Influence of sex, menstrual cycle, and oral contraceptives on cerebrovascular resistance and cardiorespiratory function during Valsalva or standing

The effects of habitual resistance exercise training on cerebrovascular responses to lower body dynamic resistance exercise: A cross-sectional study

Dynamic resistance exercise (RE) produces sinusoidal fluctuations in blood pressure with simultaneous fluctuations in middle cerebral artery blood velocity (MCAv). Some evidence indicates that RE may alter cerebrovascular function. This study aimed to examine the effects of habitual RE training on the within-RE cerebrovascular responses. RE-trained (n = 15, Female = 4) and healthy untrained individuals (n = 15, Female = 12) completed four sets of 10 paced repetitions (15 repetitions per minute) of unilateral leg extension exercise at 60% of predicted 1 repetition maximum. Beat-to-beat blood pressure, MCAv and end-tidal carbon dioxide were measured throughout. Zenith, nadir and zenith-to-nadir difference in mean arterial blood pressure (MAP) and mean MCAv (MCAvmean) for each repetition were averaged across each set. Two-way ANOVA was used to analyse dependent variables (training × sets), Bonferroni corrected t-tests were used for post hoc pairwise comparisons. Group age (26 ± 7 trained vs. 25 ± 6 years untrained, P = 0.683) and weight (78 ± 15 vs. 71 ± 15 kg, P = 0.683) were not different. During exercise average MAP was greater for the RE-trained group in sets 2, 3 and 4 (e.g., set 4: 101 ± 11 vs. 92 ± 7 mmHg for RE trained and untrained, respectively, post hoc tests all P = < 0.012). Zenith MAP and zenith-to-nadir MAP difference demonstrated a training effect (P < 0.039). Average MCAvmean and MCAvmean zenith-to-nadir difference was not different between groups (interaction effect P = 0.166 and P = 0.459, respectively). Despite RE-trained individuals demonstrating greater fluctuations in MAP during RE compared to untrained, there were no differences in MCAvmean. Regular RE may lead to vascular adaptations that stabilise MCAv during RE.

Female mice display sex-specific differences in cerebrovascular function and subarachnoid haemorrhage-induced injury

BACKGROUND

In male mice, a circadian rhythm in myogenic reactivity influences the extent of brain injury following subarachnoid haemorrhage (SAH). We hypothesized that female mice have a different cerebrovascular phenotype and consequently, a distinct SAH-induced injury phenotype.

METHODS

SAH was modelled by pre-chiasmatic blood injection. Olfactory cerebral resistance arteries were functionally assessed by pressure myography; these functional assessments were related to brain histology and neurobehavioral assessments. Cystic fibrosis transmembrane conductance regulator (CFTR) expression was assessed by PCR and Western blot. We compared non-ovariectomized and ovariectomized mice.

FINDINGS

Cerebrovascular myogenic reactivity is not rhythmic in females and no diurnal differences in SAH-induced injury are observed; ovariectomy does not unmask a rhythmic phenotype for any endpoint. CFTR expression is rhythmic, with similar expression levels compared to male mice. CFTR inhibition studies, however, indicate that CFTR activity is lower in female arteries. Pharmacologically increasing CFTR expression in vivo (3 mg/kg lumacaftor for 2 days) reduces myogenic tone at Zeitgeber time 11, but not Zeitgeber time 23. Myogenic tone is not markedly augmented following SAH in female mice and lumacaftor loses its ability to reduce myogenic tone; nevertheless, lumacaftor confers at least some injury benefit in females with SAH.

INTERPRETATION

Female mice possess a distinct cerebrovascular phenotype compared to males, putatively due to functional differences in CFTR regulation. This sex difference eliminates the CFTR-dependent cerebrovascular effects of SAH and may alter the therapeutic efficacy of lumacaftor compared to males.

FUNDING

Brain Aneurysm Foundation, Heart and Stroke Foundation and Ted Rogers Centre for Heart Research.

Effects of menstrual cycle on hemodynamic and autonomic responses to central hypovolemia

Background

Estrogen and progesterone levels undergo changes throughout the menstrual cycle. Existing literature regarding the effect of menstrual phases on cardiovascular and autonomic regulation during central hypovolemia is contradictory.

Aims and study

This study aims to explore the influence of menstrual phases on cardiovascular and autonomic responses in both resting and during the central hypovolemia induced by lower body negative pressure (LBNP). This is a companion paper, in which data across the menstrual phases from healthy young females, whose results are reported in Shankwar et al. (2023), were further analysed.

Methods

The study protocol consisted of three phases: (1) 30 min of supine rest; (2) 16 min of four LBNP levels; and (3) 5 min of supine recovery. Hemodynamic and autonomic responses (assessed via heart rate variability, HRV) were measured before-, during-, and after-LBNP application using Task Force Monitor® (CNSystems, Graz, Austria). Blood was also collected to measure estrogen and progesterone levels.

Results

In this companion paper, we have exclusively assessed 14 females from the previous study (Shankwar et al., 2023): 8 in the follicular phase of the menstrual cycle (mean age 23.38 ± 3.58 years, height 166.00 ± 5.78 cm, weight 57.63 ± 5.39 kg and BMI of 20.92 ± 1.96 25 kg/m2) and 6 in the luteal phase (mean age 22.17 ± 1.33 years, height 169.83 ± 5.53 cm, weight 62.00 ± 7.54 kg and BMI of 21.45 ± 2.63 kg/m2). Baseline estrogen levels were significantly different from the follicular phase as compared to the luteal phase: (33.59 pg/ml, 108.02 pg/ml, respectively, p < 0.01). Resting hemodynamic variables showed no difference across the menstrual phases. However, females in the follicular phase showed significantly lower resting values of low-frequency (LF) band power (41.38 ± 11.75 n.u. and 58.47 ± 14.37 n.u., p = 0.01), but higher resting values of high frequency (HF) band power (58.62 ± 11.75 n.u. and 41.53 ± 14.37 n.u., p = 0.01), as compared to females in the luteal phase. During hypovolemia, the LF and HF band powers changed only in the follicular phase F(1, 7) = 77.34, p < 0.0001 and F(1, 7) = 520.06, p < 0.0001, respectively.

