Impact of the menstrual cycle on peripheral vascular function in premenopausal women: systematic review and meta-analysis

Evidence of reduced peripheral microvascular function in young Black women across the menstrual cycle

Black women (BLW) have a higher prevalence of cardiovascular disease (CVD) morbidity and mortality compared with White women (WHW). A racial disparity in CVD risk has been identified early in life as young adult BLW demonstrate attenuated vascular function compared with WHW. Previous studies comparing vascular function between premenopausal WHW and BLW have been limited to the early follicular (EF) phase of the menstrual cycle, which may not reflect their vascular function during other menstrual phases. Therefore, we evaluated peripheral microvascular function in premenopausal WHW and BLW using passive leg movement (PLM) during three menstrual phases: EF, ovulation (OV), and mid-luteal (ML). We hypothesized that microvascular function would be augmented during the OV and ML phases compared with the EF phase in both groups, but would be attenuated in BLW compared with WHW at all three phases. PLM was performed on 26 apparently healthy premenopausal women not using hormonal contraceptives: 15 WHW (23 ± 3 yr), 11 BLW (24 ± 5 yr). There was a main effect of race on the overall change in leg blood flow (ΔLBF) (P = 0.01) and leg blood flow area under the curve (LBF AUC) (P = 0.02), such that LBF was lower in BLW. However, there was no effect of phase on ΔLBF (P = 0.69) or LBF AUC (P = 0.65), nor an interaction between race and phase on ΔLBF (P = 0.37) or LBF AUC (P = 0.75). Despite peripheral microvascular function being unchanged across the menstrual cycle, a racial disparity was apparent as microvascular function was attenuated in BLW compared with WHW across the menstrual cycle.NEW & NOTEWORTHY This is the first study to compare peripheral microvascular function between young, otherwise healthy Black women and White women at multiple phases of the menstrual cycle. Our novel findings demonstrate a significant effect of race on peripheral microvascular function such that Black women exhibit significant attenuations in microvascular function across the menstrual cycle compared with White women.

Sex differences in microvascular function across lower leg muscles in humans

Studies have reported sex-based differences in conduit artery function, however little is known about possible sex-based differences in microvascular function, and possible influence of muscle group. Blood-oxygen-level-dependent (BOLD) MR images acquired during ischemia-reperfusion assess the reactive hyperemic response in the microvasculature of skeletal muscle. We tested the hypothesis that women have greater microvascular reactivity, reflected by faster time-to-peak (TTP) and time-to-half-peak (TTHP) of the BOLD response, across all lower leg muscles. In healthy, young men (n = 18) and women (n = 12), BOLD images of both lower legs were acquired continuously during 30 s of rest, 5 min of cuff occlusion and 2 min of reperfusion, in a 3 T MR scanner. Segmentation of tibialis anterior (TA), soleus (SO), gastrocnemius medial (GM), and the peroneal group (PG) were performed using image registration, and TTP and TTHP of the BOLD response were determined for each muscle. Overall, women had faster TTP (p = 0.001) and TTHP (p = 0.01) than men. Specifically, women had shorter TTP and TTHP in TA (27.5-28.4%), PG (33.9-41.6%), SO (14.7-19.7%) and GM (15.4-18.8%). Overall, TTP and TTHP were shorter in TA compared with PG (25.1-31.1%; p ≤ 0.007), SO (14.3-16%; p ≤ 0.03) and GM (15.6-26%; p ≤ 0.01). Intra class correlations analyses showed large variation in absolute agreement (range: 0.10-0.81) of BOLD parameters between legs (within distinct muscles). Faster TTP and TTHP across all lower leg muscles, in women, provide novel evidence of sex-based differences in microvascular function of young adults matched for age, body mass index, and physical activity level.

Moving beyond inclusion: Methodological considerations for the menstrual cycle and menopause in research evaluating effects of dietary nitrate on vascular function

Recent reports have acknowledged the underrepresentation of women in the field of dietary nitrate (NO₃^-) research. Undoubtedly, greater participation from women is warranted to clarify potential sex differences in the responses to dietary NO₃^- interventions. However, careful consideration for the effects of sex hormones - principally 17β-estradiol - on endogenous nitric oxide (NO) synthesis and dietary NO₃^- reductase capacity is necessary for improved interpretation and reproducibility of such investigations. From available literature, we present a narrative review describing how hormonal variations across the menstrual cycle, as well as with menopause, may impact NO biosynthesis catalyzed by NO synthase enzymes and NO₃^- reduction via the enterosalivary pathway. In doing so, we address methodological considerations related to the menstrual cycle and hormonal contraceptive use relevant for the inclusion of premenopausal women along with factors to consider when testing postmenopausal women. Adherence to such methodological practices may explicate the utility of dietary NO₃^- supplementation as a means to improve vascular function among women across the lifespan.

