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 leg V ̇ 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 leg V ̇ 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, leg V ̇ 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 limits V ̇ 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.

Interplay of Race and Neighborhood Deprivation on Resting and Ambulatory Blood Pressure in Young Adults.

BACKGROUND: Nighttime BP and BP dipping (daytime-nighttime BP) are prognostic for cardiovascular disease. Compared with other racial/ethnic groups, Black Americans exhibit elevated nighttime BP and attenuated BP dipping. Neighborhood deprivation may contribute to disparities in cardiovascular health, but its effects on resting and ambulatory BP patterns in young adults is unclear. Therefore, we examined associations between neighborhood deprivation with resting and nighttime BP and BP dipping in young Black and White adults. METHODS: We recruited 19 Black and 28 White participants (23 M/24 F, 21±1 years, body mass index: 26±4 kg/m2) for 24-hour ambulatory BP monitoring. We assessed resting BP, nighttime BP, and BP dipping (absolute dip and nighttime:daytime BP ratio). We used the area deprivation index (ADI) to assess average neighborhood deprivation during early- and mid-childhood, and adolescence. RESULTS: Compared with White participants, Black participants exhibited higher resting systolic and diastolic BP (ps≤0.029), nighttime systolic BP (114±9 vs. 108±9 mmHg, p=0.049), diastolic BP (63±8 vs. 57±7 mmHg, p=0.010), and attenuated absolute systolic BP dipping (12±5 vs. 9±7 mmHg, p=0.050). Black participants experienced greater average ADI scores compared with White participants (110(10) vs. 97(22), p=0.002), and select ADI scores correlated with resting BP and some ambulatory BP measures. Within each race, select ADI scores correlated with some BP measures for Black participants, but there were no ADI and BP correlations for White participants. CONCLUSIONS: Our findings suggest neighborhood deprivation may contribute to higher resting BP and impaired ambulatory BP patterns in young adults warranting further investigation in larger cohorts.

Exercise intolerance in heart failure with preserved ejection fraction: Causes, consequences and the journey towards a cure.

Heart failure with preserved ejection fraction (HFpEF) accounts for over 50% of all heart failure cases nationwide and continues to rise in its prevalence. The complex, multi-organ involvement of the HFpEF clinical syndrome requires clinicians and investigators to adopt an integrative approach that considers the contribution of both cardiac and non-cardiac function to HFpEF pathophysiology. Thus, this symposium review outlines the key points from presentations covering the contributions of disease-related changes in cardiac function, arterial stiffness, peripheral vascular function, and oxygen delivery and utilization to exercise tolerance in patients with HFpEF. While many aspects of HFpEF pathophysiology remain poorly understood, there is accumulating evidence for a decline in vascular health in this patient group that may be remediable through pharmacological and lifestyle interventions and could improve outcomes and clinical status in this ever-growing patient population.

Autonomic cardiovascular control during exercise.

The cardiovascular response to exercise is largely determined by neurocirculatory control mechanisms that help to raise blood pressure and modulate vascular resistance which, in concert with regional vasodilatory mechanisms, promote blood flow to active muscle and organs. These neurocirculatory control mechanisms include a feedforward mechanism, known as central command, and three feedback mechanisms, namely, 1) the baroreflex, 2) the exercise pressor reflex, and 3) the arterial chemoreflex. The hemodynamic consequences of these control mechanisms result from their influence on the autonomic nervous system and subsequent alterations in cardiac output and vascular resistance. Although stimulation of the baroreflex inhibits sympathetic outflow and facilitates parasympathetic activity, central command, the exercise pressor reflex, and the arterial chemoreflex facilitate sympathetic activation and inhibit parasympathetic drive. Despite considerable understanding of the cardiovascular consequences of each of these mechanisms in isolation, the circulatory impact of their interaction, which occurs when various control systems are simultaneously activated (e.g., during exercise at altitude), has only recently been recognized. Although aging and cardiovascular disease (e.g., heart failure, hypertension) have both been recognized to alter the hemodynamic consequences of these regulatory systems, this review is limited to provide a brief overview on the action and interaction of neurocirculatory control mechanisms in health.

Neural control of the circulation during exercise in heart failure with reduced and preserved ejection fraction.

