Augmented sympathetic vasoconstriction in exercising forearms of postmenopausal women is reversed by oestrogen therapy

Influence of endogenous and exogenous hormones on the cardiovascular response to lower extremity exercise and group III/IV activation in young females

Oral contraceptive (OC) use can increase resting blood pressure (BP) in females as well as contribute to greater activation of group III/IV afferents during upper body exercise. It is unknown, however, whether an exaggerated BP response occurs during lower limb exercise in OC users. We sought to elucidate the group III/IV afferent activity-mediated BP and heart rate responses while performing lower extremity tasks during early and late follicular phases in young, healthy females. Females not taking OCs (NOC: n = 8; age: 25 ± 4 yr) and those taking OCs (OC: n = 10; age: 23 ± 2 yr) completed a continuous knee extension/flexion passive stretch (mechanoreflex) and cycling exercise with subsystolic cuff occlusion (exercise pressor reflex), which was followed by a 2-min postexercise circulatory occlusion (PECO) (metaboreflex). Data collection occurred on two occasions: once during the early follicular phase (days 1-4) and once during the late follicular phase (days 10-14) of their menstrual cycle (NOC) or during the placebo and active pill phases (OC). Resting mean arterial BP and heart rate were not different between phases in NOC and OC participants (P > 0.05). Hemodynamic responses to metaboreflex, mechanoreflex, and collective exercise pressor reflex activation were not different between phases in both groups (P > 0.05). In conclusion, although OCs are known to increase BP at rest, our findings indicate that neither endogenous nor exogenous (OC) sex hormones modulate BP during large, lower limb muscle exercise with or without group III/IV afferent activation in young, healthy females.NEW & NOTEWORTHY Sex differences in the cardiovascular response to exercise have been demonstrated and may be dependent on sex hormone levels. Furthermore, oral contraceptives (OCs) have been shown to exaggerate the blood pressure response to upper extremity exercise. The results of this study indicate that neither endogenous nor exogenous (OC) sex hormones modulate BP during lower extremity dynamic exercise or with group III/IV afferent activation in young, healthy females.

Aging in females has minimal effect on changes in celiac artery blood flow during dynamic light-intensity exercise

Blood flow to the active muscles and arterial blood pressure (ABP) increase during dynamic exercise, whereas blood flow to inactive organs (e.g., splanchnic organs and inactive limbs) declines. Aging leads to exaggerated ABP responses to exercise in females, but whether this is related to greater splanchnic vasoconstriction is unknown. This study sought to clarify the effect of aging in females on celiac artery blood flow during dynamic light-intensity exercise. Twelve healthy young females (YF: 20 ± 2 yr, mean ± SD) and 12 healthy older females (OF: 71 ± 4 yr) performed dynamic knee-extension and knee-flexion exercises at 30% of heart rate reserve for 4 min. The absolute changes from baseline (Δ) for mean arterial blood pressure (MAP), celiac artery mean blood flow (celMBF), and celiac vascular conductance (celVC) during exercise were calculated. ABP was measured using an automated sphygmomanometer, and celMBF was recorded by Doppler ultrasonography. The increase in MAP during exercise was greater in OF than in YF (YF: +14 ± 7 mmHg, OF: +24 ± 13 mmHg, P = 0.028). The celMBF decreased during exercise in both groups, but there was no significant difference in the response between YF and OF (YF: -93.0 ± 66.1 mL/min, OF: -89.6 ± 64.0 mL/min, P = 0.951). The celVC also decreased during exercise and remained lower than baseline during exercise. However, the response was not different between YF and OF (YF: -1.8 ± 1.0 mL/min/mmHg, OF: -1.5 ± 0.6 mL/min/mmHg, P = 0.517). These results demonstrate that aging in females has minimal influence on splanchnic artery hemodynamic responses during dynamic light-intensity exercise, suggesting that exaggerated ABP responses during exercise in OF are not due to greater splanchnic vasoconstriction.NEW & NOTEWORTHY During exercise, the splanchnic arteries vasoconstrict, contributing to blood flow redistribution and the blood pressure response. Blood pressure responses to exercise are exaggerated with aging in females; however, the physiological mechanism responsible has not been clarified. We show that celiac artery blood flow changes during light-intensity dynamic exercise do not differ with age in females. This indicates the exaggerated blood pressure to exercise with aging is likely not due to a difference in splanchnic vasoconstriction.

α-Adrenergic regulation of skeletal muscle blood flow during exercise in patients with heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) has been characterized by lower blood flow to exercising limbs and lower peak oxygen utilization (V ̇ O 2 ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ ), possibly associated with disease-related changes in sympathetic (α-adrenergic) signaling. Thus, in seven patients with HFpEF (70 ± 6 years, 3 female/4 male) and seven controls (CON) (66 ± 3 years, 3 female/4 male), we examined changes (%Δ) in leg blood flow (LBF, Doppler ultrasound) and legV ̇ O 2 ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ to intra-arterial infusion of phentolamine (PHEN, α-adrenergic antagonist) or phenylephrine (PE, α1-adrenergic agonist) at rest and during single-leg knee-extension exercise (0, 5 and 10 W). At rest, the PHEN-induced increase in LBF was not different between groups, but PE-induced reductions in LBF were lower in HFpEF (-16% ± 4% vs. -26% ± 5%, HFpEF vs. CON; P < 0.05). During exercise, the PHEN-induced increase in LBF was greater in HFpEF at 10 W (16% ± 8% vs. 8% ± 5%; P < 0.05). PHEN increased legV ̇ O 2 ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ in HFpEF (10% ± 3%, 11% ± 6%, 15% ± 7% at 0, 5 and 10 W; P < 0.05) but not in controls (-1% ± 9%, -4% ± 2%, -1% ± 5%; P = 0.24). The 'magnitude of sympatholysis' (PE-induced %Δ LBF at rest - PE-induced %Δ LBF during exercise) was lower in patients with HFpEF (-6% ± 4%, -6% ± 6%, -7% ± 5% vs. -13% ± 6%, -17% ± 5%, -20% ± 5% at 0, 5 and 10 W; P < 0.05) and was positively related to LBF, leg oxygen delivery, legV ̇ O 2 ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ , and the PHEN-induced increase in LBF (P < 0.05). Together, these data indicate that excessive α-adrenergic vasoconstriction restrains blood flow and limitsV ̇ O 2 ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ of the exercising leg in patients with HFpEF, and is related to impaired functional sympatholysis in this patient group. KEY POINTS: Sympathetic (α-adrenergic)-mediated vasoconstriction is exaggerated during exercise in patients with heart failure with preserved ejection fraction (HFpEF), which may contribute to limitations of blood flow, oxygen delivery and oxygen utilization in the exercising muscle. The ability to adequately attenuate α1-adrenergic vasoconstriction (i.e. functional sympatholysis) within the vasculature of the exercising muscle is impaired in patients with HFpEF. These observations extend our current understanding of HFpEF pathophysiology by implicating excessive α-adrenergic restraint and impaired functional sympatholysis as important contributors to disease-related impairments in exercising muscle blood flow and oxygen utilization in these patients.

Carotid Arterial Compliance during Different Intensities of Submaximal Endurance Exercise

Background: The purpose of this investigation was to determine the elastic characteristics of the common carotid artery (CCA) during endurance exercise at 3 different intensities. Methods: Twenty young healthy participants (10 males and 10 females) participated in this quasi-experimental cross-sectional study. Participants were tested in two sessions: (1) we took resting measurements of the elastic characteristics of the CCA and performed a cardiopulmonary exercise test (CPET) on a cycle ergometer to determine submaximal exercise intensities, and we conducted (2) measurements of the elastic characteristics of the CCA while exercising in a cycle ergometer at 3 intensities based on blood lactate levels of low (<2 mmol/L), moderate (2-4 mmol/L), and high (>4 mmol/L). Beta stiffness was calculated using CCA diameters during systole and diastole, measured with high-definition ultrasound imaging, and CCA systolic and diastolic pressures were measured via applanation tonometry. Results: Overall, there were no differences between males and females in terms of any of the studied variables (p > 0.05). In addition, no significant changes were found in the CCA beta stiffness and vessel diameter (p > 0.05) between exercise intensities. There was a significant exercise intensity effect on CCA systolic pressure (p < 0.05), but not on CCA diastolic pressure (p > 0.05). Conclusions: The biomechanical characteristics of the CCA, determined via compliance and beta-stiffness, do not change during cyclical aerobic exercise, regardless of exercise intensity.

The human skeletal muscle metaboreflex contribution to cardiorespiratory control in males and females in dynamic exercise

There is a significant effect of sex and muscle mass on the cardiorespiratory response to the skeletal muscle metaboreflex during isometric exercise. We therefore tested the hypothesis that sex differences would be present when isolated following dynamic exercise. We also tested the hypothesis that single and double leg post-exercise circulatory occlusion (PECO) following heavy exercise would elicit a cardiorespiratory response proportional to the absolute muscle mass. Healthy (24 ± 4 years) males (n = 10) and females (n = 10) completed pulmonary function and an incremental cycle test to exhaustion. Participants completed two randomized, 6 min bouts of intense cycle exercise (84 ± 7% V̇O2peak). One exercise bout was immediately followed by 3 min PECO (220 mmHg) of the legs while the other exercise bout was followed by passive recovery. Males completed an additional session of testing with single leg PECO. The mean arterial pressure during PECO and control was greater in males compared to females (p = 0.004). The was a significant time by condition by sex interaction in the heart rate response to PECO (p = 0.027). There was also a significant condition by sex interaction in the ventilatory response to PECO (p = 0.026). In males, we observed a dose-dependent cardiovascular, but not ventilatory, response to muscle mass occluded (all p < 0.05). Our findings suggest the metaboreflex contribution to cardiorespiratory control during dynamic exercise is greater in males compared to females. The ventilatory response induced by double-leg occlusion but not single-leg occlusion, suggests that the ventilatory influence of the metaboreflex is less sensitive than the cardiovascular response and may be linked to the greater afferent activation induced by double-leg occlusion.

