The Effect of Acute Sleep Extension on Blood Pressure Is Dependent on the Change in Sleep Efficiency

The present study investigated the effect of acute sleep extension on blood pressure and microvascular vasodilation. Sleep and daily physical activity were objectively measured at home for two weeks using wrist actigraphy in 22 adults (60 ± 15 y). Vascular measurements were made in the morning on the 8th and 15th day. Participants spent at least 10 h in bed on the night prior to one of these testing days to extend sleep. Mean arterial blood pressure (MAP) and peak reactive hyperemia in the forearm were measured on each testing day. Reactive hyperemia and MAP were unaltered (p > 0.05) by sleep extension in the total sample. However, adults who experienced improved sleep efficiency with sleep extension (n = 10, 4.2 ± 1.4%) exhibited reduced MAP (-5.5 ± 4.6 mm Hg, p = 0.005) while adults who had little change or decreased sleep efficiency (n = 12, -1.7 ± 2.9%) showed no change in MAP. The reduction in MAP was significantly different between sleep efficiency groups (p = 0.005, Hedges' g = 1.21) after adjustment for sex and moderate-to-vigorous physical activity. The results of this study suggest that sleep extension has the potential to reduce blood pressure in midlife to older adults when the additional sleep time improves the quality of sleep.

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.

Controlled ovarian stimulation leads to cardiovascular changes in patients undergoing in vitro fertilization

OBJECTIVE

To study hemodynamic changes along controlled ovarian stimulation in women undergoing in vitro fertilization.

STUDY DESIGN

Prospective observational cohort study conducted at Mother and Child Department of University Hospital Federico II, in Naples, Italy, between April 2021 and July 2022. Sixty-eight infertile patients undergoing controlled ovarian stimulation with gonadotropin, antagonist protocol and a fresh embryo transfer were included. Haemodynamic assessment was carried out using UltraSonic Cardiac Output Monitor at baseline (T1), estradiol peak (T2), fresh embryo-transfer day (T3). To evaluate relationships between quantitative variables and groups a Student T test for independent data was assessed. One-way analysis of variance (ANOVA) was used to determine the differences between the means of three time points (T1, T2 and T3) for quantitative variables. A mixed-model analysis of variance (ANOVA) was used to determine the differences between groups, among time points (T1, T2 and T3).

RESULTS

Sixty-eight patients were included. Significant differences over the three time points have been observed for CO (f = 3.78 l/min; p = 0.025), SVI (f = 3.56 ml/m2;p = 0.013), and RSVI (f = 4.84 dscm-5 m2; p = 0.009). No significant differences in trends have been found between beta hCG positive and beta hCG negative groups. There were no significant differences in maternal hemodynamic parameters at time-point T3 between patients treated with hCG 10,000 UI and with Triptorelin. Patients considered at increased risk of hyperstimulation reported a significant increase in SVI at baseline (26.9 ± 9.0 mL/m2 vs 21.9 ± 7.0 mL/m2; p = 0.010).

CONCLUSION

According to the results of our study, during controlled ovarian stimulation with antagonist protocol, patients undergo significant changes in maternal cardiovascular parameters over a very short period.

Cardiovascular responses to combined mechanoreflex and metaboreflex activation in healthy adults: effects of sex and low- versus high-hormone phases in females

