Static Handgrip Research Articles

Exercise pressor responses are exaggerated relative to force production during, but not following, thirty-minutes of rhythmic handgrip exercise.

This study tested the hypothesis that blood pressure responses would increase relative to force production in response to prolonged bouts of muscular work. Fifteen individuals performed two minutes of static handgrip (SHG; 35% MVC), followed by three minutes of post-exercise-cuff-occlusion (PECO), before and after thirty minutes of rest (control), or rhythmic handgrip exercise (RHG) of the contralateral and ipsilateral forearms. Beat-by-beat recordings of mean arterial pressure (MAP), heart rate (HR), and handgrip force (kg) were averaged across one-minute periods at baseline, and minutes 5, 10, 15, 20, 25, and 30 of RHG. MAP was also normalized to handgrip force, providing a relative measure of exercise pressor responses (mmHg/kg). Hemodynamic responses to SHG and PECO were also compared before and after contralateral RHG, ipsilateral RHG, and control, respectively. Similar to the RHG trial, areas under the curve were calculated for MAP (blood pressure index; BPI) and normalized to the time tension index (BPInorm). HR and MAP significantly increased during RHG (15.3 ± 1.4% and 20.4 ± 3.2%, respectively, both p < 0.01), while force output decreased by up to 36.6 ± 8.0% (p < 0.01). This resulted in a 51.6 ± 9.4% increase in BPInorm during 30min of RHG (p < 0.01). In contrast, blood pressure responses to SHG and PECO were unchanged following RHG (all p ≥ 0.07), and only the mean HR (4.2 ± 1.5%, p = 0.01) and ΔHR (67.2 ± 18.1%, p < 0.01) response to SHG were exaggerated following ipsilateral RHG. The magnitude of exercise pressor responses relative to force production progressively increases during, but not following, prolonged bouts of muscular work.

The effects of biological sex and oral contraception on the sympathetic neurocirculatory adjustments to static handgrip exercise in humans.

Biological sex affects the neurocirculatory adjustments to fatiguing exercise. However, the effects of sex and oral contraceptive pills (OCPs) on sympathetic action potential (AP) emission patterns and the transduction of AP discharge into vasoconstriction during static handgrip (SHG) exercise remains unknown. We tested the hypothesis that males, and females using OCPs, would demonstrate larger increases in sympathetic activation and sympathetic vascular transduction compared to naturally menstruating females during SHG and post-exercise circulatory occlusion (PECO). Young males (n=14, 25[5] yr), females using OCPs (n=16, 24[6] yr), and naturally menstruating females (n=18, 26[4] yr) underwent assessments of multi-unit muscle sympathetic nerve activity (MSNA)/AP discharge patterns (microneurography), and femoral artery blood flow (ultrasound) during fatiguing SHG at 40% maximum voluntary contraction and 2-min PECO. Sympathetic vascular transduction was determined as the quotient of the change in leg vascular conductance (LVC) and MSNA/AP discharge. Males demonstrated greater increases in APs/burst (P=0.028) and total AP clusters (P=0.008) compared to naturally menstruating females only, but not those using OCPs during exercise. Sympathetic vascular transduction of MSNA burst amplitude, APs/burst, and total AP clusters was greater in males and females using OCPs compared to naturally menstruating females (range: P=0.004-0.044). In contrast, no group differences in AP discharge were observed during PECO (range: P=0.510-0.872), and AP discharge was not related to LVC during PECO (range: P=0.08-0.949). These data indicate that biological sex and OCP use impact the central generation of efferent AP discharge, as well as the transduction of these neuronal messages into peripheral vasoconstriction during static exercise.

Aortic stiffness contributes to greater pressor responses during static hand grip exercise in healthy young and middle-aged normotensive men.

Central arterial stiffness can influence exercise blood pressure (BP) by increasing the rise in arterial pressure per unit increase in aortic inflow. Whether central arterial stiffness influences the pressor response to isometric handgrip exercise (HG) and post-exercise muscle ischemia (PEMI), two common laboratory tests to study sympathetic control of BP, is unknown. We studied 46 healthy non-hypertensive males (23 young and 23 middle-aged) during HG (which increases in cardiac output [Q̇c]) and isolated metaboreflex activation PEMI (no change or decreases in Q̇c). Aortic stiffness (aortic pulse wave velocity [aPWV]; applanation tonometry via SphygmoCor) was measured during supine rest and was correlated to the pressor responses to HG and PEMI. BP (photoplethysmography) and muscle sympathetic nerve activity (MSNA) were continuously recorded at rest, during HG to fatigue (35% maximal voluntary contraction) and 2-min of PEMI. aPWV was higher in middle-aged compared to young males (7.1±0.9 vs 5.4±0.7m/s, P<0.001). Middle-aged males also exhibited greater increases in systolic pressure (∆30±11 vs 10±8mmHg) and MSNA (∆2313±2006 vs 1387±1482%/min) compared to young males during HG (both, P<0.03); with no difference in the Q̇c response (P=0.090). Responses to PEMI were not different between groups. Sympathetic transduction during these stressors (MSNA-diastolic pressure slope) was not different between groups (P>0.341). Middle-aged males displayed a greater increase in SBP per unit change of Q̇c during HG (∆SBP/∆Q̇c; 21±18 vs 6±10mmHg/L/min, P=0.004), with a strong and moderate relationship between the change in systolic (r=0.53, P<0.001) and diastolic pressure (r=0.34, P=0.023) and resting aPWV, respectively; with no correlation during PEMI. Central arterial stiffness can modulate pressor responses during stimuli associated with increases in cardiac output and sympathoexcitation in healthy males.

