Menstrual cycle effects on sympathetic neural responses to upright tilt

Frequency-Domain Features and Low-Frequency Synchronization of Photoplethysmographic Waveform Variability and Heart Rate Variability with Increasing Severity of Cardiovascular Diseases

Objective-Heart rate variability (HRV) and photoplethysmographic waveform variability (PPGV) are available approaches for assessing the state of cardiovascular autonomic regulation. The goal of our study was to compare the frequency-domain features and low-frequency (LF) synchronization of the PPGV and HRV with increasing severity of cardiovascular diseases. Methods-Our study included 998 electrocardiogram (ECG) and finger photoplethysmogram (PPG) recordings from subjects, classified into five categories: 53 recordings from healthy subjects, aged 28.1 ± 6.2 years, 536 recordings from patients with hypertension (HTN), 49.0 ± 8.8 years old, 185 recordings from individuals with stable coronary artery disease (CAD) (63.9 ± 9.3 years old), 104 recordings from patients with myocardial infarction (MI) that occurred three months prior to the recordings (PMI) (65.1 ± 11.0 years old), and 120 recordings from study subjects with acute myocardial infarction (AMI) (64.7 ± 11.5 years old). Spectral analyses of the HRV and PPGV were carried out, along with an assessment of the synchronization strength between LF oscillations of the HRV and of PPGV (synchronization index). Results-Changes in all frequency-domain indices and the synchronization index were observed along the following gradient: healthy subjects → patients with HTN → patients with CAD → patients with PMI → patients with AMI. Similar frequency-domain indices of the PPGV and HRV show little relationship with each other. Conclusions-The frequency-domain indices of the PPGV are highly sensitive to the development of any cardiovascular disease and, therefore, are superior to the HRV indices in this regard. The S index is an independent parameter from the frequency-domain indices.

Does a single oral administration of amiloride affect spontaneous arterial baroreflex sensitivity and blood pressure variability in healthy young adults?

Preclinical models indicate that amiloride (AMD) reduces baroreflex sensitivity and perturbs homeostatic blood pressure (BP) regulation. However, it remains unclear whether these findings translate to humans. This study investigated whether oral administration of AMD reduces spontaneous cardiac and sympathetic baroreflex sensitivity and perturbs BP regulation in healthy young humans. Heart rate (HR; electrocardiography), beat-to-beat BP (photoplethysmography), and muscle sympathetic activity (MSNA, microneurography) were continuously measured in 10 young subjects (4 females) during rest across two randomized experimental visits: 1) after 3 h of oral administration of placebo (PLA, 10 mg of methylcellulose within a gelatin capsule) and 2) after 3 h of oral administration of AMD (10 mg). Visits were separated for at least 48 h. We calculated the standard deviation and other indices of BP variability. Spontaneous cardiac baroreflex was assessed via the sequence technique and cardiac autonomic modulation through time- and frequency-domain HR variability. The sensitivity (gain) of the sympathetic baroreflex was determined via weighted linear regression analysis between MSNA and diastolic BP. AMD did not affect HR, BP, and MSNA compared with PLA. Indexes of cardiac autonomic modulation (time- and frequency-domain HR variability) and BP variability were also unchanged after AMD ingestion. Likewise, AMD did not modify the gain of both spontaneous cardiac and sympathetic arterial baroreflex. A single oral dose of AMD does not affect spontaneous arterial baroreflex sensitivity and BP variability in healthy young adults.NEW & NOTEWORTHY Preclinical models indicate that amiloride (AMD), a nonselective antagonist of the acid-sensing ion channels (ASICs), impairs baroreflex sensitivity and perturbs blood pressure regulation. We translated these findings into humans, investigating the impact of acute oral ingestion of AMD on blood pressure variability and spontaneous cardiac and sympathetic baroreflex sensitivity in healthy young humans. In contrast to preclinical evidence, AMD does not impair spontaneous arterial baroreflex sensitivity and blood pressure variability in healthy young adults.

Sympathetic baroreflex sensitivity is enhanced in postmenopausal women

The sympathetic nervous system is critical for regulating blood pressure (BP) via the arterial baroreflex and sympathetic transduction in the peripheral vasculature. These mechanisms interact, and both may be altered with aging and impacted by menopause. Although age-related decreases in sympathetic transduction have been demonstrated in women, it remains unclear whether sympathetic baroreflex sensitivity (BRS) is impaired in postmenopausal women (POST). We tested the hypothesis that sympathetic BRS would be enhanced in POST compared with premenopausal women (PRE). We examined beat-by-beat BP and muscle sympathetic nerve activity (MSNA) in 19 PRE (22 ± 2 yr, 22 ± 3 kg/m2) and 12 POST (57 ± 5 yr, 24 ± 2 kg/m2) during 10 min of rest. Spontaneous sympathetic BRS was quantified as the slope of a linear regression between MSNA burst incidence and diastolic BP. Sympathetic transduction to mean arterial pressure (MAP) for the 10 cardiac cycles following spontaneous MSNA bursts was assessed via signal averaging method. Resting MAP was similar (PRE: 82 ± 8 vs. POST: 85 ± 8 mmHg, P = 0.43), whereas resting MSNA was elevated in POST (PRE: 10 ± 6 vs. POST: 45 ± 16 bursts/100 heart beats, P < 0.0001). Spontaneous sympathetic BRS was enhanced in POST (PRE: -2.0 ± 1.2 vs. POST: -5.2 ± 1.9 bursts/beat/mmHg, P < 0.0005). Sympathetic transduction to MAP was attenuated in POST (time: P < 0.001, group: P < 0.001, interaction: P < 0.01). These data suggest that sympathetic BRS may be enhanced in POST. Consistent with recent hypotheses, enhanced sensitivity of the arterial baroreflex's neural arc may signify a compensatory response to reduced efficiency of the peripheral arterial baroreflex arc (i.e., sympathetic transduction) to preserve BP buffering capacity.NEW & NOTEWORTHY Studies examining sympathetic baroreflex function with aging remain equivocal, with some studies showing an increase, decrease, or no change in sympathetic baroreflex sensitivity (BRS) in older adults compared with younger adults. With aging, women experience unique physiological changes due to menopause that influence autonomic function. For the first time, we show that postmenopausal women exhibit a greater sympathetic BRS compared with young premenopausal women.

The interactive effects of posture and biological sex on the control of muscle sympathetic nerve activity during rhythmic handgrip exercise

Body posture and biological sex exhibit independent effects on the sympathetic neural responses to dynamic exercise. However, the neural mechanisms (e.g., baroreflex) by which posture impacts sympathetic outflow during rhythmic muscular contractions, and whether biological sex affects posture-mediated changes in efferent sympathetic nerve traffic during exercise, remain unknown. Thus, we tested the hypotheses that increases in muscle sympathetic nerve activity (MSNA) would be greater during upright compared with supine rhythmic handgrip (RHG) exercise, and that females would demonstrate smaller increases in MSNA during upright RHG exercise than males. Twenty young (30 [6] yr; means [SD]) individuals (9 males, 11 females) underwent 6 min of supine and upright (head-up tilt 45°) RHG exercise at 40% maximal voluntary contraction with continuous measurements of MSNA (microneurography), blood pressure (photoplethysmography), and heart rate (electrocardiogram). In the pooled group, absolute MSNA burst frequency (P < 0.001), amplitude (P = 0.009), and total MSNA (P < 0.001) were higher during upright compared with supine RHG exercise. However, body posture did not impact the peak change in MSNA during RHG exercise (range: P = 0.063-0.495). Spontaneous sympathetic baroreflex gain decreased from rest to RHG exercise (P = 0.006) and was not impacted by posture (P = 0.347). During upright RHG exercise, males demonstrated larger increases in MSNA burst amplitude (P = 0.002) and total MSNA (P = 0.001) compared with females, which coincided with greater reductions in sympathetic baroreflex gain among males (P = 0.004). Collectively, these data indicate that acute attenuation of baroreflex-mediated sympathoinhibition permits increases in MSNA during RHG exercise and that males exhibit a greater reserve for efferent sympathetic neural recruitment during orthostasis than females.NEW & NOTEWORTHY The impact of posture and sex on cardiovascular control during rhythmic handgrip (RHG) exercise is unknown. We show that increases in muscle sympathetic nerve activity (MSNA) during RHG are partly mediated by a reduction in sympathetic baroreflex gain. In addition, males demonstrate larger increases in total MSNA during upright RHG than females. These data indicate that the baroreflex partly mediates increases in MSNA during RHG and that males have a greater sympathetic vasoconstrictor reserve than females.

Sympathetic Neural Control at Rest and During the Cold Pressor Test in Patients With Heart Failure With Preserved Ejection Fraction

BACKGROUND

We tested the hypothesis that patients with heart failure with preserved ejection fraction (HFpEF) would have greater muscle sympathetic nerve activity (MSNA) at rest and sympathetic reactivity during a cold pressor test compared with non-heart failure controls. Further, given the importance of the baroreflex modulation of MSNA in the control of blood pressure (BP), we hypothesized that patients with HFpEF would exhibit a reduced sympathetic baroreflex sensitivity.