Patients with heart failure with reduced (HFrEF) and preserved ejection fraction (HFpEF) exhibit severe exercise intolerance that may be due, in part, to inappropriate cardiovascular and hemodynamic adjustments to exercise. Several neural mechanisms and locally released vasoactive substances work in concert through complex interactions to ensure proper adjustments to meet the metabolic demands of the contracting skeletal muscle. Specifically, accumulating evidence suggests that disease-related alterations in neural mechanisms (e.g., central command, exercise pressor reflex, arterial baroreflex, and cardiopulmonary baroreflex) contribute to heightened sympathetic activation and impaired ability to attenuate sympathetic vasoconstrictor responsiveness that may contribute to reduced skeletal muscle blood flow and severe exercise intolerance in patients with HFrEF. In contrast, little is known regarding these important aspects of physiology in patients with HFpEF, though emerging data reveal heightened sympathetic activation and attenuated skeletal muscle blood flow during exercise in this patient population that may be attributable to dysregulated neural control of the circulation. The overall goal of this review is to provide a brief overview of the current understanding of disease-related alterations in the integrative neural cardiovascular responses to exercise in both HFrEF and HFpEF phenotypes, with a focus on sympathetic nervous system regulation during exercise.

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.

When it's time for the sex talk, words matter.

In recent years, the traditional, unspoken assumption in published biomedical research studies that the young, healthy (usually white) male is the "default human" has received increasing scrutiny and criticism. The historical underrepresentation of female participants in biomedical research has been increasingly recognized and addressed, including with the current call for papers at the American Journal of Physiology-Heart and Circulatory Physiology. Our goal in the present Perspectives is to discuss the topic of terminology (man/woman vs. male/female) for human research participants when considering sex as a biological variable. This important consideration is consistent with the importance of gender identity and related topics to psychological, emotional, and physical health. Just as pronouns are important, so is appropriate terminology when referring to human research volunteers. Despite some disagreement regarding terminology between our two groups of authors, we provide consensus recommendations. Importantly, we all agree that the most vital aspect of the present discussion is the broader focus on sex as a biological variable and appropriate inclusion of biological sex in in vitro, preclinical, and human research studies.

Altered central and peripheral haemodynamics during rhythmic handgrip exercise in young adults with SARS-CoV-2.

NEW FINDINGS: What is the central question of this study? Are central and peripheral haemodynamics during handgrip exercise different in young adults 3-4 weeks following infection with of SARS-CoV-2 compared with young healthy adults. What is the main finding and its importance? Exercising heart rate was higher while brachial artery blood flow and vascular conductance were lower in the SARS-CoV-2 compared with the control group. These findings provide evidence for peripheral impairments to exercise among adults with SARS-CoV-2, which may contribute to exercise limitations. ABSTRACT: The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can have a profound impact on vascular function. While exercise intolerance may accompany a variety of symptoms associated with SARS-CoV-2 infection, the impact of SARS-CoV-2 on exercising blood flow (BF) remains unclear. Central (photoplethysmography) and peripheral (Doppler ultrasound) haemodynamics were determined at rest and during rhythmic handgrip (HG) exercise at 30% and 45% of maximal voluntary contraction (MVC) in young adults with mild symptoms 25 days after testing positive for SARS-CoV-2 (SARS-CoV-2: n = 8M/5F; age: 21 ± 2 years; height: 176 ± 11 cm; mass: 71 ± 11 kg) and were cross-sectionally compared with control subjects (Control: n = 8M/5F; age: 27 ± 6 years; height: 178 ± 8 cm; mass: 80 ± 25 kg). Systolic blood pressure, end systolic arterial pressure and rate pressure product were higher in the SARS-CoV-2 group during exercise at 45% MVC compared with controls. Brachial artery BF was lower in the SARS-CoV-2 group at both 30% MVC (Control: 384.8 ± 93.3 ml min-1 ; SARS-CoV-2: 307.8 ± 105.0 ml min-1 ; P = 0.041) and 45% MVC (Control: 507.4 ± 109.9 ml min-1 ; SARS-CoV-2: 386.3 ± 132.5 ml min-1 ; P = 0.002). Brachial artery vascular conductance was lower at both 30% MVC (Control: 3.93 ± 1.07 ml min-1  mmHg-1 ; SARS-CoV-2: 3.11 ± 0.98 ml min-1  mmHg-1 ; P = 0.022) and 45% MVC (Control: 4.74 ± 1.02 ml min-1  mmHg-1 ; SARS-CoV-2: 3.46 ± 1.10 ml min-1  mmHg-1 ; P < 0.001) in the SARS-CoV-2 group compared to control group. The shear-induced dilatation of the brachial artery increased similarly across exercise intensities in the two groups, suggesting the decrease in exercising BF may be due to microvascular impairments. Brachial artery BF is attenuated during HG exercise in young adults recently diagnosed with mild SARS-CoV-2, which may contribute to diminished exercise capacity among those recovering from SARS-CoV-2 like that seen in severe cases.

