New insights into the effects of age and sex on arterial baroreflex function at rest and during dynamic exercise in humans

Baroreflex and chemoreflex interaction in high-altitude exposure: possible role on exercise performance

The hypoxic chemoreflex and the arterial baroreflex are implicated in the ventilatory response to exercise. It is well known that long-term exercise training increases parasympathetic and decreases sympathetic tone, both processes influenced by the arterial baroreflex and hypoxic chemoreflex function. Hypobaric hypoxia (i.e., high altitude [HA]) markedly reduces exercise capacity associated with autonomic reflexes. Indeed, a reduced exercise capacity has been found, paralleled by a baroreflex-related parasympathetic withdrawal and a pronounced chemoreflex potentiation. Additionally, it is well known that the baroreflex and chemoreflex interact, and during activation by hypoxia, the chemoreflex is predominant over the baroreflex. Thus, the baroreflex function impairment may likely facilitate the exercise deterioration through the reduction of parasympathetic tone following acute HA exposure, secondary to the chemoreflex activation. Therefore, the main goal of this review is to describe the main physiological mechanisms controlling baro- and chemoreflex function and their role in exercise capacity during HA exposure.

Age- and sex-related differences in sympathetic vascular transduction and neurohemodynamic balance in humans

Bursts of muscle sympathetic nerve activity (MSNA) and the ensuing vasoconstriction are pivotal determinants of beat-by-beat blood pressure regulation. Although age and sex impact blood pressure regulation, how these factors affect the central and peripheral arcs of the baroreflex remains unclear. In 27 young [25 (SD 3) yr] males (YM; n = 14) and females (YF; n = 13) and 23 older [71 (SD 5) yr] males (OM; n = 11) and females (OF; n = 12), femoral artery blood flow, blood pressure, and MSNA were recorded for 10 min of supine rest. Sympathetic baroreflex sensitivity (i.e., central arc) was quantified as the relationship between diastolic blood pressure and MSNA burst incidence. Signal averaging was used to determine sympathetic vascular transduction into leg vascular conductance (LVC) for 12 cardiac cycles following MSNA bursts (i.e., peripheral arc). Older adults demonstrated attenuated sympathetic transduction into LVC (both P < 0.001) following MSNA bursts, and smaller increases in sympathetic transduction as a function of MSNA burst size and firing pattern compared with young adults (range, P = 0.004-0.032). YM (r2 = 0.36; P = 0.032) and OM (r2 = 0.51; P = 0.014) exhibited an inverse relationship between the central and peripheral arcs of the baroreflex, whereas females did not (YF, r2 = 0.03, P = 0.621; OF, r2 = 0.06, P = 0.445). MSNA burst incidence was inversely related to sympathetic transduction in YM and OF (range, P = 0.03-0.046) but not in YF or OM (range, P = 0.360-0.603). These data indicate that age is associated with attenuated sympathetic vascular transduction, whereas age- and sex-specific changes are present in the relationship between the central and peripheral arcs of the baroreflex regulation of blood pressure.NEW & NOTEWORTHY Sympathetic vascular transduction is attenuated in older compared with young adults, regardless of biological sex. Males, but not females (regardless of age), demonstrate an inverse relationship between central (sympathetic baroreflex sensitivity) and peripheral (sympathetic vascular transduction) components of the baroreflex arc. Young males and older females exhibit an inverse relationship between resting sympathetic outflow and sympathetic vascular transduction. Our results indicate that age and sex exert independent and interactive effects on sympathetic vascular transduction and sympathetic neurohemodynamic balance in humans.

Hypobaric hypoxia and cardiac baroreflex sensitivity in young women

We sought to determine the effects of prolonged moderate hypobaric hypoxia (HH) on cardiac baroreflex sensitivity (cBRS) in young women and whether these effects are a consequence of the reduced arterial oxygen (O₂) tension and/or increased pulmonary ventilation in HH. We hypothesized that HH would reduce cBRS and that this effect would be counteracted by acute restoration of the inspiratory partial pressure of O₂ ([Formula: see text]) and/or voluntary attenuation of pulmonary ventilation. Twelve healthy women (24.0 ± 4.2 yr) were studied before (day 0) and twice during a sojourn in a hypobaric chamber (∼8 h, day 1; 4 days, day 4) where barometric pressure corresponded to ∼3,500-m altitude. Minute ventilation (V̇e; pneumotachometer), heart rate (electrocardiogram), and arterial pressure (finger volume clamp method) were recorded. cBRS was calculated using transfer function analysis between systolic pressure and RR interval. Assessments were made during 1) spontaneous breathing and (in HH only), 2) controlled breathing (reducing V̇e by ∼1 to 2 L/min), and 3) breathing a hyperoxic gas mixture that normalized [Formula: see text]. During spontaneous breathing, HH decreased cBRS (12.5 ± 7.1, 8.9 ± 4.4, and 7.4 ± 3.0 ms/mmHg on days 0, 1, and 4, respectively; P = 0.018). The normalization of [Formula: see text] increased cBRS (10.6 ± 3.3 and 10.7 ± 6.1 ms/mmHg on days 1 and 4) in HH compared with values observed during spontaneous breathing (P < 0.001), whereas controlled breathing had no effect on cBRS (P = 0.708). These findings indicate that ongoing arterial chemoreflex activation by the reduced arterial O₂ tension, independently of the hypoxic ventilatory response, reduces cBRS in young women exposed to extended HH.NEW & NOTEWORTHY We examined the effects of prolonged hypobaric hypoxia (corresponding to ∼3,500-m altitude) on cardiac baroreflex sensitivity (cBRS) in young women and investigated underlying mechanisms. We found that cBRS was reduced in hypoxia and that this reduction was attenuated by acute restoration of inspiratory oxygen partial pressure but not by volitional restraint of pulmonary ventilation. These findings help to elucidate the role of arterial chemoreflex mechanisms in the control of cBRS during hypobaric hypoxia in young women.