High-glycemic index meal acutely potentiates blood pressure response to static handgrip exercise in healthy humans.

Blood glucose levels acutely increase postprandially depending on the type of meal consumed. However, it remains unclear whether postprandial hyperglycemia temporally affects cardiovascular responses to static handgrip exercise (SHG-ex). Thus, this study aimed to examine whether increased blood glucose induced by consumption of a high-glycemic index (HGI) meal affects pressor response to SHG-ex. A total of 14 healthy participants (7 women and 7 men) consumed an HGI meal, a low-glycemic index (LGI) meal, or no meal (control). Participants performed 30% maximal voluntary contraction SHG-ex followed by a postexercise muscle ischemia (PEMI) test before the meal and 60 min after consuming the meal. Blood glucose, plasma insulin, and plasma triglyceride levels were measured, and the area under the curve until 60 min (AUC0-60 min) after meal consumption was calculated. The HGI and LGI groups showed higher blood glucose and insulin AUC0-60 min than the control group (P < 0.001). At 60 min after the meal, the changes in blood pressure during SHG-ex were significantly greater in the HGI group, but not in the LGI group, than in the control group. The changes in blood pressure at the onset and end of SHG-ex 60 min after the meal were positively correlated with blood glucose AUC0-60 min (r = 0.321, P = 0.038; r = 0.402, P = 0.008, respectively) and plasma insulin AUC0-60 min (r = 0.339, P = 0.028; r = 0.302, P = 0.052, respectively). However, no association was observed during PEMI. These data suggest that postprandial hyperglycemia and hyperinsulinemia acutely exaggerate pressor response during SHG-ex in healthy young adults.NEW & NOTEWORTHY Postprandial hyperglycemia following consumption of a high-glycemic index (HGI) meal potentiated blood pressure response to static handgrip exercise (SHG-ex) in healthy young adults. These findings provide important insight into the role of the diet on acute circulatory response to exercise in healthy adults.

Assessment of renal sympathetic control using invasive pressure and flow velocity measurements in humans.

Renal sympathetic innervation is important in the control of renal and systemic hemodynamics and is a target for pharmacological and catheter-based therapies. The effect of a physiological sympathetic stimulus using static handgrip exercise on renal hemodynamics and intraglomerular pressure in humans is unknown. We recorded renal arterial pressure and flow velocity in patients with a clinical indication for coronary or peripheral angiography using a sensor-equipped guidewire during baseline, handgrip, rest, and hyperemia following intrarenal dopamine (30 μg/kg). Changes in perfusion pressure were expressed as the change in mean arterial pressure, and changes in flow were expressed as a percentage with respect to baseline. Intraglomerular pressure was estimated using a Windkessel model. A total of 18 patients (61% male and 39% female) with a median age of 57 yr (range: 27-85 yr) with successful measurements were included. During static handgrip, renal arterial pressure increased by 15.2 mmHg (range: 4.2-53.0 mmHg), whereas flow decreased by 11.2%, but with a large variation between individuals (range: -13.4 to 49.8). Intraglomerular pressure increased by 4.2 mmHg (range: -3.9 to 22.1 mmHg). Flow velocity under resting conditions remained stable, with a median of 100.6% (range: 82.3%-114.6%) compared with baseline. During hyperemia, maximal flow was 180% (range: 111%-281%), whereas intraglomerular pressure decreased by 9.6 mmHg (interquartile range: 4.8 to 13.9 mmHg). Changes in renal pressure and flow during handgrip exercise were significantly correlated (ρ = -0.68, P = 0.002). Measurement of renal arterial pressure and flow velocity during handgrip exercise allows the identification of patients with higher and lower sympathetic control of renal perfusion. This suggests that hemodynamic measurements may be useful to assess the response to therapeutic interventions aimed at altering renal sympathetic control.NEW & NOTEWORTHY Renal sympathetic innervation is important in the homeostasis of systemic and renal hemodynamics. We showed that renal arterial pressure significantly increased and that flow decreased during static handgrip exercise using direct renal arterial pressure and flow measurements in humans, but with a large difference between individuals. These findings may be useful for future studies aimed to assess the effect of interventions that influence renal sympathetic control.

Renal vascular conductance is unrelated to leg vascular conductance or muscle sympathetic nerve activity at rest and during stress in humans.

