Villarraga, Nico

Introduction The contribution of metabolic vs mechanical stimuli related to the group III/IV afferent‐mediated exercise pressor reflex (EPR) remains incompletely understood. High pedal frequency during cycling increases type II muscle fiber recruitment and may contribute to increased anaerobically‐mediated metabolic byproduct accumulation. This may lead to an augmented rise in systolic blood pressure (SBP) and, hence, EPR in humans. Thus, we hypothesized, 1) Mean arterial pressure (MAP) will be increased during exercise with SubRCO vs without NoRCO irrespective of pedal frequency, and 2) MAP will be augmented further during exercise with SubRCO at high pedal frequencies. Methods Healthy adults (N=13; 46% men; age 36±19 yr; BMI 24±4 kg/m 2 ) participated in 2 study visits, each consisting of 2 sessions of fixed load (20 W) recumbent cycle ergometry with bilateral upper thigh pressure tourniquets for 8 min at a fixed pedal frequency of 35 (LOW) or 100 (HIGH) rpm (randomized). Cuffs remained at 0 mm Hg for the first 3 min (CTL), and were then randomized to 0 mm Hg (NoRCO) or 90 mm Hg (SubRCO) for the final 5 min of exercise. SBP and diastolic blood pressure (DBP) were measured via manual sphygmomanometry at the end of CTL and end‐exercise (END). MAP was calculated as (SBP + 2 * DBP)/3. Results There were no between or within condition differences at CTL for MAP (P>0.05). In contrast, for between SubRCO and NoRCO differences at END, MAP was increased in SubRCO vs NoRCO in both HIGH (106±12 vs 92±13 mm Hg, respectively) and LOW (94±9 vs 85±8 mm Hg, respectively) (P<0.05). At END, MAP was increased in HIGH vs LOW within both SubRCO and NoRCO (P<0.01). Within both NoRCO (129 ± 18 vs 117 ± 11 mm Hg) and SubRCO (125 ± 15 vs 113 ± 10 mm Hg) at CTL, SBP was increased in HIGH vs LOW, respectively (P<0.01). At CTL, there were no between SBP NoRCO vs SubRCO differences in HIGH or LOW. Within SBP differences for NoRCO (134 ± 19 vs 113 ± 11 mm Hg) and SubRCO (147 ± 20 vs 127 ± 12 mm Hg) in HIGH vs LOW persisted to END, respectively (P<0.01). SBP increased at END vs CTL within SubRCO for both HIGH and LOW (P<0.02), but not within NoRCO (P>0.05). Lastly, SBP increased in SubRCO vs NoRCO at END in both HIGH and LOW (both P<0.01). There were no differences for DBP at any time point (P>0.05). Conclusion These data support our hypothesis that, independent of pedal frequency, SubRCO provokes increased MAP during fixed‐load submaximal exercise as a function of increased SBP. However, high pedal rate accompanied by SubRCO results in exaggerated SBP‐mediated increased MAP. These data contribute to an improved understanding of the stimuli that activate group III/IV afferents during exercise in humans. Support or Funding Information NHLBI RO1 HL126638; AHA 16POST30260021