Conclusions

The menstrual phase had an influence on resting autonomic variables, with higher sympathetic activity being observed during the luteal phase. Central hypovolemia leads to increased cardiovascular and autonomic responses, particularly during the luteal phase of the menstrual cycle, likely due to higher estrogen levels and increased sympathetic activity.

The effects of oral contraceptives on resting autonomic function and the autonomic response to physiological stressors: a systematic review

PURPOSE

This systematic review aimed to summarize how oral contraceptives (OC) affect resting autonomic function and the autonomic response to a variety of physiological stressors.

METHODS

A search strategy was created to retrieve citations investigating physiological responses comparing OC users to non-users (NOC) in response to autonomic reflex activation.

RESULTS

A total of 6148 citations were identified across databases from inception to June 2, 2022, and 3870 citations were screened at the abstract level after deduplication. Then, 133 texts were assessed at full-text level, and only 40 studies met eligibility requirements. Included citations were grouped by the aspect of autonomic function assessed, including autonomic reflex (i.e., baroreflex, chemoreflex, mechanoreflex, metaboreflex, and venoarterial reflex), or indicators (i.e., heart rate variability, pulse wave velocity, and sympathetic electrodermal activity), and physiological stressors that may alter autonomic function (i.e., auditory, exercise, mental or orthostatic stress, altitude, cold pressor test, sweat test, and vasodilatory infusions).

CONCLUSION

OC influence the physiological responses to chemoreflex, mechanoreflex, and metaboreflex activation. In terms of autonomic indices and physiological stressors, there are more inconsistencies within the OC literature, which may be due to estrogen dosage within the OC formulation (i.e., heart rate variability) or the intensity of the stressor (exercise intensity/duration or orthostatic stress). Further research is required to elucidate the effects of OC on these aspects of autonomic function because of the relatively small amount of available research. Furthermore, researchers should more clearly define or stratify OC use by duration, dose, and/or hormone cycling to further elucidate the effects of OC.

Exaggerated postural sway improves orthostatic cardiovascular and cerebrovascular control

Introduction

Healthy individuals with poor cardiovascular control, but who do not experience syncope (fainting), adopt an innate strategy of increased leg movement in the form of postural sway that is thought to counter orthostatic (gravitational) stress on the cardiovascular system. However, the direct effect of sway on cardiovascular hemodynamics and cerebral perfusion is unknown. If sway produces meaningful cardiovascular responses, it could be exploited clinically to prevent an imminent faint.

Methods

Twenty healthy adults were instrumented with cardiovascular (finger plethysmography, echocardiography, electrocardiogram) and cerebrovascular (transcranial Doppler) monitoring. Following supine rest, participants performed a baseline stand (BL) on a force platform, followed by three trials of exaggerated sway (anterior-posterior, AP; mediolateral, ML; square, SQ) in a randomized order.

Results

All exaggerated postural sway conditions improved systolic arterial pressure (SAP, p = 0.001) responses, while blunting orthostatic reductions in stroke volume (SV, p < 0.01) and cerebral blood flow (CBFv, p < 0.05) compared to BL. Markers of sympathetic activation (power of low-frequency oscillations in SAP, p < 0.001) and maximum transvalvular flow velocity (p < 0.001) were reduced during exaggerated sway conditions. Responses were dose-dependent, with improvements in SAP (p < 0.001), SV (p < 0.001) and CBFv (p = 0.009) all positively correlated with total sway path length. Coherence between postural movements and SAP (p < 0.001), SV (p < 0.001) and CBFv (p = 0.003) also improved during exaggerated sway.

Discussion

Exaggerated sway improves cardiovascular and cerebrovascular control and may supplement cardiovascular reflex responses to orthostatic stress. This movement provides a simple means to boost orthostatic cardiovascular control for individuals with syncope, or those with occupations that require prolonged motionless standing.

Oral contraceptive use and menstrual cycle influence acute cerebrovascular response to standing

PURPOSE

To determine if the menstrual cycle and oral contraceptives (OC) influence responses to acute orthostatic stress and if these factors are clinically relevant to the diagnosis of initial orthostatic hypotension (iOH).

METHODS

Young, healthy women were recruited, including OC users (n = 12) and non-users (NOC; n = 9). Women were tested during the low hormone (LH; placebo pills; days 2-5 natural cycle) and high hormone (HH; active dose; days 18-24 natural cycle) menstrual phases. Changes in mean arterial pressure, cardiac output, heart rate, the 30:15 heart rate ratio and cerebrovascular resistance indices within 30 s of standing were examined.

RESULTS

There were no effects of OC or menstrual cycle on hemodynamic responses during standing (all p>0.05). In the LH phase, OC users had a greater fall in mean middle cerebral artery blood velocity (MCA_V) compared to NOC (p<0.05). However, this was reversed in the HH phase, where OC users had a reduced fall in mean MCA_V (p<0.05). Interestingly, 8 women (OC and NOC) had drops in systolic/diastolic blood pressure meeting the criteria for iOH, and 7 of those 8 women displayed this drop in a single phase of the menstrual cycle.

CONCLUSION

Our results indicate that chronic versus acute OC use (i.e., long-term use observed via LH phase versus short-term use observed via HH phase) have opposing effects on cerebral blood velocity during standing. Further, our results highlight that multiple assessments across the cycle may be necessary to accurately diagnose iOH, as most women met the diagnostic criteria during a single menstrual phase.