Impaired cardiopulmonary baroreflex function and altered cardiovascular responses to hypovolemia in patients with heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is associated with autonomic dysregulation, which may be related to baroreflex dysfunction. Thus, we tested the hypothesis that cardiac and peripheral vascular responses to baroreflex activation via lower-body negative pressure (LBNP; -10, -20, -30, -40 mmHg) would be diminished in patients with HFpEF (n = 10, 71 ± 7 yr) compared with healthy controls (CON, n = 9, 69 ± 5 yr). Changes in heart rate (HR), mean arterial pressure (MAP, Finapres), forearm blood flow (FBF, ultrasound Doppler), and thoracic impedance (Z) were determined. Mild levels of LBNP (-10 and -20 mmHg) were used to specifically assess the cardiopulmonary baroreflex, whereas responses across the greater levels of LBNP represented an integrated baroreflex response. LBNP significantly increased in HR in CON subjects at -30 and -40 mmHg (+3 ± 3 and +6 ± 5 beats/min, P < 0.01), but was unchanged in patients with HFpEF across all LBNP levels. LBNP provoked progressive peripheral vasoconstriction, as quantified by changes in forearm vascular conductance (FVC), in both groups. However, a marked (40%-60%) attenuation in FVC responses was observed in patients with HFpEF (-6 ± 8, -15 ± 6, -16 ± 5, and -19 ± 7 mL/min/mmHg at -10, -20, -30, and -40 mmHg, respectively) compared with controls (-15 ± 10, -22 ± 6, -25 ± 10, and -28 ± 10 mL/min/mmHg, P < 0.01). MAP was unchanged in both groups. Together, these data provide new evidence for impairments in cardiopulmonary baroreflex function and diminished cardiovascular responsiveness during hypovolemia in patients with HFpEF, which may be an important aspect of the disease-related changes in autonomic cardiovascular control in this patient group.NEW & NOTEWORTHY Data from the current study demonstrate diminished cardiovascular responsiveness during hypovolemia induced by incremental lower-body negative pressure in patients with heart failure with preserved ejection fraction (HFpEF). These diminished responses imply impaired cardiopulmonary baroreflex function and altered autonomic cardiovascular regulation which may represent an important aspect of HFpEF pathophysiology.

Age-related alterations in the cardiovascular responses to acute exercise in males and females: role of the exercise pressor reflex

Autonomic adjustments of the cardiovascular system are critical for initiating and sustaining exercise by facilitating the redistribution of blood flow and oxygen delivery to meet the metabolic demands of the active skeletal muscle. Afferent feedback from active skeletal muscles evokes reflex increases in sympathetic nerve activity and blood pressure (BP) (i.e., exercise pressor reflex) and contributes importantly to these primary neurovascular adjustments to exercise. When altered, this reflex contributes significantly to the exaggerated sympathetic and BP response to exercise observed in many cardiovascular-related diseases, highlighting the importance of examining the reflex and its underlying mechanism(s). A leading risk factor for the pathogenesis of cardiovascular disease in both males and females is aging. Although regular exercise is an effective strategy for mitigating the health burden of aging, older adults face a greater risk of experiencing an exaggerated cardiovascular response to exercise. However, the role of aging in mediating the exercise pressor reflex remains highly controversial, as conflicting findings have been reported. This review aims to provide a brief overview of the current understanding of the influence of aging on cardiovascular responses to exercise, focusing on the role of the exercise pressor reflex and proposing future directions for research. We reason that this review will serve as a resource for health professionals and researchers to stimulate a renewed interest in this critical area.

Evidence of impaired functional sympatholysis in patients with heart failure with preserved ejection fraction

Exercising muscle blood flow is reduced in patients with heart failure with a preserved ejection fraction (HFpEF), which may be related to disease-related changes in the ability to overcome sympathetic nervous system (SNS)-mediated vasoconstriction during exercise, (i.e., "functional sympatholysis"). Thus, in 12 patients with HFpEF (69 ± 7 yr) and 11 healthy controls (Con, 69 ± 4 yr), we examined forearm blood flow (FBF), mean arterial pressure (MAP), and forearm vascular conductance (FVC) during rhythmic handgrip exercise (HG) at 30% of maximum voluntary contraction with or without lower-body negative pressure (LBNP, -20 mmHg) to increase SNS activity and elicit peripheral vasoconstriction. SNS-mediated vasoconstrictor responses were determined as LBNP-induced changes (%Δ) in FVC, and the "magnitude of sympatholysis" was calculated as the difference between responses at rest and during exercise. At rest, the LBNP-induced change in FVC was significantly lesser in HFpEF compared with Con (HFpEF: -9.5 ± 5.5 vs. Con: -21.0 ± 8.0%; P < 0.01). During exercise, LBNP-induced %ΔFVC was significantly attenuated in Con compared with rest (HG: -5.8 ± 6.0%; P < 0.05) but not in HFpEF (HG: -9.9 ± 2.5%; P = 0.88). Thus, the magnitude of sympatholysis was lesser in HFpEF compared with Con (HFpEF: 0.4 ± 4.7 vs. Con: -15.2 ± 11.8%; P < 0.01). These data demonstrate a diminished ability to attenuate SNS-mediated vasoconstriction in HFpEF and provide new evidence suggesting impaired functional sympatholysis in this patient group.NEW & NOTEWORTHY Data from the current study suggest that functional sympatholysis, or the ability to adequately attenuate sympathetic nervous system (SNS)-mediated vasoconstriction during exercise, is impaired in patients with heart failure with preserved ejection fraction (HFpEF). These observations extend the current understanding of HFpEF pathophysiology by implicating inadequate functional sympatholysis as an important contributor to reduced exercising muscle blood flow in this patient group.

Effects of sex and menstrual cycle phase on celiac artery blood flow during dynamic moderate-intensity leg exercise in young individuals

The purpose of this study was to clarify the effect of sex and menstrual cycle phase on celiac artery blood flow during dynamic exercise in healthy young humans. Eleven healthy young females (21 ± 2 yr, means ± SD) and 10 males (23 ± 3 yr) performed dynamic knee-extension and -flexion exercises at 30% of heart rate reserve for 4 min. The percent changes from baseline (Δ) for mean arterial blood pressure (MAP), mean blood flow (celMBF) in the celiac artery, and celiac vascular conductance (celVC) during exercise were calculated. Arterial blood pressure was measured using an automated sphygmomanometer, and celiac artery blood flow was recorded by Doppler ultrasonography. Female subjects performed the exercise test in the early follicular phase (EF) and in the midluteal phase (ML) of their menstrual cycle. The increase in MAP during exercise was not significantly (P > 0.05) different between sexes or between menstrual cycle phases (ΔMAP, EF in females: +16.6 ± 6.4%, ML in females: +20.2 ± 11.7%, and males: +19.9 ± 12.2%). The celMBF decreased during exercise in each group, but the response was not significantly (P > 0.05) different between sexes or between menstrual cycle phases (ΔcelMBF, EF in females: -24.6 ± 15.5%, ML in females: -25.2 ± 18.7%, and males: -29.2 ± 4.0%). The celVC decreased during dynamic exercise in each group, with no significant (P > 0.05) difference in the responses between sexes or between menstrual cycle phases (ΔcelVC, EF in females: -38.3 ± 15.0%, ML in females: -41.5 ± 19.1%, and males: -43.4 ± 7.2%). These results suggest that sex and menstrual cycle phase have minimal influence on hemodynamic responses in the splanchnic artery during dynamic moderate-intensity exercise in young healthy individuals.NEW & NOTEWORTHY During dynamic exercise, splanchnic organ blood flow is reduced from resting values. Whether sex and menstrual cycle phase influence splanchnic blood flow responses during exercise remains unknown. We show that the decrease in celiac artery blood flow during dynamic leg exercise does not differ between young females and males or between menstrual cycle phases. In young individuals, sex and menstrual cycle have minimal influence on splanchnic artery hemodynamic responses during dynamic moderate-intensity leg exercise.

A single high-fat Western meal modulates vascular responsiveness to sympathetic activation at rest and during exercise in humans: a randomized controlled trial

A single high-fat Western meal transiently reduces endothelium-dependent vasodilation at rest, but the interaction with sympathetic vasoconstrictor activity during exercise remains unknown. Herein, we tested the hypothesis that a single high-fat Western meal would impair the ability of contracting skeletal muscle to offset vascular responsiveness to sympathetic activation during exercise, termed functional sympatholysis. In 18 (10 females/8 males) healthy young adults, forearm blood flow (Doppler ultrasound) and beat-to-beat arterial pressure (photoplethysmography) were measured during lower-body negative pressure (LBNP; -20 mmHg) applied at rest and simultaneously during low (15% maximum contraction) and moderate (30% maximum contraction)-intensity rhythmic handgrip exercise. The magnitude of sympatholysis was calculated as the difference of LBNP-induced changes in forearm vascular conductance (FVC) between handgrip and rest. Experiments were performed preprandial and 1 h, 2 h, and 3 h after a high- or low-fat meal. In the preprandial state, LBNP decreased resting FVC (Δ-54 ± 10%), and these responses were attenuated during low (Δ-17 ± 7%)- and moderate (Δ-8 ± 6%)-intensity handgrip exercise. Following a high-fat meal, LBNP induced attenuated decreases in resting FVC (3 h postprandial, Δ-47 ± 10%, P = 0.002 vs. preprandial) and blunted attenuation of FVC during low (3 h postprandial, Δ-23 ± 8%, P = 0.001 vs. preprandial)- and moderate (3 h postprandial, Δ-16 ± 6%, P < 0.001 vs. preprandial)-intensity handgrip exercise. The high-fat meal attenuated the magnitude of sympatholysis during low (preprandial, 38 ± 7 vs. 3 h postprandial, 23 ± 8%, P < 0.001)- and moderate (preprandial, 46 ± 11 vs. 3 h postprandial, 31 ± 10%, P < 0.001)-intensity handgrip exercise. The low-fat meal had no impact on these responses. In conclusion, a single high-fat Western meal modulates sympathetic vasoconstriction at rest and during low- and moderate-intensity handgrip exercise in young healthy adults.NEW & NOTEWORTHY We observed that a single high-fat Western meal, but not an isocaloric low-fat meal, attenuated the sympathetic vasoconstriction at rest and the ability of the active skeletal muscle to counteract the vascular responsiveness to sympathetic activation (i.e., functional sympatholysis) during low- and moderate-intensity rhythmic handgrip exercise in healthy young adults. Our findings highlight the potential deleterious vascular effect associated with the consumption of a Western diet.