Baroreceptor Sensitivity in Individuals with CKD and Heart Failure

Background

Heart failure is the most common cardiovascular complication of chronic kidney disease (CKD) and foreshadows a high morbidity and mortality rate. Baroreflex impairment likely contributes to cardiovascular mortality. We aimed to study the associations between CKD, heart failure, and baroreflex sensitivity (BRS) and their association with cardiovascular outcomes.

Methods

We retrospectively analyzed data from a cohort of 247 individuals with moderate to severe HF. All subjects underwent BRS measurements after intravenous phenylephrine along with electrocardiography, echocardiography, and laboratory measurements. We used logistic regression models to assess the association of CKD (estimated glomerular filtration rate <60 ml/min per 1.73 m²) with BRS using iterative models. Cox proportional hazards models were used to assess associations of binary BRS and subgroups according to categorizations of CKD and BRS with cardiovascular mortality.

Results

Median eGFR among individuals with CKD was 52 (IQR 44-56) ml/min per 1.73 m². eGFR was lower in those with depressed BRS (65 [IQR 54-76] ml/min per 1.73 m²) compared with those with preserved BRS (73 [IQR 64-87] ml/min per 1.73 m²; P≤0.001). The majority of individuals with CKD had depressed BRS compared with those without CKD (60% versus 29%; P=0.05). In regression models, CKD and BRS were independently associated. Cardiovascular mortality was significantly increased in individuals with or without CKD and depressed BRS compared with those with preserved BRS and CKD.

Conclusions

Cardiac BRS is depressed in patients with mild to moderate CKD and HF and associated with cardiovascular mortality. Additional study to confirm its contribution to cardiovascular mortality, particularly in advanced CKD, is warranted.

The contribution of autonomic mechanisms to pain in temporomandibular disorders: A narrative review

BACKGROUND

Temporomandibular disorders (TMD) are diagnosed based on symptom presentation and, like other functional pain disorders, often lack definitive pathology. There is a strong association between elevated stress levels and the severity of TMD-related pain, which suggests that alterations in autonomic tone may contribute to this pain condition.

OBJECTIVES

This narrative review examines the association between altered autonomic function and pain in TMD.

METHODS

Relevant articles were identified by searching PubMed and through the reference list of those studies.

RESULTS

TMD sufferers report an increased incidence of orthostatic hypotension. As in other chronic musculoskeletal pain conditions, TMD is associated with increased sympathetic tone, diminished baroreceptor reflex sensitivity and decreased parasympathetic tone. It remains to be determined whether ongoing pain drives these autonomic changes and/or is exacerbated by them. To examine whether increased sympathetic tone contributes to TMD-related pain through β₂ adrenergic receptor activation, clinical trials with the beta blocker propranolol have been undertaken. Although evidence from small studies suggested propranolol reduced TMD-related pain, a larger clinical trial did not find a significant effect of propranolol treatment. This is consistent with human experimental pain studies that were unable to demonstrate an effect of β₂ adrenergic receptor activation or inhibition on masticatory muscle pain. In preclinical models of temporomandibular joint arthritis, β₂ adrenergic receptor activation appears to contribute to inflammation and nociception, whereas in masticatory muscle, α₁ adrenergic receptor activation has been found to induce mechanical sensitization. Some agents used to treat TMD, such as botulinum neurotoxin A, antidepressants and α₂ adrenergic receptor agonists, may interact with the autonomic nervous system as part of their analgesic mechanism.

CONCLUSION

Even if dysautonomia turns out to be a consequence rather than a causative factor of painful TMD, the study of its role has opened up a greater understanding of the pathogenesis of this condition.

Effects of resistance training on baroreflex sensitivity function in healthy males

[Purpose] This experimental study examined the effects of resistance exercises with three intensities on baroreflex sensitivity (BRS) in healthy males. [Participants and Methods] This study enrolled 27 sedentary healthy males with the following demographic characteristics: mean age, 19.9 years; body mass, 63.4 kg; height, 171.7 cm; and body mass index, 21.5 kg/m². The participants performed 20 alternating knee extensions while sitting, and each excursion comprised 5-seconds contraction and rest periods with 20%, 50% and 80% loads of one repetition maximum. The main outcome measures examined in this study were autonomic nerve activities and BRS during the low-intensity resistance exercise utilizing cardiographic and hemodynamic impedance parameters for cardiac function. While measuring the spectral powers of high-frequency (HF) and low frequency (LF) regions, a continuous RR series of the heart rate was calculated. Moreover, the LF/HF ratio of the RR interval variability power and the HF normalized unit (HFnu) were calculated as parameters for sympathetic and parasympathetic nerve activities. [Results] After the low-intensity resistance training, a significant decrease in the LF/HF ratio associated with significant increases in HFnu and BRS were observed. [Conclusion] Low-intensity resistance training may enhance BRS function in healthy males.