METHODS

Twenty-eight patients with HFpEF and 44 matched controls (mean±SD: 71±8 versus 70±7 years; 9 men/19 women versus 16 men/28 women) were studied. BP, heart rate, and MSNA (microneurography) were measured during 6 to 10 minutes of supine rest and the 2-minute cold pressor test. Spontaneous sympathetic baroreflex sensitivity was assessed during supine rest.

RESULTS

Patients with HFpEF had higher resting MSNA burst frequency (39±14 versus 31±12 bursts/min; P=0.020) and lower sympathetic baroreflex sensitivity (-2.83±0.76 versus -3.57±1.19 bursts/100 heartbeats/mm Hg; P=0.019) than controls, but burst incidence was not different between groups (56±19 versus 50±20 bursts/100 heartbeats; P=0.179). During the cold pressor test, increases in MSNA indices did not differ between groups (P=0.135-0.998), but patients had a smaller increase in diastolic BP (Δ4±6 versus Δ14±11 mm Hg; P<0.001) compared with controls.

CONCLUSIONS

Despite augmented resting MSNA burst frequency, burst incidence was not significantly different between groups, and sympathetic baroreflex sensitivity was reduced in patients with HFpEF. Furthermore, patients had preserved sympathetic reactivity but attenuated diastolic BP responses during the cold pressor test. These data suggest that, during physiological stress, sympathetic reactivity is intact, but the peripheral pathway for sympathetic vasoconstriction may be impaired in HFpEF.

Influence of sex on sympathetic vasomotor outflow responses to passive leg raising in young individuals

The purpose of this study was to clarify sex differences in the inhibition of sympathetic vasomotor outflow which is caused by the loading of cardiopulmonary baroreceptors. Ten young males and ten age-matched females participated. The participants underwent a passive leg raising (PLR) test wherein they were positioned supine (baseline, 0º), and their lower limbs were lifted passively at 10º, 20º, 30º, and 40º. Each angle lasted for 3 min. Muscle sympathetic nerve activity (MSNA) was recorded via microneurography of the left radial nerve. Baseline MSNA was lower in females compared to males. MSNA burst frequency was decreased during the PLR in both males (- 6.2 ± 0.4 bursts/min at 40º) and females (- 6.5 ± 0.4 bursts/min at 40º), but no significant difference was detected between the two groups (P = 0.61). These results suggest that sex has minimal influence on the inhibition of sympathetic vasomotor outflow during the loading of cardiopulmonary baroreceptors in young individuals.

Investigation of postural sensory organization in women with and without primary dysmenorrhea in three phases of the menstrual cycle

BACKGROUND

The effects of the menstrual cycle in women with and without primary dysmenorrhea on phase-related postural sensory organization are controversial.

RESEARCH QUESTION

This study was carried out to examine postural sensory organization in three phases of the menstrual cycle in women with and without primary dysmenorrhea and to evaluate whether there is a difference between women with/without primary dysmenorrhea in this regard.

METHODS

Women aged 18-30 years were divided into two groups as primary dysmenorrhea group (PDG, n = 14) and control group (CG, n = 15). Computerized dynamic posturography were applied to the participants on the follicular, ovulation, and luteal phases of the menstrual cycle. Outcome measures were antero-posterior and medio-lateral Sensory Organization Test (SOT-somatosensory, vestibular and visual scores) and Limits of Stability test (LoS). The findings obtained were analyzed with the two-factor ANOVA, paired samples t test, and independent samples t test.

RESULTS

In the PDG, follicular phase antero-posterior somatosensory scores were lower compared to luteal phase (p = 0.002). Follicular phase antero-posterior and medio-lateral vestibular scores were lower than ovulation (p = 0.003, p = 0.004, respectively) and luteal (p = 0.005, p = 0.001, respectively) phases. Follicular phase LoS scores were lower than ovulation (p = 0.001) and luteal (p = 0.002) phases. In the CG, ovulation phase antero-posterior somatosensory scores were lower than follicular phase (p = 0.003). Follicular phase LoS scores were lower than ovulation phase (p = 0.002). The PDG had lower follicular phase antero-posterior somatosensory (p = 0.019), vestibular (p = 0.031), and medio-lateral somatosensory (p = 0.019) scores than those of the CG. The PDG had lower luteal phase antero-posterior somatosensory scores than those of the CG (p = 0.029). The PDG showed lower follicular phase LoS scores than those of the CG (p = 0.009).

SIGNIFICANCE

This study revealed that primary dysmenorrhea impairs postural sensory organization. Decreased sensory organization may predispose women to injury. The risk of injury should be investigated and necessary precautions should be taken.

Spontaneous baroreflex sensitivity is attenuated in male UCD-type 2 diabetes mellitus rats: A link between metabolic and autonomic dysfunction

Patients with type 2 diabetes mellitus (T2DM) have impaired arterial baroreflex function, which may be linked to the co-existence of obesity. However, the role of obesity and its related metabolic impairments on baroreflex dysfunction in T2DM is unknown. This study aimed to investigate the role of visceral fat and adiponectin, the most abundant cytokine produced by adipocytes, on baroreflex dysfunction in T2DM rats. Experiments were performed in adult male UCD-T2DM rats assigned to the following experimental groups (n = 6 in each): prediabetic (Pre), diabetes-onset (T0), 4 weeks after onset (T4), and 12 weeks after onset (T12). Age-matched healthy Sprague-Dawley rats were used as controls. Rats were anesthetized and blood pressure was directly measured on a beat-to-beat basis to assess spontaneous baroreflex sensitivity (BRS) using the sequence technique. Dual-energy X-ray absorptiometry (DEXA) was used to assess body composition. Data are presented as mean ± SD. BRS was significantly lower in T2DM rats compared with controls at T0 (T2D: 3.7 ± 3.2 ms/mmHg vs Healthy: 16.1 ± 8.4 ms/mmHg; P = 0.01), but not at T12 (T2D: 13.4 ± 8.1 ms/mmHg vs Healthy: 9.2 ± 6.0 ms/mmHg; P = 0.16). T2DM rats had higher visceral fat mass, adiponectin, and insulin concentrations compared with control rats (all P < 0.01). Changes in adiponectin and insulin concentrations over the measured time-points mirrored one another and were opposite those of the BRS in T2DM rats. These findings demonstrate that obesity-related metabolic impairments may contribute to an attenuated spontaneous BRS in T2DM, suggesting a link between metabolic and autonomic dysfunction.

Habitual physical activity improves vagal cardiac modulation and carotid baroreflex function in elderly women

The impact of habitual physical activity on vagal-cardiac function and baroreflex sensitivity in elderly women is poorly characterized. This study compared vagal-cardiac modulation and carotid baroreflex (CBR) function in eight physically active (67.6 ± 1.9 years; peak O2 uptake 29.1 ± 2.5 mL/min/kg) versus eight sedentary (67.3 ± 1.8 years; peak O2 uptake 18.6 ± 0.9 mL/min/kg) elderly women. Heart rate (HR) variabilities and maximal changes of HR and mean arterial pressure (MAP) elicited by 5-s pressure pulses between +40 and -80 mmHg applied to the carotid sinus were measured at rest and during carotid baroreceptor unloading effected by -15 mmHg lower-body negative pressure (LBNP). HR variability was greater in active than sedentary women in both low (0.998 ± 0.286 versus 0.255 ± 0.063 bpm2; P = 0.036) and high (0.895 ± 0.301 versus 0.156 ± 0.045 bpm2; P = 0.044) frequency domains. CBR-HR gains (bpm/mmHg) were greater (fitness factor P < 0.001) in active versus sedentary women at rest (-0.146 ± 0.014 versus -0.088 ± 0.011) and during LBNP (-0.105 ± 0.014 versus -0.065 ± 0.008). CBR-MAP gains (mmHg/mmHg) tended to be greater (fitness factor P = 0.077) in active versus sedentary women at rest (-0.132 ± 0.013 versus -0.110 ± 0.011) and during LBNP (-0.129 ± 0.015 versus -0.113 ± 0.013). However, LBNP did not potentiate CBR-MAP gains in either sedentary or active women (LBNP factor P = 0.94), and it depressed CBR-HR gains in both groups (LBNP factor P = 0.003). CBR-HR gains in the sedentary women did not differ (sex factor P = 0.65) from gains reported in age-matched sedentary men, although CBR-MAP gains tended to be greater (sex factor P = 0.109) in the men. Thus, tonic vagal modulation indicated by HR variability and dynamic vagal responses assessed by CBR-HR gain were augmented in physically active women. Enhanced vagal-cardiac function may protect against senescence-associated cardiac electrical and hemodynamic instability in elderly women.

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.

