Geriatric Research, Education, and Clinical Center, Veterans Affairs Medical Center, Salt Lake City, Utah.
Department of Internal Medicine, University of Utah, Salt Lake City, Utah.
Am J Physiol Heart Circ Physiol. 2021 Jan 1;320(1):H338-H351. doi: 10.1152/ajpheart.00266.2020. Epub 2020 Nov 8.
This study investigated the impact of HFpEF on neuromuscular fatigue and peripheral hemodynamics during small muscle mass exercise not limited by cardiac output. Eight HFpEF patients (NYHA II-III, ejection-fraction: 61 ± 2%) and eight healthy controls performed dynamic knee extension exercise (80% peak workload) to task failure and maximal intermittent quadriceps contractions (8 × 15 s). Controls repeated knee extension at the same absolute intensity as HFpEF. Leg blood flow (Q) was quantified using Doppler ultrasound. Pre/postexercise changes in quadriceps twitch torque (ΔQ; peripheral fatigue), voluntary activation (ΔVA; central fatigue), and corticospinal excitability were quantified. At the same relative intensity, HFpEF (24 ± 5 W) and controls (42 ± 6 W) had a similar time-to-task failure (∼10 min), ΔQ (∼50%), and ΔVA (∼6%). This resulted in a greater exercise-induced change in neuromuscular function per unit work in HFpEF, which was significantly correlated with a slower Q response time. Knee extension exercise at the same absolute intensity resulted in an ∼40% lower Q and greater ΔQ and ΔVA in HFpEF than in controls. Corticospinal excitability remained unaltered during exercise in both groups. Finally, despite a similar ΔVA, ΔQ was larger in HFpEF versus controls during isometric exercise. In conclusion, HFpEF patients are characterized by a similar development of central and peripheral fatigue as healthy controls when tested at the same relative intensity during exercise not limited by cardiac output. However, HFpEF patients have a greater susceptibility to neuromuscular fatigue during exercise at a given absolute intensity, and this impairs functional capacity. The patients' compromised Q response to exercise likely accounts, at least partly, for the patients' attenuated fatigue resistance. The susceptibility to neuromuscular fatigue during exercise is substantially exaggerated in individuals with heart failure with a preserved ejection fraction. The faster rate of fatigue development is associated with the compromised peripheral hemodynamic response characterizing these patients during exercise. Given the role of neuromuscular fatigue as a factor limiting exercise, this impairment likely accounts for a significant portion of the exercise intolerance typical for this population.
这项研究调查了 HFpEF 在不受心输出量限制的小肌肉群运动中对神经肌肉疲劳和外周血液动力学的影响。八名 HFpEF 患者（NYHA II-III，射血分数：61±2%）和八名健康对照者进行了动态膝关节伸展运动（80%峰值工作量）至运动失败和最大间歇性股四头肌收缩（8×15 秒）。对照者以与 HFpEF 相同的绝对强度重复膝关节伸展运动。使用多普勒超声量化腿部血流量（Q）。量化了运动前后股四头肌抽搐扭矩（ΔQ；外周疲劳）、自愿激活（ΔVA；中枢疲劳）和皮质脊髓兴奋性的变化。在相同的相对强度下，HFpEF（24±5 W）和对照组（42±6 W）的运动至失败时间（约 10 分钟）、ΔQ（约 50%）和 ΔVA（约 6%）相似。这导致 HFpEF 中每单位工作量的神经肌肉功能变化更大，这与 Q 反应时间较慢显著相关。在相同的绝对强度下进行膝关节伸展运动导致 HFpEF 中的 Q 降低约 40%，ΔQ 和 ΔVA 比对照组更大。在两组中，皮质脊髓兴奋性在运动过程中保持不变。最后，尽管 ΔVA 相似，但在等长运动中，HFpEF 中的 ΔQ 比对照组更大。总之，当在不受心输出量限制的运动中以相同的相对强度进行测试时，HFpEF 患者表现出与健康对照组相似的中枢和外周疲劳发展。然而，HFpEF 患者在给定的绝对强度下运动时更容易发生神经肌肉疲劳，这会损害其功能能力。患者对运动的 Q 反应受损至少部分解释了患者对疲劳的抵抗力减弱。在射血分数保留的心力衰竭患者中，运动时的神经肌肉疲劳易感性大大夸大。疲劳发展更快的速度与这些患者在运动过程中特征性的外周血液动力学反应受损有关。鉴于神经肌肉疲劳作为限制运动的因素的作用，这种损伤可能占该人群运动不耐受的很大一部分。