Hemodynamic characteristics and early warnings in very old patients

The hemodynamic characteristics of very old patients (VOPs) are unique. With increasing age, patients may experience reduced diastolic function, increased rates of valvular heart disease and coronary atherosclerosis, stiffer vessels, and a reduced heart response to stimulations. Structural and functional modifications are linked to cardiac aging; echocardiography reveals concentric remodeling of the left ventricle, dilation of the left atrium, thickening and calcification of the valves, modification of the large vessels, and abnormal ventricular relaxation. According to a comprehensive understanding of the insufficient compensatory mechanisms of the aging heart, arrythmia should be avoided to the maximum extent and "conservative" fluid therapy should be provided together with appropriate blood pressure control. Considering these factors will improve the success rate of resuscitation and significantly reduce economic loss. In addition, more attention should be paid to the diastolic blood pressure in VOPs.

Gender Differences in Hemodynamic Regulation and Cardiovascular Adaptations to Dynamic Exercise

Exercise is a major challenge for cardiovascular apparatus since it recruits chronotropic, inotropic, pre-load, and afterload reserves. Regular physical training induces several physiological adaptations leading to an increase in both cardiac volume and mass. It appears that several gender-related physiological and morphological differences exist in the cardiovascular adjustments and adaptations to dynamic exercise in humans. In this respect, gender may be important in determining these adjustments and adaptations to dynamic exercise due to genetic, endocrine, and body composition differences between sexes. Females seem to have a reduced vasoconstriction and a lower vascular resistance in comparison to males, especially after exercise. Significant differences exist also in the cardiovascular adaptations to physical training, with trained women showing smaller cardiac volume and wall thickness compared with male athletes. In this review, we summarize these differences.

Central autonomic network functional connectivity: correlation with baroreflex function and cardiovascular variability in older adults

Baroreflex regulates short-term cardiovascular variability via the autonomic neural system. The contributions of the central autonomic system to the baroreflex regulations of arterial blood pressure (BP) and heart rate have been reported in young healthy adults, but not in older adults. Therefore, we investigated the association between the high-level central autonomic network (CAN) connectivity and baroreflex sensitivity (BRS) under a resting condition in a healthy older population. Twenty-two older adults (68 ± 8 years old) underwent BRS assessment using the modified Oxford and transfer function methods. Resting-state brain functional MRI was performed to assess the CAN functional connectivity at rest. We found that the functional connectivity (FC) between the left amygdala and left medial frontal gyrus (MeFG), bilateral postcentral gyri and bilateral paracentral lobules (PCL) is associated with BRS and R-R interval (RRI) variability in the low-frequency (LF) range. Compared to the left amygdala, the FC map of the right amygdala only showed significant associations with BRS in the anterior cingulate cortex (ACC) and with RRI variability in the left occipital region. In addition, post hoc analysis of the functionally defined left insula sub-region confirmed the association between CAN and BRS. Overall, our study demonstrates that CAN and its related brain regions may be involved, likely in a left-lateral manner, in peripheral cardiac autonomic regulation at rest. The results highlight the potential importance of brain neural network function in maintaining cardiovascular homeostasis in older adults.

Characterization of the Asymmetry of the Cardiac and Sympathetic Arms of the Baroreflex From Spontaneous Variability During Incremental Head-Up Tilt

Hysteresis of the baroreflex (BR) is the result of the different BR sensitivity (BRS) when arterial pressure (AP) rises or falls. This phenomenon has been poorly studied and almost exclusively examined by applying pharmacological challenges and static approaches disregarding causal relations. This study inspects the asymmetry of the cardiac BR (cBR) and vascular sympathetic BR (sBR) in physiological closed loop conditions from spontaneous fluctuations of physiological variables, namely heart period (HP) and systolic AP (SAP) leading to the estimation of cardiac BRS (cBRS) and muscle sympathetic nerve activity (MSNA) and diastolic AP (DAP) leading to the estimation of vascular sympathetic BRS (sBRS). The assessment was carried out in 12 young healthy subjects undergoing incremental head-up tilt with table inclination gradually increased from 0 to 60°. Two analytical methods were exploited and compared, namely the sequence (SEQ) and phase-rectified signal averaging (PRSA) methods. SEQ analysis is based on the detection of joint causal schemes representing the HP and MSNA burst rate delayed responses to spontaneous SAP and DAP modifications, respectively. PRSA analysis averages HP and MSNA burst rate patterns after aligning them according to the direction of SAP and DAP changes, respectively. Since cBRSs were similar when SAP went up or down, hysteresis of cBR was not detected. Conversely, hysteresis of sBR was evident with sBRS more negative when DAP was falling than rising. sBR hysteresis was no longer visible during sympathetic activation induced by the orthostatic challenge. These results were obtained via the SEQ method, while the PRSA technique appeared to be less powerful in describing the BR asymmetry due to the strong association between BRS estimates computed over positive and negative AP variations. This study suggests that cBR and sBR provide different information about the BR control, sBR exhibits more relevant non-linear features that are evident even during physiological changes of AP, and the SEQ method can be fruitfully exploited to characterize the BR hysteresis with promising applications to BR branches different from cBR and sBR.