Posture-related changes in sympathetic baroreflex sensitivity during normal pregnancy

Normal pregnancy is associated with vast adjustments in cardiovascular autonomic control. Sympathetic baroreflex sensitivity has been reported to be attenuated during pregnancy in animal models, but most studies in humans are cross-sectional and findings from longitudinal case studies are inconclusive. It remains unclear how sympathetic baroreflex sensitivity is altered longitudinally during pregnancy within an individual in different body postures. Therefore, this study examined the impact of posture on sympathetic baroreflex sensitivity in 24 normal-weight normotensive pregnant women. Spontaneous sympathetic baroreflex sensitivity was assessed during early (6-11 weeks) and late (32-36 weeks) pregnancy and 6-10 weeks postpartum in the supine posture and graded head-up tilt (30° and 60°). In addition, data from the postpartum period were compared with (and no different to) 18 age-matched non-pregnant women to confirm that the postpartum period was reflective of a non-pregnant condition (online supplement). When compared with postpartum (-3.8 ± 0.4 bursts/100 heartbeats/mmHg), supine sympathetic baroreflex sensitivity was augmented during early pregnancy (-5.9 ± 0.4 bursts/100 heartbeats/mmHg, P < 0.001). However, sympathetic baroreflex sensitivity at 30° or 60° head-up tilt was not different between any phase of gestation (P > 0.05). When compared to supine, sympathetic baroreflex sensitivity at 60° head-up tilt was significantly blunted during early (Δ2.0 ± 0.7 bursts/100 heartbeats/mmHg, P = 0.024) and late (Δ1.5 ± 0.6 bursts/100 heartbeats/mmHg, P = 0.049) pregnancy but did not change postpartum (Δ0.4 ± 0.6 bursts/100 heartbeats/mmHg, P = 1.0). These data show that time-course changes in sympathetic baroreflex sensitivity are dependent on the posture it is examined in and provides a foundation of normal blood pressure regulation during pregnancy for future studies in women at risk for adverse pregnancy outcomes.

Women have a greater cardiac vagal withdrawal to heat stress compared to men

The heated environment shifts the sympatho-vagal balance toward sympathetic predominance and vagal withdrawal. Women's heart is more reliant on vagal autonomic control, while men's heart is more dependent on sympathetic control. However, sex differences in cardiovascular autonomic responses to heat stress remain unknown. We aimed to investigate the cardiovascular autonomic regulation under heat stress between sexes. Thirty-two young participants (27 ± 4 years old; 16 women) were enrolled in a single visit, resting for 30min at baseline (thermal reference condition TC; ∼24°C) and 30min under a heated environment (HOT; ∼38°C). Blood pressure (BP), skin temperature, electrocardiogram, and respiratory oscillations were continuously recorded. The heart rate variability (HRV) was assessed by spectral analysis (low-frequency [LFnu; sympathetic and vagal] and high-frequency [HFnu; vagal]), and symbolic analysis (0 V% [sympathetic] and 2UV%, and 2LV% [vagal]). The spontaneous baroreflex sensitivity (BRS) was calculated by the gain between BP and R-R within the LF band (αLF). The estimated maximal aerobic capacity and body surface area were employed as covariates in sex comparisons. The effects of HOT were the following: 1) Women have a greater cardiac vagal withdrawal to heat stress compared to men; 2) Sex differences on cardiac autonomic response to heat stress exist after controlling for the effect of estimated physical fitness and body surface area. Therefore, heat stress provokes a higher vagal withdrawal to the heart in women compared to men. It could be attributed to sex per se since significant differences between men and women were not modified after covariate analysis.

Hemodynamic stability during menstrual cycle in women undergoing elective surgery

Objective

Hemodynamic changes occur in almost one-third of patients undergoing spinal anesthesia, which are likely to effect vital organ. The aim of this study is to determine the hemodynamic effect of spinal anesthesia during different phases of menstrual cycle.

Methods

This is a descriptive cross-sectional study, two hundred and seventy-three patients who underwent spinal anesthesia for elective surgery were enrolled in this study. Of all the patients, 141 patients were in the luteal phase and 132 patients were in the follicular phase of their menstrual cycle. Analytical epidemiological study was conducted using questionnaires. Blood pressure and heart rate of patients before, immediately after, and 1 h after spinal anesthesia were recorded, and the data were analyzed using SPSS software.

Results

In the follicular phase before anesthesia, systolic blood pressure (SBP) was 127.5 ± 3.9, diastolic blood pressure (DBP) was 80.3 ± 6.2 mmHg and heart rate (HR) was 82.0 ± 8.5bpm, while, immediately after the induction of anesthesia following recordings were measured; 109.7 ± 9.13, 71.8 ± 2.8 mmHg and 70.0 ± 8.10bpm, respectively. In the luteal phase, it was 126.9 ± 3.12, 81.6 ± 9.3 mmHg and 80.2 ± 4.4bpm, and 122.0 ± 9.12, 78.6 ± 8.5 mmHg and 75.9 ± 6.5bpm respectively before and immediately after anesthesia, these changes in the menstrual phase was significant (P < 0.001). In the follicular phase an hour after spinal anesthesia, the mean SBP was 100.3 ± 3.9, DBP was 71.2 ± 7.5, MAP was 87.0 ± 4.7 mmHg and HR 67.5 ± 5.7bpm and following was seen in luteal phase; 115.4 ± 1.8, 75.9 ± 2.3, 97.3 ± 3.5 mm Hg and 74.0 ± 7.4bpm, respectively. These values were significantly lower in the follicular phase (P < 0.001).

Conclusion

Spinal anesthesia in the luteal phase as compared to the follicular phase of the menstrual cycle shows less variation in hemodynamic parameters.

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Hemodynamic changes occur in almost one-third of patients undergoing spinal anesthesia.

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Spinal anesthesia in the luteal phase as compared to the follicular phase of the menstrual cycle.

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Our study did not measure the levels of progesterone and estrogen.

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Comparative studies including women with circulatory abnormalities, preoperative and postoperative analysis.

Aging is associated with enhanced central, but impaired peripheral arms of the sympathetic baroreflex arc

We tested the hypothesis that the baroreflex control of action potential (AP) subpopulations would be blunted in older compared to young adults. Integrated muscle sympathetic nerve activity (MSNA) and the underlying sympathetic APs were obtained using microneurography and a continuous wavelet analysis approach, respectively, during 5 minutes of supine rest in 13 older (45-75 years, 6 females) and 14 young (21-30 years, 7 females) adults. Baroreflex threshold relationships were quantified as the slope of the linear regression between MSNA burst probability (%) and diastolic blood pressure (mmHg), or AP cluster firing probability (%) and diastolic blood pressure (mmHg). Integrated MSNA baroreflex threshold gain was greater in older compared to young adults (older: -7.6±3.6 %/mmHg vs. Young: -3.5±1.5 %/mmHg, P<0.001). Similarly, the baroreflex threshold gain of AP clusters was modified by aging (group-by-cluster effect: P<0.001) such that older adults demonstrated greater baroreflex threshold gains of medium-sized AP clusters (e.g., Cluster 4, older: -8.2±3.2 %/mmHg vs. Young: -3.6±1.9 %/mmHg, P=0.003) but not for the smallest- (Cluster 1, older: -1.6±1.9 %/mmHg vs. Young: -1.0±1.7 %/mmHg, P>0.999) and largest-sized (Cluster 10, older: -0.5±0.5 %/mmHg vs. Young: -0.2±0.1 %/mmHg, P=0.819) AP clusters compared to young adults. In contrast, the peak change in mean arterial pressure (MAP) following a spontaneous MSNA burst (i.e., sympathetic transduction) was impaired with aging (older: -0.7±0.3 mmHg vs. Young: 1.8±1.2 mmHg, P<0.001). We conclude that aging is associated with elevated baroreflex control over high-probability AP content of sympathetic bursts that may compensate for impaired sympathetic neurovascular transduction.

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.

Relationship Between Baroreflex and Cerebral Autoregulation in Patients With Cerebral Vasospasm After Aneurysmal Subarachnoid Hemorrhage

Introduction: Common consequences following aneurysmal subarachnoid hemorrhage (aSAH) are cerebral vasospasm (CV), impaired cerebral autoregulation (CA), and disturbance in the autonomic nervous system, as indicated by lower baroreflex sensitivity (BRS). The compensatory interaction between BRS and CA has been shown in healthy volunteers and stable pathological conditions such as carotid atherosclerosis. The aim of this study was to investigate whether the inverse correlation between BRS and CA would be lost in patients after aSAH during vasospasm. A secondary objective was to analyze the time-trend of BRS after aSAH.

Materials and Methods: Retrospective analysis of prospectively collected data was performed at the Neuro-Critical Care Unit of Addenbrooke's Hospital (Cambridge, UK) between June 2010 and January 2012. The cerebral blood flow velocity (CBFV) was measured in the middle cerebral artery using transcranial Doppler ultrasonography (TCD). The arterial blood pressure (ABP) was monitored invasively through an arterial line. CA was quantified by the correlation coefficient (Mxa) between slow oscillations in ABP and CBFV. BRS was calculated using the sequential cross-correlation method using the ABP signal.