The sympathetic nervous system is important for cardiovascular regulation, particularly during acute stress. Efferent sympathetic outflow can be regulated in an organ-dependent manner, but whether renal and leg vasoconstriction are associated at rest or during sympathetic stressors is unknown. Therefore, we sought to determine the relationships between muscle sympathetic nerve activity (MSNA), leg vascular conductance (LVC), and renal vascular conductance (RVC) at rest and during common laboratory-based sympathoexcitatory stimuli in a cohort of young healthy adults. Beat-to-beat arterial pressure (photoplethysmography), MSNA (microneurography), superficial femoral artery blood flow, and renal artery blood velocity (Doppler ultrasound) were measured at rest and during static handgrip exercise (30% maximal voluntary contraction), postexercise circulatory occlusion (PECO), and cold stress (hand in 3.8 ± 1.3°C water) in 37 young healthy adults (16 females, 21 males). At rest, RVC was unrelated to LVC (r = -0.11, P = 0.55) or MSNA burst frequency (ρ = -0.22, P = 0.26). Static handgrip, PECO, and cold stress each induced an increase in mean arterial pressure and MSNA and a reduction in RVC (all P < 0.001). LVC was unaltered during stress (all P ≥ 0.16), with the exception of a reduction during the second minute of cold stress (P = 0.03). During stress, changes in RVC were not associated with changes in LVC (handgrip: r = -0.24, P = 0.21; PECO: ρ = -0.04, P = 0.82; cold stress: r = -0.17, P = 0.38) or MSNA (handgrip: ρ = -0.14, P = 0.48; PECO: r = 0.27, P = 0.15; cold stress: r = -0.27, P = 0.16). Furthermore, MSNA was not associated with LVC at rest or during stress (all P ≥ 0.12). The present findings highlight the differential control of regional sympathetic vasoconstriction at rest and during stress in young healthy humans.NEW & NOTEWORTHY The sympathetic nervous system plays a critical role in cardiovascular regulation at rest and during stress. We demonstrate that renal artery vascular conductance is unrelated to superficial femoral artery vascular conductance or muscle sympathetic nerve activity at rest or during laboratory-based sympathetic stressors in young healthy adults. These findings support the concept of differential control of peripheral sympathetic outflow at rest and during stress in humans.

Cardiovascular responses to static handgrip exercise and postexercise ischemia in heart failure with preserved ejection fraction.

Heart failure with preserved ejection fraction (HFpEF) is characterized by reduced ability to sustain physical activity that may be due partly to disease-related changes in autonomic function that contribute to dysregulated cardiovascular control during muscular contraction. Thus, we used a combination of static handgrip exercise (HG) and postexercise ischemia (PEI) to examine the pressor response to exercise and isolate the skeletal muscle metaboreflex, respectively. Mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), and total peripheral resistance (TPR) were assessed during 2-min of static HG at 30 and 40% of maximum voluntary contraction (MVC) and subsequent PEI in 16 patients with HFpEF and 17 healthy, similarly aged controls. Changes in MAP were lower in patients with HFpEF compared with controls during both 30%MVC (Δ11 ± 7 vs. Δ15 ± 8 mmHg) and 40%MVC (Δ19 ± 14 vs. Δ30 ± 8 mmHg), and a similar pattern of response was evident during PEI (30%MVC: Δ8 ± 5 vs. Δ12 ± 8 mmHg; 40%MVC: Δ13 ± 10 vs. Δ18 ± 9 mmHg) (group effect: P = 0.078 and P = 0.017 at 30% and 40% MVC, respectively). Changes in HR, CO, and TPR did not differ between groups during HG or PEI (P > 0.05). Taken together, these data suggest a reduced pressor response to static muscle contractions in patients with HFpEF compared with similarly aged controls that may be mediated partly by a blunted muscle metaboreflex. These findings support a disease-related dysregulation in neural cardiovascular control that may reduce an ability to sustain physical activity in HFpEF.NEW & NOTEWORTHY The current investigation has identified a diminution in the exercise-induced rise in arterial blood pressure (BP) that persisted during postexercise ischemia (PEI) in an intensity-dependent manner in patients with heart failure with preserved ejection fraction (HFpEF) compared with older, healthy controls. These findings suggest that the pressor response to exercise is reduced in patients with HFpEF, and this deficit may be mediated, in part, by a blunted muscle metaboreflex, highlighting the consequences of impaired neural cardiovascular control during exercise in this patient group.