Acute hydrocortisone administration reduces cardiovagal baroreflex sensitivity and heart rate variability in young men

KEY POINTS

A surge in cortisol during acute physiological and pathophysiological stress may precipitate ventricular arrhythmia and myocardial infarction. Reduced cardiovagal baroreflex sensitivity and heart rate variability are observed during acute stress and are associated with an increased risk of acute cardiac events. In the present study, healthy young men received either a single iv bolus of saline (placebo) or hydrocortisone, 1 week apart, in accordance with a randomized, placebo-controlled, cross-over study design. Hydrocortisone acutely increased heart rate and blood pressure and reduced cardiovagal baroreflex sensitivity and heart rate variability in young men. These findings suggest that, by reducing cardiovagal baroreflex sensitivity and heart rate variability, acute surges in cortisol facilitate a pro-arrhythmic milieu and provide an important mechanistic link between stress and acute cardiac events ABSTRACT: Surges in cortisol concentration during acute stress may increase cardiovascular risk. To better understand the interactions between cortisol and the autonomic nervous system, we determined the acute effects of hydrocortisone administration on cardiovagal baroreflex sensitivity (BRS), heart rate variability (HRV) and cardiovascular reactivity. In a randomized, placebo-controlled, single-blinded cross-over study, 10 healthy males received either a single iv bolus of saline (placebo) or 200 mg of hydrocortisone, 1 week apart. Heart rate (HR), blood pressure (BP) and limb blood flow were monitored 3 h later, at rest and during the sequential infusion of sodium nitroprusside and phenylephrine (modified Oxford Technique), a cold pressor test and a mental arithmetic stress task. HRV was assessed using the square root of the mean of the sum of the squares of differences between successive R-R intervals (rMSSD). Hydrocortisone markedly increased serum cortisol 3 h following infusion and also compared to placebo. In addition, hydrocortisone elevated resting HR (+7 ± 4 beats min^-1 ; P < 0.001) and systolic BP (+5 ± 5 mmHg; P = 0.008); lowered cardiovagal BRS [geometric mean (95% confidence interval) 15.6 (11.1-22.1) ms/mmHg vs. 26.2 (17.4--39.5) ms/mmHg, P = 0.011] and HRV (rMSSD 59 ± 29 ms vs. 84 ± 38 ms, P = 0.004) and increased leg vasoconstrictor responses to cold pressor test (Δ leg vascular conductance -45 ± 20% vs. -23 ± 26%; P = 0.023). In young men, an acute cortisol surge is accompanied by increases in HR and BP, as well as reductions in cardiovagal BRS and HRV, potentially providing a pro-arrhythmic milieu that may precipitate ventricular arrhythmia or myocardial infarction and increase cardiovascular risk.

The aging heart

As the elderly segment of the world population increases, it is critical to understand the changes in cardiac structure and function during the normal aging process. In this review, we outline the key molecular pathways and cellular processes that underlie the phenotypic changes in the heart and vasculature that accompany aging. Reduced autophagy, increased mitochondrial oxidative stress, telomere attrition, altered signaling in insulin-like growth factor, growth differentiation factor 11, and 5'- AMP-activated protein kinase pathways are among the key molecular mechanisms underlying cardiac aging. Aging promotes structural and functional changes in the atria, ventricles, valves, myocardium, pericardium, the cardiac conduction system, and the vasculature. We highlight the factors known to accelerate and attenuate the intrinsic aging of the heart and vessels in addition to potential preventive and therapeutic avenues. A greater understanding of the processes involved in cardiac aging may facilitate our ability to mitigate the escalating burden of CVD in older individuals and promote healthy cardiac aging.

Effects of aging and exercise training on leg hemodynamics and oxidative metabolism in the transition from rest to steady-state exercise: role of cGMP signaling

Aging is associated with slower skeletal muscle O₂ uptake (V̇o₂) kinetics; however, the mechanisms underlying this effect of age are unclear. Also, the effects of exercise training in elderly on the initial vascular and metabolic response to exercise remain to be elucidated. We measured leg hemodynamics and oxidative metabolism in the transition from rest to steady-state exercise engaging the knee-extensor muscles in young ( n = 15, 25 ± 1 yr) and older ( n = 15, 72 ± 1 yr) subjects before and after a period of aerobic high-intensity exercise training. To enhance cGMP signaling, pharmacological inhibition of phosphodiesterase 5 (PDE5) was performed. Before training, the older group had a slower ( P <0.05) increase in femoral arterial blood flow and leg vascular conductance in the transition from rest to steady-state exercise at low- and moderate-intensity compared with the young group. The rate of increase in leg V̇o₂ was, however, similar in the two groups as a result of higher ( P < 0.05) arteriovenous O₂ difference in the older group. Potentiation of cGMP signaling did not affect the rate of increase in blood flow or V̇o₂ in either group. Exercise training augmented ( P < 0.05) the increase in leg vascular conductance and blood flow during the onset of moderate-intensity exercise in both groups without altering V̇o₂. These findings suggest that an age-related reduction in the initial vascular response to low- and moderate-intensity knee-extensor exercise is not limiting for V̇o₂ in older individuals. A lower blood flow response in aging does not appear to be a result of reduced cGMP signaling.

