Locomotor muscle group III/IV afferents constrain stroke volume and contribute to exercise intolerance in human heart failure

Thoracic load carriage impairs the acute physiological response to hypoxia in healthy males

To assess the impact of thoracic load carriage on the physiological response to exercise in hypoxia. Healthy males (n = 12) completed 3 trials consisting of 45 min walking in the following conditions: (1) unloaded normoxia (UN; FIO2:20.93%); (2) unloaded hypoxia (UH; FIO2:~13.0%); and (3) loaded hypoxia (LH; 29.5 kg; FIO2:~13.0%). Intensity was matched for absolute VO2 (2.0 ± 0.2 L·min-1) across conditions and relative VO2 (64.0 ± 2.6 %VO2max) across hypoxic conditions. With LH versus UH, there were increases in breathing frequency (5-11 breaths·min-1; p < 0.05) and decreases in tidal volume (10%-18%; p < 0.05) throughout exercise due to reductions in end inspiratory lung volumes (p < 0.05). Consequently, deadspace (11%-23%; p < 0.05) and minute ventilation (7%-11%; p < 0.05) were increased starting at 20 and 30 min, respectively. In addition, LH increased perceived exertion/dyspnea and induced inspiratory (~12%; p < 0.05 vs. UN) and expiratory (~10%; p < 0.05 vs. pre-exercise) respiratory muscle fatigue. Expiratory flow limitation was present in 50% of subjects during LH. Cardiac output and muscle oxygenation were maintained during LH despite reduced stroke volume (6%-8%; p < 0.05). Finally, cerebral oxygenated/total hemoglobin were elevated in the LH condition versus UH starting at 15 min (p < 0.05). Thoracic load carriage increases physiological strain and interferes with the compensatory response to hypoxic exposure.

Protein kinase C epsilon contributes to chronic mechanoreflex sensitization in rats with heart failure

We investigated second-messenger signalling components linked to the stimulation of Gq protein-coupled receptors (e.g. thromboxane A2 and bradykinin B2 receptors) on the sensory endings of thin fibre muscle afferents in the chronic mechanoreflex sensitization in rats with myocardial infarction-induced heart failure with reduced ejection fraction (HF-rEF). We hypothesized that injection of either the inositol 1,4,5-trisphosphate (IP3) receptor antagonist xestospongin C (5 µg) or the PKCε translocation inhibitor PKCe141 (45 µg) into the arterial supply of the hindlimb would reduce the increase in renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) evoked during 30 s of 1 Hz dynamic hindlimb muscle stretch in decerebrate, unanaesthetized HF-rEF rats but not sham-operated controls (SHAM). Ejection fraction was significantly reduced in HF-rEF (45 (19)%) compared to SHAM (80 (9)%; P < 0.001) rats. In HF-rEF rats (n = 3M/2F), IP3 receptor blockade had no effect on the peak ΔRSNA (pre: 99 (74)%; post: 133 (79)%; P = 0.974) or peak ΔMAP response to stretch (peak ΔMAP: pre: 32 (14) mmHg; post: 36 (21) mmHg; P = 0.719). Conversely, in another group of HF-rEF rats (n = 4M/3F), the PKCε translocation inhibitor reduced the peak ΔRSNA (pre: 110 (77)%; post: 62 (58)%; P = 0.029) and peak ΔMAP response to stretch (pre: 30 (20) mmHg; post: 17 (16) mmHg; P = 0.048). In SHAM counterparts, neither drug affected the mechanoreflex responses. Our findings highlight PKCε, but not IP3 receptors, as a significant second-messenger in the chronic mechanoreflex sensitization in HF-rEF which may play a crucial role in the exaggerated sympathetic response to exercise in this patient population. KEY POINTS: Skeletal muscle contraction results in an exaggerated reflex increase in sympathetic nerve activity in heart failure patients with reduced ejection fraction (HF-rEF) compared to healthy individuals, contributing to increased cardiovascular risk and impaired tolerance for mild exercise. The exaggerated reflex sympathetic responses in HF-rEF may be attributed to a chronic sensitization of mechanically sensitive thin fibre muscle afferents mediated, at least in part, by stimulation of Gq protein-coupled thromboxane A2 and bradykinin B2 receptors on muscle afferent sensory endings. The specific Gq protein-linked signalling mechanisms that produce the chronic mechanoreflex sensitization in HF-rEF have not been investigated but may involve inositol 1,4,5-trisphosphate (IP3) receptors and/or protein kinase C epsilon (PKCε). Here we demonstrate that PKCε, but not IP3 receptors, within the sensory endings of thin fibre muscle afferents plays a role in the sensitization of mechanically sensitive thin fibre muscle afferents in rats with HF-rEF.