Menstrual cycle and oral contraceptives influence cerebrovascular dynamics during hypercapnia

Women experience fluctuating orthostatic intolerance during the menstrual cycle, suggesting sex hormones may influence cerebral blood flow. Young (aged 18-30) healthy women, either taking oral contraceptives (OC; n = 14) or not taking OC (NOC; n = 12), were administered hypercapnic gas (5%) for 5 min in the low hormone (LH; placebo pill) and high hormone (HH; active pill) menstrual phases. Hemodynamic and cerebrovascular variables were continuously measured. Cerebral blood velocity changes were monitored using transcranial doppler ultrasound of the middle cerebral artery to determine cerebrovascular reactivity. Cerebral autoregulation was assessed using steady-state analysis (static cerebral autoregulation) and transfer function analysis (dynamic cerebral autoregulation; dCA). In response to hypercapnia, menstrual phase did not influence static cardiovascular or cerebrovascular responses (all p > 0.07); however, OC users had a greater increase of mean middle cerebral artery blood velocity compared to NOC (NOC-LH 12 ± 6 cm/s vs. NOC-HH 16 ± 9 cm/s; OC-LH 18 ± 5 cm/s vs. OC-HH 17 ± 11 cm/s; p = 0.048). In all women, hypercapnia improved high frequency (HF) and very low frequency (VLF) cerebral autoregulation (decreased nGain; p = 0.002 and <0.001, respectively), whereas low frequency (LF) Phase decreased in NOC-HH (p = 0.001) and OC-LH (p = 0.004). Therefore, endogenous sex hormones reduce LF dCA during hypercapnia in the HH menstrual phase. In contrast, pharmaceutical sex hormones (OC use) have no acute influence (HH menstrual phase) yet elicit a chronic attenuation of LF dCA (LH menstrual phase) during hypercapnia.

Effect of oral hormonal contraceptive pill use on the hemodynamic response to the cold pressor test

Acute increases in sympathetic nervous system activity (SNA) often elicit peripheral vasoconstriction and increases in blood pressure (BP). Given sympathetic support of BP is modulated by ovarian sex hormones (e.g., estradiol), we sought to examine the effect of menstrual cycle and oral hormonal contraceptive pill (OC) phase on the hemodynamic response to acute increases in SNA. We hypothesized sympathoexcitation via cold pressor test (CPT) would elicit greater peripheral vasoconstriction and increases BP in females with natural menstrual cycles (NC) compared with females taking OC. We further hypothesized that SNA-mediated vasoconstriction would be attenuated during the high estradiol (HE) phase versus the low estradiol (LE) phase of the menstrual/pill cycle. Female NC (n = 11, 25 ± 1 yr) and OC (n = 10, 24 ± 1 yr) participants were studied during the LE (early follicular, placebo pill) and HE (late follicular, active pill) phase of the menstrual/pill cycle. BP (finger photoplethysmography), heart rate (HR, ECG), and forearm blood flow (FBF, venous occlusion plethysmography) were measured during a 5-min baseline and a 2-min CPT. CPT elicited an increase in BP in both groups (time, P < 0.01). During CPT, OC participants exhibited greater and sustained increases in HR compared with NC participants (group × time, P < 0.01). Higher HRs were met with increases in FBF in OC participants during the CPT, which was not observed in NC participants (group × time, P < 0.01). OC participants exhibit greater increases in HR, and paradoxical vasodilation during acute sympathetic activation compared with NC participants. Group differences are unaffected by menstrual/pill phase.NEW & NOTEWORTHY Acute increases in sympathetic nervous system activity often elicit peripheral vasoconstriction and increases in blood pressure (BP). Given sympathetic support of BP is modulated by ovarian sex hormones (e.g., estradiol), we sought to examine the effect of menstrual cycle and oral hormonal contraceptive pill (OC) phase on the hemodynamic response to acute increases in sympathetic nervous system activity via the cold pressor test. We show OC participants exhibit paradoxical vasodilation during acute sympathetic activation compared with participants with natural menstrual cycles; notably, group differences were unaffected by menstrual/pill phase.

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.

Oral contraceptives and menstrual cycle influence autonomic reflex function

Progesterone and its analogues are known to influence ventilation. Therefore, the purpose of this study was to investigate the role of endogenous and pharmaceutical female sex hormones in ventilatory control during the activation of the metaboreflex, mechanoreflex, and CO₂ chemoreflex. Women aged 18–30 taking (n = 14) or not taking (n = 12) oral contraceptives (OC and NOC, respectively) were tested in the low hormone (LH) and high hormone (HH) conditions corresponding to the early follicular and mid‐luteal phases (NOC) or placebo and high‐dose pills (OC). Women underwent three randomized trials: (a) 3 min of passive leg movement (PLM), (b) 2 min of 40% maximal voluntary handgrip exercise followed by 2 min of post‐exercise circulatory occlusion (PECO), and (c) 5 min of breathing 5% CO₂. We primarily measured hemodynamics and ventilation. During PLM, the OC group had a smaller pressor response (p = .012). During PECO, the OC group similarly exhibited a smaller pressor response (p = .043) and also exhibited a greater ventilatory response (p = .024). Lastly, in response to breathing 5% CO₂, women in the HH phase had a greater ventilatory response (p = .022). We found that OC use attenuates the pressor response to both the metaboreflex and mechanoreflex while increasing the ventilatory response to metaboreflex activation. We also found evidence of an enhanced CO₂ chemoreflex in the HH phase. We hypothesize that OC effects are from the chronic upregulation of pulmonary and vascular β‐adrenergic receptors. We further suggest that the increased cyclic progesterone in the HH phase enhances the chemoreflex.

