Smith, Joshua R.

INTRODUCTION Heart failure (HF) is characterized by reduced exercise capacity resulting from central and peripheral mechanisms. A primary peripheral mechanism is augmented neural feedback (via group III/IV afferents) arising from the locomotor muscles. This enhanced locomotor neural feedback may result from a variety of mechanisms including increased 1) metabo and/or mechanoreceptor expression, 2) metabolite production, and/or 3) mechano/metaboreceptor sensitivity. Previous studies have shown elevated expression of purinergic 2X3 (P2X3) and cyclooxygenase (COX‐2) in HF compared to sham animal models. However, it is unknown if metabo and/or mechanoreceptor (e.g., Piezo 1 and 2) expression are elevated in human HF. Further, it is unclear if altered receptor expression is related to the cardiovascular and ventilatory responses during exercise attributed to locomotor neural afferent feedback. The purpose of this study was to 1) determine if differences exist in the expression of skeletal muscle proteins associated with metabo/mechanoreflex activity between healthy individuals (CTL) and HF patients and 2) determine relationships between protein expression and the change in ventilatory and cardiovascular responses with locomotor muscle afferent inhibition during exercise. We hypothesized that 1) HF patients will demonstrate greater skeletal muscle protein expression associated with mechano/metaboreflex activity and 2) the increased protein expression will be associated with changes in ventilation, mean arterial pressure (MAP), and catecholamines during locomotor muscle afferent feedback inhibition in HF patients. METHODS In a randomized, placebo controlled cross‐over design, 10 CTL and 6 systolic HF (Age: 60±12 vs. 60±4 yrs, p=0.96; BMI: 26±3 vs. 31±5 kg/m 2 , p=0.01, respectively) patients completed cycling exercise at 60%VO 2 peak with lumbar intrathecal fentanyl or sham. Arterial blood pressure and catecholamines were measured via radial artery catheter during exercise. On a follow up visit, a muscle biopsy from the vastus lateralis was performed to isolate and measure COX‐2, P2X3, transient receptor potential vanilloid type 1 (TRPV1), Piezo 1, and Piezo 2 protein expression. RESULTS Protein expression of P2X3, COX‐2, and TRPV1 were greater in HF compared to CTL (all, p<0.05), with no difference between groups in Piezo 1 and 2 protein expression (p>0.05). HF compared to CTL had a greater decrease in ventilation with fentanyl compared to sham (−11±8 vs. −3±9%, p=0.04, respectively), with no difference between groups in MAP or norepinephrine (p>0.05). In HF, COX expression was negatively related to the change in ventilation (r= −0.87, p=0.02), MAP (r= −0.93, p<0.01), and norepinephrine (r= −0.85, p=0.03) with fentanyl. CONCLUSIONS These data demonstrate that metaborecptors (i.e. P2X3, COX‐2, and TRPV1) are elevated in HF compared to CTL. Furthermore, protein expression of COX‐2 was related to the cardiovascular and ventilatory changes observed with fentanyl in HF patients. These findings suggest that elevated expression of metaboreflex associated proteins contribute to the augmented locomotor muscle afferent feedback during exercise in HF. Support or Funding Information NHLBI RO1 HL126638 AHA 18POST3990251 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Introduction Heart failure (HF) patients demonstrate augmented ventilation for a given metabolic demand which results in increased respiratory muscle work and subsequent competition for blood flow between the respiratory and locomotor muscle beds. Unloading the respiratory muscles during submaximal exercise has been shown to increase leg oxygen uptake (VO 2 ) in HF patients due increased leg blood flow via increased cardiac output and redistribution of cardiac output from the respiratory to locomotor muscles. It has been suggested that increased leg VO 2 following respiratory muscle unloading in HF during submaximal exercise is due to augmented convective O 2 transport in HF; however, it is unclear if diffusive O 2 transport also increases with