Similar inflammatory response and conduit artery vascular function between sexes following induced inflammation

NEW FINDINGS

What is the central question of this study? Are there sex differences in vascular function following induced inflammation when oestrogen is typically similar between sexes? What is the main finding and its importance? The present study suggests no sex differences in conduit artery vascular responses to acutely induced inflammation during the low-oestrogen phase of the menstrual cycle in premenopausal women. However, women exhibit lower microvascular function than men. Overall, the results underpin the role of oestrogen in previously observed sex differences and the importance of reporting the phase in the hormonal cycle when women are studied.

ABSTRACT

Sex differences in cardiovascular disease incidence in premenopausal women and age-matched men have been attributed to the cardioprotective influence of oestrogen. However, limited knowledge exists regarding sex differences following acute inflammation when oestrogen concentrations are lower in women. We evaluated sex differences in vascular responses to induced inflammation when oestrogen concentrations are typically lower in women (early follicular phase or placebo phase of hormonal contraception). In 15 women and 14 men, interleukin-6 (IL-6) concentrations and vascular function [via brachial artery flow-mediated dilatation (FMD)] were assessed at baseline (BL) and 24 (24H) and 48 hours (48H) after administration of influenza vaccine. After induction of inflammation, both sexes exhibited an increase in IL-6 concentrations at 24H [mean (SD) BL vs. 24H: women, 0.563 (0.50) vs. 1.141 (0.65) pg/ml; men, 0.385 (0.17) vs. 1.113 (0.69) pg/ml; P < 0.05] that returned to near-baseline concentrations by 48H (BL vs. 48H, P > 0.05). There were no sex differences in FMD, allometrically scaled FMD or IL-6 concentrations at any time point (P > 0.05). Notably, women exhibited significantly lower microvascular function than men at every time point [P < 0.05; reactive hyperaemic area under the curve (in arbitrary units): women, BL 35,512 (14,916), 24H 34,428 (14,292) and 48H 39,467 (13,936); men, BL 61,748 (27,324), 24H 75,028 (29,051) and 48H 59,532 (13,960)]. When oestrogen concentrations are typically lower in women, women exhibit a similar inflammatory response and conduit artery function, but lower microvascular response to reactive hyperaemia, in comparison to age-matched men.

Fitness Level- and Sex-related Differences in Macro- and Microvascular Responses during Reactive Hyperemia

PURPOSE

Reactive hyperemia (RH) is widely used for the investigation of macrovascular (Flow-Mediated Dilation, FMD) and microvascular (Near Infrared Spectroscopy-Vascular Occlusion Test, NIRS-VOT) function. Mixed results have been reported on fitness level- and sex-related differences in FMD outcomes, and little is known about microvascular differences in untrained and chronically trained males and females.

METHODS

Fifteen chronically trained (CT: 8 MALES, 7 FEMALES) and sixteen untrained (UT: 8 MALES, 8 FEMALES) individuals participated in this study. Aerobic fitness (V[Combining Dot Above]O2max) was assessed during a cycling incremental exercise test to volitional exhaustion. FMD and NIRS-VOT were performed simultaneously on the lower limb investigating superficial femoral artery and vastus lateralis muscle, respectively.

RESULTS

%FMD was not different between groups (CT MALES, 4.62 ± 1.42; CT FEMALES, 4.15 ± 2.23; UT MALES, 5.10 ± 2.53; CT FEMALES, 3.20 ± 1.67). Peak blood flow showed greater values in CT vs UT (p ≤ 0.0001) and MALES vs FEMALES (p = 0.032). RH blood flow AUC was greater in CT vs UT (p = 0.001). At the microvascular level, desaturation and reperfusion rates were faster in CT vs UT (p = 0.018 and p = 0.013) and MALES vs FEMALES (p = 0.011 and p = 0.005). V[Combining Dot Above]O2max was significantly correlated with reperfusion rate (p = 0.0005) but not with %FMD.