Normal sympathetic neural but blunted cardiovascular responses during static handgrip exercise in heart failure with preserved ejection fraction

Background: Exercise intolerance is a hallmark of heart failure, which significantly impacts activities of daily living and quality of life. In heart failure with reduced ejection fraction, exercise intolerance is associated with sympathetic nervous system hyperactivity during exercise. Whether this is also true in heart failure with preserved ejection fraction (HFpEF) is unknown. Therefore, we hypothesized that patients with HFpEF would have augmented sympathetic neural responses to exercise. Methods: Thirty-four patients with HFpEF (19 women, 70±7 [SD] yrs) and 24 age-matched healthy controls (14 women, 70±6 yrs) were studied. Mean arterial pressure (MAP; finger photoplethysmography calibrated with brachial blood pressure [BP]), heart rate (HR; lead II electrocardiogram), cardiac output (CO; derived from the Windkessel model), total peripheral resistance (TPR=MAP/CO), and muscle sympathetic nerve activity (MSNA, microneurography) were measured during 3 min of supine baseline, static handgrip (SHG) exercise at 40% of maximal voluntary contraction (MVC) force until fatigue, and 2 min of post-exercise circulatory arrest (PECA). Sympathetic transduction was estimated using diastolic BP divided by MSNA burst incidence. Results: Patients with HFpEF had a smaller MVC (24±8 vs. 30±9 kg, P=0.020) and a shorter time to fatigue during SHG (162±67 vs. 210±80 sec, P=0.012) than controls. However, there were consistent results across subgroups analyzed according to matched MVC or time to fatigue during SHG. Baseline MSNA burst frequency was higher in HFpEF patients compared with controls (36±16 vs. 24±13 bursts/min, P=0.005); however, there were no differences in MSNA responses (Δ) to SHG and PECA between the groups (SHG peak: 19±14 in HFpEF vs. 19±12 bursts/min in controls, P=0.984; PECA: 8±13 vs. 6±7 bursts/minute, P=0.596). Increases in MAP, HR, and TPR from baseline to peak SHG were smaller in patients with HFpEF than in controls (all P&lt;0.05), while the increase in CO was not different between the groups ( P=0.101). In contrast, ΔMAP, ΔHR and ΔCO from baseline to PECA were not different between the groups (all P&gt;0.05), but ΔTPR remained lower in patients with HFpEF than controls ( P=0.023). The transduction of MSNA burst incidence into diastolic BP was lower in patients with HFpEF compared with controls throughout data collection ( P=0.010). Conclusions: Contrary to our hypothesis, patients with HFpEF have normal sympathetic neural reactivity during SHG exercise despite a higher baseline. The blunted pressor response may be attributed to impaired sympathetic transduction to stress rather than a change in sympathetic neural responsiveness during exercise in HFpEF. Supported by the National Institutes of Health (P01HL137630 and R01HL091078) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Ventilatory response to peripheral chemoreflex and muscle metaboreflex during static handgrip in healthy humans: evidence of hyperadditive integration.

What is the central question of this study? What is the effect of peripheral chemoreflex and muscle metaboreflex integration on ventilation regulation, and what is the effect of integration on breathing-related sensations and emotions? What is the main finding and its importance? Peripheral chemoreflex and muscle metaboreflex coactivation during isocapnic static handgrip exercise appeared to elicit a hyperadditive effect with regard to ventilation and an additive effect with regard to breathing-related sensations and emotions. These findings reveal the nature of the integration between two neural mechanisms that operate during small-muscle static exercise performed under hypoxia. Exercise augments the hypoxia-induced ventilatory response in an exercise intensity-dependent manner. A mutual influence of hypoxia-induced peripheral chemoreflex activation and exercise-induced muscle metaboreflex activation might mediate the augmentation phenomenon. However, the nature of these reflexes' integration (i.e., hyperadditive, additive or hypoadditive) remains unclear, and the coactivation effect on breathing-related sensations and emotions has not been explored. Accordingly, we investigated the effect of peripheral chemoreflex and muscle metaboreflex coactivation on ventilatory variables and breathing-related sensations and emotions during exercise. Fourteen healthy adults performed 2-min isocapnic static handgrip, first with the non-dominant hand and immediately after with the dominant hand. During the dominant hand exercise, we (a) did not manipulate either reflex (control); (b) activated the peripheral chemoreflex by hypoxia; (c) activated the muscle metaboreflex in the non-dominant arm by post-exercise circulatory occlusion (PECO); or (d) coactivated both reflexes by simultaneous hypoxia and PECO use. Ventilation response to coactivation of reflexes (mean±SD, 13±6l/min) was greater than the sum of responses to separated activations of reflexes (mean±SD, 8±8l/min, P=0.005). Breathing-related sensory and emotional responses were similar between coactivation of reflexes and the sum of separate activations of reflexes. Thus, the peripheral chemoreflex and muscle metaboreflex integration during exercise appeared to be hyperadditive with regard to ventilation and additive with regard to breathing-related sensations and emotions in healthy adults.