Arterial Pressure, Heart Rate, and Cerebral Hemodynamics Across the Adult Life Span

Age-related alterations in systemic and cerebral hemodynamics are not well understood. The purpose of this study is to characterize age-related alterations in beat-to-beat oscillations in arterial blood pressure (BP), heart rate (HR), cerebral blood flow (CBF), cardiac baroreflex sensitivity, and dynamic cerebral autoregulation across the adult life span. We studied 136 healthy adults aged 21 to 80 years (60% women). Beat-to-beat BP, HR, and CBF velocity were measured at rest and during sit-stand maneuvers to mimic effects of postural changes on BP and CBF. Transfer function analysis was used to assess baroreflex sensitivity and dynamic cerebral autoregulation. Carotid-femoral pulse wave velocity was measured to assess central arterial stiffness. Advanced aging was associated with elevated carotid-femoral pulse wave velocity, systolic and pulse BP, cerebrovascular resistance, and CBF pulsatility, but reduced mean CBF velocity. Compared with the young and middle-aged, older adults had lower beat-to-beat BP, HR, and CBF variability in the low-frequency ranges at rest, but higher BP and CBF variability during sit-stand maneuvers. Baroreflex sensitivity was reduced, whereas dynamic cerebral autoregulation gain was elevated at rest in older adults. Multiple linear regression analysis indicated that systolic BP variability is correlated positively with carotid-femoral pulse wave velocity independent of HR variability. In conclusion, advanced aging is associated with elevated pulsatility in BP and CBF; reduced beat-to-beat low-frequency oscillations in BP, HR, and CBF; and impaired baroreflex sensitivity and dynamic cerebral autoregulation at rest. The augmented BP and CBF variability in older adults during sit-stand maneuvers indicate diminished cardiovascular regulatory capability and increased hemodynamic stress on the cerebral circulation with aging.

Carotid baroreflex function at the onset of cycling in men

Arterial baroreflex function is important for blood pressure control during exercise, but its contribution to cardiovascular adjustments at the onset of cycling exercise remains unclear. Fifteen healthy male subjects (24 ± 1 yr) performed 45-s trials of low- and moderate-intensity cycling, with carotid baroreceptor stimulation by neck suction at −60 Torr applied 0–5, 10–15, and 30–35 s after the onset of exercise. Cardiovascular responses to neck suction during cycling were compared with those obtained at rest. An attenuated reflex decrease in heart rate following neck suction was detected during moderate-intensity exercise, compared with the response at rest ( P < 0.05). Furthermore, compared with the reflex decrease in blood pressure elicited at rest, neck suction elicited an augmented decrease in blood pressure at 0–5 and 10–15 s during low-intensity exercise and in all periods during moderate-intensity exercise ( P < 0.05). The reflex depressor response at the onset of cycling was primarily mediated by an increase in the total vascular conductance. These findings evidence altered carotid baroreflex function during the first 35 s of cycling compared with rest, with attenuated bradycardic response, and augmented depressor response to carotid baroreceptor stimulation.

Impaired carotid baroreflex control of arterial blood pressure in multiple sclerosis

Multiple sclerosis (MS), a progressive neurological disease, can lead to impairments in the autonomic control of cardiovascular function. We tested the hypothesis that individuals with relapsing-remitting MS (n = 10; 7 females, 3 males; 13 ± 4 yr from diagnosis) exhibit impaired carotid baroreflex control of blood pressure and heart rate compared with sex, age, and body weight-matched healthy individuals (CON: n = 10; 7 females, 3 males). At rest, 5-s trials of neck pressure (NP; +40 Torr) and neck suction (NS; -60 Torr) were applied to simulate carotid hypotension and hypertension, respectively, while mean arterial pressure (MAP; finger photoplethysmography), heart rate (HR), cardiac output (CO; Modelflow), and total vascular conductance (TVC) were continuously measured. In response to NP, there was a blunted increase in peak MAP responses (MS: 5 ± 2 mmHg) in individuals with MS compared with healthy controls (CON: 9 ± 3 mmHg; P = 0.005), whereas peak HR responses were not different between groups. At the peak MAP response to NP, individuals with MS demonstrated an attenuated decrease in TVC (MS, -10 ± 4% baseline vs. CON, -15 ± 4% baseline, P = 0.012), whereas changes in CO were similar between groups. Following NS, all cardiovascular responses (i.e., nadir MAP and HR and percent changes in CO and TVC) were not different between MS and CON groups. These data suggest that individuals with MS have impaired carotid baroreflex control of blood pressure via a blunted vascular conductance response resulting in a diminished ability to increase MAP in response to a hypotensive challenge.