respiratory muscle unloading. We hypothesized that respiratory muscle unloading during submaximal exercise will lead to increased leg VO 2 due to combined increases in convective and diffusive O 2 transport. Methods Ten HF patients with reduced systolic function (6M/4W; 53±15 yrs; BMI: 29±6 kg/m 2 ) were recruited. Patients performed two submaximal exercise bouts (i.e. with and without respiratory muscle unloading (via mechanical ventilator) (RM unloading and control (CTL), respectively)). During exercise, leg blood flow (Q L ) was measured via thermodilution. Intrathoracic pressure was measured via esophageal balloon. Radial arterial and femoral venous blood gases were measured. Blood gases were used to calculate arterial and venous oxygen content (CaO 2 and CvO 2 , respectively). Leg VO 2 was calculated as Q L multiplied by the difference between CaO 2 ‐CvO 2 . Leg O 2 delivery was calculated as Q L multiplied by CaO 2 . Leg diffusion capacity (DO 2 ) was calculated as leg VO 2 divided by femoral venous partial pressure of O 2 . Results From CTL to RM unloading, leg VO 2 increased during submaximal exercise (0.7±0.3 vs. 1.0±0.4 L/min, p<0.01, respectively). From CTL to RM unloading, leg O 2 delivery increased during submaximal exercise (0.9±0.4 vs. 1.4±0.5 L/min, p<0.01, respectively), whereas CaO 2 ‐CvO 2 was not different (14.1±3.0 vs. 14.2±3.2 mL/dL, p=0.57, respectively). From CTL to RM unloading, leg DO 2 increased during submaximal exercise (30.4±10.8 vs. 49.7±18.6 mL/mmHg, p<0.01, respectively). There was a negative relationship between the degree of RM unloading (i.e. percent decrease in mean inspiratory esophageal pressure) and percent increase in leg DO 2 with RM unloading (r= −0.77, p<0.01). Conclusion Our results demonstrate that unloading the respiratory muscles leads to increased leg VO 2 due to convective and diffusive O 2 transport during submaximal exercise in HF patients. These findings suggest that the naturally occurring respiratory muscle work in HF compromises convective and diffusive O 2 transport and thus constrains leg VO 2 during submaximal exercise in HF. Support or Funding Information NIH HL126638 AHA 18POST3990251 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Introduction Age related declines in oxidative metabolic capacity have been attributed to slowing of O 2 delivery and utilization. While these declines are pronounced in postmenopausal women, it is unclear how these changes compare with age‐matched men. This study aimed to phenotype adjustments of muscle oxy‐ and‐ deoxygenation during transitions of low intensity fixed‐load exercise in postmenopausal women and age‐matched men. Methods Healthy postmenopausal women (PW) and men (M) (N = 7 and 6; age 57 ± 7 and 61 ± 10 years; BMI 26 ± 2 and 27 ± 4 kg/m 2 , respectively, all P >0.05) completed 3 identical 8 min transients of fixed pedal rate (=35) and load (=20W) ergometry wearing bilateral thigh cuffs. After 5 min of rest, exercise began with 3 min without thigh cuff inflation followed by 5 min of exercise+cuff inflation at 90 mm Hg (to provoke locomotor congestion). Deoxy (HHb)‐ and total (Hb tot )‐ hemoglobin were measured by near‐infrared spectroscopy (NIRS) at the right calf. Data were sampled at 1 s intervals and ensemble averaged across 3 transients and binned to 10 s epochs for each participant prior to mono‐exponential modeling: Y B + A [1 − e −(t‐TD)/τ ]; where Y B = baseline value of Y for the 30 s prior to the step transition; τ = time constant; A = asymptote; TD = time delay. Mean response time (MRT) = TD + τ. Kinetics were modelled for the transition from exercise without to exercise+cuff inflation. Results Following the exercise on‐transient, TD was 9±4 vs. 7±3 s (P=0.35) and 8±4 vs. 6±3 s (P=0.28) for PW vs. M prior to the rise in ΔHHb or ΔHb tot , respectively. For PW vs. M, the A representing the rise in ΔHHb was 8±7 vs. 15±7 μM (P=0.04) and for ΔHb tot it was 13±8 vs. 18±8 μM (P=0.17), respectively. The kinetics of HHb following the exercise+cuff onset were similar for PW and M (τ=53±38 vs. 34±9 