Females generally have smaller blood pressure (BP) responses to isolated muscle mechanoreflex and metaboreflex activation compared with males, which may explain sex differences in BP responses to voluntary exercise. The mechanoreflex may be sensitized during exercise, but whether mechanoreflex-metaboreflex interactions differ by sex or variations in sex hormones remains unknown. Thirty-one young healthy subjects (females, n = 16) performed unilateral passive cycling (mechanoreflex), active cycling (40% peak Watts), postexercise circulatory occlusion (PECO; metaboreflex), and passive cycling combined with PECO (combined mechanoreflex and metaboreflex activation). Beat-to-beat BP, heart rate, inactive leg vascular conductance, and active leg muscle oxygenation were measured. Ten females underwent exploratory testing during low- and high-hormone phases of their self-reported menstrual cycle or oral contraceptive use. Systolic BP and heart rate responses did not differ between sexes during active cycling [Δ30 ± 9 vs. 29 ± 11 mmHg (males vs. females), P = 0.9; Δ33 ± 8 vs. 35 ± 6 beats/min, P = 0.4] or passive cycling with PECO (Δ26 ± 11 vs. 21 ± 10 mmHg, P = 0.3; Δ14 ± 7 vs. 18 ± 15 beats/min, P = 0.3). Passive cycling with PECO revealed additive, not synergistic, effects for systolic BP [males: Δ23 ± 14 vs. 26 ± 11 mmHg (sum of isolated passive cycling and PECO vs. combined activation); females: Δ26 ± 11 vs. 21 ± 12 mmHg, interaction P = 0.05]. Results were consistent in subset analyses with sex differences in active cycling BP (P > 0.1) and exploratory analyses of hormone phase (P > 0.4). Despite a lack of statistical equivalence, no differences in cardiovascular responses were found during combined mechanoreflex-metaboreflex activation between sexes or hormone levels. These results provide preliminary data regarding the involvement of muscle mechanoreflex-metaboreflex interactions in mediating sex differences in voluntary exercise BP responses.NEW & NOTEWORTHY The muscle mechanoreflex may be sensitized by metabolites during exercise. We show that cardiovascular responses to combined mechanoreflex (passive cycling) and metaboreflex (postexercise circulatory occlusion) activation are primarily additive and do not differ between males and females, or across variations in sex hormones in females. Our findings provide new insight into the contributions of muscle mechanoreflex-metaboreflex interactions as a cause for prior reports that females have smaller blood pressure responses to voluntary exercise.

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.

Cardiovascular Function in Different Phases of the Menstrual Cycle in Healthy Women of Reproductive Age

Background: Sex hormones influence the cardiovascular (CV) function in women. However, it is uncertain whether their physiological variation related to the regular menstrual cycle affects the CV system. We studied changes in the hemodynamic profile and body’s water content and their relation to sex hormone concentration in healthy women during the menstrual cycle. Material and methods: Forty-five adult women were examined during the early follicular, late follicular, and mid-luteal phases of the same menstrual cycle. The hemodynamic profile was estimated non-invasively by cardiac impedance while water content was estimated by total body impedance. Results were compared with repeated measures ANOVA with post-test, if applicable. Results: There were no significant changes in most hemodynamic and water content parameters between the menstrual cycle phases in healthy women. Left ventricular ejection time differed significantly among phases of the menstrual cycle, with shorter values in the mid-luteal phase (308.4 vs. 313.52 ms, p < 0.05) compared to the late follicular phase. However, the clinical relevance of such small differences is negligible. Conclusions: Changes in sex hormones during the physiological menstrual cycle appear to have no considerable effect on healthy women’s hemodynamic function and water accumulation.

The exercise pressor reflex: An update

The exercise pressor reflex is a feedback mechanism engaged upon stimulation of mechano- and metabosensitive skeletal muscle afferents. Activation of these afferents elicits a reflex increase in heart rate, blood pressure, and ventilation in an intensity-dependent manner. Consequently, the exercise pressor reflex has been postulated to be one of the principal mediators of the cardiorespiratory responses to exercise. In this updated review, we will discuss classical and recent advancements in our understating of the exercise pressor reflex function in both human and animal models. Particular attention will be paid to the afferent mechanisms and pathways involved during its activation, its effects on different target organs, its potential role in the abnormal cardiovascular response to exercise in diseased states, and the impact of age and biological sex on these responses. Finally, we will highlight some unanswered questions in the literature that may inspire future investigations in the field.

The effect of extracellular hyperosmolality on sweat rate during metaboreflex activation in passively heated young men