Comparative Study of Static and Dynamic Hand Grip Endurance with Correlation of Deep Breathing among Pregnant Women; A Cross-sectional Study

Background: Physiology of the mother, changes constantly during pregnancy including reduced HGS that is require for carrying the child after delivery. Activities of daily living require manual gripping tasks that require dynamic and static contractions. Predictor of upper extremity function is Hand Grip Strength and handgrip endurance. Screening of hand grip strength during antenatal care is still uncommon. Objectives: To compare static and dynamic hand grip endurance in pregnant females and to find its correlation with deep breathing. Material and Methods: The study recruited 40 participants of primi-gravida of 1st and 2nd trimester, between ages 20 and 35 years from SHALAMAR GYNAE OPD. The participants assigned to the groups (Group 1: with DB, Group 2: without DB) based on their trimester and gravidity. Static and dynamic endurance assessed using hand held dynamometer. Results: Mean Age ± Standard deviation for deep and non-deep breathing groups was 22.85 ± 2.30 and 24.05 ± 0.514. Age had negative little or low correlation with all variables of deep and non-deep breathing groups. Peak hand grip strength was moderately correlated with hand grip endurance with deep and non-deep breathing group (r = -0.628, r = -0.566 respectively). Static hand grip endurance was weakly correlated with peak hand grip strength in deep breathing group (r = -0.239) whereas static hand grip endurance had little, if any correlation with peak hand grip strength in deep breathing group (r = -0.165). Clinical implication: Management of hand grip strength and endurance improves general well being of pregnancy. By employing deep breathing exercises hand grip strength can be improved. Conclusion: Peak hand grip strength and endurance improved markedly in 2nd trimester with deep breathing. Deep breathing can improve peak hand grip endurance and peak hand grip strength in pregnancy with increasing trimester. Whereas static and dynamic hand grip endurance has insignificant effect in different trimester. Keywords: Pregnancy, deep breathing, trimester, endurance, peak grip endurance

Upper and lower limb muscle sympathetic responses to contralateral exercise in healthy humans: A pilot study.

Muscle sympathetic nerve activity (MSNA) is similar between limbs at rest, although a subset of MSNA bursts do demonstrate limb-specific discharge. Whether limb differences in MSNA synchronicity are present during exercise remains controversial. We concurrently measured MSNA from the radial and fibular nerves at rest and during rhythmic handgrip (RHG), static handgrip (SHG), and post-exercise circulatory occlusion (PECO). MSNA burst frequency and incidence were similar between nerve sites during all conditions. Synchronous bursts resulted in larger increases in sympathetic-blood pressure transduction compared to isolated bursts (∆+3.6±2.1 vs. +2.3±2.4mmHg, P=0.01). The proportion of bursts firing synchronously between nerves at rest was slightly increased during RHG ([rest vs. exercise; mean±SD] 45.3±7.1 vs. 61.6±7.2%) and similar during SHG (56.2±7.2 vs. 54±10.6%). In contrast, burst firing synchronicity increased during PECO (83.8±12.4%) alongside larger burst amplitudes. Inter-limb differences in resting MSNA are preserved during handgrip exercise, whereas isolated metaboreflex activation results in greater burst synchronization between limbs.

Abstract 10665: The Glycemic and Insulin Levels Contribute to the Sympathetic Response to Exercise in Individuals With and Without Diabetes Mellitus

Introduction: Exaggerated responses in blood pressure (BP) and muscle sympathetic nerve activity (MSNA) during exercise are suggested to contribute to adverse cardiovascular events. The risk of developing cardiovascular disease is elevated in patients suffering from diabetes mellitus (DM) and pre-DM; however, the relationship between the sympathetic responses to exercise and the glycemic and insulin indices in DM and non-DM remain unclear.Hypothesis: We hypothesized that the magnitude of MSNA response to exercise is related with glycemic and insulin indices in DM and Pre-DM subjects. Method: Eleven clinically diagnosed T2DM patients (54.0 ± 2.7 yrs) and 20 non-DM subjects (58.6 ± 2.3 yrs, 10 pre-DM [5.7% ≤ HbA1c &lt; 6.5%] and 10 healthy subjects) were examined. All non-DM subjects, including pre-DM subjects, had no noted diseases and were not on any medication. Five DM patients were on antihypertensive agents. The BP and glycemic control in the DM patients was relatively well managed with medications (HbA1c, 6.8 ± 0.3 %) and were without other cardiovascular complications. Beat-by-beat BP, heart rate, and MSNA were recorded simultaneously under a resting condition and during static handgrip exercise (HGe) at 30% maximal voluntary contraction until fatigue. Results: Resting MSNA in DM was lower than non-DM subjects (P &lt; 0.05). However, the MSNA response (i.e., the change) to HGe in DM was higher than non-DM (139% vs 75% increase, P &lt; 0.05). The MSNA response to HGe was significantly correlated (R = 0.59, P &lt; 0.05) with fasting blood glucose (FBG) across all subjects. Even in only pre-DM subjects, the MSNA response to HGe was significantly correlated with glucose/insulin indices (vs. FBG, R = 0.91, P &lt; 0.05; vs. blood insulin concentration, R = 0.84, P &lt; 0.05). Conclusion: In the present study, the MSNA response to exercise in T2DM patients was greater than that in non-DM subjects. Importantly, the MSNA response to exercise was correlated with glycemic/insulin indices over a broad range. This relationship was observed even before the development of DM. We speculate that the altered glycemic/insulin levels may contribute to the exaggerated sympathetic response to stress and in turn, contribute to the higher risk of cardiovascular diseases in these individuals.