Cardiopulmonary reflex, cardiac cytokines, and nandrolone decanoate: response to resistance training in rats

This study evaluated the effects of nandrolone associated with resistance training (RT) on cardiac cytokines, angiotensin-converting enzyme activity (ACEA), and the sensitivity of the Bezold-Jarisch reflex (BJR). Male Wistar rats were divided into 3 groups: CONT (received vehicle, no training); EXERC (RT: after one week of water adaptation, rats were exercised by jumping into water twice a week for 4 weeks), and ND+EXERC (received nandrolone decanoate 10 mg/kg, twice/week, i.m, associated with RT). The BJR was analysed by measuring bradycardic and hypotensive responses elicited by serotonin administration. Myocyte hypertrophy and matrix collagen deposition were determined by morphometric analysis of H&E and picrosirius red-stained samples, respectively. TNF-α and ACEA were also studied. RT promoted physiological myocyte hyrpertrophy but did not cause changes in the other parameters. The association of ND with RT increased myocyte hypertrophy, deposition of matrix type I collagen, TNF-α and ACEA; decreased IL-10, and impairment in the BJR were observed in ND+EXERC compared with CONT and EXERC. ND is associated with alterations in cardiac structure and function as a result of the development of pathological cardiac hypertrophy (cardiac cytokine imbalance, elevation of ACEA) and cardiac injury, even when combined with resistance training.

The Baroreflex Mechanism Revisited

We state that the autonomic part of the brain controls the blood pressure (BP) and the heart rate (HR) via the baroreflex mechanism in all situations of human activity (at sleep, at rest, during exercise, fright etc.), in a way which is not, as was hitherto assumed, a mere homeostatic tool or even a resetting device, designed to bring these variables on the road to preset values. The baroreflex is rather a continuous feedback mechanism commanded by the autonomic part of the brain, leading to values appropriate to the situation at hand. Feasibility of this assertion is demonstrated here by using the Seidel-Herzel feedback system outside of its regular practice. Results show indeed that the brain can, and we claim that it does, control the HR and BP throughout life. New responses are demonstrated, e.g., to a sudden fear or apnea. In this event, large BP and HR overshoots are expected before the variables can relax to a new level. Response to abrupt downward change in the controlling parameter shows an undershoot in HR and just a gradual resetting in the BP. The relaxation from sudden external changes to various expected states are calculated and discussed and properties of the Rheos test are explained. Experimental findings for orthostatic tests and for babies under translations and rotations reveal complete qualitative agreement with our model and show no need to invoke the operation of additional body systems. Our method should be the preferred one by the Occam Razor approach. The outcomes may lead to beneficial clinical implication.

Aging alters muscle reflex control of autonomic cardiovascular responses to rhythmic contractions in humans

We investigated the influence of aging on the group III/IV muscle afferents in the exercise pressor reflex-mediated cardiovascular response to rhythmic exercise. Nine old (OLD; 68 ± 2 yr) and nine young (YNG; 24 ± 2 yr) males performed single-leg knee extensor exercise (15 W, 30 W, 80% max) under control conditions and with lumbar intrathecal fentanyl impairing feedback from group III/IV leg muscle afferents. Mean arterial pressure (MAP), cardiac output, leg blood flow (QL), systemic (SVC) and leg vascular conductance (LVC) were continuously determined. With no hemodynamic effect at rest, fentanyl blockade during exercise attenuated both cardiac output and QL ∼17% in YNG, while the decrease in cardiac output in OLD (∼5%) was significantly smaller with no impact on QL (P = 0.8). Therefore, in the face of similar significant ∼7% reduction in MAP during exercise with fentanyl blockade in both groups, LVC significantly increased ∼11% in OLD, but decreased ∼8% in YNG. The opposing direction of change was reflected in SVC with a significant ∼5% increase in OLD and a ∼12% decrease in YNG. Thus while cardiac output seems to account for the majority of group III/IV-mediated MAP responses in YNG, the impact of neural feedback on the heart may decrease with age and alterations in SVC become more prominent in mediating the similar exercise pressor reflex in OLD. Interestingly, in terms of peripheral hemodynamics, while group III/IV-mediated feedback plays a clear role in increasing LVC during exercise in the YNG, these afferents seem to actually reduce LVC in OLD. These peripheral findings may help explain the limited exercise-induced peripheral vasodilation often associated with aging.

Passive Leg Raising Correlates with Future Exercise Capacity after Coronary Revascularization

Hemodynamic properties affected by the passive leg raise test (PLRT) reflect cardiac pumping efficiency. In the present study, we aimed to further explore whether PLRT predicts exercise intolerance/capacity following coronary revascularization. Following coronary bypass/percutaneous coronary intervention, 120 inpatients underwent a PLRT and a cardiopulmonary exercise test (CPET) 2–12 days during post-surgery hospitalization and 3–5 weeks after hospital discharge. The PLRT included head-up, leg raise, and supine rest postures. The end point of the first CPET during admission was the supra-ventilatory anaerobic threshold, whereas that during the second CPET in the outpatient stage was maximal performance. Bio-reactance-based non-invasive cardiac output monitoring was employed during PLRT to measure real-time stroke volume and cardiac output. A correlation matrix showed that stroke volume during leg raise (SV_LR) during the first PLRT was positively correlated (R = 0.653) with the anaerobic threshold during the first CPET. When exercise intolerance was defined as an anaerobic threshold < 3 metabolic equivalents, SV_LR / body weight had an area under curve value of 0.822, with sensitivity of 0.954, specificity of 0.593, and cut-off value of 1504·10^-3mL/kg (positive predictive value 0.72; negative predictive value 0.92). Additionally, cardiac output during leg raise (CO_LR) during the first PLRT was related to peak oxygen consumption during the second CPET (R = 0.678). When poor aerobic fitness was defined as peak oxygen consumption < 5 metabolic equivalents, CO_LR / body weight had an area under curve value of 0.814, with sensitivity of 0.781, specificity of 0.773, and a cut-off value of 68.3 mL/min/kg (positive predictive value 0.83; negative predictive value 0.71). Therefore, we conclude that PLRT during hospitalization has a good screening and predictive power for exercise intolerance/capacity in inpatients and early outpatients following coronary revascularization, which has clinical significance.