The interactive effects of age and sex on the neuro-cardiovascular responses during fatiguing rhythmic handgrip exercise

The impact of age on exercise pressor responses is equivocal, likely because of sex-specific neuro-cardiovascular changes with age. However, assessments of the interactive effects of age and sex on muscle sympathetic nerve activity (MSNA) responses to exercise are lacking. We tested the hypothesis that older females would exhibit exaggerated increases in blood pressure (BP) and MSNA discharge patterns during handgrip exercise compared with similarly aged males and young adults. Twenty-five young (25 (2) years; mean (SD)) males (YM; n = 12) and females (YF; n = 13) and 23 older (71 (5) years) males (OM; n = 11) and females (OF; n = 12) underwent assessments of BP, total peripheral resistance (TPR; Modelflow) and MSNA action potential (AP) discharge patterns (microneurography) during incremental rhythmic handgrip exercise and post-exercise circulatory occlusion (PECO). OM demonstrated larger ∆BP and ∆TPR from baseline than YM (both P < 0.001) despite smaller increases in ∆APs/burst (OM: 0.4 (3) vs. YM: 5 (3) spikes/burst, P < 0.001) and ∆AP clusters/burst (OM: 0.1 (1) vs. YM: 1.8 (1) clusters/burst, P < 0.001) during exercise. Testosterone was lower in OM than YM (P < 0.001) and was inversely related to ∆BP but positively related to ∆AP clusters/burst in males (both P = 0.03). Conversely, YF and OF demonstrated similar ∆BP and ∆AP discharge during exercise (range: P = 0.75-0.96). Age and sex did not impact haemodynamics or AP discharge during PECO (range: P = 0.08-0.94). Altogether, age-related changes in neuro-cardiovascular reactivity exist in males but not females during fatiguing exercise and seem to be related to testosterone. This sex-specific impact of age underscores the importance of considering biological sex when assessing age-related changes in neuro-cardiovascular control during exercise. KEY POINTS: Older males have the largest increase in blood pressure despite having the smallest increases in sympathetic vasomotor outflow during rhythmic handgrip exercise. Young males demonstrate greater increases in sympathetic action potential (AP) discharge compared with young females during rhythmic handgrip exercise. Older adults (regardless of sex) demonstrate smaller increases in muscle sympathetic nerve activity (MSNA) burst amplitude and total AP clusters compared with young adults during exercise, as well as smaller increases in integrated MSNA burst frequency, incidence and total MSNA activity during post-exercise circulatory occlusion (i.e. independent effect of age). Males, but not females (regardless of age), reflexively modify AP conduction velocity during exercise. Our results indicate that age and sex independently and interactively impact the neural and cardiovascular homeostatic adjustments to fatiguing small muscle mass exercise.

Functional near infrared spectroscopy detects cortical activation changes concurrent with memory loss in postmenopausal women with Type II Diabetes

Older adults with Type II Diabetes Mellitus (DM) experience mild cognitive impairment, specifically in the domain of recall/working memory. No consistent causative structural cortical deficits have been identified in persons with DM (PwDM). Memory deficits may be exacerbated in older adult females, who are at the highest risk of cardiovascular decline due to DM. The focus of the current study was to evaluate functional cortical hemodynamic activity during memory tasks in postmenopausal PwDM. Functional Near Infrared Spectroscopy (fNIRS) was used to monitor oxyhemoglobin (HbO) and deoxyhemoglobin (HbR) during memory-based tasks in a cross-sectional sample of postmenopausal women with DM. Twenty-one community-dwelling DM females (age = 65 ± 6 years) and twenty-one age- and sex-matched healthy controls (age = 66 ± 6 years) were evaluated. Working memory performance (via N-back) was evaluated while study participants donned cortical fNIRS. Health state, metabolic data, and menopausal status data were also collected. Deficits in working memory accuracy were found in the DM group as compared to controls. Differences in HbO responses emerged in the DM group. The DM group exhibited altered PFC activity magnitudes and increased functional cortical activity across ROIs compared to controls. HbO and HbR responses were not associated with worsened health state measures. These data indicate a shift in cortical activity patterns with memory deficits in postmenopausal PwDM. This DM-specific shift of HbO is a novel finding that is unlikely to be detected by fMRI. This underscores the value of using non-MRI-based neuroimaging techniques to evaluate cortical hemodynamic function to detect early mild cognitive impairment.

Greater resting muscle sympathetic nerve activity reduces cold pressor autonomic reactivity in older women, but not older men

Previous work demonstrates augmented muscle sympathetic nerve activity (MSNA) responses to the cold pressor test (CPT) in older women. Given its interindividual variability, however, the influence of baseline MSNA on CPT reactivity in older adults remains unknown. Sixty volunteers (60-83y; 30 women) completed testing where MSNA (microneurography), blood pressure (BP), and heart rate (HR) were recorded during baseline and a 2-min CPT (~4°C). Participant data were terciled by baseline MSNA (n=10/group); comparisons were made between the high baseline men (HM) and women (HW), and low baseline men (LM) and women (LW). By design, HM and HW, vs. LM and LW, had greater baseline MSNA burst frequency (37±5 and 38±3 vs. 9±4 and 15±5 bursts/min) and burst incidence (59±14 and 60±8 vs. 16±10 and 23±7 bursts/100hbs; both P<0.001). However, baseline BP and HR were not different between the groups (all P>0.05). During the CPT, there were no differences in the increase in BP and HR (all P>0.05). Conversely, ΔMSNA burst frequency was lower in HW vs. LW (8±9 vs. 22±12 bursts/min; P=0.012) yet was similar in HM vs. LM (17±12 vs. 19±10 bursts/min, P=0.994). Further, ΔMSNA burst incidence was lower in HW vs. LW (9±13 vs. 28±16 bursts/100hbs; P=0.020), with no differences between HM vs. LM (21±17 vs. 31±17 bursts/100hbs; P=0.455). Our findings suggest that heightened baseline activity in older women attenuates the typical CPT-mediated increase in MSNA without changing cardiovascular reactivity. While the underlying mechanisms remain unknown, altered sympathetic recruitment or neurovascular transduction may contribute to these disparate responses.

Effects of sex and ageing on the human respiratory muscle metaboreflex

Intense inspiratory muscle work evokes a sympathetically mediated pressor reflex, termed the respiratory muscle metaboreflex, in which young females demonstrate an attenuated response relative to males. However, the effects of ageing and female sex hormones on the respiratory muscle metaboreflex are unclear. We tested the hypothesis that the pressor response to inspiratory work would be similar between older males and females, and higher relative to their younger counterparts. Healthy, normotensive young (26 ± 3 years) males (YM; n = 10) and females (YF; n = 10), as well as older (64 ± 5 years) males (OM; n = 10) and females (OF; n = 10), performed inspiratory pressure threshold loading (PTL) to task failure. Older adults had a greater mean arterial pressure (MAP) response to PTL than young (P < 0.001). YF had a lower MAP compared to YM (+10 ± 6 vs. +19 ± 15 mmHg, P = 0.026); however, there was no difference observed between OF and OM (+26 ± 11 vs. +27 ± 11 mmHg, P = 0.162). Older adults had a lower heart rate response to PTL than young (P = 0.002). There was no effect of sex between young females and males (+19 ± 9 and +27 ± 11 bpm, P = 0.186) or older females and males (+17 ± 7 and +20 ± 7 bpm, P = 0.753). We conclude the respiratory muscle metaboreflex response is heightened in older adults, and the sex effect between older males and post-menopause females is absent, suggesting an effect of circulating sex hormones. KEY POINTS: The arterial blood pressure response to the respiratory muscle metaboreflex is greater in older males and females. Compared to sex-matched young individuals, there is no sex differences in the blood pressure response between older males and post-menopause females. Our results suggest the differences between males and females in the cardiovascular response to high levels of inspiratory muscle work is abolished with reduced circulating female sex hormones.

Vasomotor symptoms of menopause, autonomic dysfunction, and cardiovascular disease

Cardiovascular disease (CVD), the leading cause of death among US adults, is more prevalent in menopausal females compared with age-matched males. Vasomotor symptoms of menopause (VMS; hot flashes/flushes and night sweats) are common among females undergoing menopausal transition and have been associated with elevated blood pressure (BP) and increased CVD risk. Autonomic dysregulation of BP has been posited as a contributing factor to the elevated CVD risk in menopausal females with VMS. This review includes 1) a brief overview of the relationship between VMS and CVD, 2) mechanisms of hot flushes and their potential impact on short- and long-term BP regulation, and 3) how the disruption of autonomic function associated with VMS might provide a mechanistic pathway to CVD development. Finally, this review will highlight knowledge gaps and future directions toward better understanding of hot flush physiology and VMS contributions to CVD.

One-Week L-Arginine Supplementation Had No Effect on 200m Freestyle Swimming Time Trial in Moderately-Trained Male Swimmers

Research on the effect of L-arginine supplementation on exercise performance is still inconsistent and its influence on single-bout swimming performance has not been investigated. Therefore, the aim of this study was to assess if one-week L-arginine supplementation would enhance 200-m freestyle swimming performance in trained/developmental (regularly training ∼3 times per week with a purpose to compete) male swimmers. In a randomized, cross-over, double-blind design, 8 trained/developmental male swimmers (age 25 ± 5 years; mean ± SD) completed 200-m freestyle swimming time-trial on 3 separate occasions: a control trial; and after 2 separate 7-d supplementation periods, with a daily dose of either 8 g/d of L-arginine or placebo trials. Blood lactate concentration was measured immediately post time-trial swimming. Completion time of the 200-m freestyle swimming time-trial did not differ significantly (F = 4.55; P = 0.060; ŋp2 = 0.394) between control (149.40 ± 9.88 s), L-arginine (146.02 ± 10.34 s) and placebo trials (147.58 ± 10.86 s). There was no statistically significant difference in post time-trial swimming blood lactate concentration between trials (control: 11.2 ± 2.7; L-arginine: 13.1 ± 1.8; Placebo: 12.2 ± 2.7, F = 3.52; P = 0.058; ŋp2 = 0.335). One-week of supplementation with 8 g/d of L-arginine, had no ergogenic effect on middle-distance (200-m), freestyle swimming performance in trained/developmental male swimmers.

Effects of the Follicular Menstrual Phase on Forearm Vascular Conductance in Abdominal Obese Premenopausal Women During Graded Handgrip Exercise

Purpose

Previous studies have reported a sympatholytic action of estrogen on the vasculature in response to increased sympathetic outflow, an effect most notable during exercise, providing for necessary increases in blood flow to working muscle. In contrast, elevated concentrations of progesterone can inhibit this action of estrogen, impairing increases in blood flow. We hypothesize that the peak concentration of estrogen during the proliferative portion of the follicular phase of the menstrual cycle in female humans will increase vascular conductance during exercise when the effects of progesterone are negligible. In addition, we hypothesize that overweight abdominally obese females will have an attenuated conductance response to dynamic exercise during the same menstrual phase.