s, respectively, P=0.36) as well as for Hb tot (τ=43±29 vs. 29±16 s, respectively, P=0.43). The overall time course for the change in HHb (MRT=62±35 vs. 41±8 s, P=0.27) or Hb tot (MRT=51±27 vs. 35±14 s, P=0.31) did not differ for PW and M, respectively. Conclusions Despite age‐matched men demonstrating greater ΔHHb compared with PW, these data do not support the hypothesis that following exercise onset, the rate of locomotor hemodynamic adjustment and O 2 extraction for a given metabolic demand differ between these groups. Thus, as opposed to gross factors of blood flow and O 2 delivery, effects such as slowing of the rate of activation and/or processes regulating oxidative phosphorylation and mitochondrial respiration may play a stronger role in explaining differences in oxidative metabolic capacity between PW and M. Support or Funding Information Funding for this work was supported by National Institutes of Health [RO1‐HL126638 to TPO]; and American Heart Association [16POST30260021 to EHV] and National Institutes of Health [HL138814 to EHV]. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Introduction Exercise intolerance is a hallmark of heart failure with reduced ejection fraction (HFrEF) resulting from a variety of factors including comprised oxygen delivery. A common comorbidity of HFrEF is chronic obstructive pulmonary disease (COPD), which is independently associated with reduced exercise tolerance and cardiac output (Q) as well as peripheral dysfunction similar to HFrEF. It is currently unknown if HFrEF and coexisting COPD (HFrEF+COPD) exhibit worsened exercise tolerance and whether the mechanisms thereof are similar to HFrEF alone. We hypothesized that patients with HFrEF+COPD demonstrate further reductions in peak VO 2 and workload subsequent to a lower peak Q and arterio‐mixed venous O 2 content difference (C(a‐v)O 2 ) compared to HFrEF alone. Methods HFrEF+COPD (n=16) and HFrEF (n=17) (age: 57±7 vs 54±6 yrs; EF%: 20±5 vs 21±5; height: 173±7 vs 174±7 cm; weight: 88±14 vs 86±17 kg; all p>0.18) underwent peak exercise testing during right heart catheterization. At rest and peak exercise, invasive hemodynamic, cardiac pressures, and arterial pressures were performed. Heart rate and oxygen uptake (VO 2 ) were measured at rest and peak exercise via 12‐lead ECG and metabolic measurement system, respectively. Convective oxygen delivery was calculated as Q multiplied by CaO 2 . Results Peak exercise VO 2 and workload were lower in HFrEF+COPD compared to HFrEF (7.0±1.9 vs. 9.9±2.7 mL/min/kg; 34±7 vs. 45±12 watts; both p<0.01). At peak exercise, Q and stroke volume were lower in HFrEF+COPD than HFrEF (4.8±1.3 vs. 7.0±3.0 L/min; 52±16 vs. 75±28 mL; both p<0.01). Significant relationships existed between delta VO 2 and Q (peak exercise minus resting) in HFrEF+COPD and HFrEF (r=0.84 and r=0.89; both p<0.01); however, HFrEF+COPD had a significantly lower slope (p=0.02). Peak exercise C(a‐v)O 2 was not different between HFrEF+COPD and HFrEF (12.9±2.3 vs. 12.8±2.6 mL/dL; p=0.89). No differences were present in heart rate or hemoglobin at peak exercise (p>0.73). Delta VO 2 and C(a‐v)O 2 was significantly related for HFrEF+COPD (r=0.68; p<0.01), but not HFrEF (r=0.14, p=0.57). At peak exercise, HFrEF+COPD had lower convective oxygen delivery (845±239 vs. 1230±517 mL/min; p<0.01). Conclusions Patients with HFrEF and concurrent COPD demonstrate worsened exercise tolerance compared to HFrEF resulting from reduced oxygen delivery. These data suggest HFrEF with COPD exhibit more severe central and peripheral abnormalities than HFrEF alone. Support or Funding Information NHLBI RO1 HL126638 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Key points Heart failure patients with reduced ejection fraction (HFrEF) exhibit severe limitations in exercise capacity ( peak). One of the primary peripheral mechanisms suggested to underlie exercise intolerance in HFrEF is excessive locomotor muscle group III/IV afferent feedback; however, this has never been investigated in human heart failure. HFrEF patients and controls performed an