key words related to social media, physical activity, diet, and age. The inclusion criteria were: participants age 13+ years in the general population; an intervention that used commercial social media platform(s); outcomes related to changes to diet/eating or physical activity behaviours; and quantitative, qualitative and mixed methods studies. Quality appraisal tools that aligned with the study designs were used. A mixed methods approach was used to analyse and synthesise all evidence. RESULTS: Eighteen studies were included: randomised control trials (n = 4), non-controlled trials (n = 3), mixed methods studies (n = 3), non-randomised controlled trials (n = 5) and cross-sectional studies (n = 3). The target population of most studies was young female adults (aged 18–35) attending college/university. The interventions reported on positive changes to physical activity and diet-related behaviours through increases in physical activity levels and modifications to food intake, body composition and/or body weight. The use of Facebook, Facebook groups and the accessibility of information and interaction were the main characteristics of social media interventions. Studies also reported on Instagram, Reddit, WeChat and Twitter and the use of photo sharing and editing, groups and sub-groups and gamification. CONCLUSIONS: Social media interventions can positively change physical activity and diet-related behaviours, via increases in physical activity levels, healthy modifications to food intake, and beneficial changes to body composition or body weight. New evidence is provided on the contemporary uses of social media (e.g. gamification, multi-model application, image sharing/editing, group chats) that can be used by policy makers, professionals, organisations and/or researchers to inform the design of future social media interventions. This study had some limitations that mainly relate to variation in study design, over-reliance of self-reported measures and sample characteristics, that prevented comparative analysis. Registration number: PROPSERO;CRD42020210806. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12966-021-01138-3

Improving the medical school–residency transition

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138225/1/tct12576_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138225/2/tct12576.pd

Menstrual phase influences cerebrovascular responsiveness in females but may not affect sex differences

Background and aims: Sex differences in the rate and occurrence of cerebrovascular diseases (e.g., stroke) indicate a role for female sex hormones (i.e., oestrogen and progesterone) in cerebrovascular function and regulation. However, it remains unclear how cerebrovascular function differs between the sexes, and between distinct phases of the menstrual cycle. This study aimed to compare cerebrovascular-CO(2) responsiveness in 1) females during the early follicular (EF), ovulatory (O) and mid-luteal (ML) phases of their menstrual cycle; and 2) males compared to females during phases of lower oestrogen (EF) and higher oestrogen (O). Methods: Eleven females (25 ± 5 years) complete experimental sessions in the EF (n = 11), O (n = 9) and ML (n = 11) phases of the menstrual cycle. Nine males (22 ± 3 years) completed two experimental sessions, approximately 2 weeks apart for comparison to females. Middle and posterior cerebral artery velocity (MCAv, PCAv) was measured at rest, during two stages of hypercapnia (2% and 5% CO(2) inhalation) and hypocapnia (voluntary hyperventilation to an end-tidal CO(2) of 30 and 24 mmHg). The linear slope of the cerebral blood velocity response to changes in end-tidal CO(2) was calculated to measure cerebrovascular-CO(2) responsiveness.. Results: In females, MCAv-CO(2) responsiveness to hypocapnia was lower during EF (−.78 ± .45 cm/s/mmHg) when compared to the O phase (−1.17 ± .52 cm/s/mmHg; p < .05) and the ML phase (−1.30 ± .82; p < .05). MCAv-CO(2) responsiveness to hypercapnia and hypo-to-hypercapnia, and PCAv-CO(2) responsiveness across the CO(2) range were similar between menstrual phases (p ≥ .20). MCAv-CO(2) responsiveness to hypo-to hypercapnia was greater in females compared to males (3.12 ± .91 cm/s/mmHg vs. 2.31 ± .46 cm/s/mmHg; p = .03), irrespective of menstrual phase (EF or O). Conclusion: Females during O and ML phases have an enhanced vasoconstrictive capacity of the MCA compared to the EF phase. Additionally, biological sex differences can influence cerebrovascular-CO(2) responsiveness, dependent on the insonated vessel

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)

Invisible interpretations: reflections on the digital humanities and intellectual history

Much has been made of the digital humanities, yet it remains an underexplored field in relation to intellectual history. This paper aims to add to the little literature which does exist by offering a survey of the ideas and issues facing would-be practitioners. This includes: an overview of what the digital humanities are; reflections on what they offer intellectual history and how they may be problematic in regard to, first, accessing texts, and second, analysing source material; a conclusion with three reflections on future best practices – to be sceptical of digital sources, to be reflective of methodologies and how they may need to be modified when engaging with the digital humanities, and to embrace more directly the methodological, statistical, and technical aspects behind digital humanities. The aim is not to provide all the answers – at this stage that is impossible – but to be part of an emerging and ongoing discussion