Results: A total of 73 patients with aSAH were included. The age [median (lower-upper quartile)] was 58 (50–67). WFNS scale was 2 (1–4) and the modified Fisher scale was 3 (1–3). In the total group, 31 patients (42%) had a CV and 42 (58%) had no CV. ABP and CBFV were higher in patients with CV during vasospasm compared to patients without CV (p = 0.001 and p < 0.001). There was no significant correlation between Mxa and BRS in patients with CV, neither during nor before vasospasm. In patients without CV, a significant, although moderate correlation was found between BRS and Mxa (r_S = 0.31; p = 0.040), with higher BRS being associated with worse CA. Multiple linear regression analysis showed a significant worsening of BRS after aSAH in patients with CV (R_p = −0.42; p < 0.001).

Conclusions: Inverse compensatory correlation between BRS and CA was lost in patients who developed CV after aSAH, both before and during vasospasm. The impact of these findings on the prognosis of aSAH should be investigated in larger studies.

Blood withdrawal acutely impairs cardiac filling, output and aerobic capacity in proportion to induced hypovolemia in middle-aged and older women

Blood donation entails acute reductions of cardiorespiratory fitness in healthy men. Whether these effects can be extrapolated to blood donor populations comprising women remains uncertain. The purpose of this study was to comprehensively assess the acute impact of blood withdrawal on cardiac function, central hemodynamics and aerobic capacity in women throughout the mature adult lifespan. Transthoracic echocardiography and O2 uptake were assessed at rest and throughout incremental exercise (cycle ergometry) in healthy women (n = 30, age: 47-77 yr). Left ventricular end-diastolic volume (LVEDV), stroke volume (SV), cardiac output (Q̇) and peak O2 uptake (V̇O2peak), and blood volume (BV) were determined with established methods. Measurements were repeated following a 10% reduction of BV within a week period. Individuals were non-smokers, non-obese and moderately fit (V̇O2peak = 31.4 ± 7.3 mL·min-1·kg-1). Hematocrit and BV ranged from 38.0 to 44.8% and from 3.8 to 6.6 L, respectively. The standard 10% reduction in BV resulted in 0.5 ± 0.1 L withdrawal of blood, which did not alter hematocrit (P = 0.953). Blood withdrawal substantially reduced cardiac LVEDV and SV at rest as well as during incremental exercise (≥10% decrements, P ≤ 0.009). Peak Q̇ was proportionally decreased after blood withdrawal (P < 0.001). Blood withdrawal induced a 10% decrement in V̇O2peak (P < 0.001). In conclusion, blood withdrawal impairs cardiac filling, Q̇ and aerobic capacity in proportion to the magnitude of hypovolemia in healthy mature women. Novelty: The filling of the heart and therefore cardiac output are impaired by blood withdrawal in women. Oxygen delivery and aerobic capacity are reduced in proportion to blood withdrawal.

Differential influences of dietary sodium on blood pressure regulation based on race and sex

There are clear differences between men and women, and differences among races, in the incidence and prevalence of hypertension. Furthermore, there is extensive inter-individual variability among humans in the extent to which sodium ingestion alters blood pressure. Orthostatic intolerance and orthostatic hypotension are more common in women; these are often treated with a high salt diet, which has variable efficacy in increasing blood volume and blood pressure. Conversely, people with certain forms of hypertension are often counseled to decrease their sodium intake. Non-Hispanic Black men and women have higher rates of hypertension compared to non-Hispanic White men and women and other racial/ethnic groups. In aggregate, Black women appear to have better orthostatic tolerance than White women. In the present paper, we summarize and evaluate the current evidence for mechanisms of blood pressure regulation in men and women, as well as differences between Black and White groups, with a focus on cardiovascular responses to salt and differences among these groups. We also provide a brief review of factors that are not traditionally considered to be "biological" - such as socio-economic disparities resulting from historic and contemporary inequity across racial groups. These non-biological factors have direct and substantial influences on cardiovascular mechanisms, as well as implications for the influences of salt and sodium intake on blood pressure and cardiovascular health. We conclude that both biological and socio-economic factors provide critical modulating influences when considering the impacts of sodium on cardiovascular health as functions of race and sex.

Menstrual cycle effects on sympathetic neural burst amplitude distribution during orthostasis in young women

PURPOSE

Fluctuations in ovarian hormones during the menstrual cycle impact muscle sympathetic nerve activity burst frequency and burst incidence at rest. The purpose of this study was to investigate menstrual cycle effects on sympathetic neural burst amplitude distribution during an orthostatic challenge in young women.

METHODS

This study included 11 healthy women (33 ± 10 years [mean ± standard deviation]). Muscle sympathetic nerve activity was measured in the supine position as baseline measurement and during 5 min of 60° upright tilting, during the early follicular phase (low estrogen and progesterone) and mid-luteal phase (high estrogen and progesterone) of the menstrual cycle. Relative burst amplitude distribution of muscle sympathetic nerve activity was characterized by the mean, median, skewness, and kurtosis.

RESULTS

From the supine to upright position, mean and median values of relative burst amplitude increased (both P < 0.05), regardless of phases of the menstrual cycle (P = 0.5 and P = 0.7, respectively). In comparison, during the early follicular phase, skewness and kurtosis remained unchanged (P =  0.6 and P =   0.3, respectively) and kurtosis decreased (1.25 ± 1.11 supine vs. - 0.03 ± 0.73 upright; P = 0.02); there was no change in skewness during the mid-luteal phase (P = 0.4).

CONCLUSIONS

In response to orthostasis, while the symmetry and tailedness/peakness of burst amplitude distribution do not change during the early follicular phase, the distribution during the mid-luteal phase becomes flatter with a lower but broader peak. The latter result suggests that the firing probability of large axon action potentials in response to orthostatic challenge is higher when estrogen and progesterone levels are elevated. The role of changes in sympathetic neural burst amplitude distribution in orthostatic tolerance remains to be determined.

Men Show Reduced Cardiac Baroreceptor Sensitivity during Modestly Painful Electrical Stimulation of the Forearm: Exploratory Results from a Sham-Controlled Crossover Vagus Nerve Stimulation Study

This paper presents data from a transcutaneous vagus nerve stimulation experiment that point towards a blunted cardiac baroreceptor sensitivity (cBRS) in young males compared to females during electrical stimulation of the forearm and a rhythmic breathing task. Continuous electrocardiography, impedance cardiography and continuous blood-pressure recordings were assessed in a sex-matched cohort of twenty young healthy subjects. Electrical stimulation of the median nerve was conducted by using a threshold-tracking method combined with two rhythmic breathing tasks (0.1 and 0.2 Hz) before, during and after active or sham transcutaneous vagus nerve stimulation. Autonomic and hemodynamic parameters were calculated, and differences were analyzed by using linear mixed models and post hoc F-tests. None of the autonomic and hemodynamic parameters differed between the sham and active conditions. However, compared to females, male participants had an overall lower total cBRS independent of stimulation condition during nerve stimulation (females: 14.96 ± 5.67 ms/mmHg, males: 11.89 ± 3.24 ms/mmHg, p = 0.031) and rhythmic breathing at 0.2 Hz (females: 21.49 ± 8.47 ms/mmHg, males: 15.12 ± 5.70 ms/mmHg, p = 0.004). Whereas vagus nerve stimulation at the left inner tragus did not affect the efferent vagal control of the heart, we found similar patterns of baroreceptor sensitivity activation over the stimulation period in both sexes, which, however, significantly differed in their magnitude, with females showing an overall higher cBRS.

Reliance on vascular responses for the maintenance of blood pressure in healthy older adults - Insights from the Valsalva maneuver

Effective baroreflex-mediated cardiac and vascular resistance responses are crucial for homeostatic blood pressure control. We investigated the impacts of age and sex on arterial blood pressure regulation during a standard supine Valsalva maneuver (40 mmHg, 20s) in 46 healthy young and 25 healthy older adults. Noninvasive, continuous cardiovascular parameters were recorded. In older adults, cardiac output (older: -58.4 ± 2.4%; young: -40.8 ± 1.4%; p < 0.001) and stroke volume (older: -63.6 ± 2.6%; young: -48.7 ± 1.9%; p < 0.001) fell more than in young adults and was compensated by augmented vascular resistance responses (older: +189.8 ± 17.6%; young: +105.8 ± 6.7; p < 0.001); heart rate responses were attenuated in older adults. Male and female responses were comparable in their respective age groups.

Sex differences in blood pressure regulation during the isometric exercise under heated environment

In the absence of heat stress, females increase blood pressure (BP) during isometric handgrip exercise due to cardiac output more than total peripheral resistance (TPR) compared to men. Although heat stress seems to blunt BP responses at rest and during handgrip, possible sex differences remained unknown. We hypothesized that BP responses during handgrip under a heated environment (HOT) will be different between men and women. Eight healthy men (29 ± 6 years) and eight women (26 ± 4 years) participated in this study. The experimental protocol was separated into two environmental conditions: HOT (~ 36 °C) and thermoneutral (TC; ~ 24 °C). In both conditions, participants rested for 30 min and performed the handgrip for 3 min. BP, heart rate (HR) stroke volume and cardiac output were continuously recorded, and TPR was calculated (TPR = mean blood pressure (MBP)/cardiac output). HOT reduced BP and TPR at baseline and during handgrip in females as compared to TC, while males showed similar responses in both thermal conditions. HR was higher under HOT in both groups. Cardiac output and stroke volume were not different under HOT compared to TC for females. In males, cardiac output increased at the last minute of handgrip under HOT through augmented HR, because stroke volume was unchanged. In conclusion, the main effect of HOT was to shift downwards BP and total peripheral resistance at rest and during isometric exercise in females. In males, the combination of handgrip and HOT increased cardiac output by augmented HR, whereas BP presented similar responses between thermal conditions during handgrip.