The Acute Cardiorespiratory and Cerebrovascular Response to Resistance Exercise

Resistance exercise (RE) is a popular modality for the general population and athletes alike, due to the numerous benefits of regular participation. The acute response to dynamic RE is characterised by temporary and bidirectional physiological extremes, not typically seen in continuous aerobic exercise (e.g. cycling) and headlined by phasic perturbations in blood pressure that challenge cerebral blood flow (CBF) regulation. Cerebral autoregulation has been heavily scrutinised over the last decade with new data challenging the effectiveness of this intrinsic flow regulating mechanism, particularly to abrupt changes in blood pressure over the course of seconds (i.e. dynamic cerebral autoregulation), like those observed during RE. Acutely, RE can challenge CBF regulation, resulting in adverse responses (e.g. syncope). Compared with aerobic exercise, RE is relatively understudied, particularly high-intensity dynamic RE with a concurrent Valsalva manoeuvre (VM). However, the VM alone challenges CBF regulation and generates additional complexity when trying to dissociate the mechanisms underpinning the circulatory response to RE. Given the disparate circulatory response between aerobic and RE, primarily the blood pressure profiles, regulation of CBF is ostensibly different. In this review, we summarise current literature and highlight the acute physiological responses to RE, with a focus on the cerebral circulation.

Preliminary Evidence of Orthostatic Intolerance and Altered Cerebral Vascular Control Following Sport-Related Concussion

Concussions have been shown to result in autonomic dysfunction and altered cerebral vascular function. We tested the hypothesis that concussed athletes (CA) would have altered cerebral vascular function during acute decreases and increases in blood pressure compared to healthy controls (HC). Ten CA (age: 20 ± 2 y, 7 females) and 10 HC (age: 21 ± 2 y, 6 females) completed 5 min of lower body negative pressure (LBNP; −40 mmHg) and 5 min of lower body positive pressure (LBPP; 20 mmHg). Protocols were randomized and separated by 10 min. Mean arterial pressure (MAP) and middle cerebral artery blood velocity (MCAv) were continuously recorded. Cerebral vascular resistance (CVR) was calculated as MAP/MCAv. Values are reported as change from baseline to the last minute achieved (LBNP) or 5 min (LBPP). There were no differences in baseline values between groups. During LBNP, there were no differences in the change for MAP (CA: −23 ± 18 vs. HC: −21 ± 17 cm/s; P = 0.80) or MCAv (CA: −13 ± 8 vs. HC: −18 ± 9 cm/s; P = 0.19). The change in CVR was different between groups (CA: −0.08 ± 0.26 vs. HC: 0.18 ± 0.24 mmHg/cm/s; P = 0.04). Total LBNP time was lower for CA (204 ± 92 s) vs. HC (297 ± 64 s; P = 0.04). During LBPP, the change in MAP was not different between groups (CA: 13 ± 6 vs. HC: 10 ± 7 mmHg; P = 0.32). The change in MCAv (CA: 7 ± 6 vs. HC: −4 ± 13 cm/s; P = 0.04) and CVR (CA: −0.06 ± 0.27 vs. HC: 0.38 ± 0.41 mmHg/cm/s; P = 0.03) were different between groups. CA exhibited impaired tolerance to LBNP and had a different cerebral vascular response to LBPP compared to HC.

Sex differences in the autonomic and cerebrovascular responses to upright tilt

Sex differences in the regulation of autonomic and cerebrovascular responses to orthostatic stress remain unclear. The objectives of this study were to concurrently investigate autonomic control and cerebrovascular resistance indices, including critical closing pressure (CrCP) and resistance area product (RAP), during upright tilt in men and women. In 13 women and 14 men (18-29 years), ECG, non-invasive blood pressure, middle cerebral artery blood velocity, and end-tidal CO₂ (ETCO₂) were continuously measured during supine rest and 70° tilt. Heart rate variability (HRV), cardiovagal baroreflex sensitivity (cBRS), and transfer function parameters of dynamic cerebral autoregulation were calculated. Compared to supine, upright tilt increased the low frequency-to-high frequency ratio of HRV in men only (P = 0.044), and decreased cBRS more in women (P = 0.001). Cerebrovascular resistance index (CVRi) increased during tilt only in men (sex-by-time interaction: P = 0.004). RAP was lower in women throughout tilt (main effect of sex: P = 0.022). CrCP decreased during tilt in both sexes (main effect of time: P < 0.001). Normalizing to ETCO2 did not alter the effect of tilt on cerebrovascular resistance. Men displayed a greater increase of sympathetic indices and CVRi during tilt while women had greater parasympathetic withdrawal. We hypothesize that increased sympathetic activity in men may drive sex differences in the cerebrovascular response to upright posture.

Integrative cardiovascular control in women: Regulation of blood pressure, body temperature, and cerebrovascular responsiveness

Over the past several decades, it has become increasingly clear that women have distinct cardiovascular profiles compared to men. In this review, our goal is to provide an overview of the literature regarding the influences of female sex and reproductive hormones (primarily estradiol) on mechanisms of cardiovascular control relevant to regulation of blood pressure, body temperature, and cerebral blood flow. Young women tend to have lower resting blood pressure compared with men. This sex difference is reversed at menopause, when women develop higher sympathetic nerve activity and the risk of systemic hypertension increases sharply as postmenopausal women age. Vascular responses to thermal stress, including cutaneous vasodilation and vasoconstriction, are also affected by reproductive hormones in women, where estradiol appears to promote vasodilation and heat dissipation. The influence of reproductive hormones on cerebral blood flow and sex differences in the ability of the cerebral vasculature to increase its blood flow (cerebrovascular reactivity) are relatively new areas of investigation. Sex and hormonal influences on integrative blood flow regulation have further implications during challenges to physiological homeostasis, including exercise. We propose that increasing awareness of these sex-specific mechanisms is important for optimizing health care and promotion of wellness in women across the life span.