Methods

Participants engaged in graded forearm exercise using an isotonic handgrip dynometer with sequential increases in resistance at a cadence of 30 contractions/minute until task failure. They performed exercise at time points of the menstrual cycle corresponding to low concentrations of both sex hormones and elevated estrogen, while progesterone remained low. Blood flow and vascular conductance were measured using Doppler ultrasound.

Results

This revealed a trend that abdominal obese women during a phase of low estrogen had a lower overall blood flow and vascular conductance response than healthy controls at matching resistance stages during rest and exercise. This group difference was attenuated during the proliferative phase with elevated circulating estrogen. There is not a statistically significant interaction between Ovarian Phase and Weight group (P = 0.778).

Conclusion

The results indicate that overweight women are at a disadvantage during exercise in increasing blood flow to working muscles, which can be detrimental to overall fitness improvement during the early and potentially late follicular phase of the menstrual cycle.

Effects of arm cranking exercise on muscle oxygenation between active and inactive muscles in people with spinal cord injury

Objective: We investigated the effects of the incremental arm-cranking exercise (ACE) on tissue oxygen saturation (StO₂) between active and inactive muscles, and the relationship between peak oxygen uptake (VO_2peak) and changes in the StO₂ in inactive muscles.Design: Observational study.Setting: Community-based supervised intervention.Participants: The participants were individuals with motor and sensory complete spinal cord injury (complete SCI; n = 8) and motor complete but sensory incomplete SCI (incomplete SCI; n = 8), and able-bodied (AB) individuals (n = 8) matched for age, height, and body mass index.Intervention: The ACE was performed at a rate increasing by 10 watts min^-1 until exhaustion.Outcome Measures: VO_2peak, heart rate (HR), and StO₂.Results: While VO_2peak was similar among the groups, peak HR was significantly higher in both SCI groups than in the AB (P < 0.05). In active muscles (biceps brachii), no differences in the StO₂ were observed among the groups (P > 0.05). In inactive muscles (vastus lateralis), the StO₂ in the AB and the incomplete SCI began to decrease at approximately 40% of the peak work rate; however, they remained unchanged in the complete SCI. The reductions in StO₂ in the AB were significantly greater than in the incomplete SCI.Conclusions: These results suggest that sympathetic vasoconstriction occurred in the incomplete SCI and AB, although it did not occur in the complete SCI, probably due to a reduction in sympathetic nerve activity. Sympathetic vasoconstriction in inactive muscles may not contribute to an individual's VO_2peak regardless of their group.

Sympathetic vasoconstriction in skeletal muscle: Modulatory effects of aging, exercise training, and sex

The sympathetic nervous system (SNS) is a critically important regulator of the cardiovascular system. The SNS controls cardiac output and its distribution, as well as peripheral vascular resistance and blood pressure at rest and during exercise. Aging is associated with increased blood pressure and decreased skeletal muscle blood flow at rest and in response to exercise. The mechanisms responsible for the blunted skeletal muscle blood flow response to dynamic exercise with aging have not been fully elucidated; however, increased muscle sympathetic nerve activity (MSNA), elevated vascular resistance and a decline in endothelium-dependent vasodilation are commonly reported in older adults. In contrast to aging, exercise training has been shown to reduce blood pressure and enhance skeletal muscle vascular function. Exercise training has been shown to enhance nitric oxide-dependent vascular function and may improve the vasodilatory capacity of the skeletal muscle vasculature; however, surprisingly little is known about the effect of exercise training on the neural control of circulation. The control of blood pressure and skeletal muscle blood flow also differs between males and females. Blood pressure and MSNA appear to be lower in young females compared to males. However, females experience a larger increase in MSNA with aging compared to males. The mechanism(s) for the altered SNS control of vascular function in females remain to be determined. Novelty: • This review will summarize our current understanding of the effects of aging, exercise training and sex on sympathetic vasoconstriction at rest and during exercise. • Areas where additional research is needed are also identified.

There are no differences in brachial artery endothelial shear stress and blood flow patterns between males and females during exercise

Premenopausal females have a lower cardiovascular risk than males. Sex differences on exercise-induced endothelial shear stress (ESS) and blood flow patterns may explain part of this risk reduction. The purpose of this cross-sectional study was to determine the differences in brachial artery exercise-induced ESS and blood flow patterns between males and females. Thirty subjects (13 females) were recruited to perform a three-workload steady-state exercise test based on blood lactate levels (i.e. <2.0, 2.0-4.0, >4.0 mmol/l). ESS and blood flow patterns were estimated at rest and during each workload using Womersley's approximation and Reynolds number, respectively. Both males and females showed an exercise intensity-dependent increase in antegrade and retrograde ESS. There was no significant sex effect or interaction for antegrade ESS (F_{(1, 30)}  = 0.715, p = 0.405 and F_{(1·672, 60)}  = 1.511, p = 0.232, respectively) or retrograde ESS (F_{(1, 30)}  = 0.794, p = 0.380 and F_{(1·810, 60)}  = 1.022, p = 0.361, respectively). Additionally, antegrade blood flow was turbulent during all bouts of exercise while retrograde blood flow became disturbed at moderate and high exercise intensities in both groups. There are no differences in exercise-induced ESS and blood flow patterns between males and females when the exercise load is equivalent. This suggests that the vascular benefits of exercise training are similar in both sexes from a haemodynamic standpoint.

Neurovascular Dysregulation During Exercise in Type 2 Diabetes

Emerging evidence suggests that type 2 diabetes (T2D) may impair the ability to properly adjust the circulation during exercise with augmented blood pressure (BP) and an attenuated contracting skeletal muscle blood flow (BF) response being reported. This review provides a brief overview of the current understanding of these altered exercise responses in T2D and the potential underlying mechanisms, with an emphasis on the sympathetic nervous system and its regulation during exercise. The research presented support augmented sympathetic activation, heightened BP, reduced skeletal muscle BF, and impairment in the ability to attenuate sympathetically mediated vasoconstriction (i.e., functional sympatholysis) as potential drivers of neurovascular dysregulation during exercise in T2D. Furthermore, emerging evidence supporting a contribution of the exercise pressor reflex and central command is discussed along with proposed future directions for studies in this important area of research.

Age and sex differences in blood pressure responses during hyperpnoea

NEW FINDINGS

What is the central question of this study? Increased respiratory muscle activation is associated with neural and cardiovascular consequences via the respiratory muscle-induced metaboreflex. Does ageing and/or sex influence the arterial blood pressure response during voluntary normocapnic incremental hyperpnoea? What is the main finding and its importance? The increase in blood pressure during hyperpnoea was smaller in younger females than in older females, whereas no difference was found between older males and older females. The blunted respiratory muscle-induced metaboreflex in younger females is normalized with advancing age, whereas ageing has no such effect in males.

ABSTRACT

We hypothesized that older females (OF) have a greater arterial blood pressure response to increased respiratory muscle work compared with younger females (YF) and that no such difference exists between older males (OM) and younger males (YM). To test these hypotheses, cardiovascular responses during voluntary normocapnic incremental hyperpnoea were evaluated and compared between older and younger subjects. An incremental respiratory endurance test (IRET) was performed as follows: target minute ventilation was initially set at 30% of the maximal voluntary ventilation (MVV12) and was increased by 10% of MVV12 every 3 min. The test was terminated when the subject could not maintain the target percentage of MVV12. Heart rate and mean arterial blood pressure (MAP) were recorded continuously. The increase in MAP from baseline (ΔMAP) during the IRET in OM (+24.0 ± 14.7 mmHg, mean ± SD) did not differ (P = 0.144) from that in YM (+24.3 ± 13.4 mmHg), but it was greater (P = 0.004) in OF (+31.2 ± 11.6 mmHg) than in YF (+10.3 ± 5.5 mmHg). No significant difference in ΔMAP during the IRET was observed between OM and OF (P = 0.975). These results suggest that the respiratory muscle-induced metaboreflex is blunted in YF, but it could be normalized with advancing age. In males, ageing has little effect on the respiratory muscle-induced metaboreflex. These results show no sex difference in the respiratory muscle-induced metaboreflex in older adults.

Sex-related differences in rapid-onset vasodilation: impact of aging

Rapid-onset vasodilation (ROV) in response to a single muscle contraction is attenuated with aging. Moreover, sex-related differences in muscle blood flow and vasodilation during dynamic exercise have been observed in young and older adults. The purpose of the present study was to explore if sex-related differences in ROV exist in young (n = 36, 25 ± 1 yr) and older (n = 32, 66 ± 1 yr) adults. Subjects performed single forearm contractions at 10%, 20%, and 40% maximal voluntary contraction. Brachial artery blood velocity and diameter were measured with Doppler ultrasound, and forearm vascular conductance (mL·min^-1·100 mmHg^-1) was calculated from blood flow (mL·min^-1) and mean arterial pressure (mmHg) and used as a measure of ROV. Peak ROV was attenuated in women across all relative intensities in the younger and older groups (P < 0.05). In a subset of subjects with similar absolute workloads (∼5 kg and ∼11 kg), age-related differences in ROV were observed among both women and men (P < 0.05). However, only older women demonstrated an attenuated peak ROV compared with men (91 ± 6 vs. 121 ± 11 mL·min^-1·100 mmHg^-1, P < 0.05), a difference not observed in the young group (134 ± 8 vs. 154 ± 11 mL·min^-1·100 mmHg^-1, P = 0.15). Additionally, examining the slope of peak ROV across contraction intensities indicated a blunted response in older women compared with their younger counterparts (P < 0.05), with no differences observed between older and young men (P = 0.38). Our data suggest that sex-related differences in the rapid vasodilatory response to single muscle contractions exist in older but not young adults, such that older women have a blunted response compared with older men.NEW & NOTEWORTHY While rapid-onset vasodilation (ROV) has been shown to decrease in older individuals, it is unclear if sex contributes to the decline with aging. We sought to identify if sex-related differences exist in the ROV response to single forearm contractions in young and older adults. Our data suggest sex-related differences are present among older but not young individuals, with women having an attenuated response. These data indicate sex plays a role in decreased vasodilation with aging.