Metaboreflex activation augments sweating during mild-to-moderate hyperthermia in euhydrated (isosmotic isovolemic) individuals. Recent work indicates that extracellular hyperosmolality may augment metaboreflex-mediated elevations in sympathetic nervous activity. Our primary objective was therefore to test the hypothesis that extracellular hyperosmolality would exacerbate metaboreflex-mediated increases in sweat rate. On two separate occasions, 12 young men (mean (SD): 25 (5) years) received a 90-min intravenous infusion of either 0.9% saline (isosmotic condition, ISO) or 3.0% saline (hyperosmotic condition, HYP), resulting in a post-infusion serum osmolality of 290 (3) and 301 (7) mOsm/kg, respectively. A whole-body water perfusion suit was then used to increase esophageal temperature by 0.8°C above resting. Participants then performed a metaboreflex activation protocol consisting of 90 s isometric handgrip exercise (40% of their pre-determined maximum voluntary contraction), followed by 150 s of brachial occlusion (trapping produced metabolites within the limb). Metaboreflex-induced sweating was quantified as the change in global sweat rate (from pre-isometric handgrip exercise to brachial occlusion), estimated as the surface area-weighted average of local sweat rate on the abdomen, axilla, chest, bicep, quadriceps, and calf, measured using ventilated capsules (3.8 cm²). We also explored whether this response differed between body regions. The change in global sweat rate due to metaboreflex activation was significantly greater in HYP compared to ISO (0.03 mg/min/cm² [95% confidence interval: 0.00, 0.06]; p=0.047), but was not modulated by body region (site*condition interaction: p=0.679). These findings indicate that extracellular hyperosmolality augments metaboreflex-induced increases in global sweat rate, with no evidence for region-specific differences.

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.

Combined influence of inspiratory loading and locomotor subsystolic cuff inflation on cardiovascular responses during submaximal exercise

It is unknown if simultaneous stimulation of the respiratory and locomotor muscle afferents via inspiratory loading (IL) and locomotor subsystolic cuff inflation (CUFF) influences the cardiovascular responses during exercise. We hypothesized that combined IL and CUFF (IL + CUFF) will result in greater increases in blood pressure (MAP) and systemic vascular resistance (SVR) than IL and CUFF alone during exercise. Eight adults (6 males/2 females) were enrolled and performed four 10-min bouts of constant-load cycling eliciting 40% maximal oxygen uptake on a single day. For each exercise bout, the first 5 min consisted of spontaneous breathing. The second 5 min consisted of voluntary hyperventilation (i.e., breathing frequency of 40 breaths/min) with IL (30% maximum inspiratory pressure), CUFF (80 mmHg), IL + CUFF, or no intervention (CTL) in randomized order. During exercise, cardiac output and MAP were determined via open-circuit acetylene wash-in and manual sphygmomanometry, respectively, and SVR was calculated. Across CTL, IL, CUFF, and IL + CUFF, MAP was greater with each condition (CTL: 97 ± 14; IL: 106 ± 13; CUFF: 114 ± 14; IL + CUFF: 119 ± 15 mmHg, all P < 0.02). Furthermore, SVR was greater with IL + CUFF compared with IL, CUFF, and CTL (CTL: 6.6 ± 1.1; IL: 7.5 ± 1.4; CUFF: 7.5 ± 1.3; IL + CUFF: 8.2 ± 1.4 mmHg·L^-1·min^-1, all P < 0.02). Cardiac output was not different across conditions (CTL: 15.2 ± 3.8; IL: 14.8 ± 3.7; CUFF: 15.6 ± 3.5; IL + CUFF: 14.7 ± 4.3 L/min, all P > 0.05). These data demonstrate that simultaneous stimulation of respiratory and locomotor muscle afferent feedback results in additive MAP and SVR responses than IL and CUFF alone during submaximal exercise. These findings have important clinical implications for populations with exaggerated locomotor and respiratory muscle reflex feedbacks.NEW & NOTEWORTHY Reflexes arising from the respiratory and locomotor muscles influence cardiovascular regulation during exercise. However, it is unclear how the respiratory and locomotor muscle reflexes interact when simultaneously stimulated. Herein, we demonstrate that stimulation of the respiratory and locomotor muscle reflexes yielded additive cardiovascular responses during submaximal exercise.

Ovarian status modulates cardiovascular autonomic control and oxidative stress in target organs