Introduction The exercise pressor reflex (EPR) is suggested to be linked to activated group III/IV afferents. However, the predominating mechanical and/or metabolic stimuli by which the EPR is mediated remains unclear. It is suggested that high pedal frequency increases the recruitment of type II muscle fibers, which may result in augmented production of metabolic byproducts as a function of increased anaerobic processes. Therefore, this study tested the hypothesis that compared to low frequency, high pedal frequency will be associated with increased blood pressure during postexercise suprasystolic regional circulatory occlusion (SupraRCO). Further, although subsystolic RCO (SubRCO) during exercise is suggested to provoke venous distension associated with mechanically‐mediated activation of group III/IV afferents, we hypothesized the rise in blood pressure during postexercise SubRCO will be blunted vs postexercise SupraRCO irrespective of pedal frequency. Methods Healthy adults (N=13, 6 male, 7 female), age 36±19 yrs participated in 2 days of testing, each consisting of 3 sessions of recumbent cycle ergometry at pedal frequencies of 100 (HIGH) or 35 (LOW) rpm (randomized) at 20 W for 8 min. At cessation of exercise, bilateral upper thigh pressure tourniquets were inflated to SupraRCO (200 mm Hg), SubRCO (90 mm Hg), or no inflation (NR) for 2 min (randomized). Blood pressure via manual sphygmomanometry was measured at rest, end‐exercise, and 2 min postexercise. Mean arterial pressure (MAP) was calculated as (SBP + 2 * DBP)/3. Results For both rest and end‐exercise, MAP did not differ across repeated transients for either HIGH or LOW (both P>0.05). However, mean MAP across repeated transients was greater in HIGH vs LOW at end‐exercise (P<0.05). At 2 min postexercise in HIGH, compared to NR (89±8 mm Hg), MAP was higher in SupraRCO (105±18 mm Hg; P=0.02), but not in SubRCO (98±9 mm Hg; P=0.38); whereas MAP did not differ between SupraRCO and SubRCO (P=0.70). Similarly, at 2 min postexercise in LOW, MAP was increased in SupraRCO vs NR (96±10 vs 85±7 mm Hg, respectively; P=0.02); whereas there were no differences between SubRCO (88±7 mm Hg) with either NR (P=0.91) or SupraRCO (P=0.23). Lastly, compared to LOW, MAP was greater in HIGH at 2 min postexercise for both SupraRCO (P<0.01) and SubRCO (P<0.01), but not in NR (P=0.59). Conclusions In intact exercising humans it remains challenging to elucidate exact contributions of group III/IV afferents to the EPR. However, these data are consistent with the role of group III/IV afferents in contributing to the EPR in humans. New to this field, our observations suggest that at low fixed workloads, increased pedal frequency augments the postexercise pressor response to both SupraRCO and SubRCO in healthy adults. These data contribute to an improved understanding of specific stimuli associated with the EPR linked to group III/IV afferents in humans. Support or Funding Information NHLBI R25 HL115473; NHLBI RO1 HL126638; AHA 16POST30260021

Abstract Background Exercise intolerance is the cardinal manifestation of heart failure (HF), yet its underlying mechanism(s) remain poorly understood. Measures of ventricular function such as ejection fraction often have no relationship with exercise capacity in HF. 2D-STE has proved to be more reliable method to evaluate myocardial mechanical function. Our hypothesis is Resistance exercise training (Resist-HFpEF) will improve exercise tolerance and exertional symptoms in patients with HFpEF. Purpose The study aims to evaluate myocardial mechanical function by strain imaging during resistance exercise training in Heart Failure patients with Preserved Ejection Fraction (HFpEF) Methods This is a single centre prospective pilot study. 24 HFpEF patients were enrolled and their baseline comorbidities were recorded. Baseline 2D-STE imaging was performed at rest and during exercise (Visit 1). Patients were then randomized to either a novel resistance exercise training program for 36 sessions (3 sessions per week for 12 weeks) or a standard of care control group. 2D STE imaging was then repeated at follow-up (Visit 2). Peak Global Longitudinal strain (GLS), systolic strain rate (SSR), early diastolic strain rate (SRe) were measured offline. Results Mean age of the Rehab cohort was 68.57±10.52 years and the control cohort was 68.1±6.47 years. 23 study subjects were male (96%). 17% of the study subjects were hypertensive, 63% were diabetic, 42% had NYHA I, 46% had NYHA II and 13% had NYHA III of heart failure. The mean LV ejection fraction in the control and Rehab group after the training program at rest was 61.88±2.26% & 54.74±2.07% (p-value 0.04) and during exercise was 59.90±2.05% and 53.13±2.05% (p-value 0.04). The peak GLS was −18.80±4.29% and −17.7±2.21% in controls during rest and exercise at Visit 1 (p-value 0.27) while the rehab cohort had −18.71±4.7% and −20.82±2.4% respectively (p-value 0.0268). The peak GLS was −17.40±3.05% and −17.96±2.65% in controls during rest and exercise at Visit 2 (p-value 0.3430) while rehab cohort had −17.97±6.21% and −16.57±3.82% respectively (p-value 0.67). (Figure 1a and 1b shows GLS, SRS, SRe at Baseline and after exercise program respectively) Conclusion This pilot study suggest systolic and diastolic reserve can be measured reliably during low grade exercise. These results could reflect improvement in clinical status and exercise tolerance. Figure 1. Comparison of peak GLS, SSR, SRe amongst HFpEF patients at rest and during exercise before and after the rehab training program. Funding Acknowledgement Type of funding source: None

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].