Hemodynamic Function of Forearm Muscle in Postmenopausal Women With Type 2 Diabetes

Changes in the hemodynamic function of muscle are speculated as a causal mechanism for reduced motor capabilities with aging in Type 2 diabetes mellitus (DM). The focus of this study was to evaluate changes in muscle oxygenation during sustained force production in postmenopausal women with DM compared with controls. Near-infrared spectroscopy was used to monitor deoxyhemoglobin and oxyhemoglobin in the flexor digitorum superficialis. Sensorimotor function and health state covariates were also assessed. Increased deoxyhemoglobin was found during force production, whereas oxyhemoglobin remained constant. Changes were found in the time structure of the hemodynamic data during force production. No between-group differences were found; instead, measures covaried with the health state. Sex-based differences in the manifestation of DM-related sensorimotor dysfunction are likely. These data indicate that basic cardiovascular health measures may be more beneficial to monitoring hyperemic status and muscle function in postmenopausal women with DM, compared with DM diagnosis.

Functional sympatholysis is preserved in healthy young Black men during rhythmic handgrip exercise

Black men have attenuated increases in forearm vascular conductance (FVC) and forearm blood flow (FBF) during moderate- and high-intensity rhythmic handgrip exercise compared with White men, but the underlying mechanisms are unclear. Here, we tested for the first time the hypothesis that functional sympatholysis (i.e., attenuation of sympathetic vasoconstriction in the exercising muscles) is impaired in Black men compared with White men. Thirteen White and 14 Black healthy young men were studied. FBF (duplex Doppler ultrasound) and mean arterial pressure (MAP; Finometer) were measured at rest and during rhythmic handgrip exercise at 30% maximal voluntary contraction. FVC was calculated as FBF/MAP. Sympathetic activation was induced via lower body negative pressure (LBNP) at -20 Torr for 2 min at rest and from the 3rd to the 5th min of handgrip. Sympathetic vasoconstriction was assessed as percent reductions in FVC during LBNP. The groups presented similar resting FVC, FBF, and MAP. During LBNP at rest, reductions in FVC were not different between White (-35 ± 10%) and Black men (-32 ± 14%, P = 0.616), indicating similar reflex-induced sympathetic vasoconstriction. During handgrip exercise, there were minimal reductions in FVC with LBNP in either group (White: -1 ± 7%; Black: +1 ± 8%; P = 0.523), indicating functional sympatholysis in both groups. Thus, contrary to our hypothesis, our findings indicate a preserved functional sympatholysis in healthy young Black men compared with White men, suggesting that this mechanism does not appear to contribute to reduced exercise hyperemia during moderate-intensity rhythmic handgrip in this population.

Impact of age and sex on neural cardiovascular responsiveness to cold pressor test in humans

Prior longitudinal work suggests that blood pressure (BP) reactivity to the cold pressor test (CPT) helps predict hypertension; yet the impact of age and sex on hemodynamic and neural responsiveness to CPT remains equivocal. Forty-three young (21 ± 1yr, means ± SE) men (YM, n = 20) and women (YW, n = 23) and 16 older (60 ± 1yr) men (OM, n = 9) and women (OW, n = 7) participated in an experimental visit where continuous BP (finger plethysmography) and muscle sympathetic nerve activity (MSNA; microneurography) were recorded during a 3- to 5-min baseline and 2-min CPT. Baseline mean arterial pressure (MAP) was greater in OM than in YM (92 ± 4 vs. 77 ± 1 mmHg, P < 0.01), but similar in women (P = 0.12). Baseline MSNA incidence was greater in OM [69 ± 6 bursts/100 heartbeats (hb)] than in OW (44 ± 7 bursts/100 hb, P = 0.02) and lower in young adults (YM: 17 ± 3 vs. YW: 16 ± 2 bursts/100 hb, P < 0.01), but similar across the sexes (P = 0.83). However, when exposed to the CPT, MSNA increased more rapidly in OW (Δ43 ± 6 bursts/100 hb; group × time, P = 0.01) compared with OM (Δ15 ± 3 bursts/100 hb) but was not different between YW (Δ30 ± 3 bursts/100 hb) and YM (Δ33 ± 4 bursts/100 hb, P = 1.0). There were no differences in MAP with CPT between groups (group × time, P = 0.33). These findings suggest that OW demonstrate a more rapid initial rise in MSNA responsiveness to a CPT compared with OM. This greater sympathetic reactivity in OW may be a contributing mechanism to the increased hypertension risk in postmenopausal women.

Functional neuroimaging of sensorimotor cortices in postmenopausal women with type II diabetes

Significance: Deficits in sensorimotor function in persons with type II diabetes mellitus (PwDM) have traditionally been considered a result of peripheral nerve damage. Emerging evidence has suggested that factors outside of nerve damage due to type II diabetes mellitus, such as impaired hemodynamic function, contribute significantly to both sensory and motor deficits in PwDM. Aim: The focus of the current study was to evaluate functional cortical hemodynamic activity during sensory and motor tasks in PwDM. Approach: Functional near-infrared spectroscopy was used to monitor oxyhemoglobin (HbO) and deoxyhemoglobin (HbR) across the cortex during sensory and motor tasks involving the hands. Results: Decline in HbO across sensory and motor regions of interest was found in PwDM with simultaneous deficits in manual motor tasks, providing the first evidence of functional cortical hemodynamic activity deficits relating to motor dysfunction in PwDM. Similar deficits were neither specifically noted in HbR nor during evaluation of sensory function. Health state indices, such asA 1 c , blood pressure, body mass index, and cholesterol, were found to clarify group effects. Conclusions: Further work is needed to clarify potential sex-based differences in PwDM during motor tasks as well as the root of reduced cortical HbO indices but unchanged HbR indices in PwDM.

Augmentation of endothelium-dependent vasodilatory signalling improves functional sympatholysis in contracting muscle of older adults

KEY POINTS

The ability of contracting skeletal muscle to attenuate sympathetic vasoconstriction (functional sympatholysis) is critical for maintaining blood flow during exercise-mediated sympathoexcitation. Functional sympatholysis and endothelial function are impaired with ageing, resulting in compromised blood flow and oxygen delivery to contracting skeletal muscle during exercise. In the present study, intra-arterial infusion of ACh or ATP to augment endothelium-dependent signalling during exercise attenuated α₁ -adrenergic vasoconstriction in the contracting muscle of older adults. The vascular signalling mechanisms capable of functional sympatholysis are preserved in healthy ageing, and thus the age-related impairment in functional sympatholysis probably results from the loss of a functional signal (e.g. plasma [ATP]) as opposed to an intrinsic endothelial dysfunction.

ABSTRACT

The ability of contracting skeletal muscle to attenuate sympathetic α-adrenergic vasoconstriction ('functional sympatholysis') is impaired with age. In young adults, increasing endothelium-dependent vasodilatory signalling during mild exercise augments sympatholysis. In the present study, we tested the hypothesis that increasing endothelium-dependent signalling during exercise in older adults can improve sympatholysis. In 16 older individuals (Protocol 1, n = 8; Protocol 2, n = 8), we measured forearm blood flow (Doppler ultrasound) and calculated changes in vascular conductance (FVC) to local intra-arterial infusion of phenylephrine (PE; α₁ -agonist) during (i) infusion of an endothelium-dependent vasodilator alone (Protocol 1: ACh or Protocol 2: low dose ATP); (ii) mild handgrip exercise (5% maximum voluntary contraction; MVC); (iii) moderate handgrip exercise (15% MVC); and (iv) mild or moderate handgrip exercise + infusion of ACh or ATP to augment endothelium-dependent signalling. PE caused robust vasoconstriction in resting skeletal muscle during control vasodilator infusions (ΔFVC: ACh: -31 ± 3 and ATP: -30 ± 4%). PE-mediated vasoconstriction was not attenuated by mild or moderate intensity exercise (ΔFVC: 5% MVC: -30 ± 9; 15% MVC: -33 ± 8%; P > 0.05 vs. control ACh and ATP), indicative of impaired sympatholysis, and ACh or ATP infusion during mild exercise did not impact this response. However, augmentation of endothelium-dependent signalling via infusion of ACh or ATP during moderate intensity exercise attenuated PE-mediated vasoconstriction (ΔFVC: -13 ± 1 and -19 ± 5%, respectively; P < 0.05 vs. all conditions). Our findings demonstrate that, given a sufficient stimulus, endothelium-dependent sympatholysis remains intact in older adults. Strategies aimed at activating such pathways represent a viable approach for improving sympatholysis and thus tissue blood flow and oxygen delivery in older adults.

Blood pressure and limb blood flow responses during hyperpnoea are not affected by menstrual cycle phase in young women

The purpose of this study was to clarify whether the menstrual cycle affects the cardiovascular and limb blood flow responses during hyperpnoea. Fifteen young female subjects participated. An incremental respiratory endurance test was performed at the early follicular (EF) and midluteal (ML) phases. Target minute ventilation was initially set at 30 % of maximal voluntary ventilation (MVV12) and was increased by 10 %MVV12 every 3 min. The test was terminated when the subjects no longer maintained the target ventilation. Mean arterial blood pressure (MBP) and mean blood flow in the brachial artery were continuously measured. There were no significant differences in the increase in MBP (EF: +13.0 ± 7.9 mmHg vs. ML: + 15.4 ± 12.9 mmHg during the test, F = 0.70, P = 0.59) and the decrease in brachial blood flow between the phases. These results suggest that menstrual cycle does not affect respiratory muscle-induced metaboreflex in young women.

Influence of Sex, Menstrual Cycle, and Menopause Status on the Exercise Pressor Reflex

In this review, we highlight the underlying mechanisms responsible for the sex differences in the exercise pressor reflex (EPR), and, importantly, the impact of sex hormones and menopausal status. The EPR is attenuated in premenopausal women compared with age-matched men. Specifically, activation of the metaboreflex (a component of the EPR) results in attenuated increases in blood pressure and sympathetic vasomotor outflow compared with age-matched men. In addition, premenopausal women exhibit less transduction of sympathetic outflow to the peripheral vasculature than men. In stark contrast, postmenopausal women exhibit an augmented EPR arising from exaggerated metaboreflex-induced autonomic and cardiovascular reflexes. We propose that metaboreflex-induced autonomic and cardiovascular changes associated with menopause majorly contribute to the elevated blood pressure response during dynamic exercise in postmenopausal women. In addition, we discuss the potential mechanisms by which sex hormones in premenopausal women may impact the EPR as well as metaboreflex.