Influence of blood lactate variations and passive exercise on cardiac responses

[Purpose] This study aimed to investigate cardiovascular responses, including heart rate (HR) and heart rate variability (HRV), to various hyperlactatemia-passive exercise interactions. [Participants and Methods] Nine healthy male participants performed upper limb passive cycling movement, and their HR and HRV were assessed while their blood lactate levels were manipulated by sustained handgrip exercise at control, 15% maximum voluntary contraction (MVC), and 30% MVC, followed by postexercise circulatory occlusion. [Results] HR and root mean squared standard difference (rMSSD) of HRV response remained constant at all blood lactate levels during passive exercise (HR: control, 75.8 ± 3.4 bpm; 15% MVC, 76.9 ± 2.7 bpm; and 30% MVC, 77.0 ± 3.7 bpm; rMSSD: control, 33.2 ± 6.9 ms; 15% MVC, 36.3 ± 7.3 ms; and 30% MVC, 37.3 ± 8.9 ms). [Conclusion] Manipulating metaboreflex activation did not significantly alter HR or HRV during passive exercise. These results suggest that, in healthy participants, the interactions between mechanical and metabolic stimuli do not affect HR and HRV responses, implying that passive exercise may be safely implemented.

Consequences of group III/IV afferent feedback and respiratory muscle work on exercise tolerance in heart failure with reduced ejection fraction

Exercise intolerance and exertional dyspnoea are the cardinal symptoms of heart failure with reduced ejection fraction (HFrEF). In HFrEF, abnormal autonomic and cardiopulmonary responses arising from locomotor muscle group III/IV afferent feedback is one of the primary mechanisms contributing to exercise intolerance. HFrEF patients also have pulmonary system and respiratory muscle abnormalities that impair exercise tolerance. Thus, the primary impetus for this review was to describe the mechanistic consequences of locomotor muscle group III/IV afferent feedback and respiratory muscle work in HFrEF. To address this, we first discuss the abnormal autonomic and cardiopulmonary responses mediated by locomotor muscle afferent feedback in HFrEF. Next, we outline how respiratory muscle work impairs exercise tolerance in HFrEF through its effects on locomotor muscle O2 delivery. We then discuss the direct and indirect evidence supporting an interaction between locomotor muscle group III/IV afferent feedback and respiratory muscle work during exercise in HFrEF. Last, we outline future research directions related to locomotor and respiratory muscle abnormalities to progress the field forward in understanding the pathophysiology of exercise intolerance in HFrEF. NEW FINDINGS: What is the topic of this review? This review is focused on understanding the role that locomotor muscle group III/IV afferent feedback and respiratory muscle work play in the pathophysiology of exercise intolerance in patients with heart failure. What advances does it highlight? This review proposes that the concomitant effects of locomotor muscle afferent feedback and respiratory muscle work worsen exercise tolerance and exacerbate exertional dyspnoea in patients with heart failure.

The Effect of Skeletal Muscle Oxygenation on Hemodynamics, Cerebral Oxygenation and Activation, and Exercise Performance during Incremental Exercise to Exhaustion in Male Cyclists

This study aimed to elucidate whether muscle blood flow restriction during maximal exercise is associated with alterations in hemodynamics, cerebral oxygenation, cerebral activation, and deterioration of exercise performance in male participants. Thirteen healthy males, cyclists (age 33 ± 2 yrs., body mass: 78.6 ± 2.5 kg, and body mass index: 25.57 ± 0.91 kg·m^-1), performed a maximal incremental exercise test on a bicycle ergometer in two experimental conditions: (a) with muscle blood flow restriction through the application of thigh cuffs inflated at 120 mmHg (with cuffs, WC) and (b) without restriction (no cuffs, NC). Exercise performance significantly deteriorated with muscle blood flow restriction, as evidenced by the reductions in V˙O_2max (-17 ± 2%, p < 0.001), peak power output (-28 ± 2%, p < 0.001), and time to exhaustion (-28 ± 2%, p < 0.001). Muscle oxygenated hemoglobin (Δ[O₂Hb]) during exercise declined more in the NC condition (p < 0.01); however, at exhaustion, the magnitude of muscle oxygenation and muscle deoxygenation were similar between conditions (p > 0.05). At maximal effort, lower cerebral deoxygenated hemoglobin (Δ[HHb]) and cerebral total hemoglobin (Δ[THb]) were observed in WC (p < 0.001), accompanied by a lower cardiac output, heart rate, and stroke volume vs. the NC condition (p < 0.01), whereas systolic blood pressure, rating of perceived exertion, and cerebral activation (as assessed by electroencephalography (EEG) activity) were similar (p > 0.05) between conditions at task failure, despite marked differences in exercise duration, maximal aerobic power output, and V˙O_2max. In conclusion, in trained cyclists, muscle blood flow restriction during an incremental cycling exercise test significantly limited exercise performance. Exercise intolerance with muscle blood flow restriction was mainly associated with attenuated cardiac responses, despite cerebral activation reaching similar maximal levels as without muscle blood flow restriction.