Evaluation of microvascular changes in optic disc and retina by optical coherence tomography angiography during Valsalva maneuver

PURPOSE

Optical coherence tomography angiography (OCTA) is an increasingly widespread imaging tool that allows the visualization of the microvascular structures of the eye. It should be kept in mind in clinical practice, Valsalva maneuver (VM) may have an effect on OCTA findings. We aimed to evaluate the effect of VM on the optic nerve and retinal blood flow parameters measured by OCTA.

METHODS

Sixty age- and sex-matched healthy volunteers were included into this prospective study. Optic disc status for radial peripapillary capillary (RPC) network [whole image, inside disc and peripapillary capillary densities], superficial and deep capillary plexus whole, foveal, parafoveal and perifoveal densities and foveal avascular zone (FAZ) densities of volunteers were examined by OCTA both at rest and during VM.

RESULTS

The mean age of the subjects was 31.48 ± 7.49 (18-50) years and 51.7% were male. Superficial whole, parafoveal and perifoveal vessel densities were found to be significantly decreased during VM (p = 0.008, p= 0.015, p = 0.017, respectively). Lower levels of deep whole, parafoveal and perifoveal vessel densities were also detected while VM (p < 0.001 for all). However, there were no significant differences in terms of foveal vessel and FAZ densities. Additionally, VM significantly decreased RPC densities for whole image, inside and peripapillary capillary (p = 0.005, p < 0.001, p = 0.039, respectively).

CONCLUSION

VM may cause a significant decrease in optic nerve and para-perifoveal blood flow. Therefore, patient instruction about not holding breath is required before OCTA scanning.

Comparison of diurnal variation, anatomical location, and biological sex within spontaneous and driven dynamic cerebral autoregulation measures

Presently, the literature describing the influence of diurnal variation on dynamic cerebral autoregulation (dCA) metrics is sparse. Additionally, there is little data with respect to dCA comparisons between anterior/posterior circulation beds and biological sexes using squat-stand maneuvers. Eight male and eight female participants (n = 16) performed 5 min of spontaneous upright rest and squat-stand maneuvers at 0.05 and 0.10 Hz across seven time points throughout the day. All testing sessions commenced at 8:00 a.m. each day and dCA parameters were quantified across the cardiac cycle (diastole, mean, and systole) using transcranial Doppler ultrasound to insonate cerebral blood velocity within the middle and posterior cerebral arteries (MCA, PCA). No cardiac cycle alternations were seen spontaneous (all p > .207) while a trend was noted in some driven (all p > .051) dCA metrics. Driven dCA produced much lower coefficient of variances (all <21%) compared with spontaneous (all <58%). Moreover, no sex differences were found within driven metrics (all p > .096). Between vessels, PCA absolute gain was reduced within all spontaneous and driven measures (all p < .014) whereas coherence, phase, and normalized gain were unchanged (all p > .099). There appears to be little influence of diurnal variation on dCA measures across the day (8:00 a.m. to 6:00 p.m.). Absolute gain was blunted in the PCA relative to the MCA and consistent with previous literature, driven methods demonstrated vastly improved reproducibility metrics compared to spontaneous methods. Finally, no dCA differences were found between biological sexes, demonstrating that males and females regulate in a harmonious manner, when females are tested within the early follicular phase of the menstrual cycle.

Cerebral vascular reactivity and the migraine-stroke relationship: A narrative review

Migraine, and especially migraine with aura, is associated with an increased risk of stroke and vascular events; however, the reasons for this association are unclear. Several studies evaluated cerebral autoregulation and vasomotor reactivity in patients with migraine compared with non-migraineurs, with conflicting results. Our narrative review aimed at summarizing their results to find the most reliable evidence in the field. Studies which used visual stimuli to evoke vascular responses consistently showed an increased vascular reactivity in migraineurs compared with non-migraineurs, while studies which used systemic stimuli such as hyper- or hypocapnia showed inconsistent results. Therefore, central neural mechanisms might be more important than peripheral vascular mechanisms in determining the cerebral vascular responses of patients with migraine. However, a large body of evidence supports the existence of peripheral vascular dysfunction in patients with migraine. Further studies are needed to explain the complex interactions between central neural and peripheral vascular mechanisms in determining migraine and its vascular risk. Migraine preventive treatments, and especially the most recent ones with a peripheral action, might provide important insights in this field.

Effect of a neck compression collar on cardiorespiratory and cerebrovascular function in postural orthostatic tachycardia syndrome (POTS)

Postural orthostatic tachycardia syndrome (POTS) is accompanied by reduced brain blood flow, autonomic dysfunction, and orthostatic intolerance. We hypothesized that wearing a neck compression collar would attenuate orthostatic symptoms, increase brain blood flow, and influence autonomic reflexes. Ten participants with POTS (9 women, age: 36 ± 10) underwent two trials of supine rest, paced deep breathing (6 breaths/min), Valsalva maneuver (40 mmHg for 15 s), and 70° upright tilt. For one trial, participants wore a neck compression device (Q30 Innovations). Blood pressure, heart rate (HR), brain blood flow velocity, stroke volume, respiratory rate, and end-tidal gases were continuously measured. The Vanderbilt Orthostatic Symptom Score was compiled at the end of tilt. The use of the collar reduced the orthostatic symptom score of participants with POTS during upright tilt (26.9 ± 12.5 to 18.7 ± 13.1, P = 0.04). Collar compression in the supine condition reduced the low-frequency domain of HR variability (60 ± 18 to 51 ± 23 normalized units, P = 0.04) and increased the change in HR (15 ± 5 to 17 ± 6 bpm, P = 0.02) and E:I ratio (1.2 ± 0.1 to 1.3 ± 0.1, P = 0.01) during paced deep breathing. Throughout tilt, wearing the collar reduced respiratory rate (baseline: 13 ± 3 to 12 ± 4 breath/min; tilt: 18 ± 5 to 15 ± 5 breath/min; main effect of collar P = 0.048), end-tidal oxygen (baseline: 115 ± 5 to 112 ± 5 mmHg; tilt: 122 ± 10 to 118 ± 11 mmHg; main effect of collar P = 0.026). In participants with POTS, wearing the Q-collar reduced orthostatic symptoms, increased the HR response to deep breathing, and decreased resting ventilation.NEW & NOTEWORTHY We found that using a neck compression collar alleviated orthostatic symptoms in upright posture in participants with postural orthostatic tachycardia syndrome (POTS). This could be due to compression of the baroreceptors and subsequent changes in autonomic function. Indeed, we observed increased heart rate responsiveness to paced deep breathing and reductions of respiratory rate and end-tidal O₂ (suggesting reduced ventilation). Further, wearing the collar reduced mean blood velocity in the brain during Valsalva perhaps due to higher brain blood volume.