Preserved ability to blunt sympathetically-mediated vasoconstriction in exercising skeletal muscle of young obese humans

Sympathetic vasoconstriction is attenuated in exercising muscles to assist in matching of blood flow with metabolic demand. This "functional sympatholysis" may be impaired in young obese individuals due to greater sympathetic activation and/or reduced local vasodilatory capacity of both small and large arteries, but this remains poorly understood. We tested the hypothesis that functional sympatholysis is impaired in obese individuals compared with normal-weight counterparts. In 36 obese and normal-weight young healthy adults (n = 18/group), we measured forearm blood flow and calculated forearm vascular conductance (FVC) responses to reflex increases in sympathetic nerve activity induced by lower body negative pressure (LBNP) at rest and during rhythmic handgrip exercise at 15% and 30% of the maximal voluntary contraction (MVC). FVC was normalized to lean forearm mass. In normal-weight individuals, LBNP evoked a decrease in FVC (-16.1 ± 5.7%) in the resting forearm, and the reduction in FVC (15%MVC: -8.1 ± 3.3%; 30%MVC: -1.0 ± 4.0%) was blunted during exercise in an intensity-dependent manner (P < 0.05). Similarly, in obese individuals, LBNP evoked a comparable decrease in FVC (-10.9 ± 5.7%) in the resting forearm, with the reduction in FVC (15%MVC: -9.7 ± 3.3%; 30%MVC: -0.3 ± 4.0%) also blunted during exercise in an intensity-dependent manner (P < 0.05). The magnitude of sympatholysis was similar between groups (P > 0.05) and was intensity-dependent (P < 0.05). Our findings suggest that functional sympatholysis is not impaired in young obese individuals without overt cardiovascular diseases.

Functional sympatholysis is impaired in end-stage renal disease

Patients with end-stage renal disease (ESRD) have decreased exercise capacity and exercise intolerance that contribute to cardiovascular risk. One potential mechanism underlying exercise intolerance in ESRD is impaired ability to oppose sympathetically mediated vasoconstriction within exercising skeletal muscle (i.e., functional sympatholysis, FS). We hypothesized that ESRD patients have impaired FS compared with healthy (CON) and hypertensive (HTN) controls and that impaired FS is related to circulating levels of the uremic toxin asymmetric dimethyl arginine (ADMA), an endogenous nitric oxide synthase inhibitor. Near-infrared spectroscopy-derived oxygen tissue saturation index (TSI) of the forearm muscle was measured continuously in 33 participants (9 CON, 14 HTN, 10 ESRD) at rest and during low-dose (-20 mmHg) lower body negative pressure (LBNP), moderate rhythmic handgrip exercise, and LBNP with concomitant handgrip exercise (LBNP+handgrip). Resting muscle TSI was lower in ESRD than in CON and HTN groups (CON = 67.8 ± 1.9%, HTN = 67.2 ± 1.1%, ESRD = 62.7 ± 1.5%, P = 0.03). Whereas CON and HTN groups had an attenuation in sympathetically mediated reduction in TSI during LBNP + handgrip compared with LBNP alone (P ≤ 0.05), this response was not present in ESRD (P = 0.71), suggesting impaired FS. There was no difference in plasma [ADMA] between groups (CON = 0.47 ± 0.05 µmol/l, HTN = 0.42 ± 0.06 µmol/l, ESRD = 0.63 ± 0.14 µmol/l, P = 0.106) and no correlation between plasma [ADMA] and resting muscle TSI (P = 0.84) or FS (P = 0.75). Collectively, these findings suggest that ESRD patients have lower muscle perfusion at rest and impaired FS but that these derangements are not related to circulating [ADMA].

Vasoconstrictor responsiveness through alterations in relaxation time and metabolic rate during rhythmic handgrip contractions

Increasing the relaxation phase of the contraction-relaxation cycle will increase active skeletal muscle blood flow ( Q ˙ m ). However, it remains unknown if this increase in Q ˙ m alters the vasoconstriction responses in active skeletal muscle. This investigation determined if decreasing mechanical impedance would impact vasoconstriction of the active skeletal muscle. Eight healthy men performed rhythmic handgrip exercise under three different conditions; "low" duty cycle at 20% maximal voluntary contraction (MVC), "low" duty cycle at 15% MVC, and "high" duty cycle at 20% MVC. Relaxation time between low and high duty cycles were 2.4 sec versus 1.5 sec, respectively. During steady-state exercise lower body negative pressure (LBNP) was used to evoke vasoconstriction. Finger photoplethysmography and Doppler ultrasound derived diameters and velocities were used to measure blood pressure, forearm blood flow (FBF: mL min-1 ) and forearm vascular conductance (FVC: mL min-1  mmHg) throughout testing. The low duty cycle increased FBF and FVC versus the high duty cycle under steady-state conditions at 20% MVC (P < 0.01). The high duty cycle had the greatest attenuation in %ΔFVC (-1.9 ± 3.8%). The low duty cycle at 20% (-13.3 ± 1.4%) and 15% MVC (-13.1 ± 2.5%) had significantly greater vasoconstriction than the high duty cycle (both: P < 0.01) but were not different from one another (P = 0.99). When matched for work rate and metabolic rate ( V ˙ O 2 ), the high duty cycle had greater functional sympatholysis than the low duty cycle. However, despite a lower V ˙ O 2 , there was no difference in functional sympatholysis between the low duty cycle conditions. This may suggest that increases in Q ˙ m play a role in functional sympatholysis when mechanical compression is minimized.

Cardiovascular response to trigeminal nerve stimulation at rest and during exercise in humans: does sex matter?

We sought to investigate the possibility that there are sex differences in the cardiovascular responses to trigeminal nerve stimulation (TGS) with cold exposure to the face at rest and during dynamic exercise. In 9 healthy men (age: 28 ± 3 yr; height: 178 ± 1 cm; weight: 77 ± 8 kg) and 13 women (age 26 ± 5 yr; height 164 ± 3 cm; weight 63 ± 7 kg) beat-to-beat heart rate (HR) and blood pressure were recorded. Mean arterial pressure (MAP), stroke volume (SV), cardiac index (CI), and total vascular resistance index (TVRI) were calculated. TGS was applied for 3 min at rest and in-between 10-min steady-state cycling exercise at a HR of 110 beats/min, the measurements were obtained during the last minute of each period. At rest, TGS increased MAP (men: Δ18 ± 8 mmHg; women: Δ23 ± 8 mmHg; means ± SD), TVRI (men: Δ1.1 ± 0.6 mmHg·l−1·min·m−2; women: Δ1.2 ± 1.2 mmHg·l−1·min·m−2) and SV (men: Δ19 ± 15 ml; women: Δ16 ± 11 ml) in both groups. CI increased with TGS in women but not in men. However, men presented a bradycardic response to TGS (Δ−11 ± 8 beats/min) that was not significant in women compared with baseline. Cycling exercise increased HR, MAP, SV, and CI and decreased TVRI in men and women. TGS during exercise further increased MAP in men and women and did not change CI in either group. SV and TVRI increased with TGS during exercise only in women. TGS during exercise evoked bradycardia in men (Δ−7 ± 9 beats/min), whereas HR was unchanged in women. Our findings indicate sex differences in TGS-related cardiovascular responses at rest and during exercise.

Impaired modulation of postjunctional α1 - but not α2 -adrenergic vasoconstriction in contracting forearm muscle of postmenopausal women

KEY POINTS

Contraction-mediated blunting of postjunctional α-adrenergic vasoconstriction (functional sympatholysis) is attenuated in skeletal muscle of ageing males, brought on by altered postjunctional α₁ - and α₂ -adrenergic receptor sensitivity. The extent to which postjunctional α-adrenergic vasoconstriction occurs in the forearms at rest and during exercise in postmenopausal women remains unknown. The novel findings indicate that contraction-mediated blunting of α₁ - (via intra-arterial infusion of phenylephrine) but not α₂ -adrenergic (via intra-arterial infusion of dexmedetomidine) vasoconstriction was attenuated in postmenopausal women compared to young women. Additional important findings revealed that postjunctional α-adrenergic vasoconstrictor responsiveness at rest does not appear to be affected by age in women. Collectively, these results contribute to our understanding of local neurovascular control at rest and during exercise with age in women.

ABSTRACT

Contraction-mediated blunting of postjunctional α-adrenergic vasoconstriction (functional sympatholysis) is attenuated in older males; however, direct confirmation of this effect remains unknown in postmenopausal women (PMW). The present study examined whether PMW exhibit augmented postjunctional α-adrenergic receptor vasoconstriction at rest and during forearm exercise compared to young women (YW). Eight YW (24 ± 1 years) and eight PMW (65 ± 1 years) completed a series of randomized experimental trials: (1) at rest, (2) under high flow (adenosine infusion) conditions and (3) during 6 min of forearm exercise at relative (20% of maximum) and absolute (7 kg) intensities. Phenylephrine (α₁ -agonist) or dexmedetomidine (α₂ -agonist) was administered during the last 3 min of each trial to elicit α-adrenergic vasoconstriction. Forearm vascular conductance (FVC) was calculated from blood flow and blood pressure. Vasoconstrictor responsiveness was identified as the change in FVC (%) during α-adrenergic agonist infusions from baseline (resting trial) or from steady-state conditions (high flow and exercise trials). During resting and high flow trials, the %FVC during α₁ - and α₂ -agonist stimulation was similar between YW and PMW. During exercise, α₁ -mediated vasoconstriction was blunted in YW vs. PMW at relative (-6 ± 2% vs. -15 ± 3%) and absolute (-4 ± 2% vs. -14 ± 5%) workloads, such that blood flow and FVC were lower in PMW (P < 0.05 for all). Conversely, α₂ -mediated vasoconstriction was similar between YW and PMW at relative (-22 ± 3% vs. -22 ± 4%; P > 0.05) and absolute (-19 ± 3% vs. -18 ± 4%; P > 0.05) workloads. Collectively, these findings demonstrate that despite similar α-adrenergic vasoconstrictor responsiveness at rest, PMW have a decreased ability to attenuate α₁ -adrenergic vasoconstriction in contracting skeletal muscle.

Lack of age-specific influence on leg blood flow during incremental calf plantar-flexion exercise in men and women

PURPOSE

Age-related exercising leg blood flow (LBF) responses during dynamic knee-extension exercise and forearm blood flow responses during handgrip exercise are preserved in normally active men but attenuated in activity-matched women. We explored whether these age- and sex-specific effects are also apparent during isometric calf plantar-flexion incremental exercise.