Reduction of autonomic regulation in children and adolescents with conversion disorders

OBJECTIVE

Conversion symptoms--functional neurological disturbances of body function--occur in association with extreme arousal, often in the context of emotional distress. The mechanisms that determine how and why such symptoms occur remain unknown. In this study, we used cardiac measures to assess arousal and cardiac autonomic regulation in children and adolescents who presented with acute conversion symptoms.

METHODS

Heart rate was recorded in 57 children and adolescents (41 girls; 8.5-18 years old) with acute conversion symptoms and 57 age- and sex-matched healthy controls, during a resting condition and then during tasks involving cognitive and emotional activation. Arousal and autonomic regulation were assessed by measures of heart rate and heart rate variability. Psychological measures included attachment and emotional distress.

RESULTS

Children and adolescents with conversion symptoms displayed higher autonomic arousal than did the controls, both at baseline and during task conditions (higher heart rate: baseline mean [standard deviation] = 82 [9.49] versus 74 [10.79] beats/min, p < .001; lower root mean squared successive differences-heart rate variability: 45.35 [27.97] versus 58.62 [25.69] ms(2), p = .012; and lower high-frequency heart rate variability: 6.50 [1.19] versus 7.01 [0.95] ln[ms(2)] p = .017), and decreased autonomic regulation (attenuation of heart rate increases across tasks). The baseline pattern of increased autonomic arousal was especially pronounced in children with coercive-preoccupied patterns of attachment. Autonomic measures were not correlated with measures of emotional distress.

CONCLUSIONS

High autonomic arousal may be a precondition for generating conversion symptoms. Functional dysregulations of the cardiac, respiratory, and circulatory systems may mediate fainting episodes and nonepileptic seizures, and aberrant patterns of functional connectivity between motor areas and central arousal systems may be responsible for generating motor conversion symptoms.

Yes! Sex matters: sex, the brain and blood pressure

The role of the brain in hypertension between the sexes is known to be important especially with regards to the effects of circulating sex hormones. A number of different brain regions important for regulation of sympathetic outflow and blood pressure express estrogen receptors (ERα and ERβ). Estradiol, acting predominantly via the ERα, inhibits angiotensin II activation of the area postrema and subfornical organ neurons and inhibits reactive oxygen generation that is required for the development of Angiotensin II-induced neurogenic hypertension. Estradiol activation of ERβ within the paraventricular nucleus and the rostral ventral lateral medulla inhibits these neurons and inhibits angiotensin II, or aldosterone induced increases in sympathetic outflow and hypertension. Understanding the cellular and molecular mechanisms underlying ERα and ERβ actions within key brain regions regulating blood pressure will be essential for the development of "next generation" selective estrogen receptor modulators (SERMS) that can be used clinically for the treatment of neurogenic hypertension.

Slower lower limb blood pooling in young women with orthostatic intolerance

NEW FINDINGS

What is the central question of this study? Orthostatic stress is mostly caused by venous blood pooling in the lower limbs. Venous distension elicits sympathetic responses, and increased distension speed enhances the cardiovascular response. We examine whether lower limb blood pooling rate during lower body negative pressure is linked to orthostatic intolerance. What is the main finding and its importance? A similar amount of blood was pooled in the lower limb, but at a slower rate in women who developed signs of orthostatic intolerance. The difference in blood pooling rate increased with orthostatic stress and was most prominent at a presyncope-inducing level of lower body negative pressure. The findings have implications for the pathophysiology as well as treatment of orthostatic intolerance. Vasovagal syncope is common in young women, but its aetiology remains elusive. Orthostatic stress-induced lower limb blood pooling is linked with central hypovolaemia and baroreceptor unloading. Venous distension in the arm elicits a sympathetic response, which is enhanced with more rapid distension. Our aim was to study both the amount and the speed of lower limb pooling during orthostatic stress and its effects on compensatory mechanisms to maintain cardiovascular homeostasis in women with orthostatic intolerance. Twenty-seven healthy women, aged 20-27 years, were subjected to a lower body negative pressure (LBNP) of 11-44 mmHg. Five women developed symptoms of vasovagal syncope (orthostatic intolerant) and were compared with the remaining women, who tolerated LBNP well (orthostatic tolerant). Lower limb blood pooling, blood flow and compensatory mobilization of venous capacitance blood were measured. Lower body negative pressure induced equal lower limb blood pooling in both groups, but at a slower rate in orthostatic intolerant women (e.g. time to 50% of total blood pooling, orthostatic intolerant 44 ± 7 s and orthostatic tolerant 26 ± 2 s; P < 0.001). At presyncope-inducing LBNP, the mobilization of venous capacitance blood was both reduced (P < 0.05) and much slower in orthostatic intolerant women (P = 0.0007). Orthostatic intolerant women elicited blunted arterial vasoconstriction at low-grade LBNP, activating only cardiopulmonary baroreceptors, while orthostatic tolerant women responded with apparent vasoconstriction (P < 0.0001). In conclusion, slower lower limb blood pooling could contribute to orthostatic intolerance in women. Mobilization of venous capacitance blood from the peripheral to the central circulation was both slower and decreased; furthermore, reduced cardiopulmonary baroreceptor sensitivity was found in women who developed orthostatic intolerance. Further studies including women who experience syncope in daily life are needed.