ASSESSMENT OF RENAL SYMPATHETIC CONTROL USING INVASIVE PRESSURE AND FLOW VELOCITY MEASUREMENTS IN HUMANS

Objective: Renal sympathetic innervation is important in the control of renal and systemic hemodynamics and a target for pharmacological and catheter-based therapies. The effect of a physiological sympathetic stimulus using static handgrip exercise on renal hemodynamics and intraglomerular pressure in humans is unknown. Design and method: We recorded renal arterial pressure and flow velocity in patients with a clinical indication for coronary or peripheral angiography using a sensor-equipped guidewire during baseline, handgrip, resting, and hyperemia following intrarenal dopamine (30 ug/kg). Changes in perfusion pressure were expressed as delta mean arterial pressure, changes in flow velocity as percentage with respect to baseline. Intraglomerular pressure was estimated using a Windkessel model. Results: We included 18 patients with median age 57 years (range 27–85), 61% male in the final analysis. An overview of the hemodynamic responses is given in Figure 1. During static handgrip mean renal arterial pressure increased by 15.2 mmHg (range 4.2–53.0), while flow decreased by 11.2%, but with large variation between individuals (range -13.4–49.8%). Intraglomerular pressure increased with 4.2 mmHg (range -3.9–22.1). Flow velocity under resting conditions remained stable with median 100.6% (range 82.3–114.6) compared to baseline. During hyperemia, maximal flow was 180% (range 111–281), while intraglomerular pressure decreased to 33.0 mmHg [IQR 26.7–39.8]. Changes in renal pressure and flow during handgrip exercise were correlated (rho = -0.68; p = 0.002). Conclusions: We show that there are significant variations in the response to sympathetic stimulation following static handgrip exercise using invasive renal arterial measurements. These results demonstrate that intra-arterial renal hemodynamic measurements can be used to determine the renal effect of systemic sympathetic stimulus and allows identification of patients with higher and lower sympathetic control of renal perfusion. This may be useful in determining the response to therapeutic interventions aimed at altering renal sympathetic control.

Dietary nitrate supplementation attenuates the mechanoflex in older women with early menopause: A pilot study

Women who reached early menopause (EM, 40‐44 yrs) have a greater risk for cardiovascular disease than women with normal menopause (NM, 50‐54 yrs), which may be attributed to a longer duration of estrogen loss and a greater reduction in nitric oxide bioavailability in both the peripherals and center. Previous studies have shown that dietary nitrate supplementation improves cardiovascular function in older women, but how autonomic neural control changes in daily living, such as during exercise, has been involved is unclear. We examined the hypothesis that 2wks continuous use of dietary nitrate supplements would attenuate the exercise pressor reflex in older women with EM.Six EM (65±4 [SD] yrs) and 8 NM (64±2 yrs) women participated in this randomized, placebo‐controlled, double‐blind, cross‐over pilot study. All subjects underwent 2 wks of beetroot juice (BRJ; 140 ml containing ~800 mg nitrate per day) or placebo (140 ml nitrate‐depleted BRJ, daily) intervention with ≥14 days of wash‐out. Before and after each intervention period, subjects performed SHG using the dominant hand at 40% of maximum voluntary contraction (MVC) until fatigue, followed by 2 min of PECA with an upper arm cuff inflated to 250 mmHg. Heart rate (HR; ECG), blood pressure (BP; finger photoplethysmography), muscle sympathetic nerve activity (MSNA; microneurography), and respiration (capnography) were continuously measured. In addition, 24‐h ambulatory BP standard deviation (SD) was monitored before and after each intervention (an indication of BP variability).There were no differences in baseline HR, BP and MSNA, MVC, and the time to fatigue between the EM and NM groups before and after intervention (all p&gt;0.05). At the first 30 s of SHG, the EM group showed significant decreases in MSNA burst frequency (DBF; ‐4.5±6.5 in EM vs. 2.5±6.2 bursts/min in NM, p=0.065) and burst incidence (DBI; ‐10.6±12.6 vs. 2.6±8.4 bursts/100 heartbeats, p=0.037) after BRJ intervention compared with the NM group (Figure1A and B). However, there were no differences between groups at fatiguing exercise and during PECA after the intervention. The interventional changes in 24‐h diastolic BP SD had a positive correlation with ΔMSNA BF (r=0.55, p=0.053) and BI (r=0.58, p=0.036) at the first 30 s of SHG in all subjects and EM individuals were in the left‐lower area (Figure2 A and B).These results suggest that dietary nitrate supplementation may attenuate and mechanoreflex, but not the metaboreflex, in older women with EM during static hand grip, which has a relation with BP variability during ambulation. Certainly, these preliminary observations need to be verified in more older women in future studies.

Acute changes in forearm vascular compliance during transient sympatho-excitation.