Sex Differences in Cardiac Flow Dynamics of Healthy Volunteers

Purpose

The purpose of this study was to further understand the relationship between cardiac function and flow, on the basis of sex, by quantifying cardiac flow characteristics and relating them to cardiac muscle performance in young adults.

Materials and Methods

In this cross-sectional study, cardiac four-dimensional flow (4D flow) magnetic resonance imaging (MRI) and two-dimensional cine MRI were performed on 20 male and 19 female volunteers aged 20-35. Velocity-based metrics of flow, kinetic energy, vorticity, and efficiency indices were quantified, as well as cardiac strain metrics.

Results*

Peak systolic blood kinetic energy (male: 4.76 ± 2.66 mJ; female: 3.36 ± 1.43 mJ; p=0.047) was significantly higher in the male left ventricle (LV) than in the female LV. Peak systolic vorticity index (male: 0.008 ± 0.005 rad-m²/ml-s; female: 0.014 ± 0.007 rad-m²/ml-s; p=0.007), peak diastolic vorticity index (male: 0.007 ± 0.006 rad-m²/ml-s; female: 0.014 ± 0.010 rad-m²/ml-s; p=0.015), and cycle-average vorticity (male: 0.006 ± 0.001 rad-m²/ml-s; female: 0.011 ± 0.002 rad/s; p=0.001) were all significantly higher in the LV of women than they were in the LV of men. Radial, circumferential, and long-axis strain metrics were significantly higher in the female LV than in the male LV (p<0.05). Circumferential systolic and diastolic strain rates displayed moderate correlation to peak systolic (r=-0.38, p=0.022) and diastolic vorticity (r=0.40, p=0.015) values, respectively. *Results are reported as mean ± standard deviation.

Conclusion

Left ventricular vorticity metrics were observed to be higher in women than in men and displayed moderate correlation to cardiac strain metrics. The methods and results of this study may be used to further understand the sex-based cardiac efficiency relationship between cardiac function and flow.

Cerebrovascular haemodynamics during isometric resistance exercise with and without the Valsalva manoeuvre

PURPOSE

To examine the interactive effects of VM and isometric resistance exercise on cerebral haemodynamics.

METHODS

Eleven healthy participants (mean ± SD 28 ± 9 years; 2 females) completed 20-s bilateral isometric leg extension at 50% of maximal voluntary contraction with continued ventilation (RE), a 20-s VM at mouth pressure of 40 mmHg (VM), and a combination (RE + VM), in randomised order. Mean beat-to-beat blood velocity in the posterior (PCAv_mean) and middle cerebral arteries (MCAv_mean), vertebral artery blood flow, end-tidal partial pressure of CO₂ and mean arterial pressure (MAP) were measured. RE data were time aligned to RE + VM and analysed according to standard VM phases.

RESULTS

Interaction effects (VM phase × condition) were observed for MCAv_mean, PCAv_mean, vertebral artery blood flow and MAP (all ≤ 0.010). Phase I MCAv_mean was greatest for RE [88 ± 19, vs. 71 ± 11 and 78 ± 12 cm s^-1 for VM (P = 0.008) and RE + VM (P = 0.021), respectively]. Greater increases in MCAv_mean than PCAv_mean occurred in phase I of RE only (24 ± 15% vs. 16 ± 16%, post hoc P = 0.044). In phase IIb, MAP was lower in RE than RE + VM (115 ± 15 vs. 138 ± 21 mmHg, P = 0.004), but did not reduce MCAv_mean (78 ± 8 vs. 79 ± 9 cm s^-1, P = 0.579) or PCAv_mean (45 ± 11 vs .46 ± 11 cm s^-1, P = 0.617). Phase IIb MCAv_mean and PCAv_mean was lowest in VM (66 ± 6 and 39 ± 8 cm s^-1, respectively, all P < 0.001), whereas in Phase IV, MCAv_mean, PCAv_mean and MAP were greater in VM than in RE and RE + VM (all P < 0.020).

CONCLUSION

RE and RE + VM produce similar cerebrovascular responses despite different MAP profiles. However, the VM produced the greatest cerebrovascular challenge afterward.

A New Method for Assessment of Upright Posture Intolerance

BACKGROUND

Upright posture intolerance can be seen in a variety of diseases but the current methodology is not quantifiable and limits the ability to identify response to treatment.

METHODS

A standard questionnaire was developed to assess the following aspects of upright posture tolerance: (1) How long can you stand straight without any support? (2) Do you feel any sense of sickness when you sit or lie down after standing? (3) How long do you have to wait before you are comfortable standing again after you have stood straight? (4) How effectively and fast can you get up from sitting or lying position to stand straight? and (5) rate the ability to perform activities on a standard vertical visual analog scale between 100 (can do everything) and 0 (cannot do anything). We tested the ability of the questionnaire in four patients to identify various aspects of upright posture intolerance.

