We conclude that autonomic control of HRV at rest and during mental stress is altered by dietary sodium in healthy normotensive young adult men and women.

Dietary sodium influences intermediate physiological traits in healthy young adults independent of changes in blood pressure. The purpose of this study was to test the hypothesis that dietary sodium affects cardiac autonomic function. In prospective, randomized cross‐over design separated by 1 month or more between diets, 69 normotensive healthy young adults (M/F: 26/43, ages 18–38 yr) consumed a 5‐day low (10 mmol/day), normal (150 mmol), and high sodium (400mmol) diet prior to a protocol examining cardiovascular traits including heart rate variability (HRV) by time domain and frequency domain analysis (Nevrokard). All women were studied in the low hormone phase of the menstrual cycle. Diet did not affect blood pressure, but HR (mean ± SE) was 68±1, 65±1, and 64±1 in low, normal, and high sodium conditions, resp. (RM ANOVA p < 0.01). For HRV there was a main effect of sodium on SDNN, RMSSD, HF, LFnu, HFnu, and LF/HF ratio (p < 0.01 for all). The response to low sodium was most marked and consistent with sympathetic activation, with increased LFnu and LF/HF ratio, and decreased SDNN, RMSSD, and HFnu compared to both normal and high sodium conditions (p ≤ 0.05 for all). These findings suggest that autonomic control of HRV is altered through changes in dietary sodium without changes in blood pressure. Support: UL1 TR000135, HL‐89331

BACKGROUNDIncreased activation of Group III/IV skeletal muscle afferents is suggested to play a role in exercise intolerance in heart failure (HF).PURPOSEThe purpose of this study was to examine if skeletal muscle afferent feedback inhibition improves exercise tolerance in HF.METHODS8 HF patients [59±8 yr, mean±SD] participated in two randomized incremental recumbent cycling exercise sessions to peak capacity (peak oxygen consumption, VO2). Session 1: The synthetic opioid fentanyl (50 mcg), known to block afferent feedback, was injected intrathecally (INJ) in the lumbar spine (L3‐L4 intervertebral space) prior to exercise. Session 2: Participants were prepared similarly with a sham injection (placebo, PLA). Gas exchange, dyspnea and RPE were measured.RESULTSHF patients exercised for a longer duration (Δ3±3 min, p=0.02) and reached a higher power output (PLA:109±30 vs. INJ:128±34 W, p=0.02) with locomotor afferent inhibition. Additionally, peak VO2 was non‐significantly greater (PLA:18.7±3.3 vs. INJ:21.8±4.4 ml/kg/min, p=0.10). With INJ workload matched to peak PLA workload, RPE was reduced (PLA:18±2 vs. INJ:15±2, respectively, p=0.005) and dyspnea was lower (PLA:7.5±2 vs. INJ:4.2±1, p=0.003) with no difference in VO2 (p>0.05).CONCLUSIONInhibition of group III/IV locomotor muscle afferent feedback contributes to improved exercise tolerance and exertional symptoms in HF patients.

Acute ß‐adrenergic blockade (BB) increases aortic wave reflection in young women, however, it is unknown if this effect extends to post‐menopausal women. Thus, we examined systemic BB on aortic wave reflection in 14 post‐menopausal women (58 ± 2 yr). Non‐invasive aortic pressure waveforms were synthesized from high‐fidelity radial pressure waveforms obtained from applanation tonometry before and during systemic BB (0.25mg/kg bolus, with 0.004 mg/kg/min continuous infusion of propranolol). Aortic blood pressure, augmentation index (AIx), AIx adjusted for heart rate (AIx@75), aortic augmented pressure (AP), and wasted left ventricular energy (Ew) were calculated from the aortic pressure waveform. Heart rate (60 ± 2 vs. 51 ± 2 bpm) and mean arterial pressure (95 ± 3 vs. 91 ± 3 mmHg) were reduced with BB (P < 0.05 for both). AIx increased during BB (32 ± 2 vs. 35 ± 2%, P < 0.01), however, AIx@75 was unchanged (25 ± 2 vs. 24 ± 2%, ns). Additionally, AP (20 ± 2 vs. 20 ± 2 mmHg, ns) and Ew (4313 ± 538 vs. 4277 ± 537 dyne*cm2/sec, ns) remained unchanged during BB. When compared to our previously published study in young women, indices of aortic wave reflection were significantly less affected in post‐menopausal women in response to acute systemic BB. Taken together, our data suggest that the negative effects (i.e. increased aortic wave reflection) of non‐selective BB are less pronounced in post‐menopausal women.