Effect of opioids for breathlessness in heart failure: a systematic review and meta-analysis

BACKGROUND

For the treatment of breathlessness in heart failure (HF), most textbooks advocate the use of opioids. Yet, meta-analyses are lacking.

METHODS

A systematic review was performed for randomised controlled trials (RCTs) assessing effects of opioids on breathlessness (primary outcome) in patients with HF. Key secondary outcomes were quality of life (QoL), mortality and adverse effects. Cochrane Central Register of Controlled Trials, MEDLINE and Embase were searched in July 2021. Risk of bias (RoB) and certainty of evidence were assessed by the Cochrane RoB 2 Tool and Grading of Recommendations Assessment, Development and Evaluation criteria, respectively. The random-effects model was used as primary analysis in all meta-analyses.

RESULTS

After removal of duplicates, 1180 records were screened. We identified eight RCTs with 271 randomised patients. Seven RCTs could be included in the meta-analysis for the primary endpoint breathlessness with a standardised mean difference of 0.03 (95% CI -0.21 to 0.28). No study found statistically significant differences between the intervention and placebo. Several key secondary outcomes favoured placebo: risk ratio of 3.13 (95% CI 0.70 to 14.07) for nausea, 4.29 (95% CI 1.15 to 16.01) for vomiting, 4.77 (95% CI 1.98 to 11.53) for constipation and 4.42 (95% CI 0.79 to 24.87) for study withdrawal. All meta-analyses revealed low heterogeneity (I2 in all these meta-analyses was <8%).

CONCLUSION

Opioids for treating breathlessness in HF are questionable and may only be the very last option if other options have failed or in case of an emergency.

PROSPERO REGISTRATION NUMBER

CRD42021252201.

Pharmacological Blockade of Muscle Afferents and Perception of Effort: A Systematic Review with Meta-analysis

BACKGROUND

The perception of effort provides information on task difficulty and influences physical exercise regulation and human behavior. This perception differs from other-exercise related perceptions such as pain. There is no consensus on the role of group III/IV muscle afferents as a signal processed by the brain to generate the perception of effort.

OBJECTIVE

The aim of this meta-analysis was to investigate the effect of pharmacologically blocking muscle afferents on the perception of effort.

METHODS

Six databases were searched to identify studies measuring the ratings of perceived effort during physical exercise, with and without pharmacological blockade of muscle afferents. Articles were coded based on the operational measurement used to distinguish studies in which perception of effort was assessed specifically (effort dissociated) or as a composite experience including other exercise-related perceptions (effort not dissociated). Articles that did not provide enough information for coding were assigned to the unclear group.

RESULTS

The effort dissociated group (n = 6) demonstrated a slight increase in ratings of perceived effort with reduced muscle afferent feedback (standard mean change raw, 0.39; 95% confidence interval 0.13-0.64). The group effort not dissociated (n = 2) did not reveal conclusive results (standard mean change raw, - 0.29; 95% confidence interval - 2.39 to 1.8). The group unclear (n = 8) revealed a slight ratings of perceived effort decrease with reduced muscle afferent feedback (standard mean change raw, - 0.27; 95% confidence interval - 0.50 to - 0.04).

CONCLUSIONS

The heterogeneity in results between groups reveals that the inclusion of perceptions other than effort in its rating influences the ratings of perceived effort reported by the participants. The absence of decreased ratings of perceived effort in the effort dissociated group suggests that muscle afferent feedback is not a sensory signal for the perception of effort.