RESULTS

The questionnaire was administered to four patients who reported upright posture intolerance. The patients with either intracranial hypotension syndrome, postural hypotension, or Klippel-Feil syndrome reported less than optimal performance in four of five components of the questionnaire. The patient with vertebrobasilar ischemia reported less than optimal performance in two of five components.

CONCLUSIONS

A new questionnaire is developed for self-administration to identify various components of upright posture intolerance and detect response to treatment.

Influence of a neck compression collar on cerebrovascular and autonomic function in men and women

OBJECTIVE

Neck compression collars have been proposed to reduce injury to the brain caused by head impacts. Our objective was to test if compression of the carotid artery affected the baroreflex and influenced blood pressure control.

METHODS

Cerebrovascular and autonomic responses of healthy young men and women (n = 8 each) to paced deep breathing, Valsalva, and 70o head-up tilt with or without use of a Q-collar were determined. Continuous measurements of heart rate, beat-to-beat blood pressure, transcranial Doppler, and end-tidal gases were obtained. Heart rate variability was measured during supine rest and head-up tilt. Carotid artery and jugular vein cross-sectional area were measured at end-inhalation and end-exhalation using cross-sectional ultrasound images at diastole.

RESULTS

Wearing the collar reduced carotid cross-sectional area (CSA; P = 0.022; η2 = 0.03) and increased jugular CSA (P = 0.001; η 2 = 0.30). In both men and women, wearing the collar increased systolic blood pressure during Valsalva (P<0.05; η 2 = 0.38). In only men, wearing the collar resulted in prolonged pressure recovery time during Valsalva (P = 0.02; η 2 = 0.05). In only women, wearing the collar increased baseline diastolic (P = 0.026; η 2 = 0.09) and mean (P = 0.041; η 2 = 0.06) middle cerebral artery (MCA) blood flow velocity, which attenuated the normal increase of diastolic (P = 0.01; η 2 = 0.03) and mean (P = 0.038; η 2 = 0.02) MCA blood flow velocity during Valsalva. There were no effects of sex or collar on the responses to deep breathing (P>0.05), and there were no effects of the collar on cerebrovascular function, hemodynamics, cardiovagal baroreceptor sensitivity, or heart rate variability (P>0.05) during upright tilt.

CONCLUSION

Use of the Q-collar compresses both the jugular vein and carotid artery influencing sympathetic nerve activity in both men and women while influencing brain blood flow in women.

A Systematic Review and Meta-Analysis of Within-Person Changes in Cardiac Vagal Activity across the Menstrual Cycle: Implications for Female Health and Future Studies

Interest in cardiac vagal activity (CVA; e.g., parasympathetically-mediated heart rate variability) as a biomarker of physical and mental health has increased exponentially in recent years. However, the understanding of sources of within-person change (i.e., intra-individual variance) in CVA is lagging behind. This systematic review and meta-analysis summarizes and quantifies current empirical evidence of within-person changes in measures of CVA across the menstrual cycle in naturally-cycling premenopausal females. We conducted an extensive literature search following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement in five databases to identify observational studies with repeated measures of CVA in at least two menstrual cycle phases. A broad meta-analysis (n_studies = 37; n_individuals = 1,004) revealed a significant CVA decrease from the follicular to luteal phase (d = −0.39, 95% CI (−0.67, −0.11)). Furthermore, 21 studies allowed for finer-grained comparisons between each of two cycle phases (menstrual, mid-to-late follicular, ovulatory, early-to-mid luteal, and premenstrual). Significant decreases in CVA were observed from the menstrual to premenstrual (n_studies = 5; n_individuals = 200; d = −1.17, 95% CI (−2.18, −0.17)) and from the mid-to-late follicular to premenstrual phases (n_studies = 8; n_individuals = 280; d = −1.32, 95% CI (−2.35, −0.29)). In conclusion, meta-analyses indicate the presence of CVA fluctuations across the menstrual cycle. Future studies involving CVA should control for cycle phase. Recommendations for covarying or selecting cycle phase are provided.

Dynamic cerebral autoregulation is attenuated in young fit women

Young women exhibit higher prevalence of orthostatic hypotension with presyncopal symptoms compared to men. These symptoms could be influenced by an attenuated ability of the cerebrovasculature to respond to rapid blood pressure (BP) changes [dynamic cerebral autoregulation (dCA)]. The influence of sex on dCA remains unclear. dCA in 11 fit women (25 ± 2 years) and 11 age-matched men (24 ± 1 years) was compared using a multimodal approach including a sit-to-stand (STS) and forced BP oscillations (repeated squat-stand performed at 0.05 and 0.10 Hz). Prevalence of initial orthostatic hypotension (IOH; decrease in systolic ≥ 40 mmHg and/or diastolic BP ≥ 20 mmHg) during the first 15 sec of STS was determined as a functional outcome. In women, the decrease in mean middle cerebral artery blood velocity (MCAvmean ) following the STS was greater (-20 ± 8 vs. -11 ± 7 cm sec-1 ; P = 0.018) and the onset of the regulatory change (time lapse between the beginning of the STS and the increase in the conductance index (MCAvmean /mean arterial pressure) was delayed (P = 0.007). Transfer function analysis gain during 0.05 Hz squat-stand was ~48% higher in women (6.4 ± 1.3 vs. 3.8 ± 2.3 cm sec-1 mmHg-1 ; P = 0.017). Prevalence of IOH was comparable between groups (women: 4/9 vs. men: 5/9, P = 0.637). These results indicate the cerebrovasculature of fit women has an attenuated ability to react to rapid changes in BP in the face of preserved orthostasis, which could be related to higher resting cerebral blood flow allowing women to better face transient hypotension.