Impact of high-salt versus low-salt intake on the response of sympathetic baroreflex sensitivity to orthostasis in women with a history of normal pregnancy

Previous studies have demonstrated that sympathetic baroreflex sensitivity (BRS) increases during orthostatic stress in humans. We recently showed that dietary salt intake affects sympathetic neural control in healthy premenopausal women. This study aimed to determine whether salt loading versus salt reduction would impact sympathetic BRS during orthostasis in premenopausal women with a history of normal pregnancy. Nine healthy women [42 ± 3 (SD) yr] were given a standardized isocaloric high-salt (250 mEq sodium/day) or low-salt (50 mEq sodium/day) diet for 1 wk each (∼2 mo apart with the order randomized), whereas water intake was ad libitum. Laboratory testing was performed following each high- and low-salt period in the midluteal phase of the menstrual cycle. Hemodynamics and muscle sympathetic nerve activity (MSNA) were measured at baseline (supine; 2 min) and during a graded head-up tilt (30° for 5 min and 60° for 20 min). Sympathetic BRS was assessed during baseline and head-up tilt. Hemodynamics were not different between salt conditions during baseline or tilt. Both supine and upright MSNA indices were lower in high salt than low salt (all P < 0.05), however, there was no interaction effect (P = 0.507-0.996). On moving from supine to upright, sympathetic BRS remained unchanged in high salt but increased in low salt (P = 0.028 for interaction). Thus, salt loading diminishes the responsiveness of sympathetic BRS during orthostasis compared with salt reduction in healthy premenopausal women with prior normal pregnancy. Whether this is one underlying mechanism for salt-induced development of hypertension during ambulation remains to be determined.

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.

Primary dysmenorrhea and postural control: Is it a problem only during menstruation?

BACKGROUND

The effects of the menstrual cycle and primary dysmenorrhea (PD) on phase-related cognitive and physical functions are controversial. This study was carried out to examine whether women with PD showed a different physical function or dual-tasking response than women without PD at times other than menstruation.

METHODS

Women with or without PD were recruited for the study. Individuals assessed on the first day of the menstruation and the day they reported themselves as well being (feeling good day-FGD). Zebris © FDM Type Force Platform was used to evaluate postural stability. Individuals have were asked to perform to a 3-step balance test protocol; the first session: comfortable upright standing; the second session: standing with a motor task; the third session: standing with a cognitive task (counting backward). Correctly calculated numbers were also recorded.

RESULTS

The number of correct answers given by individuals during the cognitive dual-task was similar on the first day of menstruation and FGD (p > 0.05). In the control group, no difference was observed between the first days of menstruation and the evaluations on FGD days with dual-task (p > 0.05). In individuals with PD, there was no difference between the measurements at different times (p > 0.05). However, in the assessment with the motor dual-task on the first day of menstruation; postural sway increased (p < 0,05). In FDG measurement; distortion in postural stability was observed with the cognitive task (p < 0,05). In the assessments performed on the first day of menstruation, there was no difference in any parameters between the groups (p > 0.05). In the measurements made on FGD day with the cognitive task; there was a difference between the groups (p < 0,05). Individuals with PD had higher postural sway.

SIGNIFICANCE

This study showed that the primary dysmenorrhea is not only a problem for females during menstruation, primary dysmenorrhea causes impaired ability of the individual to perform dual-tasking and continuously affects postural stability.

Physiology of Human Hemorrhage and Compensation

Hemorrhage is a leading cause of death following traumatic injuries in the United States. Much of the previous work in assessing the physiology and pathophysiology underlying blood loss has focused on descriptive measures of hemodynamic responses such as blood pressure, cardiac output, stroke volume, heart rate, and vascular resistance as indicators of changes in organ perfusion. More recent work has shifted the focus toward understanding mechanisms of compensation for reduced systemic delivery and cellular utilization of oxygen as a more comprehensive approach to understanding the complex physiologic changes that occur following and during blood loss. In this article, we begin with applying dimensional analysis for comparison of animal models, and progress to descriptions of various physiological consequences of hemorrhage. We then introduce the complementary side of compensation by detailing the complexity and integration of various compensatory mechanisms that are activated from the initiation of hemorrhage and serve to maintain adequate vital organ perfusion and hemodynamic stability in the scenario of reduced systemic delivery of oxygen until the onset of hemodynamic decompensation. New data are introduced that challenge legacy concepts related to mechanisms that underlie baroreflex functions and provide novel insights into the measurement of the integrated response of compensation to central hypovolemia known as the compensatory reserve. The impact of demographic and environmental factors on tolerance to hemorrhage is also reviewed. Finally, we describe how understanding the physiology of compensation can be translated to applications for early assessment of the clinical status and accurate triage of hypovolemic and hypotensive patients. © 2021 American Physiological Society. Compr Physiol 11:1531-1574, 2021.

Are women really more affected by vasovagal syncope than men?

It is commonly reported that vasovagal syncope (VVS) is more frequent in women. Presently, this issue has never been investigated. The purpose of this review was to evaluate, through an extensive review of the literature, whether women are really more affected by VVS than men. The gender distribution was investigated in individuals with classical and nonclassical VVS. The database PubMed was searched using the terms 'syncope', 'vasovagal syncope', 'neurally mediated syncope' and 'tilt testing'. Twelve studies dealing with classical and 75 with nonclassical VVS were eligible. In the individuals with classical (N = 1861) and nonclassical VVS (N = 9696), a trend towards a greater percentage of women emerged (P = 0.14 and 0.07, respectively). In the total population with VVS (N = 11 557), the percentage of women was significantly higher than that of men (58 versus 42%, P = 0.03). Most of the individuals were young or middle-aged. In 84% of the studies, the percentage of women was greater than that of men. A separate analysis was carried out in older VVS patients (≥60 years) and only two studies were eligible to be evaluated. Considering that almost all the studies were carried out in the western nations, where the number of men and women is almost superimposable until the age of 65 years and a bias by gender has never been reported in the management of VVS, these data strongly suggest that young and middle-aged women are more affected by VVS than their male counterparts. At present, data are too scant to draw a definitive conclusion in older VVS patients.

CORP: Standardizing methodology for assessing spontaneous baroreflex control of muscle sympathetic nerve activity in humans

The use of spontaneous bursts of muscle sympathetic nerve activity (MSNA) to assess arterial baroreflex control of sympathetic nerve activity has seen increased utility in studies of both health and disease. However, methods used for analyzing spontaneous MSNA baroreflex sensitivity are highly variable across published studies. Therefore, we sought to comprehensively examine methods of producing linear regression slopes to quantify spontaneous MSNA baroreflex sensitivity in a large cohort of subjects (n = 150) to support a standardized procedure for analysis that would allow for consistent and comparable results across laboratories. The primary results demonstrated that 1) consistency of linear regression slopes was considerably improved when the correlation coefficient was above -0.70, which is more stringent compared with commonly reported criterion of -0.50, 2) longer recording durations increased the percentage of linear regressions producing correlation coefficients above -0.70 (1 min = 15%, 2 min = 28%, 5 min = 53%, 10 min = 67%, P < 0.001) and reaching statistical significance (1 min = 40%, 2 min = 69%, 5 min = 78%, 10 min = 89%, P < 0.001), 3) correlation coefficients were improved with 3-mmHg versus 1-mmHg and 2-mmHg diastolic blood pressure (BP) bin size, and 4) linear regression slopes were reduced when the acquired BP signal was not properly aligned with the cardiac cycle triggering the burst of MSNA. In summary, these results support the use of baseline recording durations of 10 min, a correlation coefficient above -0.70 for reliable linear regressions, 3-mmHg bin size, and importance of properly time-aligning MSNA and diastolic BP. Together, these findings provide best practices for determining spontaneous MSNA baroreflex sensitivity under resting conditions for improved rigor and reproducibility of results.

Impairments in Blood Pressure Regulation and Cardiac Baroreceptor Sensitivity Among Patients With Heart Failure Supported With Continuous-Flow Left Ventricular Assist Devices

BACKGROUND

Continuous-flow (CF) left ventricular assist devices (LVADs) improve outcomes for patients with advanced heart failure (HF). However, the lack of a physiological pulse predisposes to side-effects including uncontrolled blood pressure (BP), and there are little data regarding the impact of CF-LVADs on BP regulation.