METHODS

Normally active young men (YM, n = 15, 24 ± 2 years), young women (YW, n = 8, 22 ± 1 years), older men (OM, n = 13, 70 ± 7 years) and older women (OW, n = 10, 64 ± 7 years) were tested. LBF was measured between contractions using venous occlusion plethysmography.

RESULTS

Peak force obtained was higher (P < 0.05) in men compared with women and in young compared with older individuals. However, peak LBF (YM; 971 ± 328 ml min^-1, OM; 985 ± 504 ml min^-1, YW; 844 ± 366 ml min^-1, OW; 960 ± 244 ml min^-1) and peak leg vascular conductance [LVC = LBF/(MAP + hydrostatic pressure)] responses (YM; 6.0 ± 1.8 ml min^-1 mmHg^-1, OM; 5.5 ± 2.8 ml min^-1 mmHg^-1, YW; 5.3 ± 2.1 ml min^-1 mmHg^-1, OW; 5.5 ± 1.6 ml min^-1 mmHg^-1) were similar among the four groups. Furthermore, the hyperaemic (YM; 8.8 ± 3.7 ml min^-1 %F_peak^-1 OM; 8.3 ± 5.4 ml min^-1 %F_peak^-1, YW; 8.2 ± 3.5 ml min^-1 %F_peak^-1, OW; 9.6 ± 2.2 ml min^-1 %F_peak^-1) and vasodilatory responses (YM; 0.053 ± 0.020 ml min^-1 mmHg^-1 %F_peak^-1, OM; 0.048 ± 0.028 ml min^-1 mmHg^-1 %F_peak^-1, YW; 0.051 ± 0.019 ml min^-1 mmHg^-1 %F_peak^-1, OW; 0.055 ± 0.014 ml min^-1 mmHg^-1 %F_peak^-1) were not different among the four groups. These results were accompanied by similar resting LBF responses among groups and were not affected when data were normalised to estimated leg muscle mass.

CONCLUSIONS

Our results demonstrate that exercising LBF responses during isometric incremental calf muscle exercise are preserved in older men and women, suggesting that the previously observed age-related attenuations in leg and forearm hyperaemia among women may be muscle-group specific.

Sex-specific impact of aging on the blood pressure response to exercise

An exaggerated blood pressure (BP) response to exercise has been linked to cardiovascular disease, but little is known about the impact of age and sex on this response. Therefore, this study examined the hemodynamic and skeletal muscle metabolic response to dynamic plantar flexion exercise, at 40% of maximum plantar flexion work rate, in 40 physical activity-matched young (23 ± 1 yr, n = 20) and old (73 ± 2 yr, n = 20), equally distributed, male and female subjects. Central hemodynamics and BP (finometer), popliteal artery blood flow (Doppler ultrasound), and skeletal muscle metabolism (³¹P-magnetic resonance spectroscopy) were measured during 5 min of plantar flexion exercise. Popliteal artery blood flow and high-energy phosphate responses to exercise were not affected by age or sex, whereas aging, independent of sex, attenuated stroke volume and cardiac output responses. Systolic BP and mean arterial pressure responses were exaggerated in old women (Δ42 ± 4 and Δ28 ± 3 mmHg, respectively), with all other groups exhibiting similar increases in systolic BP (old men: Δ27 ± 8 mmHg, young men: Δ27 ± 3 mmHg, and young women: Δ22 ± 3 mmHg) and mean arterial pressure (old men: Δ15 ± 4 mmHg, young men: Δ19 ± 2 mmHg, and young women: Δ17 ± 2 mmHg). Interestingly, the exercise-induced change in systemic vascular resistance in old women (∆0.8 ± 1.0 mmHg·l^-1·min^-1) was augmented compared with young women and young and old men (∆-2.8 ± 0.5, ∆-1.6 ± 0.6, and ∆-3.18 ± 1.4 mmHg·l^-1·min^-1, respectively, P < 0.05). Thus, in combination, advancing age and female sex results in an exaggerated BP response to exercise, likely the result of a failure to reduce systemic vascular resistance. NEW & NOTEWORTHY An exaggerated blood pressure response to exercise has been linked to cardiovascular disease; however, little is known about how age and sex impact this response in healthy individuals. During dynamic exercise, older women exhibited an exaggerated blood pressure response driven by an inability to lower systemic vascular resistance.

Evidence of a greater functional sympatholysis in habitually aerobic trained postmenopausal women

Habitual aerobic exercise attenuates elevated vasoconstriction during acute exercise (functional sympatholysis) in older men; however, this effect remains unknown in postmenopausal women (PMW). This study tested the hypothesis that PMW who participate in habitual aerobic exercise demonstrate a greater functional sympatholysis compared with their untrained counterparts. Nineteen PMW (untrained n = 9 vs. trained n = 10) performed 5 min of steady-state (SS) forearm exercise at relative [10% and 20% of maximum voluntary contraction (MVC)] and absolute (5 kg) contraction intensities. Lower-body negative pressure (LBNP) was used to increase sympathetic vasoconstriction during rest and forearm exercise. Brachial artery diameter and blood velocities (via Doppler ultrasound) determined forearm blood flow (FBF; ml/min). Forearm muscle oxygen consumption ([Formula: see text]; ml/min) and arteriovenous oxygen difference (a-vO_2diff) were estimated during SS-exercise and SS-exercise with LBNP. Forearm vascular conductance (FVC; ml·min^-1·100 mmHg^-1) was calculated from FBF and mean arterial pressure (MAP; mmHg). Vasoconstrictor responsiveness was determined as the %change in FVC during LBNP. The reduction in FVC (% change FVC) during LBNP was lower in trained compared with untrained PMW at 10% MVC (-7.3 ± 1.2% vs. -13.0 ± 1.1%; P < 0.05), 20% MVC (-4.4 ± 0.8% vs. -8.6 ± 1.4%; P < 0.05), and 5 kg (-5.3 ± 0.8% vs. -8.9 ± 1.4%; P < 0.05) conditions, whereas there were no differences at rest (-32.7 ± 4.4% vs. -33.7 ± 4.0%). Peripheral (FVC, FBF, and [Formula: see text]) and the magnitude change in systemic hemodynamics (heart rate and MAP) did not differ between groups during exercise. Collectively, the findings present the first evidence suggesting that PMW who participate in aerobic exercise demonstrate a greater functional sympatholysis compared with untrained PMW during mild to moderate forearm exercise. NEW & NOTEWORTHY Habitual aerobic exercise attenuates the elevated sympathetic nervous system-induced vasoconstriction during an acute bout of exercise (improved functional sympatholysis) in aging men; however, this effect remains unknown in postmenopausal women (PMW). The novel findings of this study suggest that habitual aerobic exercise results in an enhanced functional sympatholysis in PMW. Conversely, habitual aerobic exercise does not alter blood flow and oxygen utilization during acute forearm exercise compared with PMW who do not habitually exercise.

Sex differences in sympathetic vasoconstrictor responsiveness and sympatholysis

Sex differences in the neurovascular control of blood pressure and vascular resistance have been reported. However, the mechanisms underlying the modulatory influence of sex have not been fully elucidated. Nitric oxide (NO) has been shown to inhibit sympathetic vasoconstriction in resting and contracting skeletal muscle, and estrogen modulates NO synthase (NOS) expression and NO bioavailability. Therefore NO-mediated inhibition of sympathetic vasoconstriction may be enhanced in females. Thus the purpose of the present study was to investigate the hypothesis that sympathetic vasoconstrictor responsiveness would be blunted and NO-mediated inhibition of sympathetic vasoconstriction would be enhanced in females compared with males. Male (M; n = 8) and female (F; n = 10) Sprague-Dawley rats were anesthetized and surgically instrumented for measurement of arterial blood pressure and femoral artery blood flow and stimulation of the lumbar sympathetic chain. The percentage change of femoral vascular conductance in response to sympathetic chain stimulation delivered at 2 and 5 Hz was determined at rest and during triceps surae muscle contraction before (control) and after NOS blockade [N^ω-nitro-l-arginine methyl ester (l-NAME), 10 mg/kg iv]. At rest, sympathetic vasoconstrictor responsiveness was augmented (P < 0.05) in female compared with male rats at 2 Hz [F: -33 ± 8% (SD); M: -26 ± 6%] but was not different at 5 Hz (F: -55 ± 7%; M: -47 ± 7%). During muscle contraction, evoked vasoconstriction was similar (P > 0.05) in females and males at 2 Hz (F: -12 ± 5%; M: -13 ± 5%) but was blunted (P < 0.05) in females compared with males at 5 Hz (F: -24 ± 5%; M: -34 ± 8%). l-NAME increased (P < 0.05) sympathetic vasoconstrictor responsiveness in both groups at rest and during contraction. Contraction-mediated inhibition of vasoconstriction (sympatholysis) was enhanced (P < 0.05) in females compared with males; however, sympatholysis was not different (P > 0.05) between males and females in the presence of NOS blockade, indicating that NO-mediated sympatholysis was augmented in female rats. These data suggest that sex modulates sympathetic vascular control in resting and contracting skeletal muscle and that a portion of the enhanced sympatholysis in female rats was NO dependent.NEW & NOTEWORTHY Sex differences in the neurovascular regulation of blood pressure and vascular resistance have been documented. However, our understanding of the underlying mechanisms that mediate these differences is incomplete. The present study demonstrates that female rats have an enhanced capacity to inhibit sympathetic vasoconstriction during exercise (sympatholysis) and that NO mediates a portion of the enhanced sympatholysis.