incremental exercise test to volitional exhaustion to determine peak with lumbar intrathecal fentanyl or placebo. During exercise, cardiac output, leg blood flow and radial artery and femoral venous blood gases were measured. With fentanyl, compared with placebo, patients with HFrEF achieved a higher peak workload, peak, cardiac output, stroke volume and leg blood flow. These findings suggest that locomotor muscle group III/IV afferent feedback in HFrEF leads to increased systemic vascular resistance, which constrains stroke volume, cardiac output and O2 delivery thereby impairing peak and thus exercise capacity. AbstractTo better understand the underlying mechanisms contributing to exercise limitation in heart failure with reduced ejection fraction (HFrEF), we investigated the influence of locomotor muscle group III/IV afferent inhibition via lumbar intrathecal fentanyl on peak exercise capacity ( peak) and the contributory mechanisms. Eleven HFrEF patients and eight healthy matched controls were recruited. The participants performed an incremental exercise test to volitional exhaustion to determine peak with lumbar intrathecal fentanyl or placebo. During exercise, cardiac output and leg blood flow () were measured via open‐circuit acetylene wash‐in technique and constant infusion thermodilution, respectively. Radial artery and femoral venous blood gases were measured. peak was 15% greater with fentanyl compared with placebo for HFrEF (P < 0.01), while no different in the controls. During peak exercise with fentanyl, cardiac output was 12% greater in HFrEF secondary to significant decreases in systemic vascular resistance and increases in stroke volume compared with placebo (all, P < 0.01). From placebo to fentanyl, leg , and O2 delivery were greater for HFrEF during peak exercise (all, P < 0.01), but not control. These findings indicate that locomotor muscle group III/IV afferent feedback in patients with HFrEF leads to increased systemic vascular resistance, which constrains stroke volume, cardiac output and O2 delivery, thereby impairing peak and thus exercise capacity. These findings have important clinical implications as peak is highly predictive of morbidity and mortality in HF.

Introduction The exercise pressor reflex contributes to cardiovascular regulation during exercise. The primary components of the exercise pressor reflex response are the mechanically and metabolically sensitive skeletal muscle afferents (group III and IV, respectively). Experimentally, subsystolic regional circulatory occlusion (SubRCO) leads to venous distention, stimulating primarily group III afferents, thereby augmenting the exercise pressor reflex. Previous studies have reported sex differences in the metaboreflex induced exercise pressor reflex induced cardiovascular responses. Specifically, pre‐menopausal women, compared to age‐matched men, were found to have attenuated cardiovascular responses with mechanoreflex stimulation. However, it is unclear if sex differences are also present in the cardiovascular responses during exercise with locomotor limb venous distention. Therefore, the purpose of this study was to determine the influence of SubRCO during submaximal exercise in men and women. We hypothesized that women will have attenuated increases in mean arterial pressure (MAP) and systemic vascular resistance (SVR) than men during exercise with SubRCO. Methods Twelve men and thirteen women completed two study visits (Age: M: 30±6vs. W: 27±8yrs, p>0.05; BMI: M: 25.4±3.6 vs. W: 22±3 kg/m 2 , p<0.05). The first visit consisted of a peak exercise ergometry test. The second visit consisted of constant‐load cycle ergometry at 30% peak workload with different SubRCO pressures via bilateral upper thigh pressure cuffs. The cuffs remained uninflated (0 mmHg) (CTL) during the first three min of exercise, then were intermittently inflated to 20, 40, 60, 80, or 100 mmHg for two minutes (randomized order). Each inflation period was followed by a 2minute deflation period where the participant continued to exercise. Cardiacoutput (Q) and MAP were measured via continuous hemodynamic photoplethysmography and systemic vascular resistance (SVR) was calculated. Data were reported as delta changes from CTL. Results Compared to 0 mmHg, MAP increased with SubRCO inflation pressures of 60, 80, and 100mmHg in men and women during submaximal exercise (all, p<0.05); however, no differences were present between groups (60 mmHg: M: 6.2±4.2 vs. W: 8.0±5.2; 80mmHg: M: 11.6±5.5 vs. W: 15.1±4.8; 100 mmHg: M: 18.2±6.6 vs. W: 20.5±7.2 mmHg(all, p>0.05)). Similarly, SVR increased with cuff inflation pressures of60, 80, and 100 mmHg compared to 0 mmHg in men and women (p<0.05), while no differences existed between groups (60 mmHg: M: 0.3±0.4 vs W: 0.4±0.5;80 mmHg: M: 0.9±0.5 vs W: 1.1± 0.9; 100 mmHg M: 1.3±0.8vs W: 1.5±0.8mmHg/L/min (all, p>0.05)). In contrast, Q did not change with cuff inflation pressures of 20, 40, 60, 80, or100 mmHg compared to 0 mmHg in men or women during submaximal exercise(p>0.05). Conclusion In contrast to our hypothesis, the MAP and SVR responses were not different between men and women with SubRCO during submaximal exercise. Our findings suggest that sex differences are not present in the cardiovascular response to low‐intensity constant‐load exercise with stimulation of the exercise pressor reflex via lower limb venous distention.

Introduction It is well established that the exercise pressor reflex contributes to cardiovascular control (e.g. mean arterial pressure (MAP)) during exercise. One arm of the exercise pressor reflex includes the metabolically sensitive group IV afferents (i.e. metaboreflex). The metaboreflex‐induced cardiovascular responses to exercise are incompletely understood, especially in women across the aging spectrum. For example, post‐menopausal women have greater increases in MAP and systemic vascular resistance (SVR) during locomotor muscle exercise compared to pre‐menopausal women. However, it is unclear if an exaggerated metaboreflex arising from the locomotor muscles is contributing to these cardiovascular adjustments with exercise in post‐menopausal women. We hypothesized that 1) post‐menopausal women will have an augmented MAP response with isolated metaboreflex activation compared to pre‐menopausal women and 2) the exaggerated increase in MAP in the post‐menopausal women will be primarily due to greater increases in SVR. Methods Pre‐ (n= 10, 25±3yrs, 24±3 kg/m 2 ) and post‐menopausal women (n=12, 58±4yrs, 24±3 kg/m 2 ) performed 2 sessions of cycling exercise at 20 W for 5 min with bilateral upper thigh pressure tourniquets inflated to 90 mmHg. At end exercise, the recovery was randomized to post‐exercise circulatory occlusion (PECO) to isolate the metaboreflex (via bilateral upper thigh pressure tourniquets rapidly inflated to suprasystolic pressure for 2 min) or normal recovery (NR) without intervention. Systolic and diastolic blood pressure were measured via manual sphygmomanometry and MAP was calculated. Cardiac output was measured via open circuit acetylene wash‐in and systemic vascular resistance (SVR) was calculated. Data is reported as the absolute change from rest to recovery. Results MAP was elevated during PECO compared to NR in both groups (p<0.05), while MAP during PECO was greater in post‐ compared to pre‐menopausal women (20±9 vs. 13±5 mmHg, respectively) (p<0.05). Similarly, SVR was elevated during PECO compared to NR in both groups (p<0.05), while SVR was greater during PECO in post‐ compared to pre‐menopausal women (5±3 vs. 3±1 mmHg/L/min, respectively) (p<0.05). In contrast, cardiac output was not different between NR and PECO in either pre‐ (NR: 0.3±1 vs. PECO: −0.2±1 L/min) and post‐menopausal (NR: −0.1±1 vs. PECO: −0.7±0.9 L/min) (all, p>0.05). Conclusion These data demonstrate that isolated metaboreflex stimulation following whole‐body exercise results in exaggerated increases in MAP and SVR in post‐ compared to pre‐menopausal women. These data suggest that exercise pressor reflex‐mediated control of MAP during exercise is accentuated in post‐menopausal women with menopause status.