The study of vascular regulation often omits important information about the elastic properties of arteries under conditions of pulsatile flow. The purpose of this study was to examine the relationship between muscle sympathetic nerve activity (MSNA), vascular bed compliance, and peripheral blood flow responses in humans. We hypothesized that increases in MSNA would correlate with reductions in vascular compliance, and that changes in compliance would correspond with changes in peripheral blood flow during sympatho‐excitation. MSNA (microneurography), blood pressure (Finopres), and brachial artery blood flow (Doppler ultrasound), were monitored in six healthy males at baseline and during the last 15 s of voluntary end‐inspiratory, expiratory apneas and 5 min of static handgrip exercise (SHG; 20% maximum voluntary contraction) and 3 min of post‐exercise circulatory occlusion (SHG + PECO; measured in the non‐exercising arm). A lumped Windkessel model was employed to examine vascular bed compliance. During apnea, indices of MSNA were inversely related with vascular compliance, and reductions in compliance correlated with decreased brachial blood flow rate. During SHG, despite increased MSNA, compliance also increased, but was unrelated to increases in blood flow. Neither during SHG nor PECO did indices of MSNA correlate with forearm vascular compliance nor did vascular compliance correlate with brachial flow. However, during PECO, a linear combination of blood pressure and total MSNA was correlated with vascular compliance. These data indicate the elastic components of the forearm vasculature are regulated by adrenergic and myogenic mechanisms during sympatho‐excitation, but in a reflex‐dependent manner.

Does cardiovascular autonomic dysfunction contribute to fatigue in myasthenia gravis?

Myasthenia gravis (MG) is an autoimmune disease characterized by fatigable muscle weakness. Despite full spontaneous or pharmacological remission some MG patients still complain of physical and mental fatigue. Fatigue has been related to autonomic dysregulation. The aim of this study was to assess autonomic responses in a group of MG patients in complete remission but complaining of persistent fatigue. Seventeen well-regulated but persistently fatigued MG patients and 17 individually matched controls underwent echocardiography assessing systolic and diastolic heart function. Beat to beat cardiovascular responses at rest and to 30o head-up tilt, tilt-back, and 2-min static handgrip contraction were recorded. Fatigued MG patients had a statistically significant higher resting HR than their matched controls (p=0.03). The difference in resting heart rate between MG patients not using acetylcholine esterase inhibitors (AChEi) and their matched controls was even more pronounced (p=0.007). The autonomic cardiovascular adjustments to head-up tilt, tilt-back and handgrip contraction were not statistically significant different between patients and controls. We found a higher resting heart rate in all well-regulated but fatigued MG patients compared with controls. The difference was more pronounced between patients not taking AChEi compared to their matched controls. This finding may reflect a disturbed resting sympathovagal balance and this might be a contributing factor to the fatigue symptoms.

Effects of Cardiorespiratory Fitness on Cerebral Oxygenation in Healthy Adults: A Systematic Review.

IntroductionExercise is known to improve cognitive functioning and the cardiorespiratory hypothesis suggests that this is due to the relationship between cardiorespiratory fitness (CRF) level and cerebral oxygenation. The purpose of this systematic review is to consolidate findings from functional near-infrared spectroscopy (fNIRS) studies that examined the effect of CRF level on cerebral oxygenation during exercise and cognitive tasks.MethodsMedline, Embase, SPORTDiscus, and Web of Science were systematically searched. Studies categorizing CRF level using direct or estimated measures of V̇O2max and studies measuring cerebral oxygenation using oxyhemoglobin ([HbO2]) and deoxyhemoglobin ([HHb]) were included. Healthy young, middle-aged, and older adults were included whereas patient populations and people with neurological disorders were excluded.ResultsFollowing PRISMA guidelines, 14 studies were retained following abstract and full-text screening. Cycle ergometer or treadmill tests were used as direct measures of CRF, and one study provided an estimated value using a questionnaire. Seven studies examined the effects of CRF on cerebral oxygenation during exercise and the remaining seven evaluated it during cognitive tasks. Increased [HbO2] in the prefrontal cortex (PFC) was observed during cognitive tasks in higher compared to lower fit individuals. Only one study demonstrated increased [HHb] in the higher fit group. Exercise at submaximal intensities revealed increased [HbO2] in the PFC in higher compared to lower fit groups. Greater PFC [HHb] was also observed in long- vs. short-term trained males but not in females. Primary motor cortex (M1) activation did not differ between groups during a static handgrip test but [HHb] increased beyond maximal intensity in a lower compared to higher fit group.ConclusionConsistent with the cardiorespiratory hypothesis, higher fit young, middle-aged, and older adults demonstrated increased cerebral oxygenation compared to lower fit groups. Future research should implement randomized controlled trials to evaluate the effectiveness of interventions that improve CRF and cerebral oxygenation longitudinally.