CONCLUSION

Whereas NIRS-VOT outcomes identified fitness- and sex-related differences in vascular responses, %FMD did not. However, when reactive hyperemia-related outcomes from the FMD analysis were considered, fitness- and/or sex-related differences were detected. These data highlight the importance of integrating FMD and NIRS-VOT outcomes for a more comprehensive evaluation of vascular function.

A single bout of exercise improves vascular insulin sensitivity in adults with obesity

OBJECTIVE

This crossover study explored the impact of a single bout of exercise on insulin-stimulated responses in conduit arteries and capillaries.

METHODS

Twelve sedentary adults (49.5 [7.8] years; maximal oxygen consumption [VO₂ max]: 23.7 [5.4] mL/kg/min) with obesity (BMI 34.5 [4.3] kg/m² ) completed a control and exercise bout (70% VO₂ max to expend 400 kcal). Sixteen hours later, participants underwent a 2-hour euglycemic-hyperinsulinemic clamp (90 mg/dL; 40 mU/m² /min) to determine vascular and metabolic insulin sensitivity. Endothelial and capillary functions were assessed by brachial artery flow-mediated dilation and contrast-enhanced ultrasound, respectively. Metabolized glucose infusion rate, substrate oxidation (indirect calorimetry), nonoxidative glucose disposal (NOGD), and inflammation were also determined.

RESULTS

Exercise increased insulin-stimulated preocclusion diameter (p = 0.01) and microvascular blood flow (condition effect: p = 0.04) compared with control. Furthermore, exercise improved metabolic insulin sensitivity by 21%, which paralleled rises in NOGD (p = 0.05) and decreases in soluble receptors for advanced glycation end products (condition effect: p = 0.01). Interestingly, changes in NOGD were related to increased insulin-stimulated microvascular blood flow (r = 0.57, p = 0.05).

CONCLUSIONS

A single bout of exercise increases vascular insulin sensitivity in adults with obesity. Additional work is needed to determine vascular responses following different doses of exercise in order to design lifestyle prescriptions for reducing chronic disease risk.

Responders and non-responders to aerobic exercise training: beyond the evaluation of V˙O2max

The evaluation of the maximal oxygen uptake ( V ˙ O 2 max ) following exercise training is the classical assessment of training effectiveness. Research has lacked in investigating whether individuals that do not respond to the training intervention ( V ˙ O 2 max ), also do not improve in other health-related parameters. We aimed to investigate the cardiovascular and metabolic adaptations (i.e., performance, body composition, blood pressure, vascular function, fasting blood markers, and resting cardiac function and morphology) to exercise training among participants who showed different levels of V ˙ O 2 max responsiveness. Healthy sedentary participants engaged in a 6-week exercise training program, three times a week. Our results showed that responders had a greater increase in peak power output, second lactate threshold, and microvascular responsiveness, whereas non-responders had a greater increase in cycling efficiency. No statistical differences were observed in body composition, blood pressure, fasting blood parameters, and resting cardiac adaptations. In conclusion, our study showed, for the first time, that in addition to the differences in the V ˙ O 2 max , a greater increase in microvascular responsiveness in responders compared to non-responders was observed. Additionally, responders and non-responders did not show differences in the adaptations on metabolic parameters. There is an increasing need for personalized training prescription, depending on the target clinical outcome.

Blood flow restriction in the presence or absence of muscle contractions does not preserve vasculature structure and function following 14-days of limb immobilization

PURPOSE

Limb immobilization causes local vasculature to experience detrimental adaptations. Simple strategies to increase blood flow (heating, fidgeting) successfully prevent acute (≤ 1 day) impairments; however, none have leveraged the hyperemic response over prolonged periods (weeks) mirroring injury rehabilitation. Throughout a 14-day unilateral limb immobilization, we sought to preserve vascular structure and responsiveness by repeatedly activating a reactive hyperemic response via blood flow restriction (BFR) and amplifying this stimulus by combining BFR with electric muscle stimulation (EMS).

METHODS

Young healthy adults (M:F = 14:17, age = 22.4 ± 3.7 years) were randomly assigned to control, BFR, or BFR + EMS groups. BFR and BFR + EMS groups were treated for 30 min twice daily (3 × 10 min ischemia-reperfusion cycles; 15% maximal voluntary contraction EMS), 5 days/week (20 total sessions). Before and after immobilization, artery diameter, flow-mediated dilation (FMD) and blood flow measures were collected in the superficial femoral artery (SFA).