Studies have presented conflicting findings regarding the association between both fluctuation and deprivation of ovarian hormones and cardiovascular autonomic modulation and oxidative stress and their potential impact on resting arterial pressure (AP) and cardiovascular risk. This study aimed to assess cardiovascular autonomic modulation, baroreflex sensitivity (BRS), and oxidative stress in male rats (M) and in female rats during ovulatory (FOV) and non-ovulatory phases (FNOV) of the estrous cycle and after deprivation of ovarian hormones (FO). Direct AP was recorded, and BRS was assessed by using increasing doses of phenylephrine and sodium nitroprusside. AP and heart rate variability were assessed by spectral analysis. Oxidative stress profile was evaluated in cardiac, renal, and muscle tissues. In females, the ovulatory phase and ovarian hormone deprivation induced an increase in AP (FOV and FO ~ 9 mmHg) when compared to the non-ovulatory phase. Ovariectomy promoted increased cardiac sympathovagal balance (~ 17–37%) when compared to other groups. Both FOV and FO groups presented impaired BRS, associated with higher AP variability. In general, antioxidant capacity was higher in the FNOV than in the M group. Ovarian hormone deprivation induced a decrease in catalase activity in cardiac and renal tissues and an increase in lipid peroxidation in all tissues analyzed. Positive correlations (p < 0.05) were found between vascular sympathetic modulation and lipid peroxidation in cardiac (r = 0.60), renal (r = 0.60), and muscle (r = 0.57) tissues. In conclusion, both oscillation and deprivation of ovarian hormones play an important role in cardiovascular autonomic control and oxidative stress profile in target organs, which is reflected in AP changes.

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.

GABAA receptors modulate sympathetic vasomotor outflow and the pressor response to skeletal muscle metaboreflex activation in humans

KEY POINTS

The activation of the group III/IV skeletal muscle afferents is one of the principal mediators of cardiovascular responses to exercise; however, the neuronal circuitry mechanisms that are involved during the activation of group III/IV muscle afferents in humans remain unknown. Recently, we showed that GABAergic mechanisms are involved in the cardiac vagal withdrawal during the activation of mechanically sensitive (predominantly mediated by group III fibres) skeletal muscle afferents in humans. In the present study, we found that increases in muscle sympathetic nerve activity and mean blood pressure during isometric handgrip exercise and postexercise ischaemia were significantly greater after the oral administration of diazepam, a benzodiazepine that increases GABA_A activity, but not after placebo administration in young healthy subjects. These findings indicate for the first time that GABA_A receptors modulate sympathetic vasomotor outflow and the pressor responses to activation of metabolically sensitive (predominantly mediated by group IV fibres) skeletal muscle afferents in humans.

ABSTRACT

Animal studies have indicated that GABA_A receptors are involved in the neuronal circuitry of the group III/IV skeletal muscle afferent activation-induced neurocardiovascular responses to exercise. In the present study, we aimed to determine whether GABA_A receptors modulate the neurocardiovascular responses to activation of metabolically sensitive (predominantly mediated by group IV fibres) skeletal muscle afferents in humans. In a randomized, double-blinded, placebo-controlled and cross-over design, 17 healthy subjects (eight women) performed 2 min of ischaemic isometric handgrip exercise at 30% of the maximal voluntary contraction followed by 2 min of postexercise ischaemia (PEI). Muscle sympathetic nerve activity (MSNA), blood pressure (BP) and heart rate (HR) were continuously measured and trials were conducted before and 60 min after the oral administration of either placebo or diazepam (10 mg), a benzodiazepine that enhances GABA_A activity. At rest, MSNA was reduced, whereas HR and BP did not change after diazepam administration. During ischaemic isometric handgrip, greater MSNA (pre: ∆13 ± 9 bursts min^-1 vs. post: ∆29 ± 15 bursts min^-1 , P < 0.001), HR (pre: ∆23 ± 11 beats min^-1 vs. post: ∆31 ± 17 beats min^-1 , P < 0.01) and mean BP (pre: ∆33 ± 12 mmHg vs. post: ∆37 ± 12 mmHg, P < 0.01) responses were observed after diazepam. During PEI, MSNA and mean BP remained elevated from baseline before diazepam (∆10 ± 8 bursts min^-1 and ∆25 ± 14 mmHg, respectively) and these elevations were increased after diazepam (∆17 ± 12 bursts min^-1 and ∆28 ± 13 mmHg, respectively) (P ≤ 0.05). Importantly, placebo pill had no effect on neural, cardiac and pressor responses. These findings demonstrate for the first time that GABA_A receptors modulate MSNA and the pressor responses to skeletal muscle metaboreflex activation in humans.