Cardiovascular consequences of the inspiratory muscle metaboreflex: effects of age and sex

With inspiratory muscle metaboreflex activation, we hypothesized that, compared with their younger counterparts, older men and women would exhibit greater 1) increases in mean arterial pressure (MAP) and limb vascular resistance (LVR) and 2) decreases in limb blood flow (Q̇L) but 3) no sex differences would be present in older adults. Sixteen young adults [8 young men (YM) and 8 young women (YW), 18–24 yr] and 16 older adults [8 older men (OM) and 8 older women (OW), 60–73 yr] performed inspiratory resistive breathing tasks (IRBTs) at 2% and 65% of their maximal inspiratory pressure. During the IRBTs, breathing frequency was 20 breaths/min with a 50% duty cycle. At baseline and during the IRBTs, MAP was measured via automated oscillometry, Q̇L was determined via Doppler ultrasound, and LVR was calculated. The 65% IRBT led to significantly greater increases in MAP in OW (15.9 ± 8.1 mmHg) compared with YW (6.9 ± 1.4 mmHg) but not ( P > 0.05) between OM (12.3 ± 5.7 mmHg) and YM (10.8 ± 5.7 mmHg). OW (−20.2 ± 7.2%) had greater ( P < 0.05) decreases in Q̇L compared with YW (−9.4 ± 10.2%), but no significant differences were present between OM (−22.8 ± 9.7%) and YM (−22.7 ± 11.3%) during the 65% IRBT. The 65% IRBT led to greater ( P < 0.05) increases in LVR in OW (48.2 ± 25.5%) compared with YW (19.7 ± 15.0%), but no differences ( P > 0.05) existed among OM (54.4 ± 17.8%) and YM (47.1 ± 23.3%). No significant differences were present in MAP, Q̇L, or LVR between OM and OW. These data suggest that OW exhibit a greater inspiratory muscle metaboreflex compared with YW, whereas no differences between OM and YM existed. Finally, sex differences in the inspiratory muscle metaboreflex are not present in older adults.

NEW & NOTEWORTHY Premenopausal women exhibit an attenuated inspiratory muscle metaboreflex compared with young men; however, it is unknown whether these sex differences are present in older adults. Older women exhibited a greater inspiratory muscle metaboreflex compared with premenopausal women, whereas no differences were present between older and younger men.

Respiratory muscle blood flow during exercise: Effects of sex and ovarian cycle

Sex and ovarian cycle have been speculated to modify respiratory muscle blood flow control during exercise, but the findings are inconclusive. We tested the hypotheses that females would have higher respiratory muscle blood flow and vascular conductance (VC) compared with males during exercise and that this difference would be accentuated in proestrus vs. ovariectomized (OVA) females. Mean arterial pressure (carotid artery catheter) and respiratory muscle blood flow (radiolabeled microspheres) were measured during moderate-intensity (24 m/min, 10% grade) exercise in male (n = 9), female (n = 9), and OVA female (n = 7) rats and near-maximal (60 m/min, 5% grade) exercise in male (n = 5) and female (n = 7) rats. At rest, diaphragm, intercostal, and transversus abdominis blood flow were not different (P = 0.33) among groups. During moderate-intensity exercise, diaphragm (M: 124 ± 16; F: 140 ± 14; OVA: 140 ± 20 ml·min^-1·100 g^-1), intercostal (M: 33 ± 5; F: 34 ± 5; OVA: 30 ± 5 ml·min^-1·100 g^-1), and transversus abdominis blood flow (M: 24 ± 4; F: 35 ± 7; OVA: 35 ± 9 ml·min^-1·100 g^-1) significantly increased in all groups compared with rest but were not different (P = 0.12) among groups. From rest to moderate-intensity exercise, diaphragm (P < 0.03) and transversus abdominis (P < 0.04) VC increased in all groups, whereas intercostal VC increased only for males and females (P = 0.01). No differences (P > 0.13) existed in VC among groups. During near-maximal exercise, diaphragm (M: 304 ± 62; F: 283 ± 17 ml·min^-1·100 g^-1), intercostal (M: 29 ± 8; F: 40 ± 6 ml·min^-1·100 g^-1), and transversus abdominis (M: 85 ± 14; F: 86 ± 9 ml·min^-1·100 g^-1) blood flow and VC were not different (P > 0.27) between males and females. These data demonstrate that respiratory muscle blood flow and vascular conductance at rest and during exercise are not affected by sex or ovarian cycle in rats.NEW & NOTEWORTHY It has been proposed that sex and ovarian cycle modulate respiratory muscle blood flow control during exercise. We demonstrate herein that neither sex nor ovarian cycle influences respiratory muscle blood flow or vascular conductance at rest or during exercise in rats.

Regulation of skeletal muscle blood flow during exercise in ageing humans

The regulation of skeletal muscle blood flow and oxygen delivery to contracting skeletal muscle is complex and involves the mechanical effects of muscle contraction; local metabolic, red blood cell and endothelium-derived substances; and the sympathetic nervous system (SNS). With advancing age in humans, skeletal muscle blood flow is typically reduced during dynamic exercise and this is due to a lower vascular conductance, which could ultimately contribute to age-associated reductions in aerobic exercise capacity, a primary predictor of mortality in both healthy and diseased ageing populations. Recent findings have highlighted the contribution of endothelium-derived substances to blood flow control in contracting muscle of older adults. With advancing age, impaired nitric oxide availability due to scavenging by reactive oxygen species, in conjunction with elevated vasoconstrictor signalling via endothelin-1, reduces the local vasodilatory response to muscle contraction. Additionally, ageing impairs the ability of contracting skeletal muscle to blunt sympathetic vasoconstriction (i.e. 'functional sympatholysis'), which is critical for the proper regulation of tissue blood flow distribution and oxygen delivery, and could further reduce skeletal muscle perfusion during high intensity and/or large muscle mass exercise in older adults. We propose that initiation of endothelium-dependent hyperpolarization is the underlying signalling event necessary to properly modulate sympathetic vasoconstriction in contracting muscle, and that age-associated impairments in red blood cell adenosine triphosphate release and stimulation of endothelium-dependent vasodilatation may explain impairments in both local vasodilatation and functional sympatholysis with advancing age in humans.

Regulation of increased blood flow (hyperemia) to muscles during exercise: a hierarchy of competing physiological needs

This review focuses on how blood flow to contracting skeletal muscles is regulated during exercise in humans. The idea is that blood flow to the contracting muscles links oxygen in the atmosphere with the contracting muscles where it is consumed. In this context, we take a top down approach and review the basics of oxygen consumption at rest and during exercise in humans, how these values change with training, and the systemic hemodynamic adaptations that support them. We highlight the very high muscle blood flow responses to exercise discovered in the 1980s. We also discuss the vasodilating factors in the contracting muscles responsible for these very high flows. Finally, the competition between demand for blood flow by contracting muscles and maximum systemic cardiac output is discussed as a potential challenge to blood pressure regulation during heavy large muscle mass or whole body exercise in humans. At this time, no one dominant dilator mechanism accounts for exercise hyperemia. Additionally, complex interactions between the sympathetic nervous system and the microcirculation facilitate high levels of systemic oxygen extraction and permit just enough sympathetic control of blood flow to contracting muscles to regulate blood pressure during large muscle mass exercise in humans.

'Fine-tuning' blood flow to the exercising muscle with advancing age: an update

NEW FINDINGS

What is the topic of this review? This review focuses on age-related changes in the regulatory pathways that exist at the unique interface between the vascular smooth muscle and the endothelium of the skeletal muscle vasculature, and how these changes contribute to impairments in exercising skeletal muscle blood flow in the elderly. What advances does it highlight? Several recent in vivo human studies from our group and others are highlighted that have examined age-related changes in nitric oxide, endothelin-1, alpha adrenergic, and renin-angiotensin-aldosterone (RAAS) signaling. During dynamic exercise, oxygen demand from the exercising muscle is dramatically elevated, requiring a marked increase in skeletal muscle blood flow that is accomplished through a combination of systemic sympathoexcitation and local metabolic vasodilatation. With advancing age, the balance between these factors appears to be disrupted in favour of vasoconstriction, leading to an impairment in exercising skeletal muscle blood flow in the elderly. This 'hot topic' review aims to provide an update to our current knowledge of age-related changes in the neural and local mechanisms that contribute to this 'fine-tuning' of blood flow during exercise. The focus is on results from recent human studies that have adopted a reductionist approach to explore how age-related changes in both vasodilators (nitric oxide) and vasoconstrictors (endothelin-1, α-adrenergic agonists and angiotensin II) interact and how these changes impact blood flow to the exercising skeletal muscle with advancing age.

Impact of ischemic preconditioning on functional sympatholysis during handgrip exercise in humans

Repeated bouts of ischemia followed by reperfusion, known as ischemic preconditioning (IPC), is found to improve exercise performance. As redistribution of blood from the inactive areas to active skeletal muscles during exercise (i.e., functional sympatholysis) is important for exercise performance, we examined the hypothesis that IPC improves functional sympatholysis in healthy, young humans. In a randomized study, 15 healthy young men performed a 10-min resting period, dynamic handgrip exercise at 10% maximal voluntary contraction (MVC), and 25% MVC. This protocol was preceded by IPC (IPC; 4 × 5-min 220-mmHg unilateral occlusion) or a sham intervention (CON; 4 × 5-min 20-mmHg unilateral occlusion). Near-infrared spectroscopy was used to assess changes in oxygenated hemoglobin and myoglobin in skeletal muscle (HbO₂ + MbO₂) in response to sympathetic activation (via cold pressor test (CPT)) at baseline and during handgrip exercise (at 10% and 25%). In resting conditions, HbO₂ + MbO₂ significantly decreased during CPT (−11.0 ± 1.0%), which was significantly larger during the IPC-trial (−13.8 ± 1.2%, P = 0.006). During handgrip exercise at 10% MVC, changes in HbO₂ + MbO₂ in response to the CPT were blunted after IPC (−8.8 ± 1.5%) and CON (−8.3 ± 0.4%, P = 0.593). During handgrip exercise at 25% MVC, HbO₂ + MbO₂ in response to the CPT increased (2.0 ± 0.4%), whereas this response was significantly larger when preceded by IPC (4.2 ± 0.6%, P = 0.027). Collectively, these results indicate that IPC-induced different vascular changes at rest and during moderate exercise in response to sympathetic activation. This suggests that, in healthy volunteers, exposure to IPC may alter tissue oxygenation during sympathetic stimulation at rest and during exercise.

Functional sympatholysis in hypertension

Sympathetic vasoconstriction is normally attenuated in exercising muscle by local changes in muscle metabolites and other substances that reduce vascular responsiveness to α-adrenergic receptor activation. Termed functional sympatholysis, this protective mechanism is thought to optimize muscle blood flow distribution to match perfusion with metabolic demand. Emerging evidence from both animal and human studies indicate that functional sympatholysis is impaired in hypertension and may constitute an important underlying cause of skeletal muscle malperfusion during exercise in this common cardiovascular condition. Findings from studies of animal models of hypertension and patients with essential hypertension will be integrated in this review to provide insight into the underlying mechanisms responsible for inappropriate sympathetic vasoconstriction in exercising muscle and the treatment options that may restore functional sympatholysis and improve muscle perfusion during exercise.