METHODS

Twelve patients (10 males, 60±11 years) with advanced heart failure completed hemodynamic assessment 2.7±4.1 months before, and 4.3±1.3 months following CF-LVAD implantation. Heart rate and systolic BP via arterial catheterization were monitored during Valsalva maneuver, spontaneous breathing, and a 0.05 Hz repetitive squat-stand maneuver to characterize cardiac baroreceptor sensitivity. Plasma norepinephrine levels were assessed during head-up tilt at supine, 30^o and 60^o. Heart rate and BP were monitored during cardiopulmonary exercise testing.

RESULTS

Cardiac baroreceptor sensitivity, determined by Valsalva as well as Fourier transformation and transfer function gain of Heart rate and systolic BP during spontaneous breathing and squat-stand maneuver, was impaired before and following LVAD implantation. Norepinephrine levels were markedly elevated pre-LVAD and improved-but remained elevated post-LVAD (supine norepinephrine pre-LVAD versus post-LVAD: 654±437 versus 323±164 pg/mL). BP increased during cardiopulmonary exercise testing post-LVAD, but the magnitude of change was modest and comparable to the changes observed during the pre-LVAD cardiopulmonary exercise testing.

CONCLUSIONS

Among patients with advanced heart failure with reduced ejection fraction, CF-LVAD implantation is associated with modest improvements in autonomic tone, but persistent reductions in cardiac baroreceptor sensitivity. Exercise-induced increases in BP are blunted. These findings shed new light on mechanisms for adverse events such as stroke, and persistent reductions in functional capacity, among patients supported by CF-LVADs. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03078972.

Effects of salt intake on sympathetic neural and pressor responses to cold pressor test in premenopausal women with a history of normal pregnancy

Excessive salt intake is considered a risk factor for the development of hypertension. Additionally, aberrant neurocirculatory responses to a cold stimulus are associated with an increased risk of hypertension. This study aimed to determine whether salt loading versus salt reduction would impact hemodynamic and sympathetic neural responses during the cold pressor test (CPT) in premenopausal women with a history of normal pregnancy. Nine healthy premenopausal women [42 ± 3 (SD) yr] were given a standardized isocaloric high-salt (HS; 250 mEq sodium/day) or low-salt (LS; 50 mEq sodium/day) diet for 1-wk each (∼2 mo apart with the order randomized), while water intake was ad libitum. Laboratory testing was performed following each HS and LS period in the mid-luteal phase of the menstrual cycle. Subjects were in the supine position and beat-by-beat blood pressure (BP), heart rate (HR), and muscle sympathetic nerve activity (MSNA) were continuously measured during 1-min baseline followed by 2-min CPT, and 3-min recovery. BP and HR increased during the CPT (both P < 0.001); the responses were similar between HS and LS. MSNA increased during the CPT, but the increment (Δ) was greater during HS than LS (29 ± 6 vs. 15 ± 4 bursts/min; P < 0.001). The transduction of MSNA for vasoconstriction during the CPT was lower in HS (P < 0.05). Thus, salt loading augments sympathetic neural reactivity to the cold stimulus with similar pressor responses compared with salt reduction, which may be attributed to the blunted neurovascular transduction-a compensatory mechanism for hemodynamic homeostasis in premenopausal women with a history of normal pregnancy.

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.

Salt intake impacts sympathetic neural control but not morning blood pressure surge in premenopausal women with a history of normal pregnancy

Salt intake may alter blood pressure (BP) regulation, but no study has investigated the impact of salt reduction versus salt loading on morning blood pressure surge (MBPS) and sympathetic neural control in premenopausal women with a history of normal pregnancy. Nine healthy women (42 ± 3 yr; mean ± SD) were given a low-salt diet (LS; 50 mEq sodium/day) and high-salt diet (HS; 250 mEq sodium/day) for 1 wk each (~2 mo apart with the order randomized), while water intake was ad libitum. Ambulatory BP at 24 h was measured, and the percent change in blood volume (BV) was calculated following LS and HS. MBPS was defined as the morning systolic BP (averaged for 2 h after wake-up) minus the lowest nocturnal systolic BP. Beat-by-beat BP, heart rate, and muscle sympathetic nerve activity (MSNA) were measured during supine rest. Signal averaging was used to characterize changes in beat-by-beat mean arterial pressure and total vascular conductance following spontaneous MSNA bursts to assess sympathetic vascular transduction. Ambulatory BP and MBPS (32 ± 7 vs. 26 ± 12 mmHg, P = 0.208) did not differ between LS and HS. From LS to HS, BV increased by 4.3 ± 3.7% (P = 0.008). MSNA (30 ± 20 vs. 18 ± 13 bursts/100 heartbeats, P = 0.005) was higher, whereas sympathetic vascular transduction was lower in LS than HS (both, P < 0.01). Changes in MSNA from LS to HS were correlated to percent changes in BV (r = -0.673; P = 0.047). Thus, salt intake affects sympathetic neural control but not MBPS in premenopausal women with a history of normal pregnancy. The underlying mechanisms remain unknown; however, alterations in sympathetic vascular transduction may, in part, contribute.NEW & NOTEWORTHY This is the first study to demonstrate that MBPS and ambulatory BP were not affected by salt intake despite a significant change in sympathetic outflow in healthy premenopausal women with a history of normal pregnancy. This may be due to compensatory adaptations in MSNA and sympathetic vascular transduction during salt reduction versus salt loading.

Broader adaptive range of sympathetic burst size in response to blood pressure change in older women with greater arterial stiffness

KEY POINTS

In this study, we focused on muscle sympathetic nerve activity (MSNA) burst size and occurrence separately as subcomponents of the sympathetic baroreflex in older adults, and we found that the distribution (variation) of burst size against burst occurrence was greater in women than men. Older women had greater carotid artery stiffness compared with older men, while blood pressure (BP) distribution (variation) was comparable between sexes. Sympathetic baroreflex sensitivity assessed with burst incidence was less sensitive as the carotid artery became stiffer in older men and women, while that assessed with burst area was more sensitive as the carotid artery became stiffer in older women but not in older men. These results help us understand the mechanisms underlying the compensation for the impaired response of MSNA burst occurrence in older women with greater carotid artery stiffness to regulate BP similar to that in older men.

ABSTRACT

There are sex differences in arterial stiffness and neural control of blood pressure (BP) among older adults. We examined whether the sympathetic response to BP is greater in older women than men in burst size but not burst occurrence. Burst occurrence and size were assessed with burst interval and area of muscle sympathetic nerve activity, respectively, and the distributions of these indices were evaluated by range during supine rest in 61 healthy older subjects (30 men (69 ± 6 years) and 31 women (68 ± 6 years); means ± SD). Also, we analysed sympathetic baroreflex sensitivity (BRS) with burst occurrence and area simultaneously. Carotid β-stiffness was measured with B-mode ultrasonic image and carotid BP. The range of burst interval was smaller in older women than men (P = 0.002), while there was no difference in the range of burst area. Carotid β-stiffness was greater in older women than men (6.7 ± 2.7 vs. 5.1 ± 2.7, P = 0.027). Sympathetic BRS assessed with burst incidence was lower in older women than men (-2.3 ± 1.4 vs. -3.3 ± 1.4 bursts·100 beats^-1  mmHg^-1 , P = 0.007), while this sex difference was observed when assessed with burst area after adjusting for carotid β-stiffness (-116.1 ± 135.0 vs. -185.9 ± 148.2 a.u. burst^-1  mmHg^-1 , P = 0.040), but not before. Sympathetic BRS assessed with burst area was negatively (more sensitive) correlated with carotid β-stiffness in older women (r = -0.53, P = 0.002) but not men. These data suggest that the response of burst size within each burst is augmented for the baroreflex BP control despite the impaired response of burst occurrence in older women with greater carotid stiffness.

Comparison of high-fat style diet-induced dysregulation of baroreflex control of renal sympathetic nerve activity in intact and ovariectomized female rats: Renal sympathetic nerve activity in high-fat style diet fed intact and ovariectomized female rats

IMPACT STATEMENT

Over activation of renal sensory nerve in obesity blunts the normal regulation of renal sympathetic nerve activity. To date, there is no investigation that has been carried out on baroreflex regulation of renal sympathetic nerve activity in obese ovarian hormones deprived rat model, and the effect of renal denervation on the baroreflex regulation of renal sympathetic nerve activity. Thus, we investigated the role of renal innervation on baroreflex regulation of renal sympathetic nerve activity in obese intact and ovariectomized female rats. Our data demonstrated that in obese states, the impaired baroreflex control is indistinguishable between ovarian hormones deprived and non-deprived states. This study will be of substantial interest to researchers working on the impact of diet-induced hypertension in pre- and postmenopausal women. This study provides insight into health risks amongst obese women regardless of their ovarian hormonal status and may be integrated in preventive health strategies.

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.