RESULTS

Following immobilization, there was less retrograde blood velocity (+ 1.8 ± 3.6 cm s^-1, P = 0.01), but not retrograde shear (P = 0.097). All groups displayed reduced baseline and peak SFA diameter following immobilization (- 0.46 ± 0.41 mm and - 0.43 ± 0.39 mm, P < 0.01); however, there were no differences by group or across time for FMD (% diameter change, shear-corrected, or allometrically scaled) nor microvascular function assessed by peak flow capacity.

CONCLUSION

Following immobilization, our results reveal (1) neither BFR nor BFR + EMS mitigate artery structure impairments, (2) intervention-induced shear stress did not affect vascular function assessed by FMD, and (3) retrograde blood velocity is reduced at rest offering potential insight to mechanisms of flow regulation. In conclusion, BFR appears insufficient as a treatment strategy for preventing macrovascular dysfunction during limb immobilization.

Individual variation of follicular phase changes in endothelial function across two menstrual cycles

NEW FINDINGS

What is the central question of this study? The purpose of this study was to determine intra-individual reproducibility of follicular phase changes in endothelial function (flow-mediated dilatation) over two menstrual cycles in healthy, premenopausal women. What is the main finding and its importance? Phase changes in endothelial function were not consistent at the individual level across two menstrual cycles, which challenges the utility of interpreting individual responses over one cycle.

ABSTRACT

Evidence regarding the impact of menstrual phase on endothelial function is conflicting, and studies to date have examined responses only over a single cycle. It is unknown whether the observed inter-individual variability of phase changes in endothelial function reflects stable, inter-individual differences in responses to oestrogen (E₂ ; a primary female sex hormone). The purpose of this study was to examine changes in endothelial function from the early follicular (EF; low-E₂ ) phase to the late follicular (LF; high-E₂ ) phase over two consecutive cycles. Fourteen healthy, regularly menstruating women [22 ± 3 years of age (mean ± SD)] participated in four visits (EF_Visit 1 , LF_Visit 2 , EF_Visit 3 and LF_Visit 4 ) over two cycles. Ovulation testing was used to determine the time between the LF visit and ovulation. During each visit, endothelial function [brachial artery flow-mediated dilatation (FMD)], E₂ and progesterone were assessed. At the group level, there was no impact of phase or cycle on FMD (P = 0.48 and P = 0.65, respectively). The phase change in FMD in cycle 1 did not predict the phase change in cycle 2 (r = 0.03, P = 0.92). Using threshold-based classification (2 × typical error threshold), four of 14 participants (29%) exhibited directionally consistent phase changes in FMD across cycles. Oestrogen was not correlated between cycles, and this might have contributed to variability in the FMD response. The intra-individual variability in follicular fluctuation in FMD between menstrual cycles challenges the utility of interpreting individual responses to phase over a single menstrual cycle.

Effect of menopause on cerebral artery blood flow velocity and cerebrovascular reactivity: Systematic review and meta-analysis

BACKGROUND

Menopause and its associated decline in oestrogen is linked to chronic conditions like cardiovascular disease and osteoporosis, which may be difficult to disentangle from the effects of ageing. Further, post-menopausal women are at increased risk of cerebrovascular disease, linked to declines in cerebral blood flow (CBF) and cerebrovascular reactivity (CVR), yet the direct understanding of the impact of the menopause on cerebrovascular function is unclear. The aim of this systematic review and meta-analysis was to examine the literature investigating CBF and CVR in pre- compared with post-menopausal women METHODS: Five databases were searched for studies assessing CBF or CVR in pre- and post-menopausal women. Meta-analysis examined the effect of menopausal status on middle cerebral artery velocity (MCAv), and GRADE-assessed evidence certainty RESULTS: Nine studies (n=504) included cerebrovascular outcomes. Six studies (n=239) reported negligible differences in MCAv between pre- and post-menopausal women [2.11cm/s (95% CI: -8.94 to 4.73, p=0.54)], but with a "low" certainty of evidence. MCAv was lower in post-menopausal women in two studies, when MCAv was adjusted for blood pressure. CVR was lower in post- compared with pre-menopausal women in two of three studies, but high-quality evidence is lacking. Across outcomes, study methodology and reporting criteria for menopause were inconsistent CONCLUSIONS: MCAv was similar in post- compared with pre-menopausal women. Methodological differences in characterising menopause and inconsistent reporting of cerebrovascular outcomes make comparisons difficult. Comprehensive assessments of cerebrovascular function of the intra- and extracranial arteries to determine the physiological implications of menopause on CBF with healthy ageing is warranted.