Regulation of the microvasculature during small muscle mass exercise in chronic obstructive pulmonary disease vs. chronic heart failure

Aim: Skeletal muscle convective and diffusive oxygen (O2) transport are peripheral determinants of exercise capacity in both patients with chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF). We hypothesised that differences in these peripheral determinants of performance between COPD and CHF patients are revealed during small muscle mass exercise, where the cardiorespiratory limitations to exercise are diminished. Methods: Eight patients with moderate to severe COPD, eight patients with CHF (NYHA II), and eight age- and sex-matched controls were studied. We measured leg blood flow (Q̇leg) by Doppler ultrasound during submaximal one-legged knee-extensor exercise (KEE), while sampling arterio-venous variables across the leg. The capillary oxyhaemoglobin dissociation curve was reconstructed from paired femoral arterial-venous oxygen tensions and saturations, which enabled the estimation of O2 parameters at the microvascular level within skeletal muscle, so that skeletal muscle oxygen conductance (DSMO2) could be calculated and adjusted for flow (DSMO2/Q̇leg) to distinguish convective from diffusive oxygen transport. Results: During KEE, Q̇leg increased to a similar extent in CHF (2.0 (0.4) L/min) and controls (2.3 (0.3) L/min), but less in COPD patients (1.8 (0.3) L/min) (p <0.03). There was no difference in resting DSMO2 between COPD and CHF and when adjusting for flow, the DSMO2 was higher in both groups compared to controls (COPD: 0.97 (0.23) vs. controls 0.63 (0.24) mM/kPa, p= 0.02; CHF 0.98 (0.11) mM/kPa vs. controls, p= 0.001). The Q̇-adjusted DSMO2 was not different in COPD and CHF during KEE (COPD: 1.19 (0.11) vs. CHF: 1.00 (0.18) mM/kPa; p= 0.24) but higher in COPD vs. controls: 0.87 (0.28) mM/kPa (p= 0.02), and only CHF did not increase Q̇-adjusted DSMO2 from rest (p= 0.2). Conclusion: Disease-specific factors may play a role in peripheral exercise limitation in patients with COPD compared with CHF. Thus, low convective O2 transport to contracting muscle seemed to predominate in COPD, whereas muscle diffusive O2 transport was unresponsive in CHF.

Skeletal Muscle Contractile Function in Heart Failure With Reduced Ejection Fraction-A Focus on Nitric Oxide

Despite advances over the past few decades, heart failure with reduced ejection fraction (HFrEF) remains not only a mortal but a disabling disease. Indeed, the New York Heart Association classification of HFrEF severity is based on how much exercise a patient can perform. Moreover, exercise capacity-both aerobic exercise performance and muscle power-are intimately linked with survival in patients with HFrEF. This review will highlight the pathologic changes in skeletal muscle in HFrEF that are related to impaired exercise performance. Next, it will discuss the key role that impaired nitric oxide (NO) bioavailability plays in HFrEF skeletal muscle pathology. Lastly, it will discuss intriguing new data suggesting that the inorganic nitrate 'enterosalivary pathway' may be leveraged to increase NO bioavailability via ingestion of inorganic nitrate. This ingestion of inorganic nitrate has several advantages over organic nitrate (e.g., nitroglycerin) and the endogenous nitric oxide synthase pathway. Moreover, inorganic nitrate has been shown to improve exercise performance: both muscle power and aerobic capacity, in some recent small but well-controlled, cross-over studies in patients with HFrEF. Given the critical importance of better exercise performance for the amelioration of disability as well as its links with improved outcomes in patients with HFrEF, further studies of inorganic nitrate as a potential novel treatment is critical.

Exercise Intolerance in Facioscapulohumeral Muscular Dystrophy

PURPOSE

Determine 1) if adults with facioscapulohumeral muscular dystrophy (FSHD) exhibit exercise intolerance and 2) potential contributing mechanisms to exercise intolerance, specific to FSHD.

METHODS

Eleven people with FSHD (47 ± 13 yr, 4 females) and 11 controls (46 ± 13 yr, 4 females) completed one visit, which included a volitional peak oxygen consumption (V̇O2peak) cycling test. Breath-by-breath gas exchange, ventilation, and cardiovascular responses were measured at rest and during exercise. The test featured 3-min stages (speed, 65-70 rpm) with incremental increases in intensity (FSHD: 20 W per stage; control: 40-60 W per stage). Body lean mass (LM (kg, %)) was collected via dual-energy x-ray absorptiometry.