Twelve weeks of occlusal splint treatment reduces blood pressure responses to hypertensive stimuli in those with sleep bruxism

Sleep bruxism (SB) is associated with increased sympathetic tone, a risk for the future development of hypertension. It is unclear whether those with SB would demonstrate exaggerated responses to hypertensive stimuli and whether treatment with an occlusal splint could mitigate these responses. Objectives: This study compared hemodynamic responses to the cold pressor test (CPT) and static handgrip (SHG) to fatigue between controls (CON) and those with SB to determine whether those with SB have exaggerated responses. Methods: Nineteen subjects (9 CON, 10 SB) had heart rate (HR) and blood pressure (BP) responses measured during a CPT and SHG with post-exercise circulatory arrest (PECA). SB subjects underwent a 12-wk occlusal splint intervention followed by a repeat of the experimental protocol. Results: No BP differences existed with pre- (PRE) vs. post-intervention (POST) in the SB subjects. CPT induced larger ΔSBP (10±10 vs. 19±7 mmHg; p &lt; 0.05) and ΔDBP (8±8 vs. 17±9 mmHg; p &lt; 0.05) in SB subjects compared to CON. POST had attenuated ∆SBP (15±9 vs. 8±5 mmHg; p &lt; 0.03) and ∆DBP (18±10 vs. 8±6 mmHg; p &lt; 0.05) during CPT. SB subjects experienced greater ∆DBP (21±11 vs. 31±8; p &lt; 0.05) during SHG which was not different during POST. Conclusions: SB individuals may be at increased risk for the development of hypertension based on exaggerated BP responses to hypertensive stimuli. Twelve weeks of occlusal splint treatment attenuated some of these responses.

Influence of age and gender on cardiovascular response to isometric exercise in apparently healthy individuals

Objective Static exercises are an integral aspect of patient rehabilitation and are employed in advanced strength and endurance training programmes. Exercise is a form of self-induced stress leading to circulatory and respiratory changes, therefore, this study sought to determine the influence of age and gender on the cardiovascular responses of apparently healthy individuals to isometric/static exercises. Methodology Sixty apparently healthy individuals (30 males and 30 females) participated in this study. Their ages ranged between 21–50 years and were grouped into 21–30 years, 31–40 years and 41–50 years. Each participant carried out and maintained 30% of maximal isometric voluntary contraction (MIVC) using hand grip for 1, 2 and 3 minutes respectively, with 30-minutes rest period. Systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) were measured and recorded, at rest, and during each of the sustained contractions. Results There was a statistically significant increase (p &lt;0.05) in the mean SBP, DBP and HR at rest and with every increase in duration (that is, from 1 minute to 3 minutes) of static handgrip contraction, maintained at 30% MIVC in the 3 groups; except for HR for group one (that is, 21–30 years). There was no gender difference (p &gt;0.05) in SBP and DBP of the participants within the 3 groups, although male participants, particularly in group 2 had higher SBP. There was also a statistically significant increase in the HR of female participants compared to the males in group 2. Isometric contraction for 3 minutes produced the greatest change (increase) in cardiovascular parameter across all the groups but more marked among participants in group 2 (that is, 31–40 years). Conclusion The study concluded that submaximal (30% MIVC) isometric upper limb exercise increase blood pressure and heart rate in both sexes, with greatest values when the exercise was sustained for 3 minutes. Hence, efforts should be made to monitor cardiovascular parameters prior to prescribing safe level of isometric exercise. Also, 3 minutes of static/isometric exercises may be avoided, particularly during the rehabilitation of patient with cardiovascular disease.

Metaboreflex Activity is Attenuated by Transcutaneous Electrical Nerve Stimulation and Interferential Electrical Stimulation in Healthy Individuals

Background: Transcutaneous electrical nervous stimulation (TENS) and interferential electrical stimulation (IES) attenuates muscle metaboreflex by sympathetic nervous modulation. Objective: We tested the hypothesis that IES may be more effective than TENS to improves blood flow which may be linked to greater of deep tissue. Methods: Eleven health subjects were randomized to TENS (80 Hz, 150μs), IES (4000 Hz, ΔAMF=25 Hz) or sham stimulation group, during 30 minutes. The acute intervention was applied on stellate ganglion region (C7-T4). Results: Were measured metaboreflex activity by calf vascular resistance (CVR) and calf blood flow (CBF) and HRV during three times: rest, exercise (static handgrip) and postexercise circulatory occlusion (PECO+ and PECO-). At the exercise peak, compared with TENS and Sham, the IES group reduced CVR (36 ± 3 vs 43 ± 3; p&lt;0.05) and increased CBF (p&lt;0.01). Also, IES was associated with a greater reduction on the MMA (IES: 9 ± 2, TENS: 14 ± 4, Sham: 26 ± 5 units; p&lt;0.01). Furthermore, the IES group had a higher reduction of LF/HF ratio during PECO- and PECO+ (p&lt;0.05). Conclusion: The IES over the stellate ganglion region seems to have superior efficacy compared with TENS to attenuate metaboreflex activation and vasodilatory responses during exercise in healthy subjects.