The role of endothelin A receptors in peripheral vascular control at rest and during exercise in patients with hypertension.

KEY POINTS: Exercise in patients with hypertension can be accompanied by an abnormal cardiovascular response that includes attenuated blood flow and an augmented pressor response. Endothelin-1, a very potent vasoconstrictor, is a key modulator of blood flow and pressure during in health and has been implicated as a potential cause of the dysfunction in hypertension. We assessed the role of endothelin-1, acting through endothelin A (ETA ) receptors, in modulating the central and peripheral cardiovascular responses to exercise in patients with hypertension via local antagonism of these receptors during exercise. ETA receptor antagonism markedly increased leg blood flow, vascular conductance, oxygen delivery, and oxygen consumption during exercise; interestingly, these changes occurred in the presence of reduced leg perfusion pressure, indicating that these augmentations were driven by changes in vascular resistance. These data indicate that ETA receptor antagonism could be a viable therapeutic approach to improve blood flow during exercise in hypertension. ABSTRACT: Patients with hypertension can exhibit impaired muscle blood flow and exaggerated increases in blood pressure during exercise. While endothelin (ET)-1 plays a role in regulating blood flow and pressure during exercise in health, little is known about the role of ET-1 in the cardiovascular response to exercise in hypertension. Therefore, eight volunteers diagnosed with hypertension were studied during exercise with either saline or BQ-123 (ETA receptor antagonist) infusion following a 2-week withdrawal of anti-hypertensive medications. The common femoral artery and vein were catheterized for drug infusion, blood collection and blood pressure measurements, and leg blood flow was measured by Doppler ultrasound. Patients exercised at both absolute (0, 5, 10, 15 W) and relative (40, 60, 80% peak power) intensities. BQ-123 increased blood flow at rest (79 ± 87 ml/min; P = 0.03) and augmented the exercise-induced hyperaemia at most intensities (80% saline: Δ3818±1222 vs. BQ-123: Δ4812±1469 ml/min; P = 0.001). BQ-123 reduced leg MAP at rest (-8 ± 4 mmHg; P < 0.001) and lower intensities (0-10 W; P < 0.05). Systemic diastolic blood pressure was reduced (0 W, 40%; P < 0.05), but systemic MAP was defended by an increased cardiac output. The exercise pressor response (ΔMAP) did not differ between conditions (80% saline: 25 ± 10, BQ-123: 30 ± 7 mmHg; P = 0.17). Thus, ET-1, acting through the ETA receptors, contributes to the control of blood pressure at rest and lower intensity exercise in these patients. Furthermore, the finding that ET-1 constrains the blood flow response to exercise suggests that ETA receptor antagonism could be a therapeutic approach to improve blood flow during exercise in hypertension.

Chronic antioxidant administration restores macrovascular function in patients with heart failure with reduced ejection fraction.