Chemoreflex function and brain blood flow during upright posture in men and women

Orthostatic intolerance is more common in women than men, and some studies have found that women in the early follicular (EF) phase of the menstrual cycle experience the greatest feelings of lightheadedness. Chemoreflex function while supine or upright was investigated to determine the potential contribution of ventilatory control to these phenomena. Men (n = 13) and women (n = 14) were tested while supine and 70° upright (head-up tilt [HUT]) and given: (1) normoxia or (2) hypercapnia (5% CO₂ ). Women were tested during the EF phase (days 2-5) and the midluteal phase (ML; days 18-24). During HUT, all groups reduced cerebrovascular resistance index (men: 1.45 ± 0.08 to 1.42 ± 0.07 mmHg/(cm·sec), EF: 1.38 ± 0.11 to 1.26 ± 0.10 mmHg/(cm·sec), ML: 1.25 ± 0.07 to 1.09 ± 0.07 mmHg/(cm·sec); P ≤ 0.019); however, only men increased ventilation (men: 11.99 ± 0.65 to 13.24 ± 0.83 L/min; P < 0.01). In response to hypercapnia in the supine position, men had a smaller increase of diastolic middle cerebral artery velocity compared to women in the ML phase (men: +9.1 ± 2.0 cm/sec, ML: +15.7 ± 3.1 cm/sec, P = 0.039). During hypercapnia in HUT (compared to hypercapnia while supine), all groups had an augmented increase of ventilation (men: +7.46 ± 1.34 vs. +5.84 ± 1.09 L/min, EF: +6.71 ± 0.83 vs. +5.48 ± 0.66 L/min, ML: +7.99 ± 1.13 vs. +5.65 ± 0.81 L/min; P ≤ 0.028), suggesting that all groups experienced augmentation of the CO₂ chemoreflex; however, only men had an augmented increase of mean arterial pressure (+0.10 ± 0.58 to +4.71 ± 0.87 mmHg; P ≤ 0.017). Our results indicate that men have different ventilatory responses to upright tilt compared to women, and that the CO₂ chemoreflex response is enhanced in upright posture in both sexes. Furthermore, sexually dimorphic blood pressure responses to this chemoreflex enhancement are evident.

Effect of the menstrual cycle on circulation during combined spinal-epidural anaesthesia

Background

From adolescence to menopause, hormone levels during the menstrual cycle affect various body systems, from the cardiovascular system to the water and electrolyte balance. This study investigated the effect of different phases of the menstrual cycle on circulatory function relative to changes in body position and combined spinal-epidural anaesthesia (CSEA).

Methods

Forty-six women were selected who underwent scheduled gynaecological surgery, were classified as American Society of Anesthesiology (ASA) I-II, and met the test criteria. The sample was divided into the follicular and corpus luteal groups. Preoperative heart rate and blood pressure measurements were taken from the supine and standing positions. Heart rate measurements as well as systolic, diastolic, and mean blood pressure measurements were taken upon entering the operating room, at the beginning of the spinal-epidural anaesthesia, and 10, 20, and 30 min after anaesthesia was administered.

Results

The heart rates of patients in the corpus luteal group were higher than those of patients in the follicular group both before and after anaesthesia (P <  0.05). Significantly more ephedrine was used during the first 30 min of CSEA in the corpus luteal group than in the follicular group (P <  0.05).

Conclusions

Although the effect was slight, women in the follicular phase were better able to compensate and tolerate circulatory fluctuations than those in the luteal phase.

Effect of epidural blood injection on upright posture intolerance in patients with headaches due to intracranial hypotension: A prospective study

BACKGROUND

We performed a prospective study to quantify changes in various aspects of upright posture intolerance in patients with intracranial hypotension.

METHODS

Six patients were provided a standard questionnaire before, immediately after epidural blood patch injection and at follow-up visit within 1 month after epidural blood injection inquiring: (a) How long can they stand straight without any support? (b) Do they feel any sense of sickness when they sit or lie down after standing? (c) How long do they have to wait before they are comfortable standing again after they have stood straight? (d) How effectively and fast can they get up from sitting or lying position to stand straight? and (e) Rate their activities in upright posture without support on a standard vertical visual analogue scale between 100 (can do everything) and 0 (cannot do anything).

RESULTS

All patients responded that they could not stand straight for ≥30 min (four responding <5 min) on pretreatment evaluation. All patients reported improvement in this measure immediately postprocedure with two reporting ≥30 min. At follow-up, three patients reported further improvement and one patient reported worsening in this measure. The magnitude of improvement ranged from 10 to 80 points increase immediately postprocedure in their ability to perform activities, while they are standing without any support on visual analogue scale. At follow-up, four patient reported additional improvement in their ability to perform activities, while they are standing without any support (ranged from 10 to 20 points increase compared with immediately postprocedure rating).

CONCLUSIONS

We present semiquantitative data on various aspects of upright posture intolerance in patients with intracranial hypotension before and after epidural blood injection.

Influence of sex, menstrual cycle, and oral contraceptives on the cerebrovascular response to paced deep breathing

PURPOSE

Deep breathing assesses autonomic function; however, many researchers/clinicians do not account for hyperventilation, brain blood flow or blood pressure.

METHODS

Men and women (with/without oral contraceptives) participated. women participated during low and high hormone phases of the menstrual cycle. Blood pressure, end-tidal carbon dioxide, middle cerebral artery velocity and cerebrovascular resistance were assessed.

RESULTS

Deep breathing decreased end-tidal carbon dioxide and middle cerebral artery velocity while increasing cerebrovascular resistance in all participants; blood pressure decreased in men. There were no influences of menstrual cycle or oral contraceptives.

CONCLUSIONS

Men have different autonomic responses to deep breathing compared to women.