Capsaicin-based analgesic balm attenuates the skeletal muscle metaboreflex in healthy humans

The exercise pressor reflex (EPR) is comprised of group III and IV skeletal muscle afferents and is one of the principal mediators of the cardiovascular response to exercise. In animals, capsaicin-based analgesic balm (CAP) attenuates the pressor response to muscle contraction, indicating the transient receptor potential vanilloid 1 (TRPv1) receptor (localized on the group IV afferent neuron) as an important mediator of the EPR. However, whether these findings can be extrapolated to humans remains unknown. Here, we tested the hypothesis that CAP would attenuate blood pressure (BP) and muscle sympathetic nerve activity (MSNA) responses to isolated muscle metaboreflex activation in healthy men. MSNA (microneurography) and beat-to-beat heart hate (HR, by electrocardiography), and BP (finger photoplethysmography) were continuously measured in eight healthy males (23 ± 5 yr) at rest, during isometric handgrip exercise, and during postexercise ischemia (PEI). Trials were performed before and 30 and 60 min after the topical application of CAP (0.1%, CAPZASIN-HP) over the volar forearm of the subject's exercising arm. Isometric exercise evoked increases in mean BP (∆32 ± 4 mmHg) and MSNA (∆26 ± 5 bursts/min; ∆19 ± 5 bursts/100 heart beats). The increases in BP during handgrip were not affected by CAP, but the increase in MSNA was lower after 60 min of CAP application. During PEI, the increases in BP and MSNA were all significantly less than those before CAP (all P < 0.05). In conclusion, CAP attenuated BP and sympathetic responses evoked by PEI in humans. These data provide evidence that transient receptor potential vanilloid 1 receptors potentially contribute to the EPR in humans, via its metabolic component. NEW & NOTEWORTHY We found that topical application of capsaicin-based analgesic balm attenuates arterial blood pressure and muscle sympathetic nerve activity during isolated muscle metaboreflex activation following isometric handgrip exercise in healthy humans. These findings suggest that the transient receptor potential vanilloid 1 may contribute to the exercise pressor reflex in humans via its metabolic component.

Oral contraceptives modulate the muscle metaboreflex in healthy young women

There are known sex differences in blood pressure regulation. The differences are related to ovarian hormones that influence β-adrenergic receptors and the transduction of muscle sympathetic nerve activity. Oral contraceptives (OC) modulate the ovarian hormonal profile in women and therefore may alter the cardiovascular response. We questioned if OC would alter the absolute pressor response to static exercise and influence the day-to-day variability of the response. Healthy men (n = 11) and women (n = 19) completed a familiarization day and 2 experimental testing days. Women were divided into those taking (W-OC, n = 10) and not taking (W-NC, n = 9) OC. Each experimental testing day involved isometric handgripping exercise, at 30% of maximal force, followed by circulatory occlusion to isolate the metaboreflex. Experimental days in men were 7-14 days apart. The first experimental testing in W-OC occurred 2-7 days after the start of the active phase of their OC. Women not taking OC were tested during the early and late follicular phase of the menstrual cycle as determined by commercial ovulation monitor. The increase in mean arterial pressure (MAP) during exercise was significantly lower in W-NC (95 ± 4 mm Hg) compared with men (114 ± 4 mm Hg) and W-OC (111 ± 3 mm Hg) (P < 0.05), with the differences preserved during circulatory occlusion. The rise in MAP was significantly correlated between the 2 testing days in men (r = 0.72, P < 0.01) and W-OC (r = 0.77, P < 0.05), but not in W-NC (r = 0.17, P = 0.67), indicating greater day-to-day variation in W-NC. In conclusion, OC modulate the exercise pressor response in women and minimize day-to-day variability in the exercise metaboreflex.

Effect of muscle metaboreflex activation on central hemodynamics and cardiac function in humans

We sought to determine how the mode of muscle metaboreflex activation influences the central hemodynamic response and cardiac inotropic and lusotropic function in healthy humans. Ten healthy males performed (i) isometric handgrip (IHG) with and without post-exercise ischemia (PEI) to examine the influence of isolated muscle metaboreflex activation and (ii) rhythmic handgrip (RHG) with and without ischemia to examine the influence of enhanced muscle metaboreflex activation. Heart rate (HR) and blood pressure (BP) were continuously monitored. Stroke volume (SV, Doppler echocardiography) was measured, cardiac output (CO = HR × SV) and total peripheral resistance (TPR = mean BP/CO) calculated, and indices of left ventricular systolic and diastolic function were obtained (tissue Doppler imaging). During isolated muscle metaboreflex activation with PEI following IHG, mean BP (+23 ± 3 mm Hg) and TPR were elevated from baseline (p < 0.05), whereas HR, SV, and CO were unchanged. Enhanced muscle metaboreceptor activation during ischemic RHG augmented the increase in mean BP, CO, and HR (p < 0.05 ischemic vs. free-flow RHG), whereas SV and TPR were unchanged from baseline. Neither isolated (PEI) nor enhanced muscle metaboreflex activation altered left ventricular systolic function (systolic myocardial velocity), but left atrial systolic function (late diastolic myocardial velocity) was enhanced. These findings indicate that the mode of muscle metaboreceptor activation (during vs. post handgrip) determines whether the resultant pressor response is flow (CO) or vasoconstriction (TPR) mediated, and that although left ventricular systolic function is unchanged, enhanced left atrial systolic function likely aids the preservation of SV during muscle metaboreflex engagement.