RESULTS

V̇O2peak was 32% lower (24.5 ± 9.7 vs 36.2 ± 9.3 mL·kg-1·min-1, P < 0.01), and wattage was 55% lower in FSHD (112.7 ± 56.1 vs 252.7 ± 67.7 W, P < 0.01). When working at a relative submaximal intensity (40% of V̇O2peak), wattage was 55% lower in FSHD (41.8 ± 30.3 vs 92.7 ± 32.6 W, P = 0.01), although ratings of perceived exertion (FSHD: 11 ± 2 vs control: 10 ± 3, P = 0.61) and dyspnea (FSHD: 3 ± 1 vs control: 3 ± 2, P = 0.78) were similar between groups. At an absolute intensity (60 W), the rating of perceived exertion was 63% higher (13 ± 3 vs 8 ± 2, P < 0.01) and dyspnea was 180% higher in FSHD (4 ± 2 vs 2 ± 2, P < 0.01). V̇O2peak was most strongly correlated with resting O2 pulse in controls (P < 0.01, r = 0.90) and percent leg LM in FSHD (P < 0.01, r = 0.88). Among FSHD participants, V̇O2peak was associated with self-reported functionality (FSHD-HI score; activity limitation: P < 0.01, r = -0.78), indicating a strong association between perceived and objective impairments.

CONCLUSIONS

Disease-driven losses of LM contribute to exercise intolerance in FSHD, as evidenced by a lower V̇O2peak and elevated symptoms of dyspnea and fatigue during submaximal exercise. Regular exercise participation may preserve LM, thus providing some protection against exercise tolerance in FSHD.

Novel mechanosensory role for acid sensing ion channel subtype 1a in evoking the exercise pressor reflex in rats with heart failure

Mechanical and metabolic signals associated with skeletal muscle contraction stimulate the sensory endings of thin fibre muscle afferents, which, in turn, generates reflex increases in sympathetic nerve activity (SNA) and blood pressure (the exercise pressor reflex; EPR). EPR activation in patients and animals with heart failure with reduced ejection fraction (HF-rEF) results in exaggerated increases in SNA and promotes exercise intolerance. In the healthy decerebrate rat, a subtype of acid sensing ion channel (ASIC) on the sensory endings of thin fibre muscle afferents, namely ASIC1a, has been shown to contribute to the metabolically sensitive portion of the EPR (i.e. metaboreflex), but not the mechanically sensitive portion of the EPR (i.e. the mechanoreflex). However, the role played by ASIC1a in evoking the EPR in HF-rEF is unknown. We hypothesized that, in decerebrate, unanaesthetized HF-rEF rats, injection of the ASIC1a antagonist psalmotoxin-1 (PcTx-1; 100 ng) into the hindlimb arterial supply would reduce the reflex increase in renal SNA (RSNA) evoked via 30 s of electrically induced static hindlimb muscle contraction, but not static hindlimb muscle stretch (model of mechanoreflex activation isolated from contraction-induced metabolite-production). We found that PcTx-1 reduced the reflex increase in RSNA evoked in response to muscle contraction (n = 8; mean (SD) ∫ΔRSNA pre: 1343 (588) a.u.; post: 816 (573) a.u.; P = 0.026) and muscle stretch (n = 6; ∫ΔRSNA pre: 688 (583) a.u.; post: 304 (370) a.u.; P = 0.025). Our data suggest that, in HF-rEF rats, ASIC1a contributes to activation of the exercise pressor reflex and that contribution includes a novel role for ASIC1a in mechanosensation that is not present in healthy rats. KEY POINTS: Skeletal muscle contraction results in exaggerated reflex increases in sympathetic nerve activity in heart failure patients compared to healthy counterparts, which likely contributes to increased cardiovascular risk and impaired tolerance for even mild exercise (i.e. activities of daily living) for patients suffering with this condition. Activation of acid sensing ion channel subtype 1a (ASIC1a) on the sensory endings of thin fibre muscle afferents during skeletal muscle contraction contributes to reflex increases in sympathetic nerve activity and blood pressure, at least in healthy subjects. In this study, we demonstrate that ASIC1a on the sensory endings of thin fibre muscle afferents plays a role in both the mechanical and metabolic components of the exercise pressor reflex in male rats with heart failure. The present data identify a novel role for ASIC1a in evoking the exercise pressor reflex in heart failure and may have important clinical implications for heart failure patients.

Influence of locomotor muscle group III/IV afferents on cardiovascular and ventilatory responses in human heart failure during submaximal exercise