Objective Cardiovascular adjustments to exercise, including increases in blood pressure (MAP) and heart rate, occur in response to several neural mechanisms. Specifically, stimulation of respiratory (via inspiratory loading (IL)) and locomotor muscle (via subsystolic cuff inflation (CUFF)) neurologic feedback via group III/IV afferents augments the MAP response during exercise. Further, we have recently shown that simultaneous stimulation of the respiratory and locomotor muscle afferents during exercise potentiates the MAP increase compared to when these reflexes are stimulated individually. To date, interventional strategies to attenuate the augmented MAP during IL+CUFF have not been investigated. Previous studies have shown that inspiratory muscle training (IMT) attenuates the IL‐induced increase in MAP at rest in healthy adults. We hypothesized that 8 weeks of IMT will attenuate the IL+CUFF‐induced increase in MAP during exercise in healthy adults. Methods Twenty adults were recruited and randomized to the IMT (n=10) or sham group (n=10). Participants performed 8 weeks of IMT twice a day, 7 days a week at 50% (IMT) or 10% (sham) maximum inspiratory pressure (MIP). On separate visits, participants performed an incremental cycling test to volitional fatigue and a 10 min cycling exercise bout at 40% maximal oxygen uptake Pre‐ and Post‐IMT. The exercise bout consisted of 5 min of spontaneous breathing followed by 5 min of voluntary hyperventilation (i.e. breathing frequency of 40 breaths per min) with IL (30% MIP) and bilateral locomotor subsystolic cuff inflation (80 mmHg). Systolic and diastolic blood pressure (SBP and DBP, respectively) were measured using manual sphygmomanometry and MAP was calculated. SBP and MAP were reported as the change from rest. Dyspnea was measured via Borg scale (1–10). Results After 8 weeks, MIP increased in the IMT (Pre: 99±26 vs. Post: 127±26 cmH 2 O, p<0.05), but not the sham group (Pre: 126±29 vs. Post: 129±28 cmH 2 O, p>0.05). Pre‐IMT, the increase in MAP with IL+CUFF was not different between groups (IMT: 28±6 vs. sham: 31±7 mmHg) (p>0.05). Post‐IMT, the increase in MAP with IL+CUFF was attenuated in IMT, but not sham (IMT: 23±7 vs. sham: 32±5 mmHg) (p<0.05). Pre‐IMT, the increase in SBP with IL+CUFF was not different between groups (IMT: 49±12 vs. sham: 53±16 mmHg) (p>0.05). Post‐IMT, the increase in SBP with IL+CUFF was attenuated in IMT, but not sham (IMT: 42±12 vs. sham: 57±14 mmHg) (both, p<0.05). The increase in DBP with IL+CUFF was not different between groups Pre or Post‐IMT (both, p>0.05). Lastly, dyspnea was not different Pre‐IMT between groups (IMT: 4±3 vs. sham: 4±2 Borg (1–10)) (p>0.05), but was lower in the IMT, but not sham Post‐IMT (IMT: 2±2 vs. sham: 4±1 Borg (1–10)) (p<0.05). Conclusions These data demonstrate that IMT attenuates the MAP response when the respiratory and locomotor afferents are stimulated simultaneously. These findings have important clinical implications for populations that exhibit exaggerated respiratory and locomotor muscle reflexes during exercise. Support or Funding Information This work was supported by the National Institutes of Health [HL126638 to TPO] and American Heart Association [18POST3990251 to JRS].