Effects of Ovarian Cycle on Hemodynamic Responses during Dynamic Exercise in Sedentary Women

This study tested the hypothesis that effects of the menstrual cycle on resting blood pressure carry over to dynamic exercise. Eleven healthy females were studied during the early (EP; low estrogen, low progesterone) and late follicular (LP; high estrogen, low progesterone) menstrual phases. Stroke volume (SV), heart rate (HR), cardiac output (CO), systolic blood pressure (SBP), diastolic blood pressure (DBP), and total vascular conductance (TVC) were assessed at rest and in response to mild and moderate cycling exercise during EP and LP. During EP, compared to LP, baseline SBP (111±1 vs. 103±2 mmHg), DBP (71±2 vs. 65±2 mmHg) and mean arterial pressure (MAP) (84±2 vs. 78±1 mmHg) were higher and TVC (47.0±1.5 vs. 54.9±4.2 ml/min/mmHg) was lower (p<0.05). During exercise, absolute values of SBP (Mild: 142±4 vs. 127±5 mmHg; Moderate: 157±4 vs. 144±5 mmHg) and MAP (Mild: 100±3 vs. 91±3 mmHg; Moderate: 110±3 vs. 101±3 mmHg) were also higher, while TVC was lower (Mild: 90.9±5.1 vs. 105.4±5.2 ml/min/mmHg; Moderate: 105.4±5.3 vs. 123.9±8.1 ml/min/mmHg) during EP (p<0.05). However, exercise-induced increases in SBP, MAP and TVC at both work intensities were similar between the two menstrual phases, even though norepinephrine concentrations were higher during LP. Results indicate that blood pressure during dynamic exercise fluctuates during the menstrual cycle. It is higher during EP than LP and appears to be due to additive effects of simultaneous increases in baseline blood pressure and reductions in baseline TVC.

Muscle metaboreflex and autonomic regulation of heart rate in humans

We elucidated the autonomic mechanisms whereby heart rate (HR) is regulated by the muscle metaboreflex. Eight male participants (22 ± 3 years) performed three exercise protocols: (1) enhanced metaboreflex activation with partial flow restriction (bi-lateral thigh cuff inflation) during leg cycling exercise, (2) isolated muscle metaboreflex activation (post-exercise ischaemia; PEI) following leg cycling exercise, (3) isometric handgrip followed by PEI. Trials were undertaken under control (no drug), β1-adrenergic blockade (metoprolol) and parasympathetic blockade (glycopyrrolate) conditions. HR increased with partial flow restriction during leg cycling in the control condition (11 ± 2 beats min(-1); P < 0.05). The magnitude of this increase in HR was similar with parasympathetic blockade (11 ± 2 beats min(-1)), but attenuated with β-adrenergic blockade (4 ± 1 beats min(-1); P < 0.05 vs. control and parasympathetic blockade). During PEI following leg cycling exercise, HR remained similarly elevated above rest under all conditions (11 ± 2, 13 ± 3 and 9 ± 4 beats min(-1), for control, β-adrenergic and parasympathetic blockade; P > 0.05 between conditions). During PEI following handgrip, HR was similarly elevated from rest under control and parasympathetic blockade (4 ± 1 vs. 4 ± 2 beats min(-1); P > 0.05 between conditions) conditions, but attenuated with β-adrenergic blockade (0.2 ± 1 beats min(-1); P > 0.05 vs. rest). Thus muscle metaboreflex activation-mediated increases in HR are principally attributable to increased cardiac sympathetic activity, and only following exercise with a large muscle mass (PEI following leg cycling) is there a contribution from the partial withdrawal of cardiac parasympathetic tone.