Sex differences in baroreflex function in health and disease

This brief review summarizes the current knowledge on sex differences in baroreflex function, with a major focus on studies in humans. It has been demonstrated that healthy women have blunted cardiovagal baroreflx sensitivity during a rapid (i.e., within seconds) hypertensive stimulus, but baroreflex sensitivity is similar between the sexes during a hypotensive stimulus. Normal aging decreases cardiovagal baroreflex sensitivity and the rate of decline is similar in men and women. Cardiovagal baroreflex sensitivity is reduced in pathological conditions such as hypertension and type II diabetes, and the reduction is greater in female patients than male patients. There is no clear sex difference in sympathetic baroreflex sensitivity among young individuals, however, with women of more advanced age, sympathetic baroreflex sensitivity decreases, which appears to be associated with greater arterial stiffness compared with similarly aged men. The blunted sympathetic baroreflex sensitivity in older women may predispose them to an increased prevalence of hypertension and cardiovascular disease.

Acute reduction in cerebral blood velocity on supine-to-stand transition increases postural instability in young adults

We tested the hypothesis that transient deficits in cerebral blood flow are associated with postural sway. In 19 young, healthy adults, we examined the association between the drop in cerebral blood flow during supine-to-stand transitions, indexed by transcranial Doppler ultrasound [middle cerebral artery blood velocity at diastole (MCAdv)] and near-infrared spectroscopy [tissue saturation index (TSI)] and the center of pressure displacement while standing. Participants performed transitions under three conditions aimed at progressively increasing the drop in MCAdv, in a randomized order: 1) a control transition (Con); 2) a transition that coincided with deflation of bilateral thigh cuffs; and 3) a transition that coincided with both thigh-cuff deflation and 90 s of prior hyperventilation (HTC). The deficit in diastolic blood velocity (MCAdv deficit) was quantified as the difference between MCAdv and its preceding baseline value, summed over 10 s, beginning at the MCAdv nadir. Compared with Con, HTC led to greater drops in MCAdv (P = 0.003) and TSI (P < 0.001) at nadir. The MCAdv deficit was positively associated with the center of pressure displacement vector-average using repeated-measures correlation (repeated-measures correlation coefficient = 0.56, P < 0.001). An a posteriori analysis identified a sub-group of participants that showed an exaggerated increase in MCAdv deficit and greater postural instability in both the anterior-posterior (P = 0.002) and medial-lateral (P = 0.021) directions in response to the interventions. These findings support the theory that individuals who experience greater initial cerebral hypoperfusion on standing may be at a greater risk for falls.NEW & NOTEWORTHY Dizziness and risk for falls after standing might link directly to reduced delivery of oxygen to the brain. By introducing challenges that increased the drop in brain blood flow in healthy young adults, we have shown for the first time a direct link to greater postural instability. These results point to a need to measure cerebral blood flow and/or oxygenation after postural transitions in populations, such as older adults, to assist in fall risk assessment.

Heat therapy reduces sympathetic activity and improves cardiovascular risk profile in women who are obese with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) affects up to 15% of women and is associated with increased risk of obesity and cardiovascular disease. Repeated passive heat exposure [termed "heat therapy" (HT)] is a lifestyle intervention with the potential to reduce cardiovascular risk in obesity and PCOS. Women with obesity (n = 18) with PCOS [age 27 ± 4 yr, body mass index (BMI) 41.3 ± 4.7 kg/m²] were matched for age and BMI, then assigned to HT (n = 9) or time control (CON; n = 9). HT subjects underwent 30 one-hour hot tub sessions over 8-10 wk, whereas CON subjects did not undergo HT. Muscle sympathetic nerve activity (MSNA), blood pressure, cholesterol, C-reactive protein, and markers of vascular function were assessed at the start (Pre) and end (Post) of 8-10 wk. These measures included carotid and femoral artery wall thickness and flow-mediated dilation (FMD), measured both before and after 20 min of ischemia-20 min of reperfusion (I/R) stress. HT subjects exhibited reduced MSNA burst frequency (Pre: 20 ± 8 bursts/min, Post: 13 ± 5 bursts/min, P = 0.012), systolic (Pre: 124 ± 5 mmHg, Post: 114 ± 6 mmHg; P < 0.001) and diastolic blood pressure (Pre: 77 ± 6 mmHg, Post: 68 ± 3 mmHg; P < 0.001), C-reactive protein (Pre: 19.4 ± 13.7 nmol/L, Post: 15.2 ± 12.3 nmol/L; P = 0.018), total cholesterol (Pre: 5.4 ± 1.1 mmol/L, Post: 5.0 ± 0.8 mmol/L; P = 0.028), carotid wall thickness (Pre: 0.054 ± 0.005 cm, Post: 0.044 ± 0.005 cm; P = 0.010), and femoral wall thickness (Pre: 0.056 ± 0.009 cm, Post: 0.042 ± 0.005 cm; P = 0.003). FMD significantly improved in HT subjects over time following I/R (Pre: 5.6 ± 2.5%, Post: 9.5 ± 1.7%; P < 0.001). No parameters changed over time in CON, and BMI did not change in either group. These findings indicate that HT reduces sympathetic nerve activity, provides protection from I/R stress, and substantially improves cardiovascular risk profiles in women who are obese with PCOS.

Measurement of compensatory reserve predicts racial differences in tolerance to simulated hemorrhage in women

BACKGROUND

The compensatory reserve measurement (CRM) has been established to accurately measure the body's total integrated capacity to compensate for physiologic states of reduced central blood volume and predict hemodynamic decompensation associated with inadequate tissue oxygenation. We previously demonstrated that African American (AA) women have a higher tolerance to reductions in central blood volume. Therefore, we tested the hypothesis that the CRM would identify racial differences during simulated hemorrhage, before the onset of traditional signs/symptoms.

METHODS

We performed a retrospective analysis during simulated hemorrhage using lower-body negative pressure (LBNP) in 23 AA (22 ± 1 years; 24 ± 1 kg/m) and 31 white women (WW) (20 ± 1 years; 23 ± 1 kg/m). Beat-by-beat blood pressure (BP) and heart rate (HR) were recorded during progressive lower body negative pressure to presyncope. The BP waveforms were analyzed using a machine-learning algorithm to derive the CRM at each lower body negative pressure stage.

RESULTS

Resting mean arterial BP (AA, 78 ± 3 mm Hg vs. WW, 74 ± 2 mm Hg) and HR (AA, 68 ± 2 bpm vs. WW, 65 ± 2 bpm) were similar between groups. The CRM progressively decreased during LBNP in both groups; however, the rate of decline in the CRM was less (p < 0.05) in AA. The CRM was 4% higher in AA at -15 mm Hg LBNP and progressively increased to 21% higher at -50 mm Hg LBNP (p < 0.05). However, changes in BP and HR were not different between groups.

CONCLUSION

These data support the notion that the greater tolerance to simulated hemorrhage induced by LBNP in AA women can be explained by their greater capacity to protect the reserve to compensate for progressive central hypovolemia compared with WW, independent of standard vital signs.

LEVEL OF EVIDENCE

Diagnostic test, level II.

Hydration Status and Cardiovascular Function

Hypohydration, defined as a state of low body water, increases thirst sensations, arginine vasopressin release, and elicits renin–angiotensin–aldosterone system activation to replenish intra- and extra-cellular fluid stores. Hypohydration impairs mental and physical performance, but new evidence suggests hypohydration may also have deleterious effects on cardiovascular health. This is alarming because cardiovascular disease is the leading cause of death in the United States. Observational studies have linked habitual low water intake with increased future risk for adverse cardiovascular events. While it is currently unclear how chronic reductions in water intake may predispose individuals to greater future risk for adverse cardiovascular events, there is evidence that acute hypohydration impairs vascular function and blood pressure (BP) regulation. Specifically, acute hypohydration may reduce endothelial function, increase sympathetic nervous system activity, and worsen orthostatic tolerance. Therefore, the purpose of this review is to present the currently available evidence linking acute hypohydration with altered vascular function and BP regulation.

Postural Orthostatic Tachycardia Syndrome: JACC Focus Seminar

Postural orthostatic tachycardia syndrome (POTS), the most common form of orthostatic intolerance in young people, affects approximately 500,000 people in the United States alone, typically young women at the peak of their education and the beginning of their working lives. This is a heterogeneous disorder, the pathophysiology and mechanisms of which are not well understood. There are multiple contributing factors and numerous potential mimics. This review details the most current views on the potential causes, comorbid conditions, proposed subtypes, differential diagnoses, evaluations, and treatment of POTS from cardiological and neurological perspectives.