NEW FINDINGS: What is the central question of this study? We aimed to examine oxidative stress, antioxidant capacity and macro- and microvascular function in response to 30 days of oral antioxidant administration in patients with heart failure with reduced ejection fraction. What is the main finding and its importance? We observed an approximately twofold improvement in macrovascular function, assessed via brachial artery flow-mediated dilatation, and a reduction in oxidative stress after antioxidant administration in patients with heart failure with reduced ejection fraction. The improvement in macrovascular function was reversed 1 week after treatment cessation. These findings have identified the potential of oral antioxidant administration to optimize macrovascular health in this patient group. ABSTRACT: Heart failure with reduced ejection fraction (HFrEF) is characterized by macrovascular dysfunction and elevated oxidative stress that may be mitigated by antioxidant (AOx) administration. In this prospective study, we assessed flow-mediated dilatation (FMD) and reactive hyperaemia responses in 14 healthy, older control participants and 14 patients with HFrEF, followed by 30 days of oral AOx administration (1 g vitamin C, 600 I.U. vitamin E and 0.6 g α-lipoic acid) in the patient group. Blood biomarkers of oxidative stress (malondialdehyde) and AOx capacity (ferric reducing ability of plasma) were also assessed. Patients with HFrEF had a lower %FMD (2.63 ± 1.57%) than control participants (5.62 ± 2.60%), and AOx administration improved %FMD in patients with HFrEF (30 days, 4.90 ± 2.38%), effectively restoring macrovascular function to that of control participants. In a subset of patients, we observed a progressive improvement in %FMD across the treatment period (2.62 ± 1.62, 4.23 ± 2.69, 4.33 ± 2.24 and 4.97 ± 2.56% at days 0, 10, 20 and 30, respectively, n = 12) that was abolished 7 days after treatment cessation (2.99 ± 1.78%, n = 9). No difference in reactive hyperaemia was evident between groups or as a consequence of the AOx treatment. Ferric reducing ability of plasma levels increased (from 6.08 ± 2.80 to 6.70 ± 1.59 mm, day 0 versus 30) and malondialdehyde levels decreased (from 6.81 ± 2.80 to 6.22 ± 2.84 µm, day 0 versus 30) after treatment. These findings demonstrate the efficacy of chronic AOx administration in attenuating oxidative stress, improving AOx capacity and restoring macrovascular function in patients with HFrEF.

The acute effects of interrupting prolonged sitting with stair climbing on vascular and metabolic function after a high-fat meal.

PURPOSE: Frequent consumption of high-fat meals and prolonged sedentary time are prevalent lifestyles that have been associated with an increased risk of vascular and metabolic complications. This study evaluated the acute effects of interrupting prolonged sitting with stair climbing on vascular and metabolic function after a high-fat meal. METHODS: In a randomized, cross-over trial, 12 healthy adults (age: 23.5 ± 2.9 years) consumed a high-fat meal, followed by either 1) a 4-h uninterrupted sitting (sitting trial) or 2) a 4-h sitting interrupted with a 5-min stair climbing (average intensity: 66% of heart rate reserve) every hour (interrupted trial). Plasma triglyceride and glucose concentrations, as well as popliteal artery blood flow and shear rate were assessed at baseline and every hour after a high-fat meal, whereas brachial artery flow-mediated dilation was assessed at baseline and again at the end of each trial. RESULTS: Plasma triglyceride and glucose concentrations increased after a high-fat meal and returned to baseline at the end of both trials. Following a high-fat meal, brachial artery flow-mediated dilation decreased in the sitting trial, but not in the interrupted trial (sitting trial: 9.65 ± 2.63% to 7.84 ± 2.36%; interrupted trial: 9.41 ± 2.61% to 10.34 ± 3.30%, p = 0.009 for interaction). Compared with the sitting trial, the interrupted trial improved popliteal blood flow and shear rate (p = 0.004 and p = 0.008 for interaction, respectively). CONCLUSIONS: These findings suggest that interrupting prolonged sitting with stair climbing may be an effective lifestyle strategy to prevent against vascular dysfunction that might occur as a result of prolonged sitting after consuming a high-fat meal in young healthy adults.

Impact of acute antioxidant administration on inflammation and vascular function in heart failure with preserved ejection fraction.