The purpose of this study is to determine the influence of locomotor muscle group III/IV afferent inhibition on central and peripheral hemodynamics at multiple levels of submaximal cycling exercise in patients with heart failure with reduced ejection fraction (HFrEF). Eleven patients with HFrEF and nine healthy matched controls were recruited. The participants performed a multiple stage [i.e., 30 W, 50%peak workload (WL), and a workload eliciting a respiratory exchange ratio (RER) of ∼1.0] exercise test with lumbar intrathecal fentanyl (FENT) or placebo (PLA). Cardiac output ([Formula: see text]tot) was measured via open-circuit acetylene wash-in technique and stroke volume was calculated. Leg blood flow ([Formula: see text]l) was measured via constant infusion thermodilution and leg vascular conductance (LVC) was calculated. Radial artery and femoral venous blood gases were measured. For HFrEF, stroke volume was higher at the 30 W (FENT: 110 ± 21 vs. PLA: 100 ± 18 mL), 50%peak WL (FENT: 113 ± 22 vs. PLA: 103 ± 23 mL), and RER = 1.0 (FENT: 119 ± 28 vs. PLA: 110 ± 26 mL) stages, whereas heart rate and systemic vascular resistance were lower with fentanyl than with placebo (all, P < 0.05). [Formula: see text]tot in HFrEF and [Formula: see text]tot, stroke volume, and heart rate in controls were not different between fentanyl and placebo (all, P > 0.19). During submaximal exercise, controls and patients with HFrEF exhibited increased leg vascular conductance (LVC) with fentanyl compared with placebo (all, P < 0.04), whereas no differences were present in [Formula: see text]l or O2 delivery with fentanyl (all, P > 0.20). Taken together, these findings provide support for locomotor muscle group III/IV afferents playing a role in integrative control mechanisms during submaximal cycling exercise in patients with HFrEF and older controls.NEW & NOTEWORTHY Patients with HFrEF exhibit severe exercise intolerance. One of the primary peripheral mechanisms contributing to exercise intolerance in patients with HFrEF is locomotor muscle group III/IV afferent feedback. However, it is unknown whether these afferents impact the central and peripheral responses during submaximal cycling exercise. Herein, we demonstrate that inhibition of locomotor muscle group III/IV afferent feedback elicited increases in stroke volume during submaximal exercise in HFrEF, but not in healthy controls.

Sex and age interaction in fundamental circulatory volumetric variables at peak working capacity

Background

Whether the fundamental hematological and cardiac variables determining cardiorespiratory fitness and their intrinsic relationships are modulated by major constitutional factors, such as sex and age remains unresolved.

Methods

Transthoracic echocardiography, central hemodynamics and pulmonary oxygen (O₂) uptake were assessed in controlled conditions during submaximal and peak exercise (cycle ergometry) in 85 healthy young (20–44 year) and older (50–77) women and men matched by age-status and moderate-to-vigorous physical activity (MVPA) levels. Main outcomes such as peak left ventricular end-diastolic volume (LVEDV_peak), stroke volume (SV_peak), cardiac output (Q_peak) and O₂ uptake (VO_2peak), as well as blood volume (BV), BV–LVEDV_peak and LVEDV_peak–SV_peak relationships were determined with established methods.

Results

All individuals were non-smokers and non-obese, and MVPA levels were similar between sex and age groups (P ≥ 0.140). BV per kg of body weight did not differ between sexes (P ≥ 0.118), but was reduced with older age in men (P = 0.018). Key cardiac parameters normalized by body size (LVEDV_peak, SV_peak, Q_peak) were decreased in women compared with men irrespective of age (P ≤ 0.046). Older age per se curtailed Q_peak (P ≤ 0.022) due to lower heart rate (P < 0.001). In parallel, VO_2peak was reduced with older age in both sexes (P < 0.001). The analysis of fundamental circulatory relationships revealed that older women require a higher BV for a given LVEDV_peak than older men (P = 0.024).

Conclusions

Sex and age interact on the crucial circulatory relationship between total circulating BV and peak cardiac filling, with older women necessitating more BV to fill the exercising heart than age- and physical activity-matched men.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13293-021-00409-9.

Application of Inspiratory Muscle Training to Improve Physical Tolerance in Older Patients with Ischemic Heart Failure

Regardless of the management regime for heart failure (HF), there is strong evidence supporting the early implementation of exercise-based cardiac rehabilitation (CR). Respiratory therapy is considered to be an integral part of such secondary prevention protocols. The aim of the study was to evaluate the effect of inspiratory muscle training (IMT) on exercise tolerance and the functional parameters of the respiratory system in patients with heart failure involved in cardiac rehabilitation. The study included 90 patients with HF who took part in the second-stage 8-week cycle of cardiac rehabilitation (CR). They were randomly divided into three groups: Group I underwent CR and IMT; Group II only CR; and patients in Group III underwent only the IMT. Before and after the 8-week cycle, participants were assessed for exercise tolerance and the functional parameters of respiratory muscle strength. Significant statistical improvement concerned the majority of the hemodynamic parameters, lung function parameters, and respiratory muscle strength in the first group. Moreover, the enhancement in the exercise tolerance in the CR + IMT group was accompanied by a negligible change in the HR_peak. The results confirm that the addition of IMT to the standard rehabilitation process of patients with heart failure can increase the therapeutic effect while influencing some of the parameters measured by exercise electrocardiography and respiratory function.