Sex differences in the ventilatory and cardiovascular response to supine and tilted metaboreflex activation

Women have attenuated exercise pressor responses compared to men; however, their cerebrovascular and ventilatory responses have not been previously measured. Furthermore, recent evidence has shown that posture change can influence the response of the metaboreflex but this has only been tested in men. Young and healthy men (n = 14; age: 21 ± 2) and women (n = 11; age: 19 ± 1) underwent 40% MVC static handgrip exercise (HG) for 2 min followed by 3 min of post-exercise circulatory occlusion (PECO) in the supine and 70° tilted postures. In supine position during HG and PECO only men had an increase in ventilation (Men: Baseline: 12.5 ± 1.7 L/min, HG: 18.6 ± 5.3 L/min, PECO: 17.7 ± 10.3 L/min; Women: Baseline: 12.0 ± 1.5 L/min, HG: 12.4 ± 1.2 L/min, PECO: 11.5 ± 1.3 L/min; Sex × Time interaction P = 0.037). In supine position during HG and PECO men and women had similar reductions in cerebrovascular conductance (Men: Baseline: 0.79 ± 0.13 cm/sec/mmHg, HG: 0.68 ± 0.18 cm/sec/mmHg, PECO: 0.61 ± 0.19 cm/s/mmHg; Women: Baseline: 0.87 ± 0.13 cm/sec/mmHg, HG: 0.83 ± 0.14 cm/sec/mmHg, PECO: 0.75 ± 0.17 cm/sec/mmHg; P < 0.015 HG/PECO vs. baseline). When comparing the response to PECO in the supine versus upright postures there was a significant attenuation in the increase in mean arterial pressure in both men and women (Supine posture: Men: +23.3 ± 14.5 mmHg, Women: +12.0 ± 7.3 mmHg; Upright posture: Men: +15.7 ± 14.1 mmHg, Women: +7.7 ± 6.7 mmHg; Main effect of sex P = 0.042, Main effect of posture P < 0.001). Our results indicate sexually dimorphic ventilatory responses to HG and PECO which could be due to different interactions of the metaboreflex and chemoreflex. We have also shown evidence of attenuated metaboreflex function in the upright posture in both men and women.

Altered baroreflex sensitivity in young women with a family history of hypertension

A positive family history of hypertension (+FH) is a risk factor for the future development of hypertension. Hypertension is associated with reductions in baroreflex sensitivity (BRS). Therefore, we hypothesized that young women with a +FH [ n = 12, 22 ± 1 yr, body mass index (BMI) 21 ± 1 kg/m², mean arterial pressure (MAP) 79 ± 1 mmHg] would have lower BRS compared with young women without a family history of hypertension (-FH) ( n = 13, 22 ± 1 yr, BMI 21 ± 1 kg/m², MAP 77 ± 2 mmHg, all P > 0.05 between groups). Continuous measurements of muscle sympathetic nerve activity, blood pressure, and electrocardiogram derived R-R interval were recorded at rest and during a Valsalva maneuver. Both cardiovagal BRS and vascular sympathetic BRS were assessed. Resting cardiovagal BRS was reduced in the +FH women (all sequences: -FH 32.3 ± 3.7 vs. +FH 20.2 ± 2.9 ms/mmHg, P = 0.02). Cardiovagal BRS during phase IV (-FH 16.5 ± 2.7 vs. +FH 7.6 ± 1.3 ms/mmHg, P < 0.01) but not phase II (-FH 5.5 ± 0.9 vs. +FH 5.0 ± 0.8 ms/mmHg, P = 0.67) of the Valsalva maneuver was also lower in the +FH women. Vascular sympathetic BRS at rest (-FH -2.38 ± 0.7 vs. +FH -2.33 ± 0.3 bursts· min^-1·mmHg^-1, P = 0.58) and during the Valsalva (-FH -0.74 ± 0.23 vs. +FH -0.66 ± 0.18 bursts·15 s^-1·mmHg^-1, P = 0.79) were not different between groups. These data suggest that healthy young women with a positive family history of hypertension have reduced cardiovagal BRS. This may be one mechanism contributing to the increased incidence of hypertension in this population later in life. NEW & NOTEWORTHY Having a family history of hypertension increases the risk of developing future hypertension. Reductions in baroreflex function have been demonstrated in hypertension and are an important marker for future cardiovascular disease. We show that young women with a family history of hypertension have lower cardiovagal baroreflex sensitivity. This alteration in autonomic function may be one mechanism contributing to the future incidence of hypertension in this patient population.

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.

Cerebral blood flow modulations during antisaccade preparation in chronic hypotension

In addition to symptoms including fatigue, dizziness, reduced drive, or mood disturbance, individuals with chronic low blood pressure (hypotension) frequently report cognitive complaints. While attentional deficits have been empirically confirmed, it is still unknown whether the impairments also encompass executive functions. This study investigated cerebral blood flow modulations in hypotension during a precued antisaccade/prosaccade task requiring the executive function of proactive inhibition in addition to preparatory attention. Using functional transcranial Doppler sonography, bilateral blood flow velocities in the middle cerebral arteries (MCA) were recorded in 39 hypotensive and 40 normotensive participants. In the task, a stimulus appeared left or right of a fixation point 5 s after a cuing stimulus; subjects had to move their gaze to the mirror image position of the stimulus (antisaccade) or toward it (prosaccade control condition). Video-based eye tracking was used for ocular recording. A right dominant MCA blood flow increase arose during task preparation, which was smaller in hypotensive than normotensive participants. In addition, hypotensive participants exhibited lower peak velocity of the saccadic response. The extent of the reductions in blood flow and task performance in hypotension did not differ between antisaccade and prosaccade conditions. The smaller MCA flow increase may reflect reduced activity in the dorsolateral prefrontal and inferior parietal cortices during proactive inhibition and preparatory attention in hypotension. Given that group differences in blood flow and performance arose independent of task complexity and executive function load, hypotension may be characterized by basic attentional impairments rather than particular executive function deficits.

Cardiovascular Autonomic Profile in Women With Premenstrual Syndrome

Introduction: The premenstrual syndrome (PMS) is a constellation of somatic and psychogenic symptoms that appear during late luteal (LL) phase of the menstrual cycle. Since many symptoms could be related to the autonomic nervous system, we hypothesized that the sympathetic nervous system is perturbed in PMS.

Methods: The cardiovascular autonomic profile of nine women with PMS (30.4 ± 2.5 years) were compared to that of nine healthy controls (30 ± 2.5 years) during their early follicular (EF) and LL phases of the menstrual cycle. Plasma norepinephrine (NE) concentrations, power spectral analysis of heart rate and systolic blood pressure (BP), and baroreflex sensitivity (BRS) were assessed during recumbency and a head-up tilt (HUT). Cardiovascular responsiveness to α1- and β-adrenoreceptor agonists (phenylephrine and isoproterenol, respectively) were also assessed.

Results: In the LL phase, the plasma NE concentrations in women with PMS during recumbency and a HUT were lower than those in women without PMS [180 ± 30 vs. 320 ± 50 pg/ml; p = 0.04 (recumbent), and 480 ± 70 vs. 940 ± 180 pg/ml: p = 0.02 (HUT)]. In the LL phase, the dose of phenylephrine required to increase systolic BP by 15 mmHg in women with PMS was significantly greater than that in women without PMS (202 ± 30 μg vs. 138 ± 20 μg; p = 0.02). Sympathetic and vagal cardiac control indices were comparable in the two groups in the menstrual phases. In women with PMS, the value of LF_SBP in the LL phase was lower than that in the EF phase (0.98 ± 0.2 vs. 1.77 ± 0.4 mmHg², p = 0.04). The increase in LF_SBP in women with PMS in the LL phase during HUT was greater than that in the controls, 5.2 ± 0.9 vs. 3.1 ± 0.5 mmHg², p = 0.045, and this increase was associated with a significant decrease in BRS.

Conclusion: In women with PMS without psychogenic symptoms, the sympathetic control of their circulation is not dominant during the LL phase of their menstrual cycle.

Ovarian hormones modulate endothelin-1 receptor responses in young women

OBJECTIVE

We recently demonstrated ETB_R mediate vasodilation in young but not postmenopausal women; it is unclear if this is related to age or a decline in ovarian hormones. The purpose of this study was to test the hypothesis that ETB_R responses are modulated by ovarian hormones.

METHODS

We measured cutaneous vasodilatory responses in 12 young women (22 ± 1 years, 23 ± 1 kg/m² ) during the ML (days 20-25) and EF (days 2-5) phases of the menstrual cycle. Cutaneous microdialysis perfusions of lactated Ringer (control), ETB_R antagonist (BQ-788, 300 nmol/L), and ETA_R antagonist (BQ-123, 500 nmol/L) were performed, followed by local heating to 42°C.

RESULTS

Serum estradiol (ML: 118 ± 16 vs EF: 44 ± 9 pg/mL, P < 0.05) and progesterone (ML: 8.3 ± 1.0 vs EF: 0.7 ± 0.2 ng/mL, P < 0.05) were higher during ML vs EF phase. ETB_R blockade decreased vasodilation during ML (control: 91 ± 2 vs BQ-788: 83 ± 2%CVCmax, P < 0.05) but not EF (control: 89 ± 2 vs BQ-788: 89 ± 1%CVCmax). ETA_R blockade also decreased vasodilation during ML (control: 91 ± 2 vs BQ-123: 87 ± 2%CVCmax, P < 0.05) but not EF (control: 89 ± 2 vs BQ-123: 92 ± 2%CVCmax).

CONCLUSIONS

These data suggest that fluctuations in ovarian hormones modulate ETB_R and ETA_R responses in young women.