Although it is now well established that heart failure with preserved ejection fraction (HFpEF) is associated with marked inflammation and a prooxidant state that is accompanied by vascular dysfunction, whether acute antioxidant (AO) administration can effectively target these disease-related decrements has not been evaluated. Thus, the present study sought to evaluate the efficacy of an acute over-the-counter AO cocktail (600 mg α-lipoic acid, 1,000 mg vitamin C, and 600 IU vitamin E) to mitigate inflammation and oxidative stress, and subsequently improve nitric oxide (NO) bioavailability and vascular function, in patients with HFpEF. Flow-mediated dilation (FMD) and reactive hyperemia (RH) were evaluated to assess conduit vessel and microvascular function, respectively, 90 min after administration of either placebo (PL) or AO in 16 patients with HFpEF (73 ± 10 yr, EF 54-70%) using a double-blind, crossover design. Circulating biomarkers of inflammation (C-reactive protein, CRP), oxidative stress (malondialdehyde and protein carbonyl), free radical concentration (EPR spectroscopy), antioxidant capacity, ascorbate and NO bioavailability (plasma nitrate, [Formula: see text], and nitrite, [Formula: see text]) were also assessed. FMD improved following AO administration (PL: 3.49 ± 0.7%, AO: 5.83 ± 1.0%), whereas RH responses were similar between conditions (PL: 428 ± 51 mL, AO: 425 ± 51 mL). AO administration decreased CRP (PL: 4,429 ± 705 ng/mL, AO: 3,664 ± 520 ng/mL) and increased ascorbate (PL: 30.0 ± 2.9 µg/mL, AO: 45.1 ± 3.7 µg/mL) and [Formula: see text] (PL: 182 ± 21 nM, AO: 213 ± 24 nM) but did not affect other biomarkers. Together, these data suggest that acute AO administration can exert anti-inflammatory effects and improve conduit artery vasodilation, but not microvascular function, in patients with HFpEF.

No Evidence of Racial Differences in Endothelial Function and Exercise Blood Flow in Young, Healthy Males Following Acute Antioxidant Supplementation.

This study investigated the effects of acute antioxidant supplementation on endothelial function, exercise blood flow and oxidative stress biomarkers in 9 young African American compared to 10 Caucasian males (25.7±1.2 years). We hypothesized that African American males would have lower exercise blood flow and endothelial responsiveness compared to Caucasian males, and these responses would be improved following antioxidant supplementation. Ultrasonography was used to measure blood flow during handgrip exercise. Endothelial function was assessed using flow-mediated dilation, and lipid peroxidation was assessed by measuring levels of malondialdehyde-thiobarbituric acid reactive substances. African American males exhibited lower endothelial function than Caucasians at baseline (8.3±1.7 vs. 12.2±1.7%) and the difference was ameliorated with antioxidant supplementation (10.7±1.9% vs. 10.8±1.8%), but the interaction was not significant (p=0.10). There were no significant changes in malondialdehyde-thiobarbituric acid reactive substances following antioxidant supplementation. There was a significant increase in brachial blood flow and forearm vascular conductance with exercise but no differences with antioxidant supplementation. There were no group differences in exercise responses and no differences with antioxidant supplementation, suggesting a lack of influence of oxidative stress during exercise in this cohort.

Cardiac autonomic modulation and blood pressure responses to isometric handgrip and submaximal cycling exercise in individuals with down syndrome.

PURPOSE: Individuals with Down syndrome (DS) exhibit autonomic dysfunction, manifested as attenuated heart rate (HR) and blood pressure (BP) responses to sympathoexcitation. Whether a subgroup of individuals with DS with a normal HR response would have normal autonomic responses to sympathoexcitation remains unclear. METHODS: We compared autonomic modulation using HR variability (HRV) and BP responses in individuals with and without DS (controls) matched for the HR change to isometric handgrip (HG) (10 DS, 8 controls) and submaximal cycling exercise (CE) (9 DS, 9 controls). HG was performed for 2 min at 30 % of maximal voluntary contraction. CE included two 6-min stages at 0 W and at 50 % of body weight. Beat-to-beat HR and BP were recorded. HRV variables were natural log transformation (Ln) of low frequency (LF), high frequency (HF), LF/HF ratio, total power (TP), and the root mean square of successive differences (RMSSD). RESULTS: In the HG study, although individuals with DS exhibited an overall lower systolic BP, LF/HF ratio, and LnLF/LnHF, their BP and HRV responses to HG were similar to those of the controls. In the CE study, individuals with DS exhibited lower resting LnLF and an overall lower systolic BP and mean arterial pressure compared with controls. During the CE, individuals with DS exhibited an increased diastolic BP and a smaller reduction in LnTP than controls. These differences disappeared after controlling for confounders. CONCLUSIONS: Our results suggest that despite normal HR responses to sympathoexcitatory tasks, HRV was largely similar to controls, with some evidence of autonomic dysfunction in individuals with DS.

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.