Pathophysiology of Advanced Heart Failure: What Knowledge Is Needed for Clinical Management?

Understanding of heart failure (HF) has evolved from a simple hemodynamic problem through a neurohormonally and proinflammatory-driven syndrome to a complex multiorgan dysfunction accompanied by inadequate energy handling. This article discusses the most important clinical aspects of advanced HF pathophysiology. It presents the concept of neurohormonal activation and its deleterious effect on cardiovascular system and reflex control. The current theories regarding the role of inflammation, cytokine activation, and myocardial remodeling in HF progression are presented. Advanced HF is a multiorgan syndrome with interplay between cardiovascular system and other organs. The role of iron deficiency is also discussed.

Thromboxane A2 receptors contribute to the exaggerated exercise pressor reflex in male rats with heart failure

Mechanical and metabolic signals associated with skeletal muscle contraction stimulate the sensory endings of thin fiber muscle afferents and produce reflex increases in sympathetic nerve activity and blood pressure during exercise (i.e., the exercise pressor reflex; EPR). The EPR is exaggerated in patients and animals with heart failure with reduced ejection fraction (HF-rEF) and its activation contributes to reduced exercise capacity within this patient population. Accumulating evidence suggests that the exaggerated EPR in HF-rEF is partially attributable to a sensitization of mechanically activated channels produced by thromboxane A2 receptors (TxA2 -Rs) on those sensory endings; however, this has not been investigated. Accordingly, the purpose of this investigation was to determine the role played by TxA2 -Rs on the sensory endings of thin fiber muscle afferents in the exaggerated EPR in rats with HF-rEF induced by coronary artery ligation. In decerebrate, unanesthetized rats, we found that injection of the TxA2 -R antagonist daltroban (80 μg) into the arterial supply of the hindlimb reduced the pressor response to 30 s of electrically induced 1 Hz dynamic hindlimb muscle contraction in HF-rEF (n = 8, peak ∆MAP pre: 22 ± 3; post: 14 ± 2 mmHg; p = 0.01) but not sham (n = 10, peak ∆MAP pre: 13 ± 3; post: 11 ± 2 mmHg; p = 0.68) rats. In a separate group of HF-rEF rats (n = 4), we found that the systemic (intravenous) injection of daltroban had no effect on the EPR (peak ΔMAP pre: 26 ± 7; post: 25 ± 7 mmHg; p = 0.50). Our data suggest that TxA2 -Rs on thin fiber muscle afferents contribute to the exaggerated EPR evoked in response to dynamic muscle contraction in HF-rEF.

The effect of muscle blood flow restriction on hemodynamics, cerebral oxygenation and activation at rest

This study tested the hypothesis that muscle blood flow restriction reduces muscle and cerebral oxygenation, at rest. In 26 healthy males, aged 33±2 yrs, physiological variables were continuously recorded during a 10-min period in two experimental conditions: a) with muscle blood flow restriction through thigh cuffs application inflated at 120 mmHg (With Cuffs, WC) and b) without restriction (No Cuffs, NC). Muscle and cerebral oxygenation were reduced by muscle blood flow restriction as suggested by the increase in both muscle and cerebral deoxygenated hemoglobin (Δ[HHb]; p<0.01) and the decrease of muscle and cerebral oxygenation index (Δ[HbDiff]; p<0.01). Hemodynamic responses were not affected by such muscle blood flow restriction, whereas baroreflex sensitivity was reduced (p=0.009). The perception of leg discomfort was higher (p<0.001) in the WC than in the NC condition. This study suggests that thigh cuffs application inflated at 120 mmHg is an effective method to reduce muscle oxygenation at rest. These changes at the muscular level seem to be sensed by the central nervous system, evoking alterations in cerebral oxygenation and baroreflex sensitivity. Novelty bullets: • Thigh cuffs application inflated at 120 mmHg effectively reduces muscle oxygenation at rest. • Limiting muscle oxygenation appears to reduce cerebral oxygenation, and baroreflex sensitivity, at rest. • Even in healthy subjects, limiting muscle oxygenation, at rest, affects neural integration.