An afferent explanation for sexual dimorphism in the aortic baroreflex of rat

Sex differences in baroreflex (BRx) function are well documented. Hormones likely contribute to this dimorphism, but many functional aspects remain unresolved. Our lab has been investigating a subset of vagal sensory neurons that constitute nearly 50% of the total population of myelinated aortic baroreceptors (BR) in female rats but less than 2% in male rats. Termed "Ah," this unique phenotype has many of the nonoverlapping electrophysiological properties and chemical sensitivities of both myelinated A-type and unmyelinated C-type BR afferents. In this study, we utilize three distinct experimental protocols to determine if Ah-type barosensory afferents underlie, at least in part, the sex-related differences in BRx function. Electron microscopy of the aortic depressor nerve (ADN) revealed that female rats have less myelin (P < 0.03) and a smaller fiber cross-sectional area (P < 0.05) per BR fiber than male rats. Electrical stimulation of the ADN evoked compound action potentials and nerve conduction profiles that were markedly different (P < 0.01, n = 7 females and n = 9 males). Selective activation of ADN myelinated fibers evoked a BRx-mediated depressor response that was 3-7 times greater in female (n = 16) than in male (n = 17) rats. Interestingly, the most striking hemodynamic difference was functionally dependent upon the rate of myelinated barosensory fiber activation. Only 5-10 Hz of stimulation evoked a rapid, 20- to 30-mmHg reduction in arterial pressure of female rats, whereas rates of 50 Hz or higher were required to elicit a comparable depressor response from male rats. Collectively, our experimental results are suggestive of an alternative myelinated baroreceptor afferent pathway in females that may account for, at least in part, the noted sex-related differences in autonomic control of cardiovascular function.

Pathophysiological contribution of vascular function to baroreflex regulation in hypertension

BACKGROUND

We examined which pathophysiological abnormalities of vascular function might be closely associated with abnormal baroreflex regulation in subjects with hypertension.

METHODS AND RESULTS

In the cross-sectional assessment, 280 subjects with hypertension were enrolled for measurement of brachial-ankle pulse wave velocity (baPWV), radial augmentation index (rAI), flow-mediated vasodilatation (FMD) of the brachial artery and baroreceptor sensitivity (BRS). These parameters were measured again as prospective assessment in some of these subjects. In the cross-sectional assessment, after adjustment for confounding variables including anti-hypertensive medication, the baPWV, but not the rAI or FMD, was found to have a significant independent relationship with BRS (standardization coefficient, -0.149, P<0.043). In the subjects who were newly started on anti-hypertensive medication (n=40), regression of baPWV before and 1 year after the start of medication was significantly associated with change in BRS during the same period. In subjects already on anti-hypertensive medication (n=92) also, the evolutional change of baPWV over a follow-up period >1.5 years was significantly associated with change in BRS during the same period.

CONCLUSIONS

Increased stiffness of the large- to middle-sized arteries, rather than abnormal central hemodynamics or endothelial dysfunction, appears to contribute to abnormal baroreflex regulation in patients with hypertension.

Effect of aging on carotid baroreflex control of blood pressure and leg vascular conductance in women

Recent work suggests that β-adrenergic vasodilation offsets α-adrenergic vasoconstriction in young women, but this effect is lost after menopause. Given these age-related vascular changes, we tested the hypothesis that older women would exhibit a greater change in vascular conductance following baroreflex perturbation compared with young women. In 10 young (21 ± 1 yr) and 10 older (62 ± 2 yr) women, mean arterial pressure (MAP; Finometer), heart rate (HR), cardiac output (CO; Modelflow), total vascular conductance (TVC), and leg vascular conductance (LVC, duplex-Doppler ultrasound) were continuously measured in response to 5-s pulses of neck suction (NS; -60 Torr) and neck pressure (NP; +40 Torr) to simulate carotid hypertension and hypotension, respectively. Following NS, decreases in MAP were similar between groups; however, MAP peak response latency was slower in older women (P < 0.05). Moreover, at the time of peak MAP, increases in LVC (young, -11.5 ± 3.9%LVC vs. older, +19.1 ± 7.0%LVC; P < 0.05) and TVC were greater in older women, whereas young women exhibited larger decreases in HR and CO (young, -10 ± 3% CO vs. older, +0.8 ± 2% CO; P < 0.05). Following NP, increases in MAP were blunted (young, +14 ± 1 mmHg vs. older, +8 ± 1 mmHg; P < 0.05) in older women, whereas MAP response latencies were similar. Interestingly, decreases in LVC and TVC were similar between groups, but HR and CO (young, +7.0 ± 2% CO vs. older, -4.0 ± 2% CO; P < 0.05) responses were attenuated in older women. These findings suggest that older women have greater reliance on vascular conductance to modulate MAP via carotid baroreflex, whereas young women rely more on cardiac responsiveness. Furthermore, older women demonstrate a blunted ability to increase MAP to hypotensive stimuli.