Sympathetic neural responses in heart failure during exercise and after exercise training

The sympathetic nervous system coordinates the cardiovascular response to exercise. This regulation is impaired in both experimental and human heart failure with reduced ejection fraction (HFrEF), resulting in a state of sympathoexcitation which limits exercise capacity and contributes to adverse outcome. Exercise training can moderate sympathetic excess at rest. Recording sympathetic nerve firing during exercise is more challenging. Hence, data acquired during exercise are scant and results vary according to exercise modality. In this review we will: (1) describe sympathetic activity during various exercise modes in both experimental and human HFrEF and consider factors which influence these responses; and (2) summarise the effect of exercise training on sympathetic outflow both at rest and during exercise in both animal models and human HFrEF. We will particularly highlight studies in humans which report direct measurements of efferent sympathetic nerve traffic using intraneural recordings. Future research is required to clarify the neural afferent mechanisms which contribute to efferent sympathetic activation during exercise in HFrEF, how this may be altered by exercise training, and the impact of such attenuation on cardiac and renal function.

Exaggerated sympathetic and cardiovascular responses to dynamic mechanoreflex activation in rats with heart failure: Role of endoperoxide 4 and thromboxane A2 receptors

The primary purpose of this investigation was to determine the role played by endoperoxide 4 receptors (EP4-R) and thromboxane A₂ receptors (TxA₂-R) during isolated dynamic muscle mechanoreflex activation in rats with heart failure with reduced ejection fraction (HF-rEF) and sham-operated healthy controls. We found that injection of the EP4-R antagonist L-161,982 (1 μg) into the arterial supply of the hindlimb had no effect on the peak pressor response to dynamic hindlimb muscle stretch in HF-rEF (n = 6, peak ∆MAP pre: 27 ± 7; post: 27 ± 4 mm Hg; P = 0.99) or sham (n = 6, peak ∆MAP pre: 15 ± 3; post: 13 ± 3 mm Hg; P = 0.67) rats. In contrast, injection of the TxA₂-R antagonist daltroban (80 μg) into the arterial supply of the hindlimb reduced the pressor response to dynamic hindlimb muscle stretch in HF-rEF (n = 11, peak ∆MAP pre: 28 ± 4; post: 16 ± 2 mm Hg; P = 0.02) but not sham (n = 8, peak ∆MAP pre: 17 ± 3; post: 16 ± 3; P = 0.84) rats. Our data suggest that TxA₂-Rs on thin fibre muscle afferents contribute to the exaggerated mechanoreflex in HF-rEF.

Unraveling the Role of Respiratory Muscle Metaboloreceptors under Inspiratory Training in Patients with Heart Failure

Exercise intolerance may be considered a hallmark in patients who suffer from heart failure (HF) syndrome. Currently, there is enough scientific evidence regarding functional and structural deterioration of skeletal musculature in these patients. It is worth noting that muscle weakness appears first in the respiratory muscles and then in the musculature of the limbs, which may be considered one of the main causes of exercise intolerance. Functional deterioration and associated atrophy of these respiratory muscles are related to an increased muscle metaboreflex leading to sympathetic–adrenal system hyperactivity and increased pulmonary ventilation. This issue contributes to increased dyspnea and/or fatigue and decreased aerobic function. Consequently, respiratory muscle weakness produces exercise limitations in these patients. In the present review, the key role that respiratory muscle metaboloreceptors play in exercise intolerance is accurately addressed in patients who suffer from HF. In conclusion, currently available scientific evidence seems to affirm that excessive metaboreflex activity of respiratory musculature under HF is the main cause of exercise intolerance and sympathetic–adrenal system hyperactivity. Inspiratory muscle training seems to be a useful personalized medicine intervention to reduce respiratory muscle metaboreflex in order to increase patients’ exercise tolerance under HF condition.

Contemporary Strategies to Manage High Blood Pressure in Patients with Coexistent Resistant Hypertension and Heart Failure With Reduced Ejection Fraction

Resistant hypertension (RH) represents an advanced subtype of hypertension that is complex to diagnose and treat. Compared with general hypertension, RH increases the risk patients will develop more advanced cardiovascular complications, including heart failure with reduced ejection fraction (HFrEF). As expected, the prevalence of RH has increased since the introduction of lower blood pressure targets included in the recent 2017 American blood pressure guidelines. The array of pharmacotherapies available to treat both hypertension and HFrEF has also expanded within the past decade. However, the efficacy of these cutting-edge pharmacotherapies has not come without a more advanced understanding of the important adjunct role non-pharmacological therapies play in helping with the management of both hypertension and HFrEF. In this review, we provide a summary of the latest pharmacological and non-pharmacological strategies that can be used to initiate treatment and optimize long-term blood pressure control in patients